In an effort to squeeze the last ounce of performance from their audio systems, many audiophiles enlist the help of products such as power conditioners, exotic cables and vibration control devices. While the audiophile community has readily embraced such products, the same cannot be said for products designed to improve the acoustics of the listening environment. There are several reasons why this might be the case. Firstly, many audiophiles fail to recognize the importance of room acoustics, and the profound effects that room acoustics can have on the quality of sound reproduction in their homes. This is mainly because few audiophiles have had the opportunity to listen to music in a properly treated listening environment. Secondly, effective room treatment products, manufactured by companies such as Acoustic Sciences Corporation and RPG, tend to be priced prohibitively high for the average audiophile. Finally, many room treatment products are visually unattractive and result in a poor SOAF¹. The importance of this last point should not be underestimated, as the majority of audiophiles must share their listening space with the living space of other family members, some of whom might not fully understand the need for a few hundred square feet of gray foam nailed to their living room walls.

While it is largely the responsibility of the audio press to educate audiophiles about the positive effects of properly treating their listening rooms, we must defer to the manufacturers of such products to take on the challenge of producing effective and affordable, yet visually-tolerable products. One company attempting to meet this challenge head on, with its full line of decorative and relatively affordable acoustical treatments, is New York's Echo Busters.

Before getting into the specifics of Echo Busters' products and their effects on a room's acoustics, a brief introduction to acoustics, as it pertains to the typical listening room, might prove useful.

Acoustics 101
Software programs such as KB Acoustics' Visual Ears ( reviewed in Volume 2, Number 1) can be quite effective at suggesting good first approximations to loudspeaker positions, such positions often exhibiting frequency response and standing wave characteristics which are quite acceptable. Unfortunately, many rooms suffer from serious acoustical problems which cannot be fully addressed by loudspeaker placement alone. These problems include unacceptably long decay times (causing smearing, lack of image focus, and obscuring of detail), high-frequency ringing, and bass boom caused by inadequate low-frequency absorption/diffusion.

Reverberation and Absorption
Long decay times and high-frequency ringing are undesirable attributes of a "live" acoustic environment, which can be loosely defined as one which allows a sound wave to continue to propagate through the listening room without significant energy loss upon collision with room boundaries. This lack of energy loss allows a sound wave to appreciably contribute to the listening room's sound field long after initially entering it - too long in many cases. The "liveness" of a room is usually specified by its RT60, or Reverberation-Time-60, measurement which is the time required for a sound wave in the room to decay 60dB. F. Alton Everest, in his excellent book The Master Handbook of Acoustics, 3^rd Edition (ISBN 0-8306-4437-7), describes the RT60 measurement in more intuitive terminology as "the time required for a sound that is very loud to decay to inaudibility." A very low RT60 measurement can result in a very "dry" acoustic, one which is dull and lifeless. While such environments have their place in acoustical research (i.e. anechoic chambers), listening to music in such an environment would not be very pleasant. At the other end of the scale, a very high RT60 measurement implies long reverberation times and their attendant problems.

Much research has been done to determine an optimum reverberation time for an acoustic space, but no definitive answer has emerged. This research has, however, resulted in recommended reverberation times for churches, concert halls and spaces used for speech and music recording. Further studies have shown that the average listening room exhibits an RT60 time which is much longer than that which is "optimal", implying that, in general, some form of corrective action is required to reduce a room's reverberation time.

How can the reverberation time of a room be reduced? Since reverberation times are inversely proportional to the amount of energy a sound wave loses when colliding with room boundaries, increasing the amount of energy loss at room boundaries will decrease a room's reverberation time. Increasing the energy loss of a sound wave as it collides with room boundaries is most commonly achieved by adding some form of absorptive material to those boundaries. Such materials drain a sound wave's energy by dissipating some portion of it as heat caused by friction between the material and the vibrating air molecules which constitute the sound wave.

Two of the most common materials used for sound absorption are Fiberglas insulation and open-cell foam such as that used in products like Sonex. Both of these materials are effective sound absorbers at mid to high frequencies but are relatively ineffective at frequencies below about 500 Hz.

Many rooms exhibit very long reverberation times at frequencies below 500 Hz, resulting in bass boom and other undesirable effects. Resonating absorbers are used when absorption at low frequencies is required. There are many forms of resonating absorbers. Some simply consist of a diaphragm which vibrates in response to an impinging sound wave, converting a portion of the wave's energy to heat by frictional losses in the vibrating diaphragm. Others are based on the Helmholtz resonator which uses a resonant cavity, containing one or more openings, to absorb sound. Such a cavity has a certain resonant frequency at which the air in the cavity will begin to vibrate in concert with a sound wave entering it. The Helmholtz resonator absorbs the energy of a sound wave through frictional losses between the sound wave and the air contained in the cavity. One interesting property of Helmholtz resonators is that sound which is not absorbed is re-radiated in a hemispherical fashion, resulting in diffusion of the remaining sound energy.

