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Stereophile's Editor John Atkinson Interviews Designer Jim Thiel

Stereophile's March '98 issue featured an insightful interview with Jim Thiel written by Editor John Atkinson. Here is an excerpt of that interview.

John Atkinson visited the THIEL factory last year for a tour and to sit down with Jim to discuss his design philosophy. The results were published in the March 1998 issue of Stereophile.

The interview begins with a discussion about Jim getting started in the speaker business and the choice of designing dynamic speakers. After designing and marketing two bookshelf style speakers starting in 1976 "I started thinking a lot more seriously about not just making a good product, but making a product that I hoped would be better than any others available," said Jim. "I started giving a lot of thought to the inherent limits and problems of dynamic speakers and identified one area: the phase and time distortion that's introduced by typical high-order crossover networks, and the fact that the drive-units are not mounted coincident with each other."

 

After designing and marketing two bookshelf style speakers starting in 1976, "I started thinking a lot more seriously about not just making a good product, but making a product that I hoped would be better than any others available."
-Jim Thiel

The birth of Coherent Source
Jim goes on to explain the beginnings of his Coherent Source design by using phase correct first-order electrical networks and drivers mounted along a sloped baffle for proper time performance, a basic design principle that is at the core of every THIEL product built today.

Jim also discusses driver design and how THIEL's drivers have evolved over the years from using modified OEM drivers to today's completely THIEL designed and built units. This means that "we can implement designs that are more exactly what I desire," says Jim. And that speeds up development time and allows for a lot more experimentation to get the design perfected. "we'd actually made 77 different experimental versions of the CS7's lower-midrange unit. We were able to go through so many iterations that we can end up with a design that is much closer to what we want." And what Jim wants-and has achieved-are speakers with lower distortion, greater dynamics, and more accurate tonal balance.

Evolution of design
The coaxial driver mounting, short coil/long gap motor design, and the use of metal diaphragms in the latest models are also discussed as an ongoing refinement of those basic principles Jim dedicated himself to 20 years ago. "All of our products have incorporated incremental advances in various aspects of their design [over the years]: improvements in the quality of crossover components, improvements in the drivers, improvements in the cabinet construction," says Jim.

Measurements and listening
One of the more interesting aspects of the interview is Jim's comment on how he correlates measurements with listening. "I view the ear as a measurement tool. And you can use it to evaluate the differences between the sound of loudspeaker designs just as usefully as you can use a computer to evaluate objective differences," says Jim. "I can make a change to the crossover circuitry and measure the effect that has on performance, then go and listen to what effect it has on the subjective performance. And I've done that tens of thousands of times over the years. You can build up quite an understanding of the correlations between measurements and subjective impressions."

And what goals does Jim seek to achieve in future THIEL products? "One thing that would be ideal is for all the drivers in the three- or four-way system to be coincident. So you would have not only a coaxial unit, you would have a triaxial unit, or four drivers that are mounted coaxially. That would be an improvement, if you could pull off such a thing," says Jim. "There are always improvements to make, with better diaphragm materials, lower-distortion, higher-quality components, better cabinet construction methods. We just have to see what new ideas we come up with in the future."

 

Reprinted with permission from

Issue 110 March/April 1997

This article has been reprinted in its entirety from The Absolute Sound with not one word censored or deleted. The Absolute Sound is the journal of High End audio and reports its findings an audio components and recordings without fear or favor from any commercial interests. Its literate evaluations and tests take place in real space, hence, music (the absolute sound) is the measure of reference. Subscriptions may be obtained from the business office at a special yearly rate of $54.95 for eight issues in the U.S. (Canada, $60; international, $75). You may call us directly with your Amex, Visa, Mastercard in hand at (516) 676-2830 (9 a.m. - 5:30 p.m. EST) or mail your check to The Absolute Sound, P.O. Box 360, Sea Cliff, New York, 11579.

 

I interviewed Jim Thiel and Kathy Gornik last year while in the earlier stages of evaluating the Model CS7. My impressions of the speaker, necessarily, were among my first ones. I'd like to go back and speak to him again: I am sure I would ask different questions now, pressing him perhaps on the difficult load this speaker (and his model CS5) presented to amplifiers. This interview is intended as the first in a series with designers of dynamic speakers about the state of the art. And the following review of the CS7 is the beginning of a long-range investigation of the cutting edge in moving coil design.

Editor/Publisher Harry Pearson: What about your design philosophy? What are you after when you design a speaker.

Jim Thiel: What I attempt to do is to design a product that will reproduce as accurately as possible and as completely as possible the musical signal on a recording which is a slightly different concept from taking responsibility for reproducing the original performance, since I have no control over the recording process. I do take responsibility for reproducing a signal that's fed to the speaker from the amplifier.

HP: How do you do this?

JT: (laughter) Simple question.

HP: I mean, what strategies do you use?

JT: All the strategies can fall into one of two types: subjective and objective. I use a lot of measurements. I use a lot of computer simulations, but no matter how much of that you do, it's not sufficient. I think it's necessary that the speaker measure well, but it's certainly not sufficient. Measurements only tell you part of the story. A lot of advances have been made in measurements, and they tell you a larger part of the story than they did 15 or 20 years ago. But they still don't tell you nearly the whole story and, therefore, you have to use what some would call subjective evaluation techniques; in other words, listening. But I like to think that listening is actually an objective technique.

HP: You mean it's observational.

JT: Yes

HP: That's not necessarily subjective.

