Building a dedicated space for music listening is the ultimate commitment to the hobby. It’s expensive and complex, and when you’re finished there’s no guarantee that the room will sound good. But if you take that plunge and the stars align, a room specifically designed for optimizing sound quality can allow a high-end system to realize its greatest potential.
I recently realized a lifelong goal of building a serious listening room and will share my experience with you. Although I had built two homes before with dedicated rooms, this one is more ambitious. In addition to creating an optimized platform for evaluating some of the world’s finest audio equipment, the new room is also designed around the requirements of my job. I’ve been reviewing high-end audio equipment for 30 years, and for 30 years I’ve hauled big and heavy gear through the front door of a house. To avoid damage to the new house (and preserve domestic tranquility), the listening room has a secondary door that opens to a third-car garage with no step. (The room’s main door opens to a hallway in the house.) The third-car garage is a staging area for gear coming and going, as well as facility for box storage—a surprisingly important consideration for reviewers. In addition, the room is acoustically isolated from the rest of the house, saving my wife from being subjected to my musical tastes (which admittedly aren’t for everyone). I wanted to be able to listen to any music, at any hour of the day, at any listening level. This is our last house, and I wanted to get all the details right.
Before telling you about the room’s design and construction, I’d like to state that a dedicated room is most certainly not a prerequisite to musical enjoyment. My description of the room’s AC power a few issues ago prompted more than one reader to accuse me of elitism (“That was the most elitist bunch of crap I’ve ever read. A study in one-upsmanship par excellence.” See Letters, Issues 283 and 286). The letter writers believed that optimizing the AC power to an audio system is symptomatic of audiophile overkill, and of turning an audio system into nothing more than an object of status.
Elitism actually has nothing to do with it. The pursuit of fidelity in music reproduction has been a lifelong endeavor for me, ever since my brother Stephen introduced me to the joy of music at the age of 12. I’ve worked in audio all my life, from selling stereos to put myself through college (degree in Recording Engineering), recording studio owner and recording engineer, college teacher (recording engineering), CD mastering engineer, and audio writer for the past 30 years. Building a serious room—one in which I will enjoy music for the rest of my days—is a logical and natural extension of everything I’ve done in my life. Moreover, a good-sounding room is a great boon to my work—it is a platform for evaluating products that is commensurate in quality with the products themselves. My goal for this article isn’t “one-upsmanship” but rather to share with readers my experience and the techniques in the hope that they will benefit others who are considering building their own listening rooms.
Planning the Room: Size and Dimensional Ratio
The first step in any room design is choosing the room’s size and dimensional ratios—the ratio of the length to the width to the height. This ratio has a very large effect on the room’s sound, particularly in the bass. Good room ratios spread out the room’s resonant modes more evenly, resulting in smoother and more linear bottom octaves. Explaining the importance of room ratios is beyond the scope of this article (The Complete Guide to High-End Audio’s chapter on room acoustics breaks it down), but know that the length-to-width-to-height ratio is the crucial starting point.
Fortunately, acoustic-design consultant John Brant has created an excellent tool on his website (jhbrandt.net) for evaluating room dimensions. The free downloadable spreadsheet performs a detailed acoustical analysis on any set of ratios that you enter. The tool plots all the resonance modes graphically, shows you if the resonance distribution meets the “Bonello Criterion,” and suggests ideal ratios, among other analyses. In addition to the dimensional-ratio spreadsheet, the site includes many other valuable resources for room design. Art Noxon, founder of Acoustic Sciences Corporation, inventor of the famous Tube Trap, and consultant on my room explains room ratios in the sidebar accompanying this article.
In practice, the listening room’s dimensions are also influenced by real-world considerations such as the amount of real estate you’re prepared to commit to the room and how the room fits into the floorplan of the rest of the house. It’s easy to forget that the listening room is just one part of a house and must integrate with the rest of that house in many ways. Keep in mind that good room ratios span a spectrum in which you’ll get good sound. Generally, the larger the room the better the sound (assuming good dimensional ratios); a large room spreads out the resonance modes more smoothly than a small room does, resulting in flatter bass. My room is 27' long and 17' wide, and the ceiling is 11' tall. After living with the finished room for about three months at the time of this writing, I’m very happy with the size and feel of the space.
