Tag Archives: Audio

Q&A: Adam Clarkson

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Tube Amplifier Design
Brothers collaborate on a new audio system with a classic look

SHANNON BECKER: Tell us a little about your background. Where are you located? Where and what did you study?

ADAM CLARKSON: I have been working in product development for the past 10 years in Franklin, IN, for my father’s company, Agri-Tronix, where we manufacture agricultural electronics and also professional tournament fishing scales. Yes, tournament fishing is a sport and we provide the scales necessary to decide the winner. I attended Indiana University for two years after high school where I studied graphic design and pre-engineering. After my brief tour of college life, I bounced around from bartending job to bartending job before deciding to come to work for my father. It’s truly been a blessing to work for the man I most admire, I’ve learned more from him than I could ever describe. My brother, Ben, began working with me about two years ago after he graduated from the University of Southern Indiana with a Bachelor’s degree in Fine Arts.

SHANNON: What is your current occupation?

ADAM: Sales, marketing, project manager, graphic designer, technician, and anything else that needs to be done.

SHANNON: How did your interest in audio electronics develop?

ADAM: I’ve always been interested in electronics and always loved good audio. There was an allure to vacuum tubes, so we started experimenting and we really think that we’ve created something special.

Photo 1:Brothers, Adam (left) and Ben Clarkson, are working on BlueTube Audio’s classic wooden speakers designed to match their new vacuum tube amplifier.

SHANNON: How did you and your brother Ben get involved with Kickstarter? What about it appealed to you?

ADAM: The ClockOS was our first kickstarter project. I had a friend who had  decent success on Kickstarter, and I thought, “Hey I could do that.” So we set out to come up with a project to put on Kickstarter and test the waters. We came up with the ClockOS, which had  mild success. We learned so much from doing that project. And, we did some things wrong with that project that really held it back from being great. The idea of Kickstarter is really neat, and I think that a lot of people want to just help out. They want to be involved in something new, get in on the ground floor, so to speak. Even though the backers are not
investing in the company, they still have this desire to be involved. The all-or-nothing funding was the one thing that really convinced us to go with them over the other crowd-funding sites like indiegogo.com.

SHANNON: In what stage of development is the ClockOS?

ADAM: Unfortunately, this project had to be retired as the manufacturing cost was just way too high. The machine shop that originally quoted the aluminum for us came back after the project ended with a price that was three times as high. We then had to scramble to  find a new shop and what we saved in money, we sacrificed in quality. We spent many weekends reworking the machined parts, hand polishing and surface prepping each one to a show quality finish. If you added our time to the cost of the ClockOS project (which any good business owners should) we would have lost money on the ClockOS project. We learned from our first project and took it to the BlueTube amplifier to make sure it was a success. It worked.

Photo 2: BlueTube Audio’s new vacuum tube amplifer comes with two handcrafted wooden speakers.

SHANNON: Share some details about your company, BlueTube Audio. What made you and Ben go into business together?

ADAM: BlueTube Audio’s niche is “functioning art.” We want to design products that are art pieces but have function in modern society. Our new project is the BlueTube Audio vacuum tube amplifier. As for our partnership, we were already working together and, in my opinion, we make a great team. We are brothers so we do have our battles, they are usually small though, and we always work through them.

SHANNON: Describe the BlueTube Audio vacuum tube amplifier and its current status.

Photo 3: The back of the BlueTube Audio amplifier is clearly labeled for easy use.

ADAM: We decide to put the amplifier on Kickstarter as it really is a good platform for raising funds for your initial production run. We needed to have custom sheet metal plates punched, powder coated, and silkscreened for the back panels. The front panels are made of brushed stainless steel and require specialized machinery to punch and cut them. The internal chassis is really a marvel of sheet metal bending that I designed, and I am pretty shocked the sheet metal shop said they could bend them.

We have also three separate PCBs in the unit. The main board is populated with the tube sockets, the capacitors, the resistors, and the other fun components that are required for a vacuum tube amplifier. The secondary PCB has all the inputs and DC voltage circuitry on it. This board also has the USB port attached with smart charger circuitry.

Photo 4: The amplifier’s power button emits a soft blue glow when the device is on.

The circuitry automatically detects the proper voltage and current for your USB device, whether it’s an Samsung Galaxy or an iPad, we can give the device all the power it wants. This secondary PCB also has all the Bluetooth circuitry attached to it. The third board is a small one, but it is connected to the input selector switch and distributes the input signal to the amplifier and then out to your speakers.

All these things require quantity orders that we would not have been able to fund without the Kickstarter program. Now that we have the start-up capital, we can order more parts than we need and actually have inventory on the shelves—about 10 times as much inventory in some cases. Currently, production of the first units is in full swing, and we are constantly ordering parts.

SHANNON: The amplifier’s old-world look camouflages some very modern audio electronics. Why choose this combination?

Photo 5: The amplifier’s vacuum tubes provide the modern-day amplifier with some old-world charm.

ADAM: Because it looks awesome and sounds great! I love the look of the old-time tombstone radios and the handcrafted woodwork. The warm glow of the vacuum tubes. The reflection of the glass and metal. We don’t put plastic on our units because plastic looks cheap. Ben is the woodworker, and he did an amazing job handcrafting these units.

As for the new world technology, well, we don’t really want to sacrifice our convenience either. Why not have both? Great sound and the convenience of Bluetooth.

SHANNON: Do you have any advice for audioXpress readers who are thinking of building their own sound systems?

ADAM: Be careful when working with tube amplifiers. The capacitors can take hours to fully discharge and even when unplugged they can give you quite a jolt.  Also, don’t be afraid to experiment.

SHANNON: Are you planning any other speaker-related projects?

ADAM: Yes, Bluetooth and stereo. That’s all that I can say right now.

SHANNON: Where do you see the audio industry 10 years from now?

ADAM: Much as it is now; however, with the shift to digital in the last few years, there has been some sacrifice of quality. I foresee people crying for better quality. Many people, including myself, love the convenience of having their entire music library in their pocket. But I’ve noticed that I don’t buy albums like I used to. I have the shuffle bug or the skip bug and I don’t listen to a whole album through and through like I used to. I guess this isn’t really a prediction just a complaint of something that I find missing. I miss the collection of a music library. I miss sitting down and listening to an entire album. I miss the sound of good music and the music sounding good. We’re seeing a shift to better things. I just can’t say where we will end. aX

Q&A: Geoff Boyd

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Geoff Boyd is the managing director of Coleridge Design Associates.

SHANNON BECKER: Tell us a little about your background and where you live.

GEOFF BOYD: I have lived in San Jose, CA, since 2006. But, I hail from the Caribbean and spent most of my life living in UK. I am a 1970 Commonwealth Scholar and Physics and Chemistry graduate of the University of Leeds, West Yorkshire, England,  with post-graduate and post-doctoral research experience in Material Science at the Oxford University, Oxford, England. Leaving academia in the early 1980s I co-founded Memotech, one of the UK’s leading first-generation PC companies. I then led NXT, the company that introduced the world’s first computer interactive Videowall display systems, which included marketing and selling these high technology display systems into Japan.

In 2010, after more than 10 years at NXT specializing in new business development, technology innovation, and intellectual property licensing, I rekindled my entrepreneurial activities and founded Silicon Valley-based Coleridge Design Associates, which has the objective of building a team of designers, scientists, and engineers who specialize in creating intellectual property (IP) by invention and innovation aimed primarily at the consumer electronics (CE) and green energy (GE) markets. At its core is “Invention by Design” rather than “Invention by Serendipity” with the skill and experience to recognize the difference between a trip to Brighton (the seaside) and a trip to Mars.

SHANNON: What was your first personal project? Why did you build it? Is it still in use?

 

GEOFF: My exposure to electronics was as a postgraduate student in the
Department of Metallurgy, Oxford University, where those so inclined built their own electronics equipment for lab experiments. I took to this like a duck to water and became quite proficient at electronics design and construction as well as sheet metal work for enclosures. My first personal project was to build a functioning version of Peter Walker’s Quad 405 current dumping amplifier. The design with full schematics was published in a December 1975 issue of Wireless World. I was fascinated with the concept of the reactive bridge balancing technique used in the design. In fact, I remember doing a second-order calculation to fine tune the inductor’s resistance of the bridge. I added Douglas Self’s advanced preamplifier with discrete LED-biased op-amps, which was also published in Wireless World in 1976 as well as a discrete Class A headphone amplifier also published at the time. I laid out the PCBs using the “pen and tape” method and etched it in the lab. No purchased kits here! I fabricated the sheet metal enclosure under the expert tutelage of John Short, who ran the student workshop in the Department of Metallurgy at Oxford for many years. This integrated amplifier had a pride of place in my living room for many years. It eventually gave way to a Yamaha AV receiver over 10 years later.

