Rehersal Room Acoustics - Performance Space vs. Teaching Space

If you are experiencing the joys (?) of building a new choir rehearsal room or are considering changes in your existing facility, here are a few basic guidelines to be considered.

Expectations

A good beginning point is to examine expectations. Keep in mind the rehearsal room is a practice and teaching space. The sound of the choir will seldom reach performance quality in a rehearsal room.

The physical differences between the choir rehearsal and the sanctuary will result in very different acoustical characteristics. The smaller rehearsal room doesn’t allow sound to develop as in a large sanctuary. The shorter distances and the absorptive or reflective properties of surfaces negatively impact the quality of sound the director hears during rehearsal.

While the director often hears a degraded quality of sound, choir members hear themselves as strong singers with a good ensemble blend. This results in choir members developing a false sense of their size or power because the entire choir is surrounded by surfaces which reflect their vocal energy back to them.

 

Volume

The most important element in a rehearsal room is size. Space requirements for rehearsal rooms are generally thought of in terms of the square feet of floor space necessary for a given number of choir members. However, the overall volume of the space in cubic feet is more important. Even if the room is large in terms of floor space, if the ceiling is only 8 or 10 feet above the floor, the room will not provide the balance desired during practice. For instance, if the director is standing near the soprano section it will be difficult to hear other sections clearly.

Ceiling Shape

Acoustically, the most useful rehearsal room surface is the ceiling. Both the ceiling height and shape are  important. As discussed above, if the ceiling is too low, singing parts become difficult to distinguish
properly. Conversely, if the ceiling is too high, reflections arrive late and are not useful in developing the appropriate ensemble sound. Good rehearsal room design dictates that ceiling height should be a
minimum of 14 to 16 feet above the floor, with 18 to 20 feet preferred. However, the ceiling should be no higher than 22 to 24 feet.

Additionally, it is very beneficial for the ceiling to be diffuse rather than flat. That is to say, the ceiling is composed of several surfaces at a multiplicity of angles that cause the energy to be reflected into diverse directions. These reflections contribute to the random arrival of sound energy at the singers’ ears. The diffusive elements can be included in the basic architectural design or can be commercially available products added to an otherwise flat surface. If the basic architectural design approach is chosen, many small, dissimilar surfaces are preferred over a few large surfaces.

 

Wall Shape

Wall shaping is another important factor. Parallel walls allow sound to repeatedly bounce back and forth in what is appropriately termed “flutter echo.” Flutter echoes degrade intelligibility and can even make it difficult for singers to keep correct time with the music. If walls are designed to be non-parallel, flutter echoes can be controlled or eliminated. If the space chosen for the choir room must have parallel walls due to the needs of the other spaces in the building, consider constructing the room with at least two non-parallel walls. Force the room into a shape other than a square or a rectangle.

If a parallel wall problem exists, consider using wall mounted sound diffusers of various shapes and sizes.
The size of the diffuser directly affects the frequencies it can disperse. The larger the diffuser, the lower the diffusable frequencies. Therefore, purchase thelargest diffuser that will fit on the wall.

Director’s Wall

One of the most important walls to be considered is the wall directly behind the director. In a performance situation, the director faces away from the large open portion of the sanctuary to direct the choir. The
sound of the choir passes the director and travels to the far end of the room, then returns as reflected energy. This travel path allows the air to absorb some of the sound energy. Additionally, there are often
architecturally diffusive and absorptive elements that inhibit the return of the choir’s sound. Therefore, a considerable amount of vocal power is required to fill a large sanctuary.

In most smaller rehearsal rooms however, the sound of the choir passes the director and immediately encounters a large flat surface. If this surface has not been acoustically treated, that energy is reflected back to the choir. This can sound great to the choir, but is not exemplary of a performance situation.

There are many ways to address the problem of the “Director’s Wall.” The best way is to make the wall go away. Just make the rehearsal room as large as the sanctuary! That makes everyone happy except the Finance Committee.

A more practical approach is to treat the wall acoustically so that it does not reflect the choir sound. The most obvious treatment would be to add absorption. However, the room may be too “dead” with the director’s wall completely absorptive. Some diffusive treatment that provides an irregular pattern of energy reflections from the wall would help create the illusion of an open auditorium space behind the director.

Two elements already found in most rehearsal spaces can be used to help overcome this problem. These are the hanging choir robes and shelf storage. If the choir robes are hung behind the director and exposed to the room, they will act as absorbers. Also, if put in this same general area, the slots for storage of music or purses can work as diffusers. To use these existing elements acoustically, there should be no solid, reflective doors used. Using robes and storage shelves in
this way can provide economical and efficient use of the rehearsal room space.

Obviously, there are a variety of acoustical treatments that can be used successfully. Each has an aesthetic and cost impact that must be carefully considered.

Flooring

A solid floor base, such as concrete, is preferred. Hollow floors, in addition to adding a “boomy” sound to heavy footsteps, actually work as low frequency absorbers. While the surface material on the floor should reflect sound, the right
type of carpet will control noise from people shuffling feet without deadening the room. Carpet for choir rooms should be short-nap, tight weave, synthetic, glue-down carpet.

Physical Fitness

Another problem experienced by directors is lazy singers. In the smaller rehearsal room choir members are not required to project their voices much to develop a good ensemble sound. Because of this choir members don’t exercise their diaphragms well. When singing in the larger sanctuary, more energy required to fill the room. The singers just will not have the power and stamina to reach the needed level of
performance. Often, they push to compensate and tire quickly. Therefore it is very important for rehearsal room acoustics to encourage more powerful singing.

Construction

The construction techniques and materials used in the choir room are less emphasized during the design or construction phase. Choir rooms are frequently constructed with less expensive, lighter weight materials such as wood or gypsum board. By comparison, the sanctuary is often surrounded with considerable mass through the use of cinder block, brick, or plaster materials. These material differences contribute to the difference in sound.

Conclusion

One technique being used by some choir directors is to rehearse in the sanctuary. This is an excellent answer to the problems discussed. However, this does not eliminate the need for a choir room. The many other uses of this space, such as youth choir rehearsal, small ensemble rehearsal, pre-service “warm-up,” etc. justify providing a properly designed room.