A Glorious Time: AR's Edgar Villchur and Roy Allison Allison Part 2

Lander: The legendary AR turntable remained in the line, of course.

Allison: The turntable provided a big profit. I don't know how many hundreds of thousands sold. That was Eddie's concept. What I did was help in production engineering.

Lander: In 1966, Stereo Review's annual market survey indicated that AR had just under a third of the speaker market locked up. What happened between 1967 and 1972, when you left?

Allison: In those five years we doubled sales and doubled profits, but our market share was dropping because the market was expanding. It was sort of like a pyramid, with very low-end stuff building out at the base, but it was building upward, too. Medium and high-end stuff was where the profit could be achieved; a lot of low-end people were flashes in the pan and went out of business after a while. But at the end of five years, Teledyne decided they wanted to exploit that lower end more than we were doing, and they didn't renew Abe's contract. They brought in a president who was very personable but who was totally unfamiliar with the quality speaker market.

Lander: Did they offer to renew your contract?

Allison: Yes, but not on the same terms. They were going to take away some of my salary and my responsibility for manufacturing. I decided to leave.

Lander: Had you and Abe discussed forming your own company, Allison Acoustics?

Allison: No. He was going to retire. I took time off, but I didn't just put my feet up; I decided to find out what was going on with loudspeakers and room interaction. I'd had a hint of it while doing some papers at AR. There was an unexplained phenomenon—nobody could tell me why it happened: a suckout in the middle bass range in almost every loudspeaker, almost every room transmission curve that we measured. That got my curiosity aroused. I wanted to find out what was causing it.

Lander: The same speakers measured flat in an anechoic environment, did they not?

Allison: Yes. It was the goal at the time, but when you put them in real rooms, they were not flat at the low end.

Lander: How did you begin your investigation?

Allison: I bought Bröel & Kjaer test equipment, which cost the earth, and I set about measuring loudspeakers under varying conditions and doing research to see if there had been any literature about this. It turns out there had been. I came across Waterhouse and Cook's original papers. They were scientists at the National Bureau of Standards, and they had done a lot of experiments in a huge reverberant chamber. They varied the distance of a small test loudspeaker to walls in that chamber and recorded the reverberant energy. They didn't extend their work to the use of loudspeakers in homes, but they did quantify the effect of reflections from room boundaries and developed some very elegant formulas for predicting that effect.

Lander: Were other people concerned with room reflections at that time?

Allison: Not that I know of. Everybody knew about standing waves, which tended to muddy the water and make these other effects very difficult to see. I did a great deal of empirical testing of my own and racked my brain, trying to figure out how to avoid this problem—and it was indeed a problem. Reflections from room surfaces can increase or decrease the power output of a woofer. Reflected energy increases the instantaneous density of the air in front of the woofer at very low frequencies. This provides an improved impedance match, and the efficiency of the woofer is thereby increased, along with the woofer's power output. At some higher frequency that depends on the distance or distances from the room surface or surfaces, the reflected energy goes out of phase with the woofer cone motion. That decreases the instantaneous density, and the woofer efficiency decreases. That's what causes the dip.

Now if the woofer is fairly close to one room surface and distant from others, in most home listening systems, power output in the range between 100 and 300Hz will drop about 1dB below what it would be without the nearby reflecting surface. At very low frequencies, there would be a 3dB increase in power output. That means, given maximum increase and maximum decrease, there's a total variation of 4dB. With the woofer equidistant from two intersecting surfaces, the dip is 3dB; factor in the maximum rise, in this case 6dB, and you have a 9dB variation. If it's equidistant from three surfaces that intersect at right angles, the dip would be a devastating 11dB and the maximum rise 9dB—a 20dB change over the bottom octaves. If the woofer is not on the line of symmetry, which is to say the same distance from all three surfaces, the dip is less severe but can still be significant. In home listening situations, I've found this reflected impedance typically causes variations from 5 to 12dB. If a tuner or receiver exhibited variations like this, it would be rejected out of hand.

Lander: You hold a patent relating to this boundary-effects phenomenon. What does it cover?