SHANNON: You have more than 30 years of experience in technology and audio visual innovation. How did you get started?

GEOFF: In 1978 I moved from the Department of Metallurgy to the Engineering Department at Oxford University as a post doctorate researcher in mechanical properties of materials at elevated strain rates. This required recording data for tests lasting a few milliseconds with data rates at tens of MHz. Though my passion for music and interest in audio electronics remained, my electronics interest and expertise shifted to computer and memory electronics design.

SHANNON: What made you venture out on your own and start Coleridge Design?

GEOFF: I started as an entrepreneur during those heady days of the first personal computers in 1979. I plotted to start a hardware and software business with another researcher at Oxford, Robert Branton, who worked with the programming research group at Oxford. It wasn’t a difficult decision to branch out because at the time Margaret Thatcher had just become prime minister and the cushy jobs at the universities were disappearing fast. By 1981, the writing was on the wall and tenure was going to end, so I decided to forget about an academic career and start my own tech business. Our first business, Memotech, was making add-on memory packs for the Sinclair ZX81. Initially, I designed the products while still at the Engineering Department and then I jumped ship as soon as the business roared to a massive success.

The story of Memotech is interesting. The ZX81 came with 1 KB of memory, and the first thing the user needed was a 16-KB memory pack. When dynamic random access memory (DRAM) ICs were purchased, they needed to be fully tested in circuits with demanding tests, which typically lasted 3 to 4 min. In the UK, there were two contract manufactures who made Sinclair’s add-on packs—Thorn EMI and AB Electronics. They used GenRad testing machines that cost over $1 million each. You couldn’t speed up the test, so the throughput of these machines was limited. Memotech couldn’t afford these machines to test its MemoPaks, as they were called, so we built our own testing rigs using Intel 8048 8-bit microcontrollers with a complete memory test system that cost us less than $500! The MemoPaks were housed in black anodized extrusion enclosures and had a reputation for quality. Needless to say, Memotech cornered the market on Sinclair ZX81 memory add-ons, and we were able to build a multimillion-pound business within one year. I remember that we had UK retailers WH Smith, Boots, and others on allocation, and we could sell everything that we could make. In the US, the ZX81 was launched as the Timex 1000, and we experienced explosive growth and success. I hastily left the university and never had the time to submit my D-Phil thesis from the work in the Metallurgy Department at Oxford, although my research was peer reviewed and published at the time.

At Memotech, we thought all we had to do was produce a first-class product with a great design and specifications, and the buyers we had on allocation would come to us. So, we designed and manufactured the Memotech MTX 512 home computer, which was launched in 1983. We were competing against BBC Microcomputer System and never stood a chance in the UK. The buyers never came and the level of marketing required was beyond our resources, so our backers eventually pulled the plug in 1986. That was a huge lesson. I bought what was left of the business and relaunched Memotech Computers using high-resolution digital video technology that had been developed at Memotech to a new market of videowall technology. We dominated the supply of videowall controllers for nearly 10 years, from 1986 to 1995.

Another lesson I learned from 1995 to 1999 was that “things change.” We miscalculated, thinking that to have large LCD-TVs one would need to “tile” smaller displays. In 1995, it was generally accepted in the display industry that one could never manufacture LCDs larger than approximately 23” diagonal because of glass-handling issues. Another bit of wisdom at the time was that LCDs would quickly transition from amorphous silicon active matrix LCD (AMLCD) to low-temperature polysilicon technology (LTPS), which would mean the driver electronics used with AMLCD would be eliminated. And a further bit of wisdom at the time was that the yield of LCDs would never exceed about 70%. I launched Coleridge Design in 1996 to create a business to tile partially defective LTPS 23” to 25” LCD panels into 100” very large screen flat panel displays (VLS-FPDs) based on these false assumptions.

Needless to say, the business never took off as technology changed making all three assumptions on which the business was based wrong. And in 1999, I joined NXT, the UK flat-panel speaker IP company, as a display consultant to launch SoundVu where “the screen is the speaker.” For 10 years, I worked at NXT with a fabulous team of colleagues all passionate about music and sound reproduction. I worked primarily in IP business development and sales. It was a valuable experience that brought me in contact with all the great audio and consumer electronic companies of the world. I did contribute on the technology side and have a number of NXT patents to my name, but it wasn’t my day job. In 2006, the bulk of the NXT business moved to Hong Kong to be closer to its licensees and I moved to Silicon Valley to be closer to the OEMs that were licensee targets. By 2010, NXT was retrenching, having failed to make a lasting impact with its IP licensing business model, and started moving back to UK. This was my cue to relaunch my entrepreneurial career in Silicon Valley. Coleridge Design in San Jose, CA, was launched at the beginning of 2010.

SHANNON: Tell us about your work. Do the models you used 30 or even 20 years ago still function today?

GEOFF: The Coleridge Design plan is to develop IP mainly in consumer electronics audio and sound reproduction as well as in printed electronics and green energy with the “user experience” as the guiding force. I call it “inventing by design,” where I call on my extensive experience in science, technology, engineering, and mathematics (STEM) to lead a team charged with addressing neglected technology needs.

The entrepreneurial model we used in the past was based on gut feelings. We make a design and a product then put it out there to see how it sells. If the product and price was great then it would sell with moderate PR and marketing. The marketing was entirely business-to-business (B2B) or business-to-consumer (B2C), depending on the product and the target market. The Internet changed the model slightly in the last 20 years but not significantly. Today, we have a fundamental shift with the advent of social media, which in effect means that our marketing effort is dominated by consumer-to-consumer (C2C). Another significant change is the advent of Kickstarter and crowdfunding. In the context of making and taking products to market, I view it as an extension of C2C where you can test the market before you build your product. Our case with Coleridge Design and the aCUBE is a classic case of using Kickstarter to test the market and fail early.

The aCUBE uses 4.5” BMR full-range loudspeaker drivers, beautiful handmade clear cast acrylic 6.5” cube enclosures and the latest Class-D amplifier technology from Maxim Integrated.

SHANNON: Your most recent innovation is the aCUBE. How did this design come to be? What makes it so unique?

GEOFF: In about 2004, Dr. Graham Bank, a colleague at NXT, made a breakthrough in loudspeaker technology inventing the balance mode radiator (BMR) loudspeaker. The BMR is a full-range loudspeaker driver, which provides outstanding performance. My personal view is that this is the most significant advance in loudspeaker technology since 1925 when Rice & Kellogg invented the loudspeaker as we know it today.

BMR technology has appeared in many stand-alone loudspeaker products. However, these have largely been in either expensive Hi-Fi or in performance compromised speaker systems. The advantages of BMR speaker technology are many, but primarily relate to its pinpoint accuracy yet wide dispersion and extended frequency range. Together this allows the design realization of a high-performance, single-drive system such as the aCUBE.

This project takes the 4.5” BMR full-range loudspeaker drivers from CSS, a company owned by my former NXT colleagues, Dr. Graham Bank and Jon Vizor, and marries these drivers with beautiful handmade clear-cast acrylic 6.5” cube enclosures and the latest Class-D amplifier technology from Maxim Integrated. The result: The best in-class performance speakers optimized as near-field active loudspeakers that are stylish, exceptional quality, affordable, and convenient.

The use of acrylic is quite by accident. I have tended to use aluminum extrusions in most of my designs. The MemoPak 64K, the Memotech MTX 512 computer, and the Memotech DDFS videowall controllers were all made with black anodized aluminum preferably brushed. So we designed and prototyped a range of BMR speakers in anodized aluminum enclosures. However, before we made the protototypes, we built some acrylic enclosures as proofs of concept to test the BMR drivers from Cotswold Sound Systems. They sounded fabulous. However, when we used the aluminum prototypes, the enclosures rang like a bell and we had to take drastic measures to dampen the sound. Due to my materials science background, I realized that the acrylic sounded fabulous because of the material’s high internal damping over the entire audio bandwidth due to viscoelasticy. That was the reason the relatively thin walled enclosures sounded so well. Once we decided to make the aCUBE out of acrylic sheet, we had to find a supplier who could make perfect cubes using CNC and the latest techniques in bonding and polishing. The beauty in cast acrylic sheet is how it renders the light through perfect edges.

I have to confess, the aCUBE Kickstarter project was a bit of a Trojan horse in an attempt to gauge whether the consumer electronics market has an appetite for a new audio brand in quality sound reproduction and whether crowdfunding is a viable route to launching such a brand. It didn’t take long to see that in its present form, the Coleridge Design brand will not be a viable vehicle for launching the groundbreaking, disruptive audio technologies as I envisaged. Another valuable lesson learned from this early failure is that very little has changed and launching a new brand is still all about marketing, albeit nowadays C2C social media marketing.

The Lunatik Touch Pen, available in several different colors, is currently in prototype development. The accessory can be used both as a regular ink pen and as an implement for your tablet

SHANNON: Describe your touch-pen technology and how it works.

