An Interview with Billy Woodman, Founder of ATC Loudspeakers

Many people in the hi-fi industry claim to be musicians. Billy Woodman, of the Acoustic Transducer Company, better known as ATC, isn’t one of them. Yet he worked as a professional musician for more than 20 years and still plays in several bands. He’s played so often and for so many years that he’d even forgotten that he once played a gig with the famous UK guitarist Gilbert Biberian.

I haven’t played with Gilbert,’ he said when I asked him about it. ‘Yes you did,’ I told him. ‘It was back in 2011. You played a fund-raising concert for the Japanese Tsunami relief fund.’ After a pause of a few minutes, he laughed. ‘Oh yes, so I did’, he answered. ‘I’d completely forgotten. It was arranged by the flautist in my band, Carlos Alvaras.’ You can catch a sample of Billy’s piano playing here, at the Stroud Imperial Hotel.  Don’t miss his solo just around three minutes in… it’s really smooth. Alvaras is playing flute, with Mike Waite on bass and Mark Bharucha on drums.

Australian Hi-Fi Magazine: How many bands do you play in?

Billy Woodman: I really only play in the one band, but we change our name depending on the venue. If we do Latin gigs we call the band Zanzibar, whereas if it’s a more traditional gig we’re the Billy Woodman Quartet. We have a number of different names.

Australian Hi-Fi Magazine: What type of piano do you play?

Billy Woodman: I have three. The two in my home in England are both Bechsteins: an upright downstairs and a grand in the upstairs music room. Here in my home in Australia I have a Yamaha professional upright rehearsal piano. It’s a lovely instrument. I generally use a Roland electric piano when I’m performing, because most of the venues we play don’t have a piano.

Pictured Above: Billy Woodman, pictured playing a piano in the home of Peter Orehov, Audio Products Manager at CDA Professional Audio, the Australian distributor for ATC Professional Products.

Australian Hi-Fi Magazine: It was your love of music that got you into the loudspeaker business wasn’t it?

Billy Woodman: It was listening to live jazz that fired my interest in loudspeaker design, so that by the time I was 17 I was already building my own loudspeakers. I was born in Australia where I was fortunate enough to have had the opportunity to hear many of the best American jazz players playing in Melbourne.

Australian Hi-Fi Magazine: So how did you get started in the loudspeaker business?

Billy Woodman: I studied electrical engineering at the Bendigo Institute of Technology and wrote my final year thesis on loudspeaker design. I then went to work for Plessey-Rola in Richmond, Melbourne, as an R&D engineer. Plessey at that time had one of the flashest loudspeaker factories in Asia. It was amazing. They built 20,000 drive units a week, made their own cones, made their own magnets, did their own metal-bashing… even made their own magnet winding wire. I left in 1970 and by 1976 it had all been closed.

Australian Hi-Fi Magazine: Why did you leave Plessey-Rola?

Billy Woodman: I had an opportunity to play piano on a cruise ship… it was as simple as that.

Australian Hi-Fi Magazine: So how did you end up working as an R&D engineer for Goodmans, in the UK?

Billy Woodman: When the cruise gig ended, the last port was going to be in England, so I wrote to Goodmans and said I’m a loudspeaker design engineer, and I’m coming to England and I’d like a job. An interview was arranged, and I was hired. At that time Goodmans used to put all their young engineers through the Master of Science and Acoustics course at London University, so I also graduated from there while still working as an R&D engineer for Goodmans. It was all going well until Goodmans moved from Wembley down to Havant, which meant that I’d have a two-hour commute.

Australian Hi-Fi Magazine: Why didn’t you just move to Havant?

Billy Woodman: I couldn’t move because I had a night job playing piano in London, so each evening I'd come back from Havant, play piano until 2.00am, go home then get up at 6.00am to travel down to Havant again in the morning to start work. I did that for two years. It was mad, but I was young back then. That continued until I started ATC in 1974.

Pictured Above: Billy Woodman, founder of ATC, circa 1991.

Australian Hi-Fi Magazine: So what was the catalyst for going out on your own?

Billy Woodman: After moving to Havant, Goodmans decided it would be a good idea to have a range of drivers to compete with JBL, so I was put in charge of that bit of R&D and we developed ribbon wire-winding techniques and annealing and enamelling machines for making our own ribbon wire, all of which resulted in a range of three products… at least at that stage. But then, because of other factors, they decided not to go ahead, so I left the company and used all that knowledge to start ATC.