Once you’ve decided on the room’s dimensions, the next consideration is the room’s wall construction. There’s a wide spectrum of framing and construction techniques that improve the room’s sound quality as well keep sound in the listening room from getting into the rest of the house. You must decide how important this sound-proofing is to domestic harmony, and then choose the wall-construction technique that fits your budget and needs. I’ll share with you just a few examples of the vast range of wall constructions. But first you should know that a wall’s “transmission loss” (reduction in sound amplitude from one side of the wall to the other) is specified as an STC (“sound transmission class”) rating. The higher the number the greater the wall’s attenuation of sound. A standard 2x4 wood-framed wall (16" on-center) filled with insulation and with 1/2" gypsum board (drywall) on both sides is specified as STC-35—not a very high value. With music playing at a moderate level inside this room, standing just outside the room you would be able to clearly hear and identify the music. The next step up is to use 2x6 plate with 2x4 studs that are staggered. This costs next to nothing, but increases the STC rating. For a nominal additional cost you can use 5/8" Type X Sheetrock on the wall outside the listening room and gain a few dB of additional transmission loss. Acoustic supply houses sell gypsum board composed of two layers of gypsum separated by a viscoelastic polymer (SoundBreak XP from National Gypsum, for example) that blocks more sound than does conventional drywall. You can also hang vinyl material inside the wall for even greater isolation. Double drywall adds to the transmission loss. I’ve mentioned this small sample of materials and techniques to illustrate that you can dial-in the amount of isolation you need, and balance it against your budget, with great precision. The gypsum board manufacturers (USG and National Gypsum, for examples) publish a wealth of useful information about the various wall-construction techniques and their sound-blocking performances. As Art Noxon explains in the sidebar, however, soundproofing and optimizing audio quality inside the listening room is more complex than simple soundproofing. The wall inside the listening room should be treated very differently from the wall outside the listening room, as we’ll see.
One of the problems of frame construction is that bass energy from inside the listening room puts the wooden-frame-and-drywall structure into motion—a bass impact, for example, makes the wall move. That wall motion, unfortunately, converts the stored mechanical energy in the wall back into sound after the transient is over (Fig. 1). Art Noxon has called this phenomenon “wall shudder.” Wall shudder colors the bass tonally because the walls will vibrate at their natural resonant frequencies, adding energy at that frequency. Moreover, the wall movement is chaotic. It doesn’t take much wall motion to hear tonal coloration because the acoustic output of a vibrating object is a function of the object’s excursion (how far it moves) and its surface area. With a large surface area such as a wall, even a very small excursion can produce an acoustic output.
Wall shudder also distorts music’s dynamics. Some of the transient’s acoustic energy is turned into structural resonance of the wall, diminishing the transient’s attack and thus the sense of suddenness and dynamic life. Then, as the wall releases that energy over time, the transient’s decay is smeared. The result is a distortion of an instrument’s dynamic envelope and thus a diminution of music’s dynamic expression. Moreover, wall shudder masks the delicate spatial cues that our brains need to form the sense of a fully developed soundstage, the space within it, and the impression of bloom and air around instrumental outlines. All these subtle forms of distortion add up and contribute to a hi-fi system sounding like a facsimile rather than like the real thing.
Another way in which listening rooms color the sound is familiar to anyone who has set up a full-range speaker: tubby and lumpy bass. The listening room selectively reinforces some frequencies and cancels others, with the frequencies reinforced and canceled determined by the room’s dimensions and the speakers’ and listener’s positions. This is one reason why some sort of bass trap is essential in every room.
To summarize, the three primary problems inherent in music-listening rooms are: 1) sound leaking from the music room into the rest of the house; 2) wall shudder; and 3) excess bass that requires bass traps in the listening room.