GEOFF: A couple of weeks after I got my first iPhone in 2007, I designed and built a capacitive-touch pen using conductive silicone rubber to emulate the finger. There are two requirements for a capacitive touch pen. The first is that it must form a flat conductive area of about 0.5 to 1 cm2 on the touch glass surface. The second is that this conductive area must be electrically connected to an electrical “sink” such as the human body or “large” lump of metal. The first touch pen that we built had a mild steel core of about 100-mm long × 3-mm diameter embedded in a silicone rubber “pen” about 110-mm × 8-mm diameter. We built a few hundred prototypes, but it wasn’t viable because there was no IP protection.

So we came up with a design in which the rubber grip of a gel pen was made out of conductive silicone rubber and modified so that when the pen refill was retracted the silicone rubber tip would collapse and could be used as a touch pen even when the pen body was plastic because the grip would conduct through the fingers.

Coleridge Design licensed the technology exclusively to Scott Wilson at Lunatik.com who launched it on Kickstarter, his second project after his very successful TikTok project that created the Lunatik Brand. (For more information, visit www.kickstarter.com/
projects/1104350651/lunatik-touch-pen-the-evolution-of-thestylus.)

This is the licensing business model that we generally want to use for the IP we develop. The key is to make a whole product that is ready for market. Most of the time it is not that easy because the technology is not a “whole product” and needs one or more entities in the supply chain to complete the product. In many cases, it might be an OEM or brand to take the product to market as well as suppliers to change the way they make products. That is very hard and needs to be driven by the OEM. That was the reasoning behind trying to make Coleridge Design an audio brand. If one cannot take it to market then one has to make it worth the while of the OEM or brand to get on board. That generally means some degree of exclusivity. Say a time-limited exclusivity or even an outright sale or fully paid up license.

SHANNON: What do you see as some of the greatest audio innovations of your time?

GEOFF: In the last 40 years, we have come a long way in improving the user experience but only if we use convenience as the main metric. To speak to that, I would say three of the great innovations of “my time” include: The Digital Audio revolution, which has led to surround sound and iTunes; the Class-D filterless audio amplifier; and distributed mode loudspeaker (DML) culminating in Dr. Graham Bank’s BMR. However, in so many ways, we have gone backward in the user experience of audio, mostly in the name of convenience. I recall valve amplifier systems from the 1960s and 1970s with very large speakers, some of them built into the users’ homes, which outperform most systems I have heard in the last 20 years.

How do we get great-sounding audio out of relatively “small” enclosures? I clearly remember an encounter I had with Michael Gerzon, who it would be reasonable to say invented surround sound. It was sometime in 1975, just after he had published his work on surround sound in Wireless World in December 1974. I was invigilating as a student’s part-time job on Friday evenings at the Radcliffe Science Library in Oxford and Michael, who was at the Oxford Mathematics Institute, had reserved some books on Matrix theory. I spotted his name on the ticket and when he came to collect his books I pumped him with questions on surround sound. I came away with two pieces of information, which I clearly remember to this day. The first was that the minimum number of speakers required for full surround sound would be six at the corners of an octahedral arrangement. Two at the top front, one at the bottom center, two at the bottom back, and one at the top center. But the bad news, he said, was that for the equations to work they all had to be full-range speakers (i.e., including bass). This has remained with me for 40 years.

SHANNON: Are you currently working on or planning any other speaker-related projects?

GEOFF: Coleridge Design has been developing IP on three audio related projects:

A personal surround-sound headphone system (PX3) based on design work we did on motorcycle helmet audio (www.youtube.com/watch?v=ilfSA_FoiaU). The new development seeks to achieve the same Helmet-Blaster unbelievable surround-sound performance in similar form factor and power requirements as conventional headphones.

The magnetless voice coil actuator (M-LVCA), which is a green initiative to eliminate rare earth magnets in loudspeaker motors at reduced cost without loss in performance and increase in weight. This is based on recent advances in insulated iron soft magnetic composites (SMCs) coupled to audio digital signal processing. It is scalable to all sizes of loudspeaker motor. There are possible spin off applications in electric vehicle technology

The extended range flat-panel bass (flatBASS) loudspeaker with active shallow enclosure technology. My 1975 encounter with Michael Gerzon makes this what I consider the holy grail of loudspeaker technology!

SHANNON: Can you recommend any useful new parts or promising technologies to audioXpress readers? Anything you’re using now that you think readers should know about?

GEOFF: I would recommend Graham Bank’s BMR loudspeaker drivers from Cotswold Sound Systems mounted in naturally damped “thin-walled” acrylic enclosures. Thin-walled clear cast acrylic sheet typically 4-mm thick for 3” to 4” cubes, say 6-mm thick up to 6” to 8” cubes and say 10-mm thick up to 12” to 15” cubes.

There has been rapid improvement in lowering the cost and increasing the performance of the latest filterless class-D amplifiers from Maxim Integrated and Texas Instruments (TI). They are very efficient and worth evaluating in new designs but good quality power supply design is critical. Also the bridge tied load (BTL) output configuration of modern Class-D is pretty much mandatory but care must be taken to switch both ends when using speaker switch boxes.

Another new technology worth considering in modern audio designs is the use of supercapacitors from, say, Maxwell and PowerStor, particularly for battery designs, which are now really viable with the new super-efficient filterless Class-D amplifiers. Audiophiles love the concept of a battery-powered audio amplifier! Quiescent current of these amplifiers is the key efficiency metric. Supercapacitors have drawn much attention in recent years due to their high power density, reversibility, and long cycle life. They are found in a wide range of applications from smart phones to electric vehicles and the rapid price reduction in recent years has made them affordable in applications like this.

These low-cost supercapacitor devices are typically 2.5 to 3 V maximum so one needs to incorporate active balancing when these devices are used in series. For example, AA batteries would be configured in series for relatively high peak powers into 4-Ω loads from typically 15 or 12 V (primary or rechargeable respectively). However, particularly when partially discharged, these battery stacks are very poor at delivering the intermittent heavy-power transients required for high quality audio. A series bank of active balanced supercapacitors can supplement the battery pack and completely counteract this.

SHANNON: Do you have any advice for audioXpress readers who want to build their own sound systems?

GEOFF: In the words of Nike, “Just do it.” I don’t mean to be flippant, but I firmly believe that you really learn when you make stuff. I include circuit simulations in “making stuff.” I tend use TI’s TINA-TI and other free tools for analog simulation. I don’t breadboard until I have it working in simulation. But, in the end, it has to be prototyped and tested. In analog audio electronics, this is getting really hard as we move to smaller fine-pitch ICs. My advice is to make use of manufacturer’s reference board designs and take a stab at laying out your designs using the many free tools available from PCB fabricators. I tend to use old fashioned axial and radial devices for breadboarding small sections, but more often than not, the working simulations allows one to go straight to SMD PCBs, typically 0603 passive devices for prototypes and preproduction only moving to 0402 if board space is an issue. Another golden rule I have for analog audio is to always use full differential designs, particularly when interfacing to digital ICs with analog outputs. aX

April New Products and News

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AmpliVox Wireless PA Supports many Media Devices

Amplivox SW720 Wireless PA system

The updated SW720 Wireless PA system includes several practical accessories.

AmpliVox Sound Systems has unveiled its newly updated SW720 Wireless PA system, a versatile PA package that supports all types of external media. The SW720 PA enables audio or video to be played from MP3s, CDs, DVDs, or any iDevice from Apple (e.g., iPhones, iPads, or iPods), complemented by a wireless handheld mic for voice amplification. For audiences of up to 500 people and rooms as large as 2,500 ft2, the SW720 is an all-in-one solution for multimedia presentations.

The revamped SW720 Wireless PA system with a remote-controlled DVD player now includes AmpliVox’s S1732 cable and adapter, enabling iPads and other Apple devices to be simultaneously played and charged. The unit also contains an integrated DVD/CD/MP3 disc player with a USB/SD card reader and video output that enables DVDs to be viewed with a projector or other video display. For voice amplification, the SW720 features a built-in UHF selectable 16-channel wireless receiver with a 300’ range wireless handheld microphone.

The SW720’s straightforward controls customize presentations. A voice priority switch mutes music when the mic is in use, and separate bass/treble controls enable easy sound adjustments. Weighing 11.5 lb, the molded plastic enclosure is durable and portable. A protective cover offers many pockets for accessory storage. The SW720 can run for up to 6 h on its built-in rechargeable battery, or it can be powered with the included AC power cord.

For more information, visit www.ampli.com/ipod-pa-system.

Dayton Audio’s DVC Subwoofer

Dayton Audio Ultimax DVC

Dayton Audio’s DVC subwoofers are designed to improve power handling and reduce power compression.