Australian Hi-Fi Magazine: Surely Goodmans can’t have been happy about that?

Billy Woodman: They were fine with it. They’d stopped the project, so I don’t think they viewed me as a competitor. In fact we remained on such good terms that they actually gave me all their tooling for their 18-inch driver for nothing… for free… you rarely get opportunities like that in life!

Australian Hi-Fi Magazine: But for you, that was the second opportunity of a life-time, because I’ve been told that for the first year you were in business, you were supplied with all your magnets for free.

Billy Woodman: Yes, that’s true. You have to remember that back then, there were five magnet manufacturers in England, all competing for the  same business… and there were lots of loudspeaker manufacturers in the UK back then. While working for Goodmans, I had discovered that one of those manufacturers, Swift-Levick, had supplied Goodmans with free magnets for its first year of operation to help get them going, so I went down to see Frank Levick, who was still alive. We talked and he said that since he’d given Goodmans free magnets for a year, it seemed fair that he’d do it for me as well. You can’t even imagine that happening now, but England was certainly a different place back then!

Pictured Above: ATC designer Ben Lilly demonstrating the excursion capability of an ATC woofer. For a full video of the demonstration, click HERE

Australian Hi-Fi Magazine: But your run of luck didn’t stop there, because then you became famous for supplying the loudspeakers for Supertramp’s first world tour.

Billy Woodman: That came about because I was supplying my PA75-314 12-inch driver—which handled more power and produced less distortion at higher sound pressure levels than any other driver at the time—to another Australian, Dave Martin, of Martin Audio, who was originally from Perth. He used the PA75-314s to build the first big touring PA system for Supertramp. It was that good fortune that got ATC started. It wasn’t just the number of drivers he ordered, it was the reputation—that Supertramp was using ATC speakers. That was just a terrific stroke of luck.

Australian Hi-Fi Magazine: To my knowledge, ATC is the only loudspeaker manufacturer that builds all its speakers in-house, in the same factory: tweeters, midranges, bass drivers, crossovers, cabinets, everything. And the most famous of those drivers is your 3-inch soft-dome midrange driver, which I understand you’ve supplied to other manufacturers, including Yamaha. Were you were the first to build a soft-dome 3-inch midrange?

Pictured Above: ATC's famous 3-inch soft-dome midrange driver.

Billy Woodman: Edgar Vilchur built a two-inch soft-dome midrange when he was at Acoustic Research, but when you look into the history, it’s not clear as to who was the first—there are a lot of competing claims—so I certainly wouldn’t put a bet on who was first! However, we were the first to build a successful three-inch soft-dome midrange. There’d been smaller ones around for ages, but they didn’t go down low enough in frequency. The benefits of the 3-inch soft-dome are the power bandwidth extension at the low-frequency end and that you can get the resonance down low enough that you can cross it at a low enough frequency.

Australian Hi-Fi Magazine: But why use a dome for a midrange driver at all?

Billy Woodman: One of the aspects of making a really high-quality three-way speaker system is that you can never produce a single drive unit that will perform consistently for more than a decade, so that’s 20Hz to 200Hz; 200Hz to 2kHz; and 2kHz to 20kHz. Almost all manufacturers of three-way loudspeaker use something like a six-inch midrange, and that’s too big really, so you have to manipulate its performance to make it work; it’s very directional at the top end of its range and also has poor performance at the upper end of its range.

That’s why the 3-inch soft-dome came to be. We run it from 350Hz to 3.5kHz, which it does within ±1.5dB, so the tweeter doesn’t have to work very hard—and the tweeter is the weakest link in any system, because it has such a small voice coil, which can’t take too much power—and the bass driver is doing 35Hz to 350Hz which is well within its capability. This means you can make the crossover frequencies completely seamless, so you’ll never be aware there’s been a transition from one driver to another—it will appear as the one device. If the mid is any bigger, that becomes less and less true.

The other advantages are that the 3-inch soft-dome has very low harmonic distortion—typically –45dB second harmonic and –63dB third harmonic—and it’s the only transducer I have encountered where the mass of the drive system equals the mass of the diaphragm assembly, thus ensuring maximum power transfer. The voice-coil is 75mm diameter and under-hung (3.5mm long coil in a 5.0mm magnet gap) to minimise distortion and maximise power handling capacity. The voice-coil also has a double suspension to minimise diaphragm wobble modes.

