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| May 1, 2007 Searching for the Extreme: Terry Montlick on Room AcousticsThose of you who read my three-part series, "The World’s Best Audio System," about the Music Vault -- the listening room I built in 2005 -- saw the transformation of a raw, unfinished space into a superb listening room. In those articles I highlighted all the construction details, but more important was the design of the room, in which special emphasis was placed on the project’s acoustical outcome. Perhaps more profound than the physical transformation of the room, however, were the changes wrought in me, especially in my understanding of the importance of proper acoustic design. In building the Music Vault, I came to regard the room as the overriding determinant of the sound heard from any audio system. I also learned that a good acoustical engineer can perform sonic miracles. However, it wasn’t a merely "good" acoustic engineer who designed my room, but perhaps one of the best in the world. Terry Montlick, of Terry Montlick Labs, graduated from MIT, then went on to the University of Oregon where he did graduate work in neurobiological sound communication. He has written a book on object-oriented programming, The Distributed Smalltalk Survival Guide [Cambridge University Press, 1998], and holds five patents in the field of audio digital signal processing (DSP), where he has also done extensive consulting work. He has been a member of the Acoustical Society of America, the professional society for acousticians, since the late 1970s. I’m still amazed that audiophiles can hire such brain power for the reasonable fees Terry charges. Now that I’m almost two years removed from the Music Vault building project, I figured it was time Terry and I revisited the issue of room acoustics, to continue the dialogue we began in the articles referenced above. Because I think it’s important to understand just how important the room is, I began by asking him just how much of the room’s signature we actually hear. Or, put another way: How much of what we hear is the room, and how much the direct sound from the speakers? Here’s what he had to say. "It’s hard to give a percentage, but most of what we hear in reproduced sound is the room. It is interesting to see how differently two industries have dealt with the room. "First is the motion-picture industry. Since the beginning of talking pictures in the late 1920s, movies have had to deal with sound reproduction. Even though the sound was of low quality by modern standards, it still presented a problem. This hit the movie-studio execs in the late 1920s like a pie in the face! "The old vaudeville theaters had acoustics that were terrible for understanding ‘the talkies.’ Since the Hollywood studios owned the big theaters, they acted immediately. The theaters underwent acoustical treatment that would improve and standardize their sound. Ironically, dialogue intelligibility remains a key problem in untreated or incorrectly treated home theaters. "Then there is the home audio business. Historically, this is an equipment business, not an entertainment business like the movies. The model is completely different. There are showrooms for audio equipment, just like cars. People audition the equipment they hear in the showroom, take it home, and plug it in. The sound comes out nicely. Everybody is happy. That’s the convenient fiction, anyway. "If your equipment can’t do the whole job, then there must be something wrong with it, right? It is not in the interest of equipment manufacturers or retailers to let you know about room acoustics. They do not control the venues, like the old movie studios did. So who is to say what is good sound? That pesky dialogue problem that makes you unable to follow the plot of the movie does not exist in home audio (except for the home theater part of the business). So the emperor’s new clothes continue to be worn." To me, it’s quite obvious: The listening room should be treated as the primary component in an audio system. This raises the question of just what an audiophile should do to improve his or her room. I asked Terry what he thought are the most common acoustic issues in untreated listening rooms of average size. "The primary issues we encounter are reverberation times and early reflections. Uneven reverberation across the audio spectrum can seriously color the sound. Experts differ on the optimal reverberation times for a room. But they seem to agree that if reverberation is too low or too high in any one frequency range, the room can intrude on the sound. "An ‘early reflection’ is a psychoacoustic phenomenon that has been much studied over the years. It is known that if two similar sounds are heard within a short time period (measured in the milliseconds), you will hear them as one sound. If these two sounds happen to be the direct sound from your speaker followed closely by a discrete reflection from a nearby wall, then you may have an early-reflection problem. Because the two sounds get integrated into one, you may not be able to accurately localize the direction of the sound. If one of your goals is to have a tight soundstage, and be able to point to the different musical instruments that you hear, then early reflections may seriously compromise your listening experience."
I often hear audiophiles state that they have a really good room. Certainly, some rooms are better than others from the outset. But can any room, even the ones regarded by their owners as "good," be improved by treatment? "Generally speaking, yes. Of course, tastes and goals vary. Even if a room colors the accurate reproduction of sound, if the owner likes this sound, how can anybody disagree with a personal preference? "And of course, there is the notorious issue of people perceiving what they desire to perceive. If you have spent thousands of dollars on a particular electronic tweak, then you sure better hear the difference! The double-blind testing that is mandatory for all serious peer-reviewed acoustical research does not happen much in the home listening room." Some folks will always believe that they know more about complex subjects than they actually do. Before I started on the Music Vault project, you could have counted me among them. I asked Terry to tell me about some of the common misconceptions about room acoustics and room treatment. "One is that it shouldn’t be necessary if your equipment is top-notch. I’ve already talked about that. Another is that room treatment looks ugly and is intrusive. The fact is that if you have the money to spend on hiding all acoustical treatment behind acoustically transparent fabric walls, you cannot even see it." Technological advances in DSP have made possible some very advanced audio products. I asked Terry to explain his position on passive room treatment vs. digital room correction. "Digital room correction continues to make significant advances, due both to research and to the greater power of real-time signal processors. Here is the ‘state of the art,’ as I see it: Electronic room correction can be extremely successful in improving sound at low frequencies. At mid and high frequencies, it can greatly improve the spectral balance of the sound. But at such frequencies, it cannot improve things such as reverberation time. Creating a perfect ‘inverse filter’ to correct all room issues at higher frequencies is theoretically possible, but it is extremely sensitive to listening position. If you try to ‘de-reverberate’ a room at high frequencies using known technology, you cannot move your head by even a centimeter or you may hear room-correction artifacts that violate causality -- you can detect a little trace of a cymbal crash slightly before it hits! "So passive room treatments are always the preferred way to go. This is often not feasible at the lowest audio frequencies, because in order for the treatment to be effective, it has to be of comparable size (thickness, generally) to a wavelength of the sound it is correcting. But a 50Hz sound has a 20’ wavelength! You would have to devote comparable room volume for low-frequency room treatment as for the listening space." There you have it. If you haven’t addressed the acoustic profile of your room, I suggest you contact a professional to do so. You don’t have to go to extremes; small investments here and there, when coupled with professional analysis, will pay huge dividends in the performance of your system. The bottom line for me? If I haven’t paid attention to my room’s acoustics, the performance of my system has not been optimized. The acoustic output of your system plus the room around it is what actually engages your ears. There’s no separating the sound you hear from the acoustics in your room. ...Jeff Fritz To learn more about Terry Montlick and his company's products, visit www.tmlaboratories.com.
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