JT: No, it's not subjective necessarily. The problem is you can't prove that you're being objective, but just because I can't prove it to a third party doesn't mean that I am not objective, that my ears can't take a reliable measurement of the sound the speaker is producing. My attempt is to develop a product that is musically accurate, rather than attempting to make a product that produces a sound I am pleased with, regardless of its accuracy. I'm not just trying to please myself, but I am trying to be true to the recording.

HP: What things are necessary for an accurate rendition of a recording? What do you have to do to get it? What are the basics?

JT: Certain things, I think, are agreed upon as being desirable. For example, a flatter uniform frequency response. This is a good example, though, because I think nobody would argue that flat frequency response is undesirable. Some people will take the extreme position that that's essentially the only thing that matters. Other people will say, well, it might be nice for frequency response to be accurate, but it's not really that important because there are so many other things that are more important musically than an accurate frequency response. I happen to believe that accurate frequency response is very important, and even a necessity, but, again, not sufficient.

HP: Okay, what next, after frequency response?

JT: Well, the ones that are kind of universally agreed upon are flat frequency response; low distortion; a wide, even dispersion of energy at all frequencies; a reasonably high dynamic capability; and reasonably deep bass reproduction. The loudspeaker should not store energy internally.

HP: It seems to me that, with the CS7, you paid particular attention to time, to time's domain.

JT: Well, we started thinking about time problems right as we were starting our business in 1976. Back then, being a rather skeptical engineering type, I was not at all convinced that this was important to music reproduction. There were speakers at that time whose designers asserted that they had achieved improved phase performance; or, in other cases, some also asserted that phase was not an important phenomenon. So we decided to experiment for ourselves and to see if we thought it was important, or not. I was developing the speaker that later become our model 03, and the drivers, the basic cabinet design, and I had a phase coherent crossover system worked out for it. We decided to also make a version of the speaker that used more conventional crossover systems that did introduce the typical amounts of phase shift, and to compare the sonic results of both of these products. And our impression, my impression, was that the phase coherence made a very significant difference. It was quite important. It's hard to put a measure on how important a single musical characteristic is. Is it twice a good? Ten times as good? How do you say how much it's worth? You could say that it was a subtle thing, and I would have to agree that somebody off the street who is not particularly interested in music or the quality reproduction of music, that, okay, it's not as important as a reasonably balanced frequency response. But to somebody who is very interested in the subtleties of music, it makes a most important difference. I was convinced that this is something of value.

HP: You're saying subtlety on a first-time listening. What about the long run? Over time what you say is subtle is not.

JT: You're right, you're right. to this day, I don't have good words. Being more of an engineer than a word person, I haven't really developed words for it. What I heard was that the phase-correct design sound much more real in the sense. I still don't have words for it.

Kathy Gornik: That experience was really funny. There we had two speakers that were virtually identical in every way except for the phase-coherent concept; we had the same drivers. And we could measure and test them before we installed them, and we built the cabinets identically. It was the kind of experience that made you leap out of your seat because you heard something that you hadn't known, until then, you were missing.

JT: Something you didn't expect to hear.

KG: And the other thing that was so funny is that a new problem cropped up. There was a difference to the sound in the phase-coherent speaker that didn't exist on the non-phase coherent speaker.

HP: What was that?

KG: Well, you have this uniform wave front, you can hear cabinet diffractions, you can hear grill frames. So that's how we got into this whole thing with the anti-diffraction-shaped baffles and grille and foam.

HP: In other words, you began to hear the cabinet and the diffraction of the grille.

KG: And you couldn't hear that in a non-phase coherent system!

JT: It's not nearly as obvious.

KG: So that was fun.

HP: Flaws become obvious that you had not heard before.

JT: Right. At the same time as you had a sense of realism that you could almost fall into a kind of coherent transparency might be a good word. The non-phase coherent design seemed artificial, it never felt like the sound was in the room with you.

HP: So what did you do then?

JT: Well, after running this experiment we decided that the only speakers we were going to design, from that time on, would be phase coherent loudspeakers. What I've always wanted to do is make speakers that were as good as I could make them, and hope that if enough people bought them, they'd finance my hobby of trying to make better speakers.

HP: The 03 wasn't your first design. There were two before, weren't there?

JT: Yes. Our previous two products were--well, our first product was kind of interesting from an engineering point of view, in that it helped us achieve a uniform frequency response, low distortion, etc.--the standard design goals. Its uniqueness was that it included electronic equalization so that we could get bass response down to 30 cycles without having a very large cabinet, and that was kind of an interesting engineering problem. But the 03 was the first speaker that was kind of a sonic quest for better sound.

HP: So in a sense, you might look at the 03 as being a foundation for all the work that is to succeed it.

JT: Yes

HP: So, if you have to summarize in 5,000 words or less what you've learned that lead up to the CS7--how has your design thinking evolved since that product?

JT: Well, I should say, actually before the 03, I was still investigating what type of loudspeakers I wanted to make, and I built several electrostatic, omni-directional, and corner horn loudspeakers, kind of evaluating the benefits and deficiencies of various approaches. And I came to the conclusion that, while dynamic speakers were far from perfect (and, in many ways membrane speakers were clearly superior subjectively), I wanted to pursue the design of dynamic products because I felt that none of the problems were inherent. I felt that they all had, potentially, solutions, whereas the limitations of other types of products, I felt were

HP: Inherent in their design, like an electrostatic. Problems you can't get around.

JT: Right.

HP: Would you like to illustrate a couple of those and then talk about a problem like stored energy and a dynamic driver.

