Bouncing Off the Walls: Controlling Acoustics in a Monolithic Dome

Sound and Walls

Sound reverberates in all spaces except outer space. Sound waves travel out from their source forever – unless they impinge on to a surface where they are absorbed, or reflected, or both. Sound tends to travel in a straight line. It will bounce in much the same way as light reflects.

All rooms have their own acoustic behaviors. Sounds bounce from wall to wall and ceiling until they are absorbed. If a room is empty and the surfaces are hard, sound bounces many more times before it dies. If the room is padded, the sound quickly dies as it is absorbed by the padding.

Sound in Monolithic Domes

Monolithic Domes are shaped perfectly to reflect most sound through their focal point – their centers. This means we can capture the sound and absorb it at its center without covering all other surfaces.

Sound generally follows line of sight. If you see only absorbers, you can bet the sound only sees absorbers. The absorbers (soft, lumpy, no reflective surfaces, many angles of reflection) can be people, carpet, upholstery, acoustic ceiling tile, furniture of all kinds and shapes, plants, flags, etc.

The point is that all extra sound in any room is a bother. It needs to be absorbed. In the dome it concentrates in the center. This concentration makes it more noticeable. In many ways that is good as it provides a much smaller area that must be treated to absorb the extra sound.

Sound Treatments

The simplest sound treatment is a cloud of sound absorbing material hanging in the center (focal point) of the dome. For beauty or effect, the absorbing cloud can be designed as a series of small clouds or as a single hung ceiling. Flagging, vertically suspended, also works well.

A Word of Caution

With all acoustic treatments, it’s imperative that the treatment does not compromise the dome’s huge heat sink. That heat sink is part of the dome’s heating system. It’s the passive solar part of the building. Air must be allowed to flow freely through the cloud so the heat can interact with the dome shell. This can be done by properly spacing the clouds or the flagging, or by using power ventilation.

Spraying the dome with fuzzy sound absorbers is a quick fix for short sound waves. It does not help much with long sound waves. And it definitely will foul up the quick heat sinking ability of the concrete shell. The shell stores enormous quantities of heat.

Great care must be taken not to lose this feature, especially in domes where crowds of people will be occupying the building from time to time.

Acoustic Panels: Inexpensive calming of the sound bounce in a Monolithic Dome

Monolithic Domes have an interesting technological feature. When they are clear and open they concentrate sound. Concentrated sound can be dealt with. We have many experts telling us how to do it. Their advice varies. But we have learned a few things by just doing. One way to calm the sound is to hang sound absorbing blankets in the center of the dome. It is a very simple and inexpensive cure.

One of our office domes had too much sound bounce. The dome was open with a few office cubicles around the edge. We had several people give us advice about calming the sound bounce. One that made the most sense was a salesman selling sound panels – quilted soft panels. Without further guidance, we ordered 24 panels, began hanging them a few at a time and testing the results. Surprise! We achieved solid calming with just four panels in the dome’s center.

Since that worked, we used 32 larger panels in Italy ISD’s Multipurpose Facility/ Gym. It helped immensely. But they were installed around the perimeter. There is no doubt in my mind that a small number of the larger panels in the center of a gym would do wonders to calm sound.

Sound blankets are simple to install, inexpensive, colorful, attractive and virtually indestructible. Balls thrown against them are not a problem.

If you do not have current sound mitigation, consider the panels. Call us for names of suppliers and installation methods.

^{Reprinted from the Roundup, Summer 2000}