Every jazz fan knows that intimate clubs like the Village Vanguard sound different from large venues like Carnegie Hall. Clearly, the space we listen in matters. But many of us never consider the effect that our own rooms have on sound. A bad room can ruin the sound of even the best speakers—and a small investment in acoustical treatment can make any speaker sound better.
Rooms can help the sound, because the reflections of sound waves around the room increase the sense of spaciousness you hear. But they can also hurt the sound, causing some bass notes to boom loudly and others to nearly disappear, as if someone were randomly flicking the volume control on Ron Carter’s amp. Bare walls and floors can make sounds bounce rapidly back and forth, a distracting effect called “flutter echo.”
Highs and Lows
To understand room acoustics, it’s important to know about the Schroeder frequency, sometimes called the transition frequency. In most residential rooms, it’s between 200 and 250 Hertz. Below the Schroeder frequency, in the bass and lower midrange, a room resonates like a jug—its physical characteristics will amplify certain frequencies of sound and cancel others, and which notes get boosted or cut will vary in different places in the room. Above the Schroeder frequency, in the midrange and treble, a room acts like a billiards table—sound waves will bounce around until they hit a soft surface that absorbs them.
Although it’s worth addressing acoustics above the Schroeder frequency, the human ear tends to adapt to those higher-range problems—after all, your friend’s voice doesn’t sound different when you step from your living room into the backyard. But having certain bass notes booming out is annoying.
The easiest way to fix acoustical problems below the Schroeder frequency is to send all the bass frequencies to a subwoofer (or two or four) and tune the sound of the subwoofer so it sounds best in your listening chair. You can do this with an equalizer, such as the MiniDSP 2×4, or with the room correction technologies, such as Dirac Live and Audyssey MultEQ XT, which are built into many surround-sound systems.
However, most regular stereo systems don’t allow you to route all of the bass to a subwoofer. And it’s difficult to control bass frequencies using acoustic treatment, because it requires large devices. Products such as ASC TubeTraps and MSR Acoustics SpringTraps can regulate the low end well, but they’re four feet tall, and thus best suited to dedicated listening rooms. So for stereo systems without subwoofers, the most appealing solution may be just to experiment with moving your speakers closer to or further from the wall behind them, or moving your listening chair forward or backward to see where the bass sounds best.
More Like the Real Thing
While improving your room’s sound at higher frequencies isn’t usually a must, it can give you more focused imaging between the speakers and a more spacious sound. A method that works well in most rooms is called “dead end/live end.” It uses absorptive material in the front of the room, behind the speakers, and diffusers in the back of the room to scatter the reflections, thus reducing flutter echo and increasing the sensation of being in the space where the music was recorded.
Simple fiberglass or foam panels behind the speakers can do the deadening, but they need to be thick. A good minimum is three inches for fiberglass and four inches for foam. If you use the two-inch-thick “wedge foam” panels sold at pro audio stores, the sound will get “shouty,” because you’ll kill the higher frequencies but leave most of the range of the human voice unaffected. Start with a two-by-four-foot absorptive panel behind each speaker, then add more if you like.
You can also add absorptive panels at the “points of first reflection”: the places on side walls between you and your speakers where the sound bounces from the speakers to your ears. If you want a more spacious sound, use diffusers here instead.
Diffusers need to be at least a foot thick if they’re simple geometric shapes, or eight inches thick if they’re professionally engineered designs. Placing two or three on each side wall and perhaps four more on the back wall will usually get the job done. I made my own by cutting concrete forming tubes in half and covering them with fabric. You can also use shelves full of CDs, albums, and tchotchkes as diffusers.
Many companies, including RPG Acoustical Systems, MSR Acoustics, and AcoustiMac, manufacture absorbers and diffusers in a wide variety of designs and colors, and some can even cover them in your choice of artwork. Most are happy to advise you on your acoustic treatment, and some can do the installation for you too. Whichever way you go, it’s a safe bet you’ll get significantly better sound, for less than the cost of upgrading your speakers.