JT: For example, take electrostatic loudspeakers. There is a limitation that has to do with output capability versus size versus bass extension. And that's one fundamental to the electrostatic design approach that's never been gotten around, and, I feel, never will be gotten around. But one of the great advantages to membrane speakers is that they don't use cabinets, are therefore do not have the problems of resonances and stored energy that can color the sound horribly in a dynamic speaker. Theoretically, there is no reason why a completely inert dynamic cabinet cannot be made. Make it out of two feet of reinforced concrete and you'll have a perfect sound! (laughter) That's an impractical solution. But it illustrates to me what was a very important point in that I felt none of the limitations of dynamic speakers were fundamental.

HP: And therefore there was greater potential for future development?

JT: Yes, exactly. That's been my approach for all these years: to identify a problem that's causing a sonic imperfection, then try to solve and eliminate that problem. So that, step by step, I try to develop more and more solutions to more and more problems that exist and therefore, hopefully get closer and closer to reproducing the real sound that is there.

HP: In fact, I hear people say that this is the most exciting era for dynamic driver designs that we've had in two decades.

JT: I think so.

HP: Tell me how and why?

JT: For example, the fact that cones of cone loudspeakers break up and resonate and color the sound has been well known for many decades. But, in the commercial market anyway, not many people did much about it for a long time. And I don't think it was for lack of materials. For example, in our newest product, the CS7, we use aluminum diaphragms, while aluminum, as you know, in not a modern space age 90s material. It is, in my opinion, far, far superior to materials used today. But really I think the development in moving coil speakers reflects a greater seriousness on the part of engineers to take this goal of accurate music reproduction very seriously. And you're right, there is a lot happening these days, and not just with diaphragm materials, but with motor design in the lab. I'm a little more excited about what's happening with motor design than in diaphragms.

HP: What are we doing? What are we finding out?

JT: We're finding out things that have been well known to physicists for all these years. For example, the strength of the ceramic magnets that power loudspeakers is not constant, as it was once assumed to be. When you take this big amplifier here and you run tens of amps of current through the voice coil of the loudspeaker, the voice coil itself generates a magnetic field that pushes against the magnetic field of the ceramic magnet it is powering, actually decreasing the strength of that magnet. Your amplifier is actually demagnetizing the driver on every half cycle and re-magnetizing it on the other half cycle. And it's an obvious form of distortion that can be measured. Solutions can be found. But in the case of a driver's magnet being de-magnetized by the power of the amplifier, we put a massive copper ring around the center pole piece of the driver and we also put an extruded copper cap onto the pole of the driver, and then we listened with these copper parts and without these copper parts.

HP: Do you want to tell me what you heard, specifically with the copper ring?

JT: The first product that incorporated the switch was the CS3.5 woofer. We heard tonality in the bass frequencies, a type of tightness or tonality--solidity--and as a type of solidity that we have not heard before.

HP: In other words, a consistency of weight.

JT: Yeah, that would be a good way to describe it.

HP: In 1978, when we first met, the CS7 would not have been possible to design, would it? I'm just trying to figure out if there are materials or advances in technology that were not available to you 20 years ago in this speaker, or is this speaker basically the old master's summation of what he's known to date.

JT: I now have computer software that will allow me to simulate advanced magnet systems, and of course, to make practical a lot of measurements that did not exist 20 years ago. The audio industry, in the past, has been hurt by the fact that not many competent engineers took the subtleties of sound seriously enough, and that's a big thing that's changed recently. I think a lot of people are involved in this industry who are very competent engineers and who do appreciate how exquisitely sensitive the ear is. Twenty years ago there were plenty of people willing to rely on their ear, but for the most part they weren't people who were also technically competent and appreciates the receptivity of the ear, instead of the typical engineering approach, which is to say, "If I can't measure it, it's not important."

HP: It doesn't exist.

JT: Yes, it doesn't exist and that's just ridiculous. I mean, there are all kinds of things I do measure in 1996 that I wasn't able to measure in 1978. Should I have not believed in their existence in 1978 because I couldn't measure them?

HP: So, let's come to the "7." What I hear is a level of resolution in a dynamic speaker I haven't heard before. But this resolution is not achieved at the expense of musicality. You keep getting deeper and deeper levels of detail, but it doesn't ever become amusical.

JT: There are not actually many people, I think, who could distinguish between musical subtlety that is overemphasized from a greater degree of correctly balanced musical subtlety. They are really two different things. What most people think of when they hear a speaker that's, say, very potent on some details, often is just a speaker that has an exaggerated frequency--frequency errors that make such detail more apparent. There's a real difference between that and actually reproducing more detail.

HP: One of the things that struck me, and I think it's the best I've heard in a dynamic speaker to date, is its decay characteristic. And I know you've done something sneaky there, because one of the big problems in listening to dynamic drivers is the long delay fall, the long decay. A sound does not fall away consistently like it does in life.

JT: Actually, interestingly, I consider both of the characteristics you just mentioned, from an engineering point of view, to be just different aspects of the same thing. We think in terms of just resolution for clarity as covering both of those elements. For the most part, anything you do to reveal more of true subtleties in the music will also give you faster, better decay. Because, to a great degree, that massive subtlety of music lies in the decay of the signal, the unnaturally long decay of previously stored energy. There are a lot of technical reasons--the big ones are the cabinet itself, the concrete baffle, and the well-braced interior.

HP: You'd better tell me what the baffles are made of.