Pictured Above: Ben Lilly demonstrating the excursion capabilities of one of ATC's smaller bass/midrange drivers. Note the size of the magnet!

Australian Hi-Fi Magazine: One thing you haven’t mentioned so far is that ATC winds its own edge-wound voice coils, and I read an article somewhere in which it was printed you had invented the edge-wound voice coil. That seemed unlikely to me, and now I’m in a position to ask you directly whether that’s true or false?

Billy Woodman: It’s bullshit! The edge-wound voice-coil was developed in the 30s by Westrex in London, and Jim Lansing, who was working for them at the time, took it across to the United States. What we developed was a unique way of winding edge-wound voice coils.

Pictured Right: Billy Woodman, Founder of ATC, checking out a story on his favourite pianist, Bill Evans, before playing with his trio at the Maurocco Bar, in Castlemaine, Australia, in January 2014. 

Australian Hi-Fi Magazine: What is the advantage of edge-winding?

Billy Woodman: It’s simple. When you do round-wire coils they end up sitting across each other and the best you can do is 55 per cent copper. If you wind edge-wise, there’s a bit of air and glue space, but it’s possible to get up to 95 per cent copper. The more copper, the higher the efficiency. With very small coils it doesn’t work because once you get down to around a 1-inch diameter, coverage drops to around 80–85 per cent. The other benefits are that because the close proximity of the windings to the pole you get rid of heat better, and that because you also have only a single layer, you also get much improved thermal efficiency. Also, you can hold tighter tolerances with a single-layer coil than you can with a multi-layer coil. The space between our coil and the magnet is just 0.254mm… and you couldn’t do that unless you were using a single-layer coil. The benefit of having a small air-gap is that the bigger the air-gap, the greater the thermal barrier and the hotter the coil becomes. We’ve done lots of experiments on our midrange driver, abusing the hell out of it, and the coil never got more than a 100-degree temperature rise… so it would never get that hot in normal use.

Australian Hi-Fi Magazine: Which begs the question I guess, which is that if the performance of a three-inch soft-dome midrange is so good, why isn’t everybody using them?

Billy Woodman: Because they’re difficult to make and they’re bloody expensive! You think about it. That dome gets a hell of a hammering: I still get amazed that we can make it at all, because if the dome is too soft, it implodes and if it’s too hard the frequency response goes all over the place because you start getting high-Q resonances. Buying and retaining the stiffness of the dome material, before damping, has been one of the banes of our lives… but it’s completely critical. That’s one of the reasons we now use poly-cotton. We used to make them out of polyester, but we couldn’t get the consistency, so we were throwing a lot away. It’s because they’re so difficult to make that Yamaha ended up buying them from us: they wanted them for a specific project, and the quantity of drivers they required didn’t justify them tooling-up for it. We’ve also supplied the driver to Pioneer in the past.

Pictured Above: One of ATC's smaller midwoofers. The company's 15-inch bass drivers were used during the Falklands War to reduce the noise levels on British warships.

Australian Hi-Fi Magazine: In fact you supply drivers to many other companies, including the military…

Billy Woodman: We build a lot of special, small-run custom drivers for government as well as for the military. But in fact we only get the work from them because we’re the only manufacturer left in the UK that’s capable of producing specialised transducers.

Australian Hi-Fi Magazine: What did the military want with your drivers?

Billy Woodman: During the Falklands war, they put our 15-inch drivers on the funnels of warships to reduce the noise they made. It was actually a project developed by Andrew Jones when he was at the University of Essex, doing research into active noise control, before he’d got into loudspeaker design. I think he spent three years on it, during which he managed to achieve noise reduction figures of around 20dB… but to do it he required our drivers to produce sound pressure levels of around 135dB at 30Hz, which meant ten drivers and 6,000-watts of amplification for each funnel.

Australian Hi-Fi Magazine: You build two different 25mm dome tweeters, both of which are unusual because they don’t use ferro-fluid. What’s the difference between them… and why no ferro-fluid?

