Richard Vandersteen: Keep on Truckin' Page 2

It turns out that the internal diffraction problems of dynamic drivers are far greater or as great a problem as the problems with the baffle, because there's as much energy coming off the rear of the cone as the front of the cone, and here you have a big magnet and a basket and everything, with all of this crap delayed only two inches—in time a few milliseconds—before the sound is reflected back. We probably pioneered minimizing the external diffraction problems involving time and phase—people have said that they enjoy what it does for us, and I think it's real—so the natural extension was to work on our own drivers where we have no reflective surfaces behind the radiating diaphragm. We're applying for a couple of patents on it; we're using very, very powerful magnets I bought in England. They're very expensive, but that's the secret, because the structure can be very, very small. And the basket is configured in such a way that it has no reflective surface; it's like a spider's web.

Now, this vectoring thing I told you about where you can look at what's coming from the cone: you can vector it out and look at what's coming from elsewhere. I measure it with the microphone in front of the cone, using the Crown TEF machine. You can eliminate the sound that came immediately from the diaphragm, take it out of the picture, and look at what's left a very small period of time later. It turns out it's only about 20dB down and is not linear: it's a lot of garbage.

Drivers have always been designed to be flat to take into account the negative effects that come back from all this structure, so without them, the cone itself has to be flat, without these reinforcements and cancellations and so forth going on at certain frequencies. It's been a very difficult four-year project, we've got an incredible amount of money involved in it, but it's finished now; the Vandersteen 3A's here, and that midrange driver is in it.

Kessler: Would you classify this as the first dynamic driver with all the beneficial properties of a planar driver?

Vandersteen: We don't know. The market will tell. I think this midrange approaches some of what drove me crazy for so many years about the planar speakers. We have more of that now. Do we have as much in all areas? Probably not. But then the planar speakers have other problems, so you're talking about tradeoffs here. Maybe we've made it close enough in that area so that some of the other advantages of a small point source are going to sway some people.

It's not a problem—we sell a lot of speakers—but when I listen, I always miss that midrange; midrange I could hear in a planar design so dreadful no one would give it a second listen. But if I listened around all that, it still had that midrange character I wanted.

Kessler: Because this midrange unit is a relatively new type of driver, doesn't it have its own signature that causes discontinuities?

Vandersteen: Our tweeters have already had that effect incorporated in them for the last three years. With a woofer, although it won't work in a two-way, in a three-way you can crossover out of them low enough to where these negative effects from the physical structures are happening at a higher frequency than you're using the driver to cover. A woofer's structure is basically transparent as long as you get out of it soon enough. Now at some point you get into the same problem as in the midrange frequencies, at 3–4kHz; a well-made, cast-aluminum basket, 8" woofer, any one of many good ones available, will have the same problem. But that's the whole beauty of a four-way or a three-way design—you can get out of it before that frequency.

We have had to redesign the woofer, but that was done because we were using the same basic woofer in our 1B, which is a little two-way. The reflection of the backwave is a great problem in a two-way. That was dealt with acoustically, not as well as in the midrange driver, but enough to keep it from nagging us on a three-way design. And it helped the two-way, but it just minimized the problem rather than solving it.

Kessler: What is the next stage in the refining of the baffleless system?

Vandersteen: The drivers have literally to be meshed to 0.1dB to make the concept work, because you don't have the averaging with the baffle anymore. So the crossovers and the drivers have to be fanatically matched to one another, and that is a production problem. It's also a design problem in that I have to find a faster way to do it. I'm very involved in computers right now. We've always done this, but I would like to match the drivers even more accurately to one another without having to jack the price up. That's something the Dutch in me won't allow to happen.

Kessler: You're now at a stage where you have models covering just about every level—though none of your speakers are actually budget designs—all the way up to the high end. Now, aside from production problems, which are refinements and have nothing to do with design, I believe that the next step in the development of the Vandersteen family has been working with subwoofers.

Vandersteen: Powered subwoofers. The only way to do it.

Kessler: Don't you find it a hindrance in the sense that you're supplying the amplifier, and that it forces the end-user to match whatever amplifier they want to buy with the characteristics of the amplifier you're using?

Vandersteen: We've got a unique solution for that. Our subwoofer is bizarre in that it has a first-order passive filter, nothing but a capacitor between the amp and preamp, rolling off the main amplifier and the main speakers at 6dB per octave, below 60, 80, or 100Hz—your choice. When I was developing the subwoofer, I found that the thing had to be quick, and it had to be floor-mounted so that you always knew its acoustic environment—the one thing we all have is floors in our homes. This thing is slot-loaded and floor-mounted. That makes things very predictable in low frequencies. That's one advantage. It causes some problems, but we can use a feedforward concept to solve those. The other thing I discovered was that many times the reason a subwoofer wasn't seamless was because you had different amplifiers, or different amplifier characteristics. And that was a big problem. So that delayed the subwoofer for three years.

We took an input circuit from an oscilloscope, which is a dual-differential floating input, so it doesn't matter if an amp's bridged: ground is not really ground. Our subwoofer samples at the amplifier output terminals. So you bi-wire, or if you're already bi-wiring your speakers, you tri-wire off the output terminals. The input impedance of the subwoofer/amplifier is about 4 Megohms. So the amplifier hasn't the foggiest notion the subwoofer is even there. It's like putting an oscilloscope across the terminals to see what's happening. It then samples that. Now remember, the amplifier is being rolled off below 80Hz by the passive filter, but those frequencies aren't gone, they're just attenuated as they go down. The subwoofer input circuit knows that this signal's been attenuated and restores it, meaning that you pay a 6dB penalty in noise. This is not a problem in the deep bass, at least not with the circuitry we're using.

