Page 2: Wes Dooley & Audio Engineering Associates

Ribbon Rebirth

Not only are AEA's mics entirely made on site: so too are some of their tools, like this device which is used to hand-crinkle the ribbons.

As the 1960s progressed, Dooley dropped out of college but continued working with the college's radio station. His engineering skills led him to build some early project studios for musicians in Los Angeles, including rooms designed around the new Moog synthesizers. John Stephens, who had worked at the NASA Jet Propulsion Laboratory, was building innovative tape machines, including an eight-track that you could carry — a far more appealing prospect for Dooley than the large, heavy and sometimes unreliable Ampex multitrack machines. By the early 1970s, Dooley was travelling in Europe and Africa, sitting in on recording sessions, visiting microphone manufacturers, and making location recordings. He saw Decca classical sessions in London, watched the BBC trying to figure out how to record John Cage at the Roundhouse in Camden Town, and recorded traditional music for anthropologists working in Zambia. Back in Pasadena, he founded the AEA company with Bob Gerbracht. Their first product was a tall microphone stand that was light enough to carry around with you.

The heart of an AEA KU4 cardioid ribbon microphone, with crinkled ribbon held loosely in the vertical magnet gap by two small clamps.In 1976, RCA exited the ribbon microphone business. Dooley had been shown how to re-ribbon a mic by Dick Knoppow, AEA's chief engineer and vintage ribbon aficionado. Knoppow knew Jon Sank, an engineer who had been working at RCA on the classic mic designs from 1960 until the department closed. (Jon's son, Stephen Sank, continues the family tradition with the Cloud ribbon microphones, reviewed in Sound On Sound December 2011.) It became clear that there was a niche business in servicing the needs of ribbon mic users. Demand from the studios meant that AEA began to manufacture new parts so they could service the vintage RCA mics. In the UK, Coles were still making the 4038 studio ribbon and 4104 lip microphone for the BBC, and so AEA began servicing these mics for North American customers.

When AEA began producing their own ribbon designs in the early 1980s, Dooley and his engineers were adamant that they would not compromise on quality. They wanted to mesh art, music and technology, and produce microphones that served all three. Their design approach relied on critical listening, comparing live and control-room sound, before any measurements were made. AEA's first reissue of an RCA microphone, the 44, did not even come with a spec sheet. It was only when Oscar-winning film sound engineer Shawn Murphy said that the reissued mic sounded as good as his original RCA 44 mics that Dooley knew the goal had been achieved. Eddie Van Halen bought a pair of the AEA 44s for stereo recording, having noticed that the original RCA mic sounded the closest to what he heard when standing in front of a drummer. Les Paul told Dooley that the AEA R44 was his favourite mic.

Smooth Operators

The KU4, like the RCA KU3A on which it is based, is unusual in not having a figure-8 polar pattern. Its cardioid directionality is achieved using this acoustic labyrinth.

One significant benefit that Wes hears in ribbon mics is a lack of annoying high-end resonances. "We were raised up on Altec 604E monitors, which are like microscopes. They put things a little more forward than they really are. If you can make it sound good on those, it's probably going to sound good on a wide variety of things, but they're not accurate. Same problem with older Tannoys and JBLs, they have that edgy sound, which is the same sort of sound you get on condenser mics. You get high-Q resonances on large-diaphragm mics in the 8-12 kHz range, that 'tizz' which is so noticeable on a U47 or a AKG 414. If you play it loud with that edginess at the top end, either from loudspeakers or microphones, that's the reason you have less hearing sensitivity as the day wears on, and you turn it up. Eventually your ears can't protect themselves, and you become deaf.

"Ribbons don't have any extra high end; ribbons are low-tuned, as opposed to condensers being high-tuned like a drum skin, with a sound of their own. With low-tuned systems you put the ribbon in just tight enough to stay in the magnet gap. A big ribbon like the 44 that we do is very low-tuned. Most ribbons are in the 15-65 Hz range for tuning, ours are 16.5Hz and run down to about 12Hz. By the time you're up to a few hundred Hertz, the resonant structure has pretty much gone away. If it's a thin ribbon, it doesn't store energy. That's why the BBC uses a 0.6 micron ribbon in the Coles 4038. They went to 1.8 micron on the RCA mics, and Beyer went up to the 4-6 micron range where it's treated more like a piston. It's not quite as thick as in ribbon tweeters where you're trying to make it as sturdy as possible.”

Another great advantage of most ribbon designs — especially at low frequencies — is their very well-behaved and consistent figure-8 polar pattern, as compared with multi-pattern capacitor mics. "Ribbons hold pattern down to 20Hz because they're native figure-8. Condenser mics that try to be figure-8s do two things. Below about 400Hz they roll off in level, but they also go omni. The native pattern for a stretched-diaphragm condenser is omni, that's where they want to go. The original RCA 44 held pattern well, and sounded good off-axis, so you could wrap people around it. For nominal omnis, the BBC would tell you to only have people plus or minus 20 degrees [from the axis]. Yes, it's an omni, but it's only a good omni in that area.”