Diffusion
Diffusion of sound waves, upon reflection from room boundaries, is another desirable property of an acoustical environment. Diffusion of a sound wave occurs when the wave strikes a room boundary and is reflected back into the room such that its energy is evenly distributed in all directions. Diffusion is desirable because it inhibits the creation of standing waves which might otherwise result in frequency response problems. Diffusers range in complexity and effectiveness from open-cell foam panels and polycylindrical surfaces, to reflection phase-grating designs like those made popular by RPG. Many products combine both absorption and diffusion. For example, polycylindrical corner bass traps absorb a portion of the energy from a low frequency sound wave and diffuse the wave which is reflected from its surface.

It is very common for a listening room to provide inadequate absorption and diffusion across the frequency band, resulting in blurring, ringing, bass boom and other problems. Judicious use of room treatment can often turn an acoustically-poor listening room into one which does not impose too strong a sonic signature on music created or reproduced within it.

The Echo Busters Solution
The goal of Echo Busters' Michael Kochmann is to provide a line of acoustical room treatment products which are effective, affordable and visually attractive. An effective line of room treatments is one which provides adequate amounts of absorption and diffusion across the frequency band. To this end, Echo Busters provides four separate products: the aptly named Echo Buster, the Double Buster, the Bass Buster, and the Corner Buster, the latter not included in the review package.

The Echo Busters family: (left to right) Echo Busters, Bass Busters, and Double Busters, (standing rear) Echo Busters.

The Echo Buster is intended to provide absorption at mid to high frequencies. If the manufacturer's claims are true, and I have no reason to believe that they aren't, it is a very effective absorber from above 4kHz down to about 350Hz, its effectiveness tailing off sharply below that. This implies that the Echo Buster is a much more effective absorber in its intended frequency range than the 2" Sonex panels that currently adorn the walls of my listening room. Echo Busters are very lightweight, rectangular wood-frame panels, inset with egg-crate foam and covered with fabric. The panels are available in widths ranging from 12"-24" and heights ranging from just over 4' to 6' and are intended to be wall-hung with supplied hangers.

The Double Buster serves the dual purpose of both absorption and diffusion. The Double Buster's design is based on that of a bicylindrical diffuser, composed of a center beam down the length of the panel and two bent "wings" of plywood extending rearward from the center beam to the panel's edges. This constitutes a convex surface which diffuses impinging plane waves by reflecting them back into the listening environment in a hemispherical pattern. Externally, the Double Buster is a rectangular, fabric covered panel, similar in appearance to an Echo Buster. Double Busters are available in widths ranging from 18"-24" and in 5' or 6' heights. The panels can either be wall-hung or left floorstanding with the help of optional wood stands.

The goal of the Bass Buster is to absorb and diffuse low frequency sound waves. The polycylindrical Bass Buster is based on the Helmholtz resonator with, according to Kochmann, "a few proprietary curves thrown in." Bass Busters are intended to be left standing in the corners of the listening room, where it is known that the build-up of low frequencies occurs. The units are constructed from solid MDF with a curved wood face. As with all resonators of the Helmholtz variety, the front face of the Bass Buster is perforated, with the perforations chosen to tune the cavity for peak absorption between 65 and 120Hz. Also in common with resonators of this type, the Bass Buster will hemispherically re-radiate non-absorbed frequencies, resulting in diffusion of waves at these frequencies.

I found Echo Busters to be one of the least visually offensive room treatments I've encountered. They looked far better than the Sonex panels they replaced, and even my wife, who wasn't too thrilled when the Sonex went up in our listening room, gave the Echo Busters the aesthetic thumbs up.

Echo Busters, Double Busters, and Bass Busters can be purchased individually or as part of one of four Echo Busters packages. For the purposes of this review, I was provided with four 24" wide Standard Echo Busters, two 18" wide Standard Double Busters, and two four foot high, eight inch diameter Standard Bass Busters.

Setup
The most common problem faced by people attempting to use acoustical room treatment products like Echo Busters is placing the panels so as to maximize their effectiveness. A brief two-page manual, providing some general suggestions on placement, is included with Echo Busters products, but experimentation with placement will likely be required to get the panels positioned just right in your listening room. Fortunately, the portable, lightweight, Echo Busters make such experimentation a breeze.

After some experimentation, I wound up with the placement shown in figure 1.

Figure 1. Echo Busters Setup

Two Echo Busters panels were hung on the wall behind the loudspeakers and two were placed on the side walls at the point of first reflection. The Double Busters were cited in front of the two sliding glass doors directly behind the listening seat. This placement diffused early rear wall reflections which may have adversely affected imaging and soundstaging. Each of the two Bass Busters were placed in a corner behind the loudspeakers.