Pictured Above: ATC 25mm dome tweeters awaiting magnet assemblies

Billy Woodman: We do a standard version and a super version, same as we do with the midrange dome. The essential difference between them is that one runs at 1.5 Tesla and the other at 2.2 Tesla, so there are efficiency and bandwidth differences. The dome is made from polyester fabric with a polyester based coating and is driven by a neodymium magnet. We don’t need to use ferro-fluid because, like the midrange driver, we use a double-suspension, and one of the reasons we use a double-suspension is precisely because we don’t want to use ferro-fluid.

Australian Hi-Fi Magazine: Why don't you want to use ferro-fluid?

Billy Woodman: Because when speakers are driven hard in professional studios, the ferro-fluid will evaporate and you’ll start losing sensitivity on your high-frequency devices.

Australian Hi-Fi Magazine: But that wouldn’t happen when speakers are used in a home…

Billy Woodman: If someone is playing rock music at home they’ll start evaporating the ferro-fluid. If home speakers using ferro-fluid are hard-used with rock, I’d expect the ferro-fluid to thicken after about two years.

Pictured Above: An ATC tweeter. Tweezers point to the double suspension, the use of which means the company does not have to use ferro-fluid. For a full video showing technical details of ATC's tweeter, click HERE

Australian Hi-Fi Magazine: You’ve claimed that the Super Linear Magnetic System used in your bass and bass/midrange drivers is the most important development in speaker design over the past fifteen years. So what exactly is it?

Billy Woodman: I actually said ‘probably the most important development in speaker design’, but anything that reduces distortion by 15dB is obviously going to be a significant advance in loudspeaker design. The sound quality of our drivers improves dramatically as a direct result of our Super Linear technology, because low-level sounds that were previously masked become clearly audible, which provides an enhanced sense of realism. Essentially, it reveals another layer of information to the listener.

Australian Hi-Fi Magazine: Could you explain how it works?

Billy Woodman: There’s a White Paper on our website that says it better than I could (HERE), but if you want a single sentence explanation, one of the sources of third harmonic distortion in speakers is a result of eddy currents that form in the pole and in the front plate adjacent to the coil. What we’ve done is used two rings, one inside the front plate and another over the pole. These rings are made of pure iron in granular form, with an oxide coating around the outside, formed under extremely high-pressure.

By having pure iron as granules you maintain good magnetic performance while preventing eddy currents forming because of the high resistance. So you’re getting good magnetic permeability but a high electrical resistance, which changes the shape of the impedance curve which in turn reduces the relative level of odd-order harmonic distortion by between 12 and 15dB. It’s most useful on the bass/midrange driver in two-way designs, but we also use it on the bass drivers of our three-way designs. We didn’t patent it, so it’s readily available to whoever wants to use it.

Australian Hi-Fi Magazine: But it isn’t only the magnetic circuit that makes ATC’s bass drivers different is it? You’re also using a special cone material.

Billy Woodman: We use constrained layer damping (CLD) because, as a cone flexes, the central damping material is forced into a shape that shears the adjacent material sections. The alternating shear strain dissipates the vibration energy as frictional heat. The benefits of this are seen in reduced harmonic distortion, a high-frequency extension of around an octave—which eases constraints on crossover frequencies and slopes—and improved performance off-axis, because the dispersion performance of a CLD cone approximates that of a smaller driver as its effective radiating area gradually reduces with frequency.

Pictured Above: Some of ATC's drivers.

Australian Hi-Fi Magazine: So you’re not a fan of polypropylene cones then?

Billy Woodman: Polypropylene cones don’t have the structural integrity of using a fabric. With a fabric, as the cone wants to go into resonance you’ve got these fibres all rubbing against each other and you’re dissipating that resonant energy as heat. With a polypropylene cone, you get what’s called the polywobbles because when you drive it hard, it just suddenly becomes non-linear and the diaphragm will just start breaking up. That’s why they sound fairly nasty when you drive them hard. If you’re using plastic in a fibre, you get enough internal damping for it to retain its integrity.

Australian Hi-Fi Magazine: In addition to loudspeakers, ATC also manufactures a range of hi-fi electronics—pre-amplifiers, power amplifiers and integrated amplifiers, even a ‘CD-Amplifier’. Are these also built in your factory in Gloucestershire?