JT: Well, the baffle is made of concrete reinforced with fiberglass and steel, and is cast--in some cases, three of four inches thick. In some places it's cast with the curve shape, which has the benefit of reducing diffraction. So the baffle itself is extremely rigid, well-braced internally, and that is also contributive. The separate sub enclosures for the low- to mid-range driver and the upper-range driver are shaped to eliminate any internal standing waves.

HP: What about the internal standing waves?

JT: Well, by shaping the internal sub enclosures in a unique way, you could essentially eliminate internal standing waves. Of course, other contributing factors are the driver diaphragms, the metal ones in particular. We have to eliminate any internal diaphragm resonances in the frequency range of the drivers. We're not just damping resonances and making them less apparent. There are actually none whatsoever in the operating range--or even an octave or two outside the operating range of the driver--to color the sound. Everything I can possibly think of is incorporated.

HP: The summation of your knowledge is in this speaker.

JT: That's true of every new product we make, even if it's a lower price figure, because you are always learning new things.

HP: I gather from this that what you've applied here, you'll apply elsewhere.

JT: I'll incorporate more of those things into it. I mean, I'll start off incorporating everything into that new design that I now know and I will, I hope, learn additional things to add to that process. And for that reason I fully believe that most of our newer products, even if they're low-cost products, in some ways are better than our premium and older products--because that are based on the results I've achieved before.

KG: The good things in upper models are present in all the lower models. In other words, we don't use cheaper capacitors or cheaper drivers.

HP: You don't?

KG: No

HP: So when you make a less expensive speaker, what makes it less expensive?

JT: Well, it's difficult. For one, we don't make very much less expensive products at all because we are not able to.

HP: You're not able to because you won't cut corners?

JT: Right.

HP: You wouldn't put a bad capacitor into a speaker just to make a price level. Are you saying that? Doesn't that sort of make you the rarest avis of rara birds?

JT: Well, I don't know. It's very important to us that all the products we make are products we can be proud of. I think that's a necessary part of success also. If we weren't proud of our product we probably wouldn't be successful anyway, so why make

HP: So you are not going to put out anything to make the price drop?

JT: No, no. I will certainly make lower-priced products because I realize that everybody doesn't have $5,000 to spend on just the speaker. And I'm interested in seeing how good I can make a speaker that will cost only $2,000 or $1,500. That's a good engineering challenge.

HP: So you give yourself a challenge.

JT: Right, but like Kathy says, if you go out and pull random people off the street and say, "What would you expect in a $1,000 loudspeaker?"--you'll know this probably better than I would--most of these people, unaware of High End audio, would think, "Wow, a $1,000 for a pair of loudspeakers. That's a lot of money. I bet I can get all kinds of bass, I can blow may windows out with a pair of $1,000 loudspeakers." But of course when we or other High End manufacturers design such a loudspeaker, the first thing we think is well, you're not going to get the bottom octave-and-a half of bass. We find it a lot more agreeable to accept that trade-off in lowering the price than using poor quality capacitors and cheap drivers. So Kathy's original point was that even our lowest-priced products use the same cabinet wall material, a cast driver chassis. And the products are internally braced. We use the same internal wire on our lowest priced speakers that we do on our highest priced speakers. We use the same type of capacitors (There's fewer of them.) And to answer your question--"How can we make lower-priced speakers?"--we basically give up the bass extension and loudness capability. I'm also willing to give up a little bit in terms of other characteristics--tonal accuracy or clarity.

HP: But you achieve, in my experience, good octave-to-octave balance, so you don't really notice so much bass missing. How do you do that?

JT: Well, you say it a little differently than I would. What's more important to your ear is that what is there is naturally balanced, that there's nothing there that seems unnatural. Whatever you do provide in sonic output should never sound unnatural, and, if you can do that, then the speaker can sound quite good. There's just a lack of something that otherwise would be there.

HP: Could you make a better speaker than the 7?

JT: Yes.

 


Reprinted with permission from

 

On Screen: Jim Thiel

by Editor Gary Reber

Issue 19 May/June 1996

 

Subscriptions to Widescreen Review may be obtained at a rate of $25 for six issues. Telephone 909-676-4914 or 888-WSR-SUBS, or send your check to:
Widescreen Review, 26864 Mandelieu Drive, Murrieta, CA 92562

Jim Thiel is the founder, chairman and chief designer of Thiel Coherent Source Loudspeakers, a leading and respected designer of advanced time coherent reproducers. A matched THIEL CS7 system is one of the magazines valued reference systems, often used to evaluate other system components. Jim Thiel was interviewed by Editor Gary Reber for this exclusive On Screen Feature.

 

Gary Reber, Widescreen Review: One of the major things that separate the many speaker designs on the market today is radiation pattern. What are your views on point source, line source, monopole, dipole, and bipole designs? Would you please explain each one of those terms for the benefit of our readers?

Mr. Jim Thiel: A point source radiates sound energy equally in all directions from a small-sized source with no reverse phase energy. Because the source size is small, the intensity decreases proportionately to the distance from the source. Real world speakers referred to as point sources almost always have reduced dispersion of energy at the higher frequencies, so they are not true point sources. But their radiation patterns are still similar to a point source because the sound source is small, resulting in a wide radiation pattern, and because there is no reverse polarity energy.

Both dipoles and bipoles radiate energy both to the front and to the rear. In the dipoles the rear energy is of reverse phase to the forward energy and this causes, in addition to reverse phase energy in the room, a cancellation of energy to the sides of the speaker. In the case of a bipole radiator the rearward energy is of the correct phase, so it can be looked at as an attempt to make a truer point source, one that radiates more uniformly in all directions.