The Sound Of Silence
Upon installing the Echo Busters, I immediately noticed that the usually-live acoustic of my listening room was now much less so. The "hand clap" test revealed much less echo and high-frequency ringing than it did with both the untreated room and the room treated with 2" Sonex panels. In all fairness, I didn't have as many Sonex panels at my disposal as I did Echo Busters panels, so it wasn't strictly an apples-to-apples comparison. On the other hand, I have previously used a full complement of RoomTune products, including CornerTunes, TuneStrips, EchoTunes, and Deluxe RoomTunes, but I don't recall experiencing quite the same level of acoustical control as I did with the Echo Busters.

If I had to choose one word which best described the sound of the listening room when treated with Echo Busters, it would be silence. The treated room's ambient noise level seemed to be reduced significantly, and reproduced music appeared to emerge from an astonishingly black background. Silences between musical notes were more silent that I'd heard in my listening room before. Musical lines were more articulate as the decay of one note didn't interfere with the attack of the next to the same degree as in the untreated room. This high-level of articulation allowed complex musical passages to be unraveled by the ear/brain much more readily, resulting in far less listener fatigue during extended listening sessions. Removing the Echo Busters and listening to the same complex passages left me somewhat frustrated, as my ear/brain struggled to make sense of the music amidst a host of new reflections and reverberations. The control over the listening room's acoustics offered by the Echo Busters, allowed me to direct more of my attention to what was happening in the music and less to filtering out the room's "noise" superimposed over it.

As well as allowing complex musical passages to be more easily deciphered, the treated room more readily revealed the cues necessary to determine the size and shape of the recorded acoustic, such cues previously being masked by the untreated room's own sonic signature. In an untreated or poorly treated listening room, the sound one hears is the sum of the retrieved recorded acoustic and the room's own acoustic. The Echo Busters seemed to be able to remove the room's own acoustic from the equation better than the other room treatments I've used before.

Although I'm at a loss to provide a technical explanation for it, music played back in the treated room had subjectively more visceral impact than before the room was given the Echo Busters treatment. Percussion and guitar transients exploded into the listening room with more energy and impact than in the untreated room. I suppose it's possible that I was hearing a note's attack more completely, without the smearing or blurring associated with early reflections from the side and rear walls. Whatever the explanation, the effect was real and heightened the illusion of reality.

Music played back in the treated room also took on a newfound ease and smoothness, giving me the freedom to lean more heavily on the volume control in an effort to recreate realistic sound levels.

Music's lower octaves were served very well by the Bass Busters' absorption of low frequencies in the room's corners. The bottom end of the ProAc Studio 150s never sounded so deep and tight, the 150's two five inch bass drivers once again surprising me with their ability to plumb music's nether regions. The Bass Busters lived up to their name, ameliorating the slight tendency towards bass boominess, and its ill effects on the lower midrange, which characterized my untreated listening room.

It is all too easy to abuse room treatment products and over-treat a listening room. Such over-treatment often results in a dull, lifeless listening environment not conducive to musical enjoyment. I was initially concerned that six absorptive panels and two bass absorbing resonators would result in over-treatment of my smallish 12' X 16' listening room, but my fears were unfounded. The full Echo Busters treatment did not overdamp the room, but instead left it with a very natural sounding acoustic.

After hearing the major sonic improvements wrought by the Echo Busters, it was hard to go back to listening to music in the untreated room. Let's just say that the comparison sessions with the untreated room were short and not particularly sweet.

Conclusions
The complete treatment package consisting of four Echo Busters, two Double Busters and two Bass Busters, was very effective at eliminating the acoustical problems (slap echo, high-frequency ringing, smearing, and boomy bass) that I normally associate with my untreated room. Music played back in the treated room emerged from a silent background, and exhibited more detail, a better sense of the recorded acoustic, more dynamic impact, and tighter, deeper bass. In fact, the Echo Busters had more of a positive sonic impact on my system than some previous equipment upgrades. In my opinion, Echo Busters acoustical treatments more than lived up to their claim of being affordable, effective and decorative, and are a must-audition for anyone trying to get the most out of their audio system.

¹Significant-Other Acceptance Factor. How's that for political correctness?

Manufacturer's Comment

All I can say is thank you very much. It is most gratifying for us to find out that we improved the acoustics in your room. The most satisfying review we can get is the one where the reviewer is pleasantly surprised to find that our products effected a very noticeable improvement. We are all audiophiles first and improving the musical experience is what we are all after.

All we'd like to add is that we're always improving our products to make them more effective and more attractive, and everybody should know that we build custom sizes and colors at just a small additional cost. Our standard colors are White, Black, Quartz (beige), Light Gray and Dark Gray.