Room Acoustics

Room acoustics affect the tone of a piano far more than is often realized. Sometimes adjusting the room acoustics is the easiest and most effective way of "voicing" a piano to a particular loudness level or balance between treble and bass, after which hammer voicing can take care of the fine adjustment from note to note.

My own piano is a good example. When I was in high school, my parents bought what was supposed to be a very fine grand piano, but at the time I was convinced it was a lemon. The sound was very muffled and I had to bang on the piano to get what I wanted out of it. I was told, of course, that it would get louder in time, but years went by and it never did, despite the strenuous workout I gave to it.

When I was in my late twenties, I inherited the piano and moved it to my apartment in Boston, expecting to do some major work on it to improve the tone (I had, by that time, become a piano technician). To my surprise, the piano came alive without a stitch of work on my part. The hardwood floor and the relative lack of furniture in the room did the work for me. Whereas my parents' living room had been heavily carpeted and draped and filled with upholstered chairs and sofas, my apartment was filled with sound-reflecting surfaces and few sound absorbers.

The sound we hear, especially indoors, comes in part in the form of direct sound and in larger part from reverberant sound—sound reflected from walls, floor, ceiling, windows, and so forth. Acousticians have studied the phenomenon of reverberant sound for many years in relation to the design of auditoriums and concert halls, but relatively little work has been done on the acoustical design of small rooms—practice rooms, living rooms, and rehearsal studios.

In the study of auditorium acoustics, great emphasis is placed on the reverberation time—the amount of time it takes for a burst of sound to decay by sixty decibels (to one-millionth of its original intensity). The larger the volume of the room and the more reflective the surfaces, the longer the reverberation time. But too long a reverberation time will create a "muddy" sound, as one sound runs into the next. By placing more sound-absorbent surfaces in the room, the reverberation time can be decreased, but this will also decrease the intensity of the sound, because sound will not be able to "build up". Too short a reverberation time will thus create a "dry" sound, and the performer may have to work too hard to be heard. Acousticians have found that concert halls sound best when reverberation time is between 1.5 and 2.0 seconds. The slightly higher reverberation times work best for Romantic orchestral music, lower for Classical orchestral music, and lower still for chamber music.

In a small room, such as a living room or music room, the reverberation time will usually be much shorter. Efforts to make a small room sound like a concert hall by increasing the amount of reflective surface until reverberation time reaches concert-hall levels usually won't work because in a reverberant small room certain individual resonant frequencies become prominent, producing a "shower room" type of reverberation. Anyway, it has been found through listening tests that piano music in small rooms sounds best to most people at a reverberation time of about 1.1 seconds, though individual tastes will vary. Although it's not practical, of course, for a homeowner to measure reverberation time, it is possible, when designing a small room, to adjust it to some extent to one's taste an to balance the treble and bass. The key is in the balance between absorbent and reflective surfaces, and in the diffusion or "scattering" of sound so it is evenly dispersed.

Each kind of building and decorating material absorbs sound differently, and the ability to absorb sound varies with the frequency, too. A smooth concrete floor, for example, is an excellent reflector of sound of all frequencies—too good, in fact. A think carpet on concrete will continue to reflect low frequencies, but will absorb most sounds of high frequency. Putting a pad under the carpet will significantly increase its ability to absorb sound at all frequencies.

A wooden floor is also a good reflector, though a little less so at low frequencies. A carpet on the floor, especially right under the piano, may help to create a better balance if the treble is too brilliant. Because the piano case also vibrates—particularly a grand piano case—it makes sense to put the rug under the legs of the piano, too, or to replace metal casters with rubber-wheeled ones so that the wooden floor doesn't become another soundboard.

Window glass and plywood paneling reflect high frequencies while somewhat absorbing lower ones. some of the large window or paneled areas can be covered with a drapery, which will do just the opposite. Large multi-purpose rehearsal rooms that may have a band rehearsal one day and a chamber music rehearsal the next may benefit by hanging a drapery along one wall that can be extended or drawn into a corner as needed to provide the correct amount of sound absorption. This technique can also be used for teaching studios that must accommodate the tastes of several different teachers. Upholstered furniture, of course, is always useful as a sound absorber. One can also experiment with different kinds of window shades and draperies, wall textures and wall hanging, open vs. closed doors, and the placement of art objects and other things about the room, all of which will absorb, reflect, or scatter sound.

A living room or music room with a reverberation time of 1.1 seconds, mentioned above, is a fairly "live" room, one with more reflective surfaces than absorbent ones. One acoustical engineer consulted suggested that for best results the room should be at least twice as long as the (grand) piano. Ceilings shouldn't exceed around 12 feet or reverberation time may increase to the point where the sound becomes muddy. If there are two acoustically different ends to the room, the piano should be placed at the "live" end so the sound can develop and diffuse before being absorbed by the objects at the other end. Others I spoke with thought that a little shorter reverberation time, and more absorbent surfaces, yielded better results.

Small practice rooms should be sound-insulated between rooms, and should have acoustic tile ceiling. One problem that may develop in these small rooms is "flutter echo," where flat, reflective, parallel-sided walls cause the sound to bounce back and forth annoyingly. Orienting the piano differently in relation to the walls or putting it in a corner may help, but putting sound absorbing material on the walls or using large sound-absorbing panels is the best remedy. When designing small practice rooms, try to avoid having two sets of parallel walls; one or two walls should be at an angle to avoid echos. Larger practice rooms are preferable acoustically, but may not be economical.

Making a room sound more "live"—increasing the sound reflecting—is generally more difficult than deadening it because people are usually more reluctant to remove carpets, drapes, and furniture than they are to add them but, unfortunately, that is exactly what is required.

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