A line source refers to a radiator that is big in the vertical direction. There can be monopole, dipole or bipole line sources.

My view is that a modified point source is the ideal, a point source that's somewhat modified in its radiation pattern so that the higher frequencies are radiated only to the front. I like this radiation pattern because it is most similar to real world sound sources. What I don't like about dipoles is that there is reverse phase energy radiated by the speaker which is completely unlike most real life instruments. The dipole radiation pattern does tend to give a spatial special effect, but I consider it unnatural and therefore undesirable. The bipole designs, not having reverse phase energy, I consider superior to the dipole. But in all the real world implementations of bipole designs there are what I consider to be significant interference problems between the forward and rear radiation which result in uneven and changing off-axis response. I consider the line source also to have the problem of not having a natural real life characteristic, in the case that their loudness does not diminish proportionately with distance as a live instrument would. They also do not radiate as much total energy into the room. So I consider the modified point source radiation pattern to be ideal, most like the sound sources we are reproducing.

WSR Reber: So you're saying bipole is a better design than dipole?

Thiel: I consider the bipole better because I don't like the idea of out of phase energy that the dipole produces. But I consider the modified point source to be superior to both in terms of natural reproduction.

WSR Reber: How these different designs interface with the room also differentiates them. Are your speakers designed to be used at or near room boundaries, away from room boundaries, on the floor or stand mounted?

Thiel: Our speakers are designed to be used away from room boundaries on the floor because this can give you the most natural spatial reproduction. The advantage of designing a speaker to be used near the room boundaries is to get additional bass reinforcement, and therefore, everything being equal, you will get a little more bass output or a little more sensitivity. But the problem with such a speaker is the interaction of the mid frequency energy with the boundary which causes colorations--unnatural tonal characteristics. Here again is an advantage of the modified point source radiation pattern. Not having much rearward energy at the higher frequencies means that this type is much less interactive with the room. It's much easier to get good results. The dipole and bipole designs are much more interactive with the room boundary and the results that you get are much more dependent upon the room and the speaker placement in the room. With point source designs, being away from room boundaries doesn't necessarily mean it must be far away, although theoretically it is more ideal to be far away. Even distances of one foot to two feet can give you most of the benefits of uncolored midrange reproduction.

WSR Reber: So optimally, you would suggest something like three or four feet?

Thiel: Yes, three to four is very good and five feet is even better, but you're really at the point of diminishing returns beyond that.

WSR Reber: What do you do in terms of getting a smooth frequency response and bandwidth?

Thiel: I feel that it is often not appreciated how sensitive your hearing is to minor tonal alterations. It is often assumed that because they may not be noticeable on a cursory listening, that they don't matter. I think that, in fact, even minor colorations significantly impair your long term enjoyment of sound reproduction and, therefore, I place a very high value on achieving extremely accurate tonal balance. Of course, many factors are involved in actually achieving a smooth frequency response, including the willingness to invest the engineering time and the additional costs required. There are three approaches to getting good frequency response. The first is to design drivers that have a very good response, which is more complicated than you might think. The second is to reduce cabinet diffraction which detrimentally alters the frequency response of the drivers. And the third is to engineer the electrical network to correct frequency response problems. We aggressively pursue all three approaches and we probably take the third approach further than anyone else. Our networks are very complex and much of the complexity is to correct small frequency response problems. Some people feel that using so many electrical components can degrade the sound quality, but I think this is only true if the electrical parts are of the usual poor types, like electrolytic capacitors. The down side of correcting these frequency response problems with complex circuitry of high quality parts is the cost.

WSR Reber: Should speakers used in a multichannel system be voiced differently than stereo speakers--for example, flat vs. a warm tonal balance?

Thiel: I don't think so. I subscribe very strongly to the philosophy that the speakers should accurately reproduce the signal that they are fed. Interestingly, Gordon Holt seems to feel that when accurate speakers are used in a multichannel playback array that you then, for the first time, get an experience that is as warm as life rather than with a stereo system where he feels that the playback is not as warm as it should be.

WSR Reber: Do you subscribe to "timbre matching" of the rear or side speakers, the idea that a rear speaker should be voiced differently than its opposite in front, as THX states, to counteract the different head related transfer function the listener experiences when sounds arrive from the side and rear?

Thiel: No, I don't subscribe to that. If the ear hears sounds differently from the rear, then that is true both in real life and when listening to playback. So if the speaker reproduces the signal as it was recorded then your ear will hear the reproduced music the same as it would have heard the live sound. So I don't feel that the speakers should be altered to predistort the signal to be what your ear would hear because your ear is going to hear it from the rear and make the alteration itself.

WSR Reber: Do you subscribe to the idea of identically matched speakers in a multichannel array?

Thiel: Yes, that is ideal. However, that is often not possible, especially for the center channel. What is most important is that the tonal characteristics through the midrange and the radiation pattern be very similar. I feel this is an advantage of our speakers. Since all our models possess very accurate tonal balance, you can mix and match any of our models to satisfy your budget or space requirements and still obtain a well balanced total system.

WSR Reber: Do you favor room treatments to alter acoustics? If so, what type?

Thiel: Well, of course, it depends. In general, I think that sometimes people worry too much about the reverberant characteristics of the room. I think almost all rooms that people are actually comfortable in and live in have quite acceptable reverberant characteristics and so, for the most part, I think it is unusual that people really need treatment. Now in some cases they do, but I think it's rather unusual.

WSR Reber: How about electronic equalization of the in-room response?