Dayton Audio’s Ultimax Series DVC subwoofers are purpose-built to move air and create clean, articulate, and fast bass. To improve power handling, increase thermal management, and reduce power compression, Dayton Audio designed the Ultimax Series with large black anodized formers and vented pole pieces, under-spider ventilation, and two-layer copper voice coils.

The Ultimax’s “Tall-Boy” rubber surround is intended for extra-long linear excursion without reducing the Nomex honeycomb/woven glass-fiber laminated cone’s surface area. Copper shorting rings and a pole piece cap reduce inductance and distortion, while the Ultimax’s dual spiders maintain linearity at high drive levels.

Dayton Audio’s Ultimax Series dual voice coil subwoofers are engineered and built using the latest in subwoofer technology. They are now available in 10”, 12”, and 15” sizes. Dayton Audio products can be purchased in the US through Parts Express (www.parts-express.com).

For more information, visit www.daytonaudio.com.

DANLEY Improves SYNERGY HORNS SH Series

Danley Sound Labs SH-96 HO

Danley raises the sound pressure level (SPL) on its Synergy Horns SH Series

Danley Sound Labs recently announced improvements to many of its already highly-regarded SH Series full-range loudspeakers. The new versions are identified by the suffix “HO,” which stands for “high output.” For example, if someone wants to get the most performance out of the Danley SH-96, order the Danley SH-96 HO.

The new designs use a more powerful two-way high frequency. As a result, the low- and mid-frequency drivers can be used to their full potential yet maintain Danley’s characteristic frequency response, phase response, and fidelity. In conjunction, the HO designs use a new crossover and have additional options for bi-amping and for changing the low-frequency impedance. Because the cabinets themselves haven’t changed, the new versions retain the coverage and frequency loss patterns of the originals. The new models include the SH-95 HO, the SH-96 HO, and the SH-64 HO.

Because the new switch panel cannot operate reliably if left exposed to the elements, weatherized versions of the new high-output loudspeakers must be pre-ordered with specified biamping and impedance settings.

For more information, visit www.danleysoundlabs.com.

B&K Precision Launches “pwrApp” for Apple Products

B&K Precision pwrApp

B&K Precision’s new “pwrApp” can be used on an iPad, an iPhone, and an iPod touch.

B&K Precision launched its new “pwrApp” for iPad, iPhone, and iPod touch. Adding greater value to its DC power solutions, B&K Precision’s pwrApp enables full monitoring and control of a network-connected (via WLAN) XLN-GL series of power supplies over local wireless networks.

The pwrApp’s primary function is remote operation of all XLN-GL power supplies’ functions. The pwrApp’s features include live visual monitoring and interactive power supply control, visual data graphing, audible trigger alarms within the app, and data export.

Fully functional in-app demos of devices, monitoring, and programs are available with or without a connected XLN power supply. B&K Precision’s pwrApp for iPad and iPhone offers full interface control in English, French, German, Portuguese, Spanish, and traditional Chinese via a simple selection menu. Future versions of pwrApp will offer control of additional select WLAN-enabled B&K Precision power supplies. Available for immediate download via iTunes, pwrApp is free of charge to all users.

For pwrApp and XLN information, as well as hardware/software requirements, visit www.bkprecision.com/pwrapp.

NUGEN Audio offers Stand-Alone LM-Correct Loudness Tool

NUGEN Audio LM Correct

NuGen Audio now offers a new stand-alone version of its LM-Correct loudness analysis and correction tool.

NUGEN Audio, a creator of intuitive tools for audio professionals, has released a new stand-alone version of its LM-Correct loudness analysis and correction tool, which was originally only available as an AudioSuite plug-in. For the first time, LM-Correct is available as a file-based program, taking its speed and simplicity beyond the Avid digital audio workstation (DAW) environment. LM-Correct provides EBU R128|ATSC A/85 (CALM Act)-compliant loudness correction with unmatched simplicity, providing users with a rapid two-click solution for loudness normalization and conformance.

Part of NUGEN Audio’s range of innovative and easy-to-use loudness correction tools, LM-Correct is a faster-than-real-time tool that calculates and corrects for integrated program loudness and short-term maximum loudness. LM-Correct includes an internal true-peak limiter that transparently handles any intersample peaks.

LM-Correct’s settings include presets for current loudness standards, short-term loudness, overall integrated program loudness measurement and correction, maximum true-peak level targeting, and “EBU Mode.” The software also supports mono through 5.1 audio.

LM-Correct is available immediately for OS X and Windows operating systems. For more information about LM-Correct and other NUGEN Audio products, visit www.nugenaudio.com.

Saelig Introduces Handheld RF Spectrum Analyzer

Saelig PSA2702

Saelig’s PSA Series II RF spectrum analyzers feature long, rechargeable battery life.

Saelig Company has introduced the PSA Series II RF spectrum analyzers. Available in 1.3- and 2.7-GHz versions, these new instruments are smaller, lighter, and have a longer battery life than other more expensive handheld RF products. PSA Series II analyzers incorporate a 4.3” (11 cm) backlit thin-film transistor (TFT) color touchscreen display, with a high-capacity rechargeable Lithium-ion battery to produce more than 8-h operation per charge. The PSA Series II PSA1302 has a 1-to-1,300-MHz frequency range, while the PSA Series II PSA2702 operates up to 2,700 MHz. Dynamic range is 80 dB with a noise floor at –100 dBm. Resolution bandwidth is selectable down to 15 kHz.

The PSA Series II’s features include sweep modes (e.g., continuous, single, peak hold, and sweep average), AM/FM audio demodulation with built-in speaker, and data logging for traces, data points, or screen images (with storage for 10,000 entries per file triggered from a key press, internal timer, external trigger, or the limits comparator). Traces or complete screen images can be saved to file and compensation tables for antennae or other external transducers can be created and loaded. USB host and device connectors enable the use of USB flash drives or direct connection to a PC.

PSA Series II analyzers are controlled via finger-operated touchscreen soft keys in a hierarchical menu system that provides rapid access to menu functions. All functions can also be operated using just the hard keys.

The ruggedized casing incorporates a rubber protection buffer, a bench stand, and screen protection. For bench-top use, the instrument can be operated from its AC charger. For portable use, its 8-h battery life can be further extended by selecting auto-off, which turns the instrument off (retaining all data) after a selectable delay of 5 to 60 min. from the last key press. The compact, handheld PSA Series II RF Spectrum analyzers weigh 20 oz, making them suitable for any portable RF service kit. For more information, visit www.saelig.com.

Member Profile: Ethan Winer

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Ethan Winer

Location: New Milford, CT

Education: Two years college for music

Occupation: Audio engineer, technical author, professional musician, and co-owner of RealTraps, a popular acoustic treatment manufacturer

Member Status: He has subscribed to audioXpress for approximately seven years.

Affiliations: Ethan does not currently hold official memberships with any audio organizations.

Audio Interests: Ethan is interested in all aspects of audio and music, but especially acoustics, and how fidelity is defined.

Most Recent Purchase: A Focusrite Scarlett 8i6 USB sound card

Current Audio Projects: Ethan has just completed creating a 2.5 hour music theory video course, “Basic Music Theory.” (The course is available for free on YouTube )

Dream System: He said he has his dream systems. Yes, plural. Ethan has two systems: A large home recording studio (two channel), and a 5.1 home theater in his living room. He said the key to excellence with both systems is more in the acoustic treatment of the rooms than the specific gear.

Member Profile: Garth Wasson

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Garth Wasson

Garth Wasson

Location: North Vancouver, British Columbia, Canada

Education: Garth has a BA and an LLB from the University of British Columbia and a certificate from King’s College London University, London, England.

Occupation: Retired barrister and solicitor (a lawyer)

Member Status: He has subscribed to audioXpress since 2005.

Affiliations: He currently holds no official memberships with any audio organizations.

Audio Interests: Garth said he is most interested in classical music.

Most Recent Purchase: A digital multimeter that measures inductance and capacitance

Current Audio Projects: Garth said he has just completed two 100-W, push-pull El34 amplifiers with output transformers that Doc Hoyer designed and built.

Dream System: He said the system would include a couple 100-W amplifiers with a good preamp, a good turntable, and Klipsch horn enclosures. He would also add a quality FM tuner, digital inputs, and a large TV with good sound input. Garth said he doesn’t care too much about surround sound, but he admitted that he does have a couple 50s he could use with his dream system.  “Obviously, I would want two more Klipsch horns there, too,” he added.

Q&A: Ron Tipton

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Ron Tipton

Photo 1: Ron Tipton tackles a project in his home work space.

SHANNON BECKER: Tell us a little about your background and where you live.