Billy Woodman: One of the few things that ATC does that no-one else does is that we’re vertically integrated: we make everything in-house. We subcontract some cabinets, some metalwork and our surface-mount electronics, but all our discrete electronics are made in-house. And, as I said before, all the drivers are made in-house, including all the voice-coil winding and the magnets are assembled and magnetised in-house as well.

Australian Hi-Fi Magazine: Did you design the amplifiers yourself?

Billy Woodman: No, that was all the work of Tim Isaac, who’s my partner in the business and one of the best analogue people in the UK.

Australian Hi-Fi Magazine: So no Class-D at ATC then?

Billy Woodman: I really don’t like the sound of Class-D amplifiers, they always cut off the decay of sounds—particularly piano!—plus, from a technical point of view, there is hysteresis in the comparators and rise time problems in the output, so all ATC amplifiers have Class A/B outputs.

Pictured Above: ATC SIACD combination CD Player/Integrated Amplifier.

Australian Hi-Fi Magazine: Your combination of a CD player and integrated amplifier in the same chassis, the SIACD, is a bit unusual. What caused you to develop it?

Billy Woodman: I’m really excited about the SIACD, which was a request from ATC China and ATC Hong Kong, which for the last seven years have been our strongest markets. They told us that 50 per cent of Chinese listen to classical and jazz music, and that professional women in China didn’t want clutter in their homes. That was the idea behind the SIACD…everything’s in the one box: You just add speakers.

Australian Hi-Fi Magazine: Yet you’re on record as saying that 80 per cent of your loudspeaker sales are of your active models, with passive models accounting for only 20 per cent.

Billy Woodman:That’s true, but it’s all come about because of my two passions: engineering and music. That’s why I’ve worked so studiously for such a long time getting rid of the anomalies in loudspeakers. Having active speakers makes it possible to do that because you can get not only the frequency response correct across the crossover frequency, but also a true minimum phase response, which in turn delivers tonal accuracy and a completely stable image. You can’t do that with a passive design.

Australian Hi-Fi Magazine: Is there a particular venue in which ATC speakers are used of which you’re the most proud?

Billy Woodman: One that gives me great pleasure is that Doug Sax, of Sheffield Labs, not only uses ATC speakers in his mastering studio, but also in his home. I am also very proud that every single studio in the Library of Congress’s Sound Archives is equipped with a pair of ATC speakers. Given that Americans are so parochial, for them to have bought loudspeakers from a small company from another country is pretty extraordinary. But another thing I think is quite extraordinary is that Gramophone magazine made us an ‘All-Time Audio Classic’ for our SCM-150, an honour which we share with Quad’s ESL and B&W’s 801. And obviously I’m proud that ATC speakers are used in the Sydney Opera House.

Pictured Above: ATC's Logo, and its SCM20ASL Pro V2

Australian Hi-Fi Magazine: I am surprised you haven’t mentioned that James Guthrie used ATC speakers to master the 5.1-channel SACD version of Dark Side of the Moon, and then also used them for the launch in New York.

Billy Woodman: James is a very close friend and he’s been very supportive of me personally over the years, as well as of ATC as a company.

Australian Hi-Fi Magazine:You spend three months every year here in Australia in Castlemaine, visiting your brother in Bendigo and your sister in Geelong, plus you’re still a gigging musician… so who runs the company while you’re not there?

Billy Woodman: We have over 30 people working at ATC and I’m not involved in day-to-day operations at all… that’s all done by Bob Polley, my ops manager, who used to work for Martin Audio. One of my main men, Toby, has been with me since I started, and I also have two young engineers in their thirties who will end up running the company. I’ve always run ATC like a family business, so we’ve always had very loyal staff and because of that loyalty, everything really becomes self-regulating.

Australian Hi-Fi Magazine: Apart from some good fortune at the beginning, and self-evidently the sound quality and performance of your speakers, what else do you think has made ATC so successful?

Billy Woodman: Personal relationships have been a large part of our success: I am enormously grateful to all the people who have believed in ATC and supported us over all the years. But another reason is because we take an enormous amount of care in everything we do. We’d never have built up such a reputation in the pro industry unless our products were consistent and reliable. #

Interview by Greg Borrowman, Editor, Australian Hi-Fi Magazine (First Published 2014).

Pictured Below: Billy Woodman, ATC Loudspeakers, with Peter Orehov, Audio Products Manager of CDA Professional Audio, which distributes ATC Pro in Australia.