Thiel: Well, I'm usually not in favor of it for two reasons. One is that it is practically impossible to equalize your reverberant energy to compensate for the characteristics of the room without also altering the sound that you hear directly from the speakers. And I would go to great lengths to avoid that. And the other reason is that room characteristics are different for different listening positions. So even if you could achieve a correction of the room characteristics for one location, you're likely to make the room characteristics worse at another listening location.

There's an important concept to think about when you're understanding how you hear loudspeakers in a room. When you listen in a room, you're hearing two different signals so to speak. First, you are hearing the direct sound that comes directly from the speaker to your ear which does not encounter any reflections or interactions with the room boundaries. Secondly, you are also hearing the reverberant energy, which is energy that first interacts with a room boundary before it gets to your ear. You hear the reverberant energy later in time because that energy has taken a more indirect path from the speaker to your ear and has traveled a greater distance and has maybe bounced around the walls a few times before you hear it.

The important idea here is that your brain separates the direct sound from the reverberant sound. And what your brain and ear primarily tune into is the tonal character and balance of the direct sound which is not influenced by the room. The only way for that direct sound to have the correct tonal balance is for the speaker itself to have an accurate anechoic frequency response.

The effect of the room is that it will change the character of only the reverberant energy. So if you are in a very live room, the reverberant energy will sound very live, and if you are in a very dead room, the reverberant energy will sound dead. Your ear will be able to interpret what kind of acoustics space you are listening in based on the character of the reverberant energy, but the direct sound will not change because of the room.

So if, for example, you are in a very lively room that accentuated the high frequency reverberant soundfield, and you tried to compensate by reducing the high frequency output from the speaker, you would succeed in achieving more accurate tonal balance of reverberant energy. But you would've also unnaturally altered the tonal balance of the direct sound, making it too weak in the high frequencies. And I consider the value of the direct sound to be much higher than the value of the reverberant sound. So for both those reasons, I don't think it's a practical idea.

If you really have to do something about the sound of the room, it would be better to try to do it acoustically than to try to do it electronically.

WSR Reber: Do you believe that what's right for stereo is right for multichannel in the context of speaker directivity on the precision of imaging when more than two channels are present?

Thiel: Yes. I really don't see any fundamental difference in the requirements of imaging and speaker directivity depending on how many channels there are.

WSR Reber: There is a lot of discussion about bass loading methods. Do you favor second order sealed boxes, fourth order vented, or passive radiator designs, band pass, dipole, bipole, or other methods?

Thiel: Second order sealed boxes have a little tighter, cleaner bass character than the fourth order vented or passive radiated designs which are essentially equivalent. However, the comparison really shouldn't be between a sealed box system and a vented system with the same bass extension because, in the real world, what you really have to compare is two speakers that have equal sensitivity and equal size. Given a sealed system with the same sensitivity and same size as a vented system, the difference becomes that the sealed system will simply have less extended bass than the vented system. Therefore, it's really a question of whether or not you want more extended bass. For that reason, I design vented systems because, for a given sensitivity and size, you get more bass extension.

WSR Reber: What are your views on subwoofers?

Thiel: That they're very difficult to integrate well with the main speakers. There are several problems. The subwoofer is in a different physical location and is also working into a different acoustic environment. It's a different distance from the listener than the main speakers, and then the level matching is a problem also. In addition, there are serious problems with most of the crossover systems used for subwoofers. So these problems make it very difficult to integrate subwoofers well.

WSR Reber: Does that mean to imply that THIEL is not planning on producing any stand-alone subwoofers?

Thiel: Well, these are the reasons we have not to this point. However, I am now working on a subwoofer, and although there still will be integration difficulties, we're incorporating a couple of new ideas to achieve better integration than usually can be achieved with separate subwoofers.

WSR Reber: I have found that one of the advantages of subwoofers, at least in terms of reproducing modern day motion picture soundtracks, is that the level of bass extension is very deep and also the SPL level of the bass is very loud and powerful. Without a subwoofer you're not really able to achieve all of the impact of the soundtrack.

Thiel: That's true, although there's no theoretical reason why a normal integrated full range speaker could not produce the same output level and bass extension as the subwoofer. But, in fact, I agree with you that very few full range integrated speakers produce the output levels and bass extension that some people like for movie soundtrack reproduction. Therefore, there's certainly a practical benefit of using subwoofers.

WSR Reber: Do you recommend a dedicated subwoofer to reproduce the ".1" low frequency effects or LFE channel for maximum impact?

Thiel: If you need the output capability of a subwoofer to get the impact then that's a value judgment that needs to be made, and quite likely it would be the best thing to do.

WSR Reber: Do you think that bi-wiring offers an audible improvement that justifies the cost? Can your speakers be easily bi-wired?

Thiel: Our speakers cannot be bi-wired in the traditional sense of the speakers having two sets of input terminals to feed different frequency sections of the speaker. They can, however, be bi-wired in the sense of using two sets of wires, both sets connected to the same input terminals. And, surprisingly, this will give you most of the advantages of using bi-wiring in a traditional form, because just using two sets of wire in parallel means that you are cutting the resistance in half and the inductance in half.

In general, we don't recommend bi-wiring because I feel people are usually better off taking the amount of money that they would spend on two sets of wires and buying one set of higher quality cable. I think in most cases people get better results by using on set of better cable than using two sets of lesser cable.

WSR Reber: Do you believe that time and phase are audible parameters in loudspeakers? Do you favor first order cross-over slopes or steeper slope designs? Do you physically time align the drive elements in your designs? Is diffraction important? What if anything do your designs use to effect diffraction?