RON TIPTON: I was born in Chicago, IL, and by the age of eight, I was spending many Saturdays haunting the exhibits at the Museum of Science and Industry with friends. I suppose that was an indication of where my main interests lay. We moved to Kansas City, MO, when I was 10, and I had to content myself with scientific books and magazines: no science museums. I moved to Las Cruces, NM, in 1956 to attend what was then the New Mexico College of Agriculture and Mechanic Arts as a junior in the Electrical Engineering department. (The college became New Mexico State University in 1960.) I did pick up a couple of EE degrees, but I didn’t complete my doctorate because of business. I started Testronic Development Laboratory (TDL) in 1957. Except for a few years in northwest Arkansas (more about that later) and back in Kansas City for a while, I’ve lived in the Las Cruces area since 1956.

SHANNON: Describe your career as an electrical engineer and your job at White Sands Missile Range.

RON: In the early 1960s, the telemetry (radio transmission of data from an air- or space-borne vehicle back to the ground) band was around 220 MHz. There were a number of reasons, including smaller antennas, to move the band to 2,200 MHz. I was part of the project to accomplish this move. These were the days of vacuum tubes, so designing and building a transmitter was a big challenge because any vibration in the missile (there was a lot of it) vibrated the tube grids causing frequency modulation of the output, which had to be very low to be acceptable. Several contractors tried and failed but one, Microdot, was successful. It was a big day when we flight tested the transmitter on a missile and it worked fine. Now, of course, the transmitters and receivers are all solid-state and reliable operation is taken for granted.

Most of my other work was with various passive tracking systems. Unlike radar, which is an active tracking system, passive systems use the emissions from the vehicle, usually the telemetry transmitter, to perform the tracking. This usually requires a ground-based antenna field, because they are phase and phase-difference measuring systems, so they benefited from the smaller antennas at 2,200 MHz. By knowing the antenna spacing and the telemetry transmitter carrier frequency, data was collected that was later converted to a track by computer analysis. I retired in 1995, so with the increases in computer performance real-time tracking is probably used today.

The telemetry transmitter’s carrier had to be very stable for this to work. The various detection oscillators in the ground-based receiver were set so the output to the tracking system was usually 5 kHz. The usual phase detectors were period counters. The track data 5 kHz started a high-frequency counter and the reference 5 kHz stopped it so there was some ambiguity in the count. I designed and built a very precise 5-kHz autocorrelation phasemeter using a Motorola DSP56156 digital signal processor. This resulted in 1,700 samples per cycle with a phase measurement resolution of 0.212° with a corresponding lower tracking error. I have never followed up on it, but this technique could be used to design a very precise audio phasemeter.

SHANNON: How did you become interested in audio electronics?

RON: I think it was a result of my love for music. In the early 1950s, I bought an inexpensive 33-1/3/45-rpm turntable, and I needed a preamplifier and power amp to use it. I decided to build them so I found a combination preamp, low-power amplifier in some book. I bought all the parts from Burstein-Applebee in Kansas City, built it, and it worked fine. It used vacuum tubes, of course. I was hooked.

SHANNON: Can you tell us about your work with active filters and pseudo-random noise generators? Do the models you used then still function today?

RON: By the mid 1960s, useful op-amps were available—in particular the LM741 general purpose, the LM301A for better performance, and the higher frequency NE531. It was practical to design and build active filters using either the voltage follower or multi negative feedback topology. I built them in potted modules and as plug-in cards. I had several orders for sets of third-octave bandfilter cards that exactly fit a Hewlett-Packard audio spectrum analyzer. I sold them for less than the HP price! I still have a few of the potted module filters and they work just as they did 50 years ago. Two 50-year-old active filter modules are shown in Photo 2.

Photo 2

Photo 2: Ron built these two active filter modules 50 years ago. The left-hand unpotted module is a tunable low-pass filter as part of the GMS piano tuning aid.

The left-hand unpotted module is a tunable low-pass filter mentioned in the next question as part of the GMS piano tuning aid. It is 2” square to give you an idea of its size. The six gold-plated brass terminal pins extend about 0.2” out of the epoxy potting material to make the electrical connections to the circuit.

The first pseudo-random (P-R) noise generator I designed and built, the model 105, used RTL logic. This was an early logic family in standard DIP packages. I didn’t sell even one of them but it was an interesting learning experience! Next came the model 108, which used 7800 series TTL logic. The 108 and its variants (i.e., the 108-M4, 108-M5, 109, and 111) all sold fairly well.

Perhaps I should mention that P-R noise is just random noise within each sequence but the sequences exactly repeat with the sequence length dependent on the shift-register length and the clock frequency. Thus, we have a random signal with a known period just like a sine or square wave. My article: “Audio Testing With Noise,” Voice Coil, December 2010, discusses P-R noise details.

The 108-M4 and 108-M5 were both “gated” generators. They could put out a noise burst with the duration and repetition rate set on the front panel or triggered by a pulse from a remote location. These were both custom models designed to meet the customer’s needs. This was economical for the customer because the 108-series all used the same size plug-in circuit cards with each card performing a certain function: clock generation, shift-register, gate generator, and so forth. The cards could be “mixed” to provide the required performance. You can find more on this topic, including photos, in the Voice Coil article mentioned earlier.

Photo 3

Photo 3: A typical plug-in card is used to perform a certain function (e.g., clock generation, shift-register, gate generator, etc.)

Photo 3 shows a typical plug-in card. They measure 4.6” wide by 4.7” high.

SHANNON: What kind of audio products did you build for GMS? Can you share some of the challenges involved with the designs?

RON:  I designed two lines of guitar amplifiers for GMS and both were marketed by Gretsch. The lower-cost line was the Broadkasters about which I don’t remember much or have any documentation. The premium line was the Nashville series, which included the Pro-Lead, Pro-Steel, and the Pro-Keyboard models. These were rather straight-forward designs with a few exceptions.

The reverb units were mechanical springs in a metal housing with a small loudspeaker without a cone driver at one end and an inductive pickup coil at the other end. I needed some power to drive it because there was quite a bit of loss in the spring, which was about 10” in length. I designed a small power amplifier in a potted module with an aluminum baseplate to transfer the heat to the amplifier’s chassis. A circuit diagram and photo can be found at www.tdl-tech.com/nashville.htm.

The Pro-Lead model had a tremolo circuit, which was also built as a potted module because Gretsch wanted to keep the circuit under wraps. It had rate and intensity controls on the front panel, a foot-switch jack to turn it on and off, and an LED that illuminated when it was on. I thought it was a rather clever design at the time. Details can also be found on my website.

The Pro-Keyboard had what we called an Accent module which was controlled by a three-pedal footswitch which enabled the musician to instantly change the volume. I though this design was rather innovative because I used the three pedals to get five levels of volume change by sensing how deeply the pedal was depressed. This circuit was also built as a module to hide the design. It used a 4066 analog switch to change the gain of an LM301A op-amp. The other logic chips just decoded the foot pedal positions to control the 4066. The circuit diagram for this design can also be found on my website.

In addition to the guitar amps, I designed a digital piano-tuning aid for the Baldwin grand piano manufacturing plant in Conway, AR. It was a box that produced the 88 piano notes through a built-in 6” speaker. The note to be played was selected by a row of 12-note push buttons and a row of eight octave push buttons or by a two-pedal foot switch, one pedal for the octave and the other for the note. There was also a front panel rotary switch for the normal equally tempered scale, a quarter semitone high or a half semitone high. (Pianos were often tuned slightly high so the structure could settle into the proper tuning.)

The heart of the piano-tuning aid was a 4059 programmable frequency divider, also called a divide by N divider where N was an integer number and the output frequency was the clock frequency divided by N. The integer numbers, N, were read from a PROM. The 4059 output was a square wave which contained too many harmonics to be useful in tuning a piano. (The person doing the tuning matched the output of the piano-tuning aid to the piano note by tightening or loosening the tuning pin.) So I needed to low-pass filter the output. I did this with a frequency-to-voltage converter whose DC output voltage controlled the cut-off frequency of a voltage tunable low-pass filter. The output was a sine wave because the filter’s cut-off frequency tracked the output frequency. I considered this one of my more interesting designs! (The F to V converter and the tunable low-pass filter were potted modules to conserve space and all of the logic chips used were RCA 4000-series CMOS because RCA was a major supplier to the Baldwin Piano and Organ at that time.)

SHANNON: You have been TDL’s founder and principal designer for many years. What has been your best experience?

RON: I think the most interesting task was designing the “Hot Strings” guitar for Chet Atkins. (It was marketed by Gretsch as the “Chet Atkins Super Axe.”)  This project is fully described in my article: “Designing the ‘Hot Strings’ Guitar for Chet Atkins” (Multi Media Manufacturer, May/June 2006). But I’ll recount some of the highlights.