Good figure-8 mics have very deep nulls off-axis, and for Dooley, this is a hugely valuable property when trying to fulfil Wally Heider's principle of achieving as much as possible through mic placement alone. "That's the key to the interaction between the mics and the room, and with the PA system. How does the microphone sound on the dark side, where it has less output, and how does that influence your bleed? How much can you let the musicians hear each other, and how much do you have to block them out and run on headphones? Our rule of thumb is that the more the musicians can hear each other and play with eye contact, the less they have to think about technical stuff, like not liking the headphone mix. Everyone having 24 tracks of headphone mix burns through a huge amount of time, and starts putting technology in the way.”

Not To Be Sneezed At

In addition to critical listening, impulse response tests are now used to evaluate each mic's performance.

Ribbon microphones have a reputation for fragility; according to Wes Dooley, this is largely undeserved, though he acknowledges that sudden blasts of air are a hazard. "People say the mics are fragile — but a sneeze can be in the 50 to 100 mile-an-hour range!” And many failures are down to user error. Dooley recalls a conversation with an engineer at United/Western about a particularly egregious example: "The mic setup guys at Western had rolled a mic stand, in the wind and rain, with an RCA 77 on it and no plastic around the microphone, between Western and United, a block away.” The engineer at United told them to roll it right back and explain to the chief engineer at Western what they had done. Another time, a customer enquiring about a repair on a Coles 4038 explained that the weight of the mic meant the stand kept falling over. After the third time it had fallen over, the mic had stopped working. Dooley suggested investing in a gym weight to place on the base of the stand.

In fact, there's a trade-off between transient response (which is best in a ribbon with very low mass) and durability, as newer ribbon designs have shown. Mics such as the Fostex M11RP and M88RP, for instance, featured an aluminium ribbon on a circular plastic substrate. "You can do things like the printed circuit ribbons that Fostex did, which were like neodymium-magnet headphone drivers turned into a microphone. The Crowley & Tripp approach, now bought by Shure, is the same, except that you're holding the ribbon at the ends instead of all the way round, like a moving-coil diaphragm. It weighs more, but when something really bad happens, like when someone unplugs a guitar amplifier and the cone jumps out an inch, you're going to trash pretty much anything other than the Crowley & Tripp/Shure. The thing I love about the Shure is that it's in the same tradition as the SM57 and 58. You can take it anywhere and it's not going to hurt. For years I told people the Shure SM81 was the microphone to use on the junior high school stage. You need a mic which will take repeated drops from four feet.”

On the other hand, Wes Dooley does agree with another widely held belief about ribbon mics: that their performance is quite dependent on the choice of mic preamp and, in particular, that low-impedance inputs don't get the best out of them. "There's a really good 1950's paper that an engineer wrote about how at resonance, a mic's impedance rises dramatically, just like any loudspeaker. A mic with a narrow, high-Gauss gap like the RCA 77 goes up into the 1400-1800Ω range from a nominal 250Ω. If you're going into a 1000Ω input impedance, you have dips in the output of more than 6dB at resonance. A typical resonance for those ribbons would be around 50Hz. As one person said when we loaned them an AEA 18,000+Ω input impedance preamp, 'I didn't know 77s had any bass!' He'd never heard them with the right electronics before.”

He is, however, at pains to point out that capacitor mics can be sensitive to preamp choice too. "Forty-eight Volt phantom power was a wonderful thing for the original Neuman KM-series mics that only needed 0.4mA of current. The P48 power specification requires 10mA to be available per microphone, but many lower-cost or battery powered units don't have that sort of capacity. Tube mics came with bespoke power supplies, but now we have a one-size-fits-all approach, which leads to unintended consequences. Some P48 condenser mics need 10mA of current during start-up but only 4mA while operating. If mics like these are starved for start-up current, they will still deliver audio, but they don't sound quite right.

"A more common P48 problem, rarely diagnosed, occurs when pin two or three shorts to ground. Almost 7mA of current then magnetises the core of your mic's output transformer, which changes its sound. Once the shorted microphone cable has been fixed or the phantom power is turned off, the output transformer core remains magnetised. The transformer will sound different until it is deliberately demagnetised, or used to record a kick drum or a pipe organ.”

The Past & The Future

Although the operating principle behind the ribbon mic hasn't changed, and AEA's own designs retain a strong RCA influence, the process of improvement and refinement is ongoing. "We designed the R84 to be easier to manufacture today, and to have less stray fields. You put two together and they don't go 'clunk' like the RCA 44s and 88s do.” A paper-clip is enough to cause a major problem for a vintage RCA ribbon mic, due to its huge magnets, whereas the AEA R84 is somewhat more practical. "It doesn't weigh 8lb — we tried to make it light enough that it didn't cause stands to fall over.”

And, like the RCA mics before them, AEA's mics are built to last. "Here we've seen everything from 70-year-old ribbons that ran fine, to Abbey Road where they have 1935 Blumlein ribbons that they use all the time. These microphones don't have an inherent lifetime limit; they're real sturdy, if you don't sneeze into them! Since we work regularly with microphones that are that old, we make decisions. Instead of zinc cast parts, we do bronze and machined brass because we've seen failures at 50, 60 or 70 years — zinc is not a good material to work with! We're making microphones where we're going to be dead and gone, and the guys that buy them are going to be dead and gone, and if we don't have a nuclear meltdown or the asteroid hits, the mic are going to be in service and people will be doing music. We hope that electricity continues, and people are going to be recording!”