Good Acoustic Design Guidelines
Now that we understand what causes the issues in the venue, let’s take a look at what can be done in order to make even the worst reverberating venue into an acceptable acoustic venue.
First of all, see if it is possible to add some sound absorption in the room. Whether it is carpet or acoustical panels on the ceiling, the additional absorption will reduce the reverberation significantly and will definitely help the room's acoustics. This is the first and most important step. It also may be the easiest and simplest solution. In the example above, if the gymnasium had several carpets rolled out on the open hard wood areas, the room’s acoustics would be significantly improved. Even some curtains added to the walls would have an effect. The most basic absorption that is commonly overlooked is people. If the venue is nearly empty vs. full of people sitting in the bleachers, there will be a significant difference. Spreading the people out over the bleachers will help reduce reverberation from the hardwood bleachers.
Acoustical treatments such as ceiling panels or acoustical spray on the ceiling are generally very expensive. Another factor is the architectural design constraints. Spaces such as a glass conference room or marble walled auditorium were specifically chosen for their aesthetic effects. Covering them up with acoustical panels or spray is not an option. In this kind of case the next best thing that can be done is to focus on the design of the system. Determine where the audience is going to be and locate the speakers so that they are pointing directly at the audience. Also reduce the volume level of the sound system so that it is at the minimum possible for the application. The more sound there is in the venue, the more the venue will reverberate. The less sound the speaker introduces, the less reverberation and the better the intelligibility.
Moving the speaker is another option that will help improve the acoustical system. Sound propagates as it passes through air. This means that it loses energy as you increase distance from the speaker. If the speaker is emitting 94 dB at 20 feet away, then at 10 feet away from the speaker the SPL is 100 dB. The general rule of thumb is that you lose 6 dB for every doubling of distance. Reduce the distance from the speaker and the audience and also decrease the volume level in order to improve intelligibility. Some very reverberant spaces such as churches or cathedrals use built-in-pew speakers. These speakers are located right in the pew and are directed at the audience at a very close range at a low volume level. This helps reduce the immense reverberation that would be present if the speakers were shooting sound out into the entire venue. This example of multiple speakers is called a distributed audio system. This is preferable to a cluster speaker system in a reverberant venue.