Chet heard about my modules in the piano-tuning aid so he came to the GMS plant in the fall of 1975 to discuss the idea of putting some effects modules inside the guitar body. We finally settled on a compressor (2” × 2” × 0.5”) and a phaser (2” × 3” × 0.5”). By the end of August 1976, I had an assembled guitar ready for trial. Chet came to Prairie Grove about mid-September to give it a try. He was generally pleased with the performance, but he wanted a couple of changes. This was also the time he picked the “Hot Strings” name. We made the changes and my final set of drawings is dated January 19, 1977. I’ve never seen a production Super Axe, but I do have several photos.

The rear cover of RCA Records LP APL1-2786 (1978), “Chet Atkins and Les Paul: Guitar Monsters” shows 12 photos of Chet and Les. This guitar can be clearly seen in five of them.

Through the years, I’ve heard from several owners of a Super Axe and replacement modules are now available from the TDL website.

SHANNON: What was your first personal project? Why did you build it? Is it still in use?

RON: My first personal project was the mono phono preamp/power amp I mentioned previously. No, it’s not still in use, and I have no idea what happened to it.

SHANNON: You wrote an article, “A Vintage Turntable Revisited,” in audioXpress, September 2012. Why did you think it was important to revisit it?

RON: The revisit was important because of the carbon fiber tube tone arm which let me lengthen it and thus, reduce the tracking error. While it is true that this resulted in a rather large turntable, I think it was worth it. It is still much in use because it sounds very nice.

SHANNON: Can you share the details on some other personal audio projects?

RON: I usually have quite a few projects going at the same time, but I’ll talk about two of them that may be of interest.

I’m building a stereo pair of three-way speakers, that is, three inputs: base, mid-range and upper frequencies (see Photo 4).

Photo 4

Photo 4: This will be a stereo pair of three-way speakers. The three inputs will be: base, midrange, and upper frequencies, once Ron completes the project.

These will be sealed enclosures and you can see the internal bracing in the photo. The front and rear panels are 13-ply Baltic birch with 0.75” MDF for the sides, top, bottom, and braces. The box was computer designed for all Dayton (Parts Express) drivers. The top and bottom “holes” are for the 8” reference-shielded woofers (295-366), the next two holes toward the center are for the 2” dome midrange (285-020), and the center hole is for the 0.75” neodymium dome tweeter (275-035). The tweeter is rear-mount, but I have solved that construction problem! The seams are caulked, the black patches on the inside walls are barium-filled vinyl for sound absorption, and the woofer and midrange drivers have T-nuts installed for their mounting screws.

I have built active crossovers, each with the required three outputs, but a Behringer DCX2496 can also be used. The performance comparison will be interesting. Yes, it does require six power amplifiers, but that’s not such a big deal these days even though it would be best if they were all the same type. The simulated overall frequency response looks good.

Some of my projects are studies and they are difficult to describe or to photograph until finished. It’s also difficult to photograph a construction project for which I have all the material, but I haven’t started putting it together yet. So I’ll just tell you what it’s about.

As some of you may know, my company, TDL Technology builds audio equipment for sale. We do a 100-hour burn-in for quality control so our failure rate is nearly zero. But I’ve wondered about doing more. What about bad solder joints or microphonic parts (rare, but possible even with solid-state parts)? It occurred to me that a vibration test might be useful but commercial shake tables are out of my budget. So, what about building one?

The top surface to which the device under test will be fastened is a piece of 20” × 12” × 0.5” thick piece of ceramic tile cemented to a 20” × 12” sheet of 0.75” 13-ply Baltic birch plywood. On the underside of the plywood, two Aura Pro Bass Shakers (Parts Express 299-028) are mounted and wired in series. This composite platform will be supported above its heavy base at its four corners by 0.25” diameter rods and neoprene vibration isolators (McMaster-Carr 94955K31). The device under test will be attached to the top surface with cotton webbing belts fitted with ladder-lock buckles. Accelerometers (Measurement Specialties ACH-01) will be cemented to the top surface and mechanically attached to the device under test to monitor the vibration level.

The Shakers have a frequency response of 20 to 80 Hz so a low-pass filter will be used at the output of the noise generator. I expect white or pink noise will be the most useful. It’s possible that it would also be a useful subwoofer!

SHANNON: You have done a lot of work with audio restoration. Why do you think it is important?

RON: Personal (home) restoration is important because it’s fun and because the music needs to be saved. Record companies have released a tremendous number of records in the past 100-plus years and a few have been remastered and rereleased—a very few. Record archives do their best at restoration but many collections are very large and funds are always limited. I think it’s up to amateur restorers to do as much as possible.

SHANNON: We went from vinyl to cassette to CD to DVD to music servers. What do you think the next audio format will be?

RON: I hope the next big breakthrough will be holographic recording—but we’ll have to wait and see.

SHANNON: What do you see as some of the greatest audio innovations of your time?

RON: The invention of solid-state electronics is at the top of the list. It changed our world. And, I don’t mean just the transistor. LEDs and solid-state lasers made possible so many innovative audio products.

SHANNON: Do you have any advice for audioXpress readers who are thinking of building their own sound systems?

RON: I’ve been building most of my own audio equipment for more than 60 years so it’s possible that I’m prejudiced. As I sit here writing this I can see 10 different power amps and three different phono preamps that I’ve built. Getting into building your own can be addictive so beware! But if you have the inclination and the means, go for it! You will also learn a lot in the process, not only about audio techniques but also how to properly do the construction.

New Year, New Goals

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With the January issue we mark the start of a new year. Our main aim is to discover and publish insightful articles about innovative DIY audio projects, handy design tips, essential acoustic theory, top industry events, and audio product news and reviews. In addition, we have goals for 2013 relating to the magazine’s layout and its website. Take some time to think about what we’re planning and feel free to let us know what you think. This is your magazine.

In his audioXpress January 2013 article, Doug Ford describes the design of a passive-matrix surround-sound decoder. The decoder features an analog time-delay that he implemented with a large number of cascaded all-pass networks. (Source: D. Ford, AXJan13)

In the near future, we’ll unveil a redesigned, modern layout you’re sure to find interesting, aesthetically pleasing, and useful all at once. Don’t worry. We’re spending ample time considering everything from fonts and colors to table styles and equation presentation. To address the needs of 21st-century readers, we’re asking relevant questions such as: How should we present  different forms? Can we incorporate additional graphics and images (e.g., infographics) to enhance the readers’ experiences with each issue? Can we use the magazine’s layout to engage more readers directly and foster more discussion and idea sharing in the audio community? The answers will influence the final product.

As for the website, we’ll build on 2012’s upgrades: we consolidated the content sections (e.g., audioXpress and Voice Coil) into one site; we chose an effective, easy-to-read blog-style  format; and we made membership management more user-friendly. From here, we’ll bring you more content on a more frequent basis. For example, we plan to deliver hi-fi product news in real time. We’ll also enable more authors to post articles on the site.

We hope you’re as excited as we are about these upcoming changes. For now, though, enjoy the January issue.

Q&A: Andrew Spitz (Sound + Interaction Designer)

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Andrew Spitz is a Copenhagen, Denmark-based sound designer, interaction designer, programmer, and blogger studying toward a Master’s interaction design at the Copenhagen Institute of Interaction Design (CIID). Among his various innovative projects is the Arduino-based Skube music player, which is an innovative design that enables users to find and share music.

The Arduino-based Skube

Spitz worked on the design with Andrew Nip, Ruben van der Vleuten, and Malthe Borch. Check out the video to see the Skube in action.

On his blog SoundPlusDesign.com, Spitz writes:

It is a fully working prototype through the combination of using Arduino, Max/MSP and an XBee wireless network. We access the Last.fm API to populate the Skube with tracks and scrobble, and using their algorithms to find similar music when in Discover mode.

The following is an abridged  version of an interview that appears in the December 2012 issue of audioXpress magazine.

SHANNON BECKER: Tell us a little about your background and where you live.

Andrew Spitz: I’m half French, half South African. I grew up in France, but my parents are South African so when I was 17, I moved to South Africa. Last year, I decided to go back to school, and I’m now based in Copenhagen, Denmark where I’m earning a master’s degree at the Copenhagen Institute of Interaction Design (CID).

SHANNON: How did you become interested in sound design? Tell us about some of your initial projects.

Andrew: From the age of 16, I was a skydiving cameraman and I was obsessed with filming. So when it was time to do my undergraduate work, I decided to study film. I went to film school thinking that I would be doing cinematography, but I’m color blind and it turned out to be a bigger problem than I had hoped. At the same time, we had a lecturer in sound design named Jahn Beukes who was incredibly inspiring, and I discovered a passion for sound that has stayed with me.

Shannon: What do your interaction design studies at CIID entail? What do you plan to do with the additional education?

Andrew: CIID is focused on a user-centered approach to design, which involves finding intuitive solutions for products, software, and services using mostly technology as our medium. What this means in reality is that we spend a lot of time playing, hacking, prototyping, and basically building interactive things and experiences of some sort.

