WEB-EXCLUSIVE: Acoustics 101Latest News Wednesday, August 6th, 2014
By Vance Breshears
What pastors need to know about how acoustics supports the spoken word
Just like people in low light can experience eyestrain, people listening in a space where the intelligibility is low can be strained when they listen to try to understand. Everything is about the signal-to-noise ratio; you have to improve signal (what you want to hear) and decrease noise (what you don’t want to hear).
There has to be enough of a gap between the signal level — in this case, the pastor teaching — and the noise level — ambient background noise — for speech to be clearly understood. The wider the gap, the better the intelligibility. The remedy for a low signal-to-noise ratio is to either increase the signal level or lower the noise. Noise can be the results of a poor acoustical environment (reflections or reverberation) or high mechanical or traffic noise levels. Some common methods for making improvements are to:
- Reduce reverberation by adding sound absorption.
- Absorb or redirect reflections using materials/shaping.
- Use high directivity speakers or use a distributed sound system.
- Make sure that mechanical systems are designed for quiet operation.
- Control and isolate the space from external noise sources.
- Whatever the remedy for speech intelligibility problems needs to also consider the acoustical requirements for the style of music that is played during worship.
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- Need an acoustical intervention?
What determines the acoustics?
The size, shape and finishes of a room are what defines the acoustics, with size being the dominant influencer. And here is the thing: All these elements are about the architecture. Therefore, acoustics equals architecture. In existing rooms, it is difficult to change the size or shape of the room, so the only practical means is to change the finishes. In new construction, the architectural design of the space will determine the acoustics so the architect and acoustical designer need to work together, even early in the concept phase of the design.
What consultants measure — and why
The two acoustical attributes that are more often analyzed by acoustic consultants are reverberation and reflected sound energy.
Reverberation is diffused sound energy that exists in an enclosed or semi-enclosed space after the initial source has been terminated. In simple terms, after a word has been spoken, how long does it take for the sound to die away? Generally (but not always), longer reverberation times can be good for certain types of music but a problem for speech intelligibility.
Reflected sound energy late in time can usually be perceived and identified by a listener as a distinct echo. In general, the later the sound arrives (following the direct sound) and the higher level at which it arrives, the more noticeable the reflection will be. The design goal is to attenuate or eliminate any late-arriving reflections that will degrade clarity or intelligibility.
The ratio of the direct sound to reverberant sound (D/R) is one specific application of signal-to-noise. For example, two people standing at either end of a racquetball court trying to talk would have great difficulty understanding each other. Even if they speak loudly, there would be difficulty understanding because so much sound energy is bouncing around the room. However, in the same room, when the two people stand right next to each other, they don’t have to talk as loud. The listener still hears the direct sound at the same level, but there is much less bouncing around. This is an example of improvement in the direct-to-reverberant ratio.
The use of carefully designed acoustical ceiling clouds with proper angles and finishes can help provide for good acoustical balance. One type of cloud will provide a reflective bottom that will help reflect direct sound back to the listener while providing absorption on the top to reduce excessive reverberation. Another type of cloud will absorb and control sound from the sound system while reflecting congregational singing back to the congregation for a “singing in the shower” feel.
Good speech intelligibility is the cornerstone to communicating the message. It just takes an understanding of the issues while carefully developing and coordinating the best solution.
Vance Breshears has more than 25 years of experience creating environments for worship. He teaches acoustics at the New School for Architecture and leads the San Diego office of Idibri (previously Acoustic Dimensions.)