This technique means that the amplifier playing your woofers sounds like you've got a great big version of whatever amplifier you had in your main system. The first negative comment we get is, "Wait, I've got a tube amp and it's not so great in the bass. You know, I don't really want that character carried on into the bottom." But a tube amplifier into a four Megohm load has a damping factor of how many thousand? It's only when tube amps have to deal with the mass and the movement of woofers that they take on that character. Their signal is state-of-the-art until it has problems dealing or interfacing with a large woofer.

In this case it has a four Megohm resistor to deal with, so it's no problem. Then you go through a high-current situation and there're three floor-mounted 8" drivers in there, a 300W amp, and it goes for it. So it will take on the little phase nuances and so forth that one amp has from the other. We don't know how to measure all these things, but we all know they sound different. But this thing will take on whatever character of amp you put on the top, minus some of the negative things. Those characteristics of an amplifier that are caused by a design problem are not passed on into the bass because that design problem has been removed. It's very innovative; I think it will be very widely copied in the future.

Kessler: Have you patented it?

Vandersteen: It is a patentable concept, but I basically don't believe in patents because, you know, who has the time to spend enough money and the time in court to back it up? In this industry there's not that much copying going on because the designers have a fair amount of ego, and no one will ever do it as cheaply as we can. I think it will be pretty obvious in the future who came up with the idea; I'll just let the market take care of it. Patents really don't protect anything. The US government will issue me a patent, but they're not responsible for enforcing it. That's done in the courts.

Kessler: Where it would cost a lot of money.

Vandersteen: Well, it's not the money, it's the time and the hassle. I've got better things to do. We're getting a patent on the concept behind this new midrange, however, because I think that is special, and easier to enforce.

Kessler: What is the next stage of development?

Vandersteen: At this point, we're selling a lot of product in Europe, and I want to come up with a ".5," a very high-quality mini-monitor of some sort. That's the present project. In addition, for the last three years I've been doing a lot of work in surface-mount speakers, trying to make them work in a wall—I'm very frustrated by that. The environment just doesn't make it! I could make one a little better than somebody else's maybe, but I'm still investigating a way to make it really work. I guess it's because they just don't make recordings with the mikes against the wall. The bass has some great advantages, but in the mids and highs you get so many time distortions that you just can't make it sound real. You can make it sound good and pleasant enough that many people would buy them, but I'm not really interested in how many we can sell. Obviously I want to stay in business and make a profit, but I want them to be something unique and special.

Kessler: Wall-mounting a speaker would seem automatically to defeat the notion of the baffleless design.

Vandersteen: Exactly! Absorption is an option, but I haven't found a material yet that absorbs well enough and is linear enough.

Kessler: But the non-linearity is something you can compensate for in a known design.

Vandersteen: Somewhat, but that's almost like saying you can use feedback, and we don't like to use feedback; look at our subwoofer. There are many feedback servo-type subwoofer systems that go lower than hell, that will buckle the walls, that have low distortion numbers, but they sound like damn computers to me—they don't sound like music. I think the reason for it is that you can't let a woofer screw up and then say "Oh no! We screwed up! Measure how much!", and then bring it back around and correct for it. It's a fatally flawed concept.

Kessler: The servo subwoofers that I've heard have sounded overdamped.

Vandersteen: Yeah, but overdamping is easy to correct—you raise the Q, don't damp it quite as well. However, then you have another problem: it always seems to have something not quite right. You can't let something screw up and then decide to fix it later with feedback, because it's after the fact—again, a time distortion. We don't know how to measure that, don't know at what point it's too much, or less, or not enough. One advantage tube amps have traditionally had is that designers use less feedback in them.

Kessler: Tube amps do have lower damping factors.

Vandersteen: So what? You deal with those problems in other ways. If a guy makes a nice impedance curve on his speaker and put a little bit of output impedance in his formula when he designed the box in the first place, then a low damping factor works fine. It's only the guy who designs a speaker assuming zero output impedance who's going to have a problem. I don't think that's wise anyway—all amplifiers have output impedance. Even if they didn't, you still have speaker wire you have to connect it with, so our speaker works unusually well with tube amps with solid-conductor cable—I'm not saying I agree with that technology, but it works well—because we put some output impedance in the formula. We didn't assume an amplifier with an infinite amount of damping factor and zero-output impedance. Again, that's a problem, but you can control all those things, especially in a subwoofer with an amp. But there're so many advantages in low bass, knowing what woofer's going to be there, what box, how it's going to be configured, plus this other little trick we're playing, that it's a real advantage.

It's real important for systems to be musical. We can't turn ourselves into pieces of test equipment and try to measure how these things perform. You have to react emotionally. Music was Valium in the old days. If it's done properly and if the system's working properly, that is its function. It has been for centuries. We should address these things from a musical standpoint. Even though I'm very technological in my measurements, the ears are the bottom line, the final piece of test equipment. All you do is hope enough people agree with you that they keep you in business.

ARTICLE CONTENTS
Share | |

X
Enter your Stereophile.com username.
Enter the password that accompanies your username.
Loading