I’ve really committed to the shift from sound design to interaction design and it’s now my main focus. That said, I feel like I look at design from the lens of a sound designer as this is my background and what has formed me. Many designers around me are very visual, and I feel like my background gives me not only a different approach to the work but also enables me to see opportunities using sound as the catalyst for interactive experiences. Lots of my recent projects have been set in the intersection among technology, sound, and people.

SHANNON: You have worked as a sound effects recordist and editor, location recordist and sound designer for commercials, feature films, and documentaries. Tell us about some of these experiences?

ANDREW: I love all aspects of sound for different reasons. Because I do a lot of things and don’t focus on one, I end up having more of a general set of skills than going deep with one—this fits my personality very well. By doing different jobs within sound, I was able to have lots of different experiences, which I loved! nLocation recording enabled me to see really interesting things—from blowing up armored vehicles with rocket-propelled grenades (RPGs) to interviewing famous artists and presidents. And, documentaries enabled me to travel to amazing places such as Rwanda, Liberia, Mexico, and Nigeria. As a sound effects recordist on Jock of the Bushvelt, a 3-D animation, I recorded animals such as lions, baboons, and leopards in the South African bush. With Bakgat 2, I spent my time recording and editing rugby sounds to create a sound effects library. This time in my life has been a huge highlight, but I couldn’t see myself doing this forever. I love technology and design, which is why I made the move...

SHANNON: Where did the idea for Skube originate?

Andrew: Skube came out of the Tangible User Interface (TUI) class at CIID where we were tasked to rethink audio in the home context. So understanding how and where people share music was the jumping-off point for creating Skube.

We realized that as we move more toward a digital and online music listening experience, current portable music players are not adapted for this environment. Sharing music in communal spaces is neither convenient nor easy, especially when we all have such different taste in music.

The result of our exploration was Skube. It is a music player that enables you to discover and share music and facilitates the decision process of picking tracks when in a communal setting.

audioXpress is an Elektor International Media publication.

Differences in Amp Sound: What’s the Truth?

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Back in the 1960s, after crossover distortion was tamed in the better solid-state amplifiers, many serious audiophiles remained convinced that tube amps sounded better than any solid-state ones. Then in the 1970s, after Matti Otala and others had demonstrated the effects, cause, and prevention of slewing-induced distortion, the percentage of serious audiophiles who preferred tube amps may have declined slightly, but it certainly did not drop to zero.

THE GREAT DEBATE

The first tests to determine the cause of the difference in sound, if any, were mostly performed by engineers, who concluded that since the frequency response and distortion performance of the best tube and the best solid-state amplifiers were comparable, there must not be any difference (see Photo 1). Thus began the so-called “Great Debate.” I believe we are now in a position to put this debate to rest.

Photo 1: Tubes or transistors? A listener’s preference is a subjective choice.

First, I must affirm, as mentioned in a previous article, that subjective amplifier judgments are, by nature, individual perceptions. Every perception is a fact to the person perceiving. Thus, if you tell me you can hear a difference between two amplifiers, I have to believe you. If I can hear no difference, then perhaps you are a more critical listener than I am. If neither I nor any of a dozen other skilled listeners can hear a difference, then you have indeed heard a subjective difference, but since the perceived difference is not a shared reality, we cannot say there is an objective difference. If you cannot prove in a properly designed double-blind test that you can repeatedly hear a difference, then we must conclude that the difference you do hear does not proceed from physical, and therefore, determinable, causes.

THE GOLD STANDARD

In last month’s article, I discussed blind and double-blind testing. Both assume that the equipment under test is presented in a pair: two amplifiers or two speakers and so forth are being compared. In a blind amplifier test, the test subject (i.e., the person providing opinions about the equipment under test) does not know which amplifier is playing at a given time, in order to avoid the effects of extraneous variables (e.g., manufacturer preferences or finish details). Long ago, experimenters found that test operators (e.g., set-up technicians or other persons involved with the experiment) would sometimes unintentionally provide clues via facial expression or body language that could give away the identity of the equipment under test. Thus, double-blind tests, in which no one involved in the test operation knows which piece of equipment is being used at a given time, were developed. Double-blind tests are the gold standard for any tests involving human perception.

Some people do not like double-blind tests, believing themselves to be immune to hidden biases. However, there is no evidence to prove that even the best of intentions enable a person to avoid subconsciously tilting his/her test responses in a preferred direction. (Perhaps a Vulcan could?)

Resistance to double-blind testing is not limited to those who believe tube amplifiers sound better, although some of those listeners still offer objections to the elaborate test protocols. Some people firmly believe that any well-designed IC-based amplifier sounds better than any hollow-state amplifier and still claim that double-blind testing is unnecessary for them. Perhaps the most convincing for me personally was an individual who told me he made a change that was expected to make an amplifier sound better, but he was surprised to find that it sounded worse. No details of the test protocol were given. Of course, this amounts to hearsay, and thus cannot be considered scientific evidence.

DISTORTION MEASUREMENTS

In 1977, the British magazine Hi-Fi News and Record Review published an article by Jean Hiraga detailing sensitive distortion measurements made in Japan on a variety of tube and solid-state amplifiers that operated well below clipping. The article was reprinted by audioXpress in the March, 2004 issue. This article showed conclusively that differences in the distortion spectra of excellent amplifiers do exist, but no effort was made to correlate these measured differences with perception.

In the March, 1980 issue of High Fidelity magazine, “The Great Ego-Crunchers: Equalized Double-Blind Tests” by Daniel Shanefield was published. This article directly addressed the perception issue. Shanefield mentions the division of audiophiles into “golden ears” who insisted that they could hear differences in amplifiers and “nonbelievers,” who constitute the majority. He makes the statement: “In the next few years (after 1970) several small-circulation magazines espoused the golden-ear point of view, though they often disagreed with each other about which components were truly excellent and even changed their minds drastically from issue to issue.” Shanefield’s conclusion was that audible differences among good-to-excellent amplifiers do indeed exist, but that if the frequency response of all amplifiers under test was equalized to be flat within 0.25 dB, no perceptible difference remained. He includes the somewhat startling detail that when he compared three Dynaco 400 samples, frequency response differences of a few tenths of a decibel did exist, and the amplifiers did sound different. His experimental protocol ensured that the amplifiers were operated well below clipping. Shanefield’s tests were subsequently replicated by several members of the Boston Audio Society.

A/B/X TESTS

In October 1991, David Clark of DLC Design presented the paper, “Ten Years of A/B/X Testing” at the 91st Convention of the Audio Engineering Society. A/B/X amplifier tests compare an unknown amplifier “X” with two known amplifiers, “A” and “B.” The test subject’s goal is to determine whether “X” is “A” or “B.” For example, an excellent amplifier can be used as “A,” and a medium-grade amplifier as “B.” The test subject can switch at will among “A,” “B,” and “X,” but the switches may be connected so that position “X” is actually amplifier “A” (see Photo 2). If the subject can reliably identify “A” is “X,” then clearly the difference between “A” and “B” is perceptible to him. If not, we cannot conclude that there are physical causes for the differences that some listeners perceive under less-controlled conditions.

Photo 2: A flick of the switch enables test subjects to switch amplifiers. Sometimes “X” was the same amplifier as “A” or “B.”

A/B/X tests are usually double blind, but they do not require the equipment’s brand/model under test be kept from the listeners, since neither the listener nor the test operator knows which is “A,” “B,” or “X.” Test subjects are not permitted to communicate with each other.

In an A/B/X test, the listener chooses when to flip the switch, allowing whatever amount of time he feels is needed to properly identify the unit under test as “A” or “B.” A test may span several listening sessions, if the listener so chooses, or may be finished quickly if the listener is confident he has determined the identity of “A” or “B” as “X” in a short time.

A/B/X testing excels at finding perceptible differences, if any exist, but is not designed to establish levels of accuracy or preferability. The A/B/X test itself was compared with long-term listening as a method of identifying a calibrated 2.5% total harmonic distortion (THD) component that was added to a musical signal. The Audiophile Society acted as the “golden ears.” The Southwestern Michigan Woofer and Tweeter Marching Society (SMWTMS) acted as the “engineers.” Neither group could identify the distortion at a 5% confidence level in long-term listening tests. However, using A/B/X testing, the SMWTMS not only correctly proved the audibility of the distortion in 45 min. of testing, but also correctly identified a lower amount of distortion. In the complete series of tests, THD was found to be audible at 4% using big-band jazz music, 2% using flute music, and 0.4% using a sine wave. The spectrum of the harmonic distortion was not specified in Clark’s AES paper (AES Preprint 3167).

Clark added a note in his 1991 paper, based on a private conversation with Thomlinson Holman (the “TH” of THX). Holman has found that a number of professional power amplifiers do distort audibly when driving highly reactive loads (e.g., some theater speakers) when playing explosive movie sounds. The cause could well be that under such severe load conditions, the amps’ power supplies experience instantaneous drops in voltage. This condition would be easy to identify using an oscilloscope.