Thiel: Yes, I do believe that time and phase are audible parameters in loudspeakers. Very audible actually. It's not the kind of thing that's going to immediately make you say, "Wow this sounds incredibly different!" But it is certainly the kind of performance that adds a sense of realism and naturalness to the reproduction, and I think it's a major factor in being able to reproduce sounds so that they really do sound live and not reproduced. Correct phase performance contributes to a sense of natural space, enhances clarity of subtleties, and provides a greater sense of realism. I think it's quite audible and quite important, and therefore, I do favor first order crossover slopes in the loudspeaker as the only way of maintaining complete time, phase, and power response accuracy. We utilize first order crossover slopes in all our products.

We also physically time align the drive elements in all of our speakers by either of one of two methods--mounting the drivers along a sloped baffle so that the distance from the listener to each of the drivers is the same, or by using coincidently mounted tweeters that are physically time aligned.

I also consider diffraction to be important in loudspeaker design. It is important in terms of reducing the speaker's cabinet as a source of sound coloration. If the speaker cabinet edges diffract energy, it gives your ear/brain clues to the size, shape, and location of the speaker that's reproducing the sound, and the speaker starts sounding more like a speaker that's occupying it's location rather than the musical instrument's sound that it is trying to reproduce. So we reduce diffraction in our products by rounding the edges of the baffle quite strongly in three dimensions to significantly reduce diffracted energy.

WSR Reber: In addition to test instruments what source material do you use to evaluate loudspeaker? Music? What do you recommend that consumers use? How should they listen?

Thiel: We use music. Most of what I use is female voice because most of my listening and design process involves evaluating the tonal accuracy of the speakers. Some speaker performance parameters don't need to be evaluated subjectively nearly as much as the tonal character does. For example, the imaging capability of the speaker is pretty much predictable from the radiation pattern, the phase characteristics and the diffraction characteristics. If you get all these things right, the speaker will image wonderfully. You don't have to spend a lot of time subjectively evaluating different design options to optimize imaging performance. Whereas, in terms of tonal characteristics of the speaker, your ears are extremely sensitive to very small inaccuracies that are difficult to interpret from the measurements. We spend a lot of time, mostly by using female voice, evaluating the tonal characteristics of the speaker.

In terms of what the consumer should use, and I presume you mean to evaluate speakers that they may be buying, they have to evaluate a broad range of performance characteristics. We like to simplify everything that a speaker does into four performance characteristics; tonal characteristics; clarity; spatial realism; and dynamics. I think the consumer is very well served by focusing on those four characteristics and evaluating each of those with a different type of music. I think the best type of music for evaluating the tonal characteristic of the speaker is voice and that the customer should listen for naturalness of the voice reproduction. For evaluating clarity, you want to use any type of music that's quite complex. Often if you get a recording that's been made, say, in an old cathedral where you have a lot of reverberation from the original acoustic space, you can evaluate the clarity and musicality of the reverberant energy as a good way of zeroing in on and evaluating the clarity of the loudspeaker. In evaluating the spatial naturalness of the speaker, you want to make sure that the recording is made with a simple mic setup. And often some of the smaller jazz groups have recordings where you can best evaluate the spatiality of the speaker. For dynamics, you want to listen for the speaker not becoming strained or distorted at higher output levels. So if the buyer zeros in on those four characteristics, it makes it a lot easier to try to objectively compare speakers.

WSR Reber: In your designs, do you subscribe to a wide dispersion pattern or to a very narrow, focused, controlled dispersion pattern?

Thiel: I subscribe to a wide dispersion pattern. But even more important than wide dispersion is that the dispersion pattern be uniform at all frequencies as much as possible. Often in loudspeakers, if you measure the energy radiation off-axis, you will get some areas of the spectrum that are reproduced weakly, which result in unnaturally balanced reverberant energy in your listening environment. If the reverberant energy is unnaturally balanced tonally and also balanced differently than the direct sound, the sound becomes disconcerting and unnatural. So I think the most important thing is for the dispersion pattern to be even and not change with frequency. That's another benefit of the first order crossover approach: you get a very even dispersion pattern of overall energy. But I do consider it desirable to have a wide dispersion pattern. It gives you more naturally spacious reproduction.

WSR Reber: The Home THX program subscribes to the idea that it should be a very highly focused dispersion pattern to reduce or eliminate any room boundary reflections, particularly ceiling and floor.

Thiel: Right. Well, I think there are a couple of problems with that. First, any method I know of to reduce dispersion, to make the dispersion pattern more tightly focused, causes audible degradation of the natural sound characteristics. Another problem is that you end up with reproduction that has little reverberant energy content so that what you hear is a higher percentage of direct sound, which is an unnatural experience. The reason they give for having a focused dispersion pattern is to increase the intelligibility of dialogue on movie soundtracks. I think the problem there is often that the speakers just lack the clarity or the natural tonal balance they need to make the dialogue intelligible. The real solution is to get speakers that have better clarity.

WSR Reber: What is your view on the suitability of home theater systems for music reproduction and vice versa?

Thiel: This reminds me of the 70's when people would say "Speaker X" is really great for rock music but not good for classical music, and "Speaker Y" is vice versa. And it is a bit like that, I think. The argument about rock speakers and classical speakers was that rock music needed speakers that had good bass and dynamic reproduction and didn't particularly need a speaker that had good spatial characteristics or tonal accuracy. So that if you had a speaker with good dynamics and bass reproduction then it was great for rock, but it was not necessarily great for classical music because the sound character might be unnatural and the spatial reproduction poor.

