Three factors affect intelligibility: noise, reverberation, and echoes. The effective transfer of audiovisual information from the presenter to the audience relies on a balance between both the audio and visual elements.
For this column, we're going to look at an important aspect of the audio element--the effect of room acoustics on the transfer of information.
Human and Acoustic Factors How do we measure the effectiveness of the transfer of aural information? In the field of "psycho-acoustics" (yes, Virginia, there is one) the standard we use is intelligibility, measured using the concept "articulation-loss of consonants." In other words, how many of the consonants in the talker's spoken language are lost in the path from the mouth through the public address system and room acoustics, to the listener's ear?
Three main room acoustics factors contribute to the intelligibility--or degradation--of language: noise, reverberation, and echoes. Let's take a look at each of these.
Noise Acousticians define noise as unwanted sound. Period. It includes such indirect sounds as reverberation and echoes. It also includes background noises, from the hum of the air conditioning system to the sounds heard from adjacent spaces through partitions or doors.
How to test for noise? Listen! Ask the facility manager to turn the air conditioning on full blast so you can hear how it sounds. Have an associate go to the room next door and talk loudly or clap their hands. Then send your associate into the service corridor to make noise. Ideally, visit the facility during a function and observe the space in use.
Reverberation Reverberation, a subset of noise, occurs as sound bounces around a room and is absorbed over time by the air, room finishes, and contents of the room (including meeting attendees). The time it takes for a noise to dissipate by a factor of 60 decibels is referred to as Rt60. An ideal Rt60 for a small meeting room is 0.8 seconds; a large room or a ballroom should not exceed Rt60 of 1.2 to 1.5 seconds.
How to test for reverberation? Clap you hands sharply and listen! When the reverberation time is too long, the room will sound hollow or boomy. When the reverberation is "just right" for a large room, you will hear a short whoosh as room furnishings, walls, and the air absorb the sound energy. When the room is small, you may not hear anything at all; it may seem as if the sound of your clap just went away.
Echoes Echoes are caused by sound reflecting off hard, flat surfaces such as a back wall or a hard partition. They can become a problem especially when the room has portable speakers that vector their sound energy sideways, as compared to
built-in sound systems that beam sound energy down into the audience from ceiling speakers.
How to test? Once again, clap you hands together sharply and listen! Often event planners stand in the middle of the meeting room when performing this exercise. It's much more effective to stand where the presenter will be speaking. Listen for the reflection from the back of the room--that is typically where it comes from--and, if possible, have the facility demonstrate its sound system for you.