AUDIO PRO’S CHALLENGE

Audio professional Richard Clark (note: this is a different Clark), originally a believer that different amplifiers sound different, set up a $10,000 challenge: anyone who, by listening only, can identify which of two amplifiers is which, under rules he has established, will receive the prize. The rules can be found at http://tom-morrow-land.com/tests/ampchall/rcrules.htm. They primarily include minimum-quality levels for participating amplifiers, level matching, and so forth, all of which are essential to the validity of any comparative test.

In the years since the challenge was first offered, most large groups have obtained accuracy  of  49–51%, which are essentially the results one would expect to occur by chance. Smaller groups have never gotten more than 60% correct. In any statistical sampling, small test groups are more likely to deviate from chance results. As the test population is increased, test results converge toward a specific value. For a random process, a larger test population is likely to converge toward chance results. The fact that Clark found more nearly chance results when measuring larger groups is itself a strong indicator the test subjects’ responses were random, not ordered as would be the case if there were perceptible differences between the amplifiers being tested. These are averaged scores for the groups. No individual has ever reached 65% correct. These results do not permit us to say no person can ever hear differences between two good amplifiers, but they do strongly indicate that any such differences must not be very robust (see Photo 3).

Photo 3: Listeners must often determine for themselves what they hear (e.g., if this sound plotted here is actually clipping on transients).

No test such as David Clark’s or Richard Clark’s can ever show that there are no perceptible differences in amplifier sound. Proving the non-existence of anything is philosophically problematic because we can truthfully say only that any experiment did not find such-and-such a thing. However, we cannot perform all possible experiments. As an analogy, we cannot say there are no white crows, because we cannot look everywhere at once. If we postulate the nonexistence of white crows, the person who finds a single example will prove us wrong. So far, however, no person has demonstrated publicly in a scientific fashion that he can reliably distinguish between the sound of two good amplifiers with identical frequency response and low noise driven below clipping. And yet the perception remains that there are real differences in amp sound. As a consultant in acoustics and sound/video system design, I regularly encounter people who assume I must have a vacuum-tube stereo system “because everyone knows they’re better.”

It is true that almost all tube power amplifiers have a very slight high-frequency rolloff (tenths of a dB), but no test has convincingly shown that such a small deviation from flat is perceptible (see Photo 4). (If it is, and makes the sound better, should we all add inexpensive RC low-pass filters to our amplifiers to improve the sound so they sound like tube amps?)

Photo 4: One factor could be whether or not the output transformer affects the sound.

THE SEARCH CONTINUES

There are still serious researchers who are trying to find the elusive ingredient to tube sound. In October, 2011, Shengchao Li of Potomac, MD, presented a paper, “Why Tube Amps Have Fat Sound While Solid-State Amplifiers Don’t,” to the Audio Engineering Society’s 131st convention in New York. The paper was reviewed by two qualified anonymous reviewers. Li begins from the assumption that tube amps do indeed sound different. He proceeds to explain that the differences arise from output-tube nonlinearities, amplifier output impedance, and output-transformer nonlinearity resulting from the core material’s B-H curve. These nonlinearities, Li says, interact to reduce the low-frequency output of the amplifier under some conditions. The speakers, whose nonlinearity is worst at low frequencies, thus have less signal at those frequencies and thus produce less distortion. In this manner, some low-frequency output is traded for reduced low-frequency distortion. The first two mechanisms suggested by Li have been discussed in earlier Hollow-State columns. The third may be significant in low-feedback amplifier designs, but in more typical Williamson designs, transformer nonlinearities are largely compensated by negative feedback. Certainly all three mechanisms will be exacerbated at levels approaching or exceeding clipping. It would be instructive to see if a low-feedback tube amplifier could be identified in A/B/X testing, and just what level of overdriving is necessary to permit objective identification of any amplifier.

CHOOSING A SIDE

Let us now step bravely into the hornets’ nest. After four decades of testing by a number of very capable scientists, no evidence has been published that shows any objective difference among the sound of good-to-excellent audio amplifiers operated well below clipping, if the frequency responses are equalized within 0.25 dB of flat. Does this indicate there is no “tube sound”? It does not, for several reasons.

First, almost no home-music listener (or even recording studio engineer) equalizes the amplifiers flat within 0.25 dB. Virtually no speaker pairs are matched that closely all across the passband. And a flat response is not always everyone’s first choice. Hi-Fi systems of the 1950s usually had “scratch” and “rumble” filters to remove the sound of artifacts on vinyl recordings. These typically applied a 3-dB/octave high cut  above 8 kHz, and low cut below 80 Hz, respectively. Presumably they were included because equipment manufacturers found that their customers wanted and used them: at least under some conditions, listeners did not prefer flat response.

Second, a significant number of audio amplifiers are made for instrument amplification. The distortion used intentionally with electric guitars is well-known. I have also played with professional keyboardists who preferred tube-type Hammond organs because of the “growl” they produce at high volumes. This growl comes from distortion—largely intermodulation distortion—in the tube power amplifiers. A smaller percentage of audio listeners, but still a non-negligible number, prefer some distortion even in their music reproduced from recordings. Naturally, the distortion spectrum  is quite important to such people. As shown in a previous column and in Hiraga’s 1977 tests, that spectrum is very different for a tube amplifier versus a solid-state amplifier. It is a safe generalization to say that most people prefer tube distortion over the distortion of a solid-state amplifier. Most probably prefer triode tube distortion specifically.

Third, there are conditions under which distortion, even if not desired, occurs in an audio chain. It can happen when a person is listening to music at high levels, especially if low-efficiency speakers and/or underpowered amplifiers are being used. I believe this occurrence is the rule rather than the exception for many serious music listeners. Not only rock music, but also symphonic music, pipe organ music, and big-band jazz require a lot of amplifier power in order to play through typical home-stereo speakers at realistic levels without clipping. Aside from amplifiers for music listening, another place where “tube sound” is much hyped is in microphone preamps for audio recording. In this application, it is not uncommon for the microphone to put out surprisingly high voltages. Capacitor microphone cartridges, especially, are almost immune to clipping, so when exposed to high sound pressures, they can produce output voltages close to 1,000 times their normal output levels. Under these conditions, preamp clipping is pretty much inevitable. Again, the distortion spectrum is very important, and most recording engineers prefer the spectrum provided by tube pre-amps.

So in this columnist’s codgerly opinion, there is indeed a “tube sound” under some conditions, and many excellent technicians, engineers, and audiophiles find it preferable for specific applications. It is not, however, scientifically accurate to claim that hollow-state amplifiers are better or worse than—or even perceptibly different from—solid-state ones for all applications.

Purely audio considerations aside, many audiophiles prefer the aesthetics of a “warm,” artistically designed (perhaps handcrafted) amplifier over the usual “high-tech” appearance of most solid-state amplifiers. And many of us enjoy the “legacy” feel of the equipment setup when operating vacuum tubes are visible. These are valid reasons to buy hollow-state equipment, if it appeals to you.

TEST FOR YOURSELF

If you are still not satisfied about the topic of “tube sound,” you are invited to take part in an online test. The test has two parts. In the first part, you will be invited to use quality headphones (please, not computer speakers) to listen to a pair of .wav files of a short clip played by the lead guitarist of Darrell Harwood and the Coolwater Band. One file was made by recording directly to digital from the guitar, then playing the recording through a solid-state power amplifier adjusted to produce an acceptable amount of distortion for proper artistic effect. The other file uses the same digital recording, played through a tube amplifier adjusted in the same way. Both recordings were made using the same speaker and cabinet, and were recorded using a type 1 calibrated measurement microphone with a tensioned stainless steel diaphragm. The same physical setup was used for both recordings, and the levels of the recordings were carefully matched. You may play the files as many times as you wish, and will then be requested to send an e-mail stating which file, “A” or “B,” sounded better to you. If you choose to include your opinion as to which is the tube-amp and which is solid-state recording, please do that as well. The purpose of this part of the test is to illustrate the sound of the different distortion spectra of tube versus solid-state amplifiers.

The second part of the test consists of three .wav recordings of a brief clip of classical music. There is a reference clip made directly from the CD, a clip of the selection being played through a McIntosh hollow state power amplifier, and a clip of the selection being played through a commercial solid-state power amplifier.  Both of the “amplifier” recordings were made using an Evenstar Pro Peregrin studio monitor speaker, recorded using the measurement microphone described above, with the same physical setup. No equalization was applied to either amplifier, and the amplifiers were operated well below clipping. The reference (“X”) straight-through recording is identified, and you are asked to listen to the “A” and “B” recordings, determine which sounds more like the reference, and e-mail your results. The test can be found online at www.edcsound.com/amptest. It will be available until the end of 2012. Instructions for participating are included on the website.