It's a similar argument here. It's true that in a home theater system, the bass output capability is a lot more important than it is for normal music reproduction. Therefore, a speaker that could be very good for music may not necessarily be practical for home theater reproduction. And very often the speakers that do provide the bass you want for home theater can have poor tonal and spatial performance and poor clarity and so sound bad when reproducing music. But, in fact, you can make a speaker that has bass output capability for movie soundtracks and also has the accurate tonal characteristics and natural spatial characteristics needed for good music reproduction. Therefore, the ideal would be a speaker that can do everything well.

WSR Reber: So your conviction is there should be one speaker for all types of reproduction?

Thiel: Yes, a good speaker is a good speaker, given this one consideration that you may need greater bass output capability for home theater reproduction. A speaker doesn't care where it's signal comes from--whether it comes from a music recording or a movie soundtrack or, for that matter, a computer game. A signal is a signal as far as the speaker is concerned and will reproduce what it's fed.

WSR Reber: Do you advocate using identical speakers in each position in a multichannel system?

Thiel: Ideally, yes. A lot of people won't choose to spend the money it would take to have five great speakers, but ideally it would be good.

WSR Reber: Since you put it that way, do you feel that it would be better for a consumer on a tight budget to invest in five speakers of lesser cost than invest in two main speakers--left front, right front--of much higher cost and three lesser speakers?

Thiel: I guess it depends on what he's planning to use the speakers for. If he's planning on using the system to listen to both music and movies, the second purchase would definitely be better. And this approach can also work well with movie soundtracks if the bass energy is redirected toward the left and right front speakers or to separate subwoofers. Then there's not as much requirement for the other three speakers in terms of bass and output capability. But it's still very important that the other speakers have very similar tonal balance and radiation patterns, but that can be achieved. You can get small, less expensive speakers that are of good quality, but of limited output and bass extension.

Now if the system is only used for movie soundtrack reproduction, then this argument would have less force, and it might make more sense to have five of the same speakers.

WSR Reber: Now, in terms of subwoofer capability in that sense, do you subscribe to a single mono subwoofer, or do you subscribe to the idea of at least two or more?

Thiel: I think more is better--four or five would be best-- and you are getting back to the approach of the speakers being full range. But a benefit of multiple subwoofers is that they improve the spatial experience, regardless of the opinion of some people that low frequency energy is not directional. Also, if you use only one subwoofer, you tend to have more of a problem activating room resonances. The more subwoofers you use in different locations the fewer problems you'll tend to have with low frequency resonances in the room So I prefer more subwoofers--at least two.

WSR Reber: Do you recommend identical time distance relationships of each speaker from the sweet spot listening position in a multichannel system?

Thiel: Yes. Depending upon the source it can be important for maintaining a sense of natural space.

WSR Reber: How do you view speaker placement to optimize phantoms between left front and left back speakers and conversely right front and right back speakers, or for that matter left back and right back? What about along the diagonals between left front and right back and right front and left back?

Thiel: There's a lot of appeal to using the four corners of the square--at 10:30, 1:30, 4:30, and 7:30 positions. Some people argue that you can't get a good enough phantom image behind the 9:00 and 3:00 positions, so you might want to pull the back speaker forward to the 8:30 and 3:30 positions.

WSR Reber: Should speakers in a multichannel system have identical full range capabilities for each discrete channel?

Thiel: Again, that's the ideal.

WSR Reber: Do you subscribe to the Home THX specification for dissimilar speakers using direct radiators in the front hemisphere of the room and dipoles in the rear hemisphere of a multichannel system?

Thiel: No, I do not subscribe to that, although it can work fine for most movie soundtracks. By using dipoles in the rear, you tend to make all the energy coming from the rear speakers diffused and non localized, regardless of what the movie producer intended. Since the movie producer can make the sound non localizable on the soundtrack, you don't need the speaker to impose that characteristics onto everything it reproduces. The problem with having speakers with radiation patterns that diffuse the sound is that you are then limited to hearing only diffused sounds from the rear speakers. And there are sounds, even on movie soundtracks, that should be localized and they are not able to be if you have speakers with such radiation characteristics. So I think the speakers should be point sources for all the playback channels, and if the sounds are meant to be diffused and non localizable, then they need to be recorded that way. Then you retain the capability in your playback system of reproducing localizable sounds, which it otherwise would not.

WSR Reber: Particularly with discrete digital soundtracks now, there is the capability to localize and have phantom images--even diagonally.

Thiel: Yes, and if you have speakers that are diffusing all of the sounds that they are reproducing, then you are losing the capability of experiencing the multichannel music recordings the way they were intended to be experienced.

WSR Reber: Is a different model speaker permissible for the center channel?

Thiel: I think so. But it's important that the tonal characteristics be well matched to the other speakers, particularly left and right front, and for the radiation characteristics to be well matched. Of course, it's ideal to have the same model because you then have a perfect match. But I think that you can get center channel speakers that are well matched, especially if you stick within the same manufacturer.

WSR Reber: To what extent is the digital 5.1 discrete format effecting your approach, both in terms of speaker design and application in room placement in the context of a multichannel multi-speaker system?

Thiel: Well, it's not particularly effecting our approach at all since our philosophy is to make speakers that accurately reproduce the signal they are fed. There is nothing in our design approach that is incompatible with multichannel. In fact, I feel that our approach is particularly good for multichannel systems because we have always made speakers that have imaging as a strong performance aspect. And imaging is what multichannel is all about.


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