Allison: The design of cabinets that get the woofer very close to one or more adjacent room surfaces. That changes the frequency range of the dip, because the closer the woofer is to a surface or to the point where surfaces intersect, the higher in frequency the dip occurs. In the case of a three-way system, it's possible to position the woofer so the dip is above its operating range, and to place the midrange driver far enough away from an intersection for the dip to occur below its range. In effect, that eliminates the problem. This approach really isn't feasible with two-way systems, because the woofer has to handle frequencies high enough to put the destructive reflections within its range. But you can build a cabinet that has the woofer very close to one surface—the best place is on top—and then position that cabinet so distances to the other nearby room surfaces are staggered. Doing that creates mild dips that are spaced along the frequency axis. They aren't able to add in the nonlinear manner that they would if the distances between the woofer and all adjacent room surfaces were equal.

Lander: You then applied all this to speakers meant for very specific room placement. The first, the floorstanding Allison Model One, which had a pair of 10" woofers in each cabinet, and the Model Two, a smaller version that used 8" woofers, were both designed to be backed up to walls away from corners. The floorstanding Model Three needs corner placement to compensate for the dip. Model Four was a bookshelf unit, and there were other models as well. You also designed the midranges and tweeters that your speakers used.

Allison: Developing midrange and tweeter systems that were high enough in quality to complement the woofer we anticipated making was much more difficult. I worked out a configuration that I thought would produce extremely wide dispersion, which I deemed essential. I always wanted maximum dispersion of energy at all frequencies, and preferably the same amount of energy at all frequencies, and I set about to get it. That resulted in what was then a unique design for a tweeter-and-midrange configuration: what is essentially half a pulsating sphere. When you make it flexible—from paper—and clamp the outer edge to the mounting plate, then drive it at the midway point, the surface of this driver is going to be forced to change its radius of curvature so that there's a relatively large component of motion at right angles to the voice-coil as well as in line with the voice-coil motion.

Lander: And this gave you the dispersion you were after. Do you still favor paper cones?

Allison: Yes, I do. Not for a woofer, where the material doesn't matter very much as long as it works like a piston. At the other end of the spectrum, I don't want it to work like a piston, because even a small tweeter, if it's big enough to produce any reasonable amount of energy, is going to become directional at very high frequencies. So I have to use a very flexible material, and paper has a nice ratio of stiffness to sound-energy absorption when it flexes. With the right configuration and density and stiffness, paper can behave in a unique way. It's aided in my design by the material used to clamp the outer edge to the mounting plate—a very thin layer of foam, which is pretty effective in absorbing any energy that wants to reflect back from the edge and cause nonuniform response.

Lander: You began corresponding with the speaker expert Dick Small when he was working on his PhD thesis in Australia, and maintained that relationship. In fact, you played the first pair of production Model Ones for him. Tell us that story.

Allison: He and his colleague Neville Thiele were making a speaking tour of the United States and had dinner with Nancy and me and our children. So after dinner we sat them down and played some music for them on Model Ones. Their response was very polite but unenthusiastic. It turned out that they were used to hearing speakers, characteristic of the Commonwealth, that had very precise, pinpoint imaging. The imaging of Model Ones was satisfactory to almost everyone who heard them, but not to people as enthusiastic as they were about the concept.

I had emphasized dispersion in order to re-create as best I could the performance-hall ambience. I don't want to put up with a sweet spot, and I'd rather have less dramatically precise imaging but a close simulation of what you hear in a concert hall in terms of envelopment. For that, you need reverberant energy broadcast at very wide angles from the loudspeakers, so the bulk of the energy has a chance to do multiple reflections before it reaches your ear. I think pinpoint imaging has to do with synthetically generated music, not acoustic music—except perhaps for a solo instrument or a solo voice, where you might want fairly sharp localization. For envelopment, you need widespread energy generation.

Lander: That could explain why your Allison Acoustics speakers met with what you admit was a mixed response. You've also speculated that their appearance, which I've always liked, put some people off.

Allison: They looked unusual. People didn't expect speakers to look like that, and unconventional things can create suspicion.

Lander: Nevertheless, your volume did become substantial—and that was a time when new speaker companies kept popping up like weeds. At one point, though, sales began to drop off.

Allison: Sales picked up gradually, but we weren't growing as fast as I thought we should have to become really viable in the long run. Our overseas sales, mostly in France and Italy, accounted for a little more than half our total. Then we had a recession, and it really hurt Europe badly. That's when our slide downhill started.

Lander: It's easy to be nostalgic about the past, but music seems to have meant much more to people back in your AR years and in the early years of Allison Acoustics.

Allison: Actually, it was a glorious time.

1 Stereophile founder J. Gordon Holt joined Allison as an equipment reviewer at High Fidelity in 1955.—Ed.