Testing A Room
There are two quick, easy tests that can be used to judge the basic acoustical merits of a room. I call them “the hand clap” and “the two talker” tests.
Hand clap. This one is real common and can be done solo. It’s used to evaluate the presence of problematic “flutter” echo and provide a rough idea of a room’s reverberation time (T60). Executing this test is no more difficult than having the ability to produce a single, loud hand clap. The fingers of one hand striking the palm of the other works best for me.
Walk around the venue. Occasionally stop and clap your hands one time. Then just listen. In almost all locations, you should hear and notice either echoes, reverberation, or both. If you hear echoes, with little or no reverb, look around for any large, hard, parallel surfaces you may be standing between. These flutter echoes are symptomatic of acoustical problems that, at the very least, will reduce clarity and intelligibility. Move around the room and repeat as needed.
If you hear a smooth, obvious, reverberant tail after the hand clap, without any obvious echoes, try to count the number of seconds it takes for the reverb tail to become inaudible. Count up from zero, as in “zero Mississippi, one Mississippi, two Mississippi.” If you get to more than about 1.5 “Mississippis,” it’s an indication the room probably has too much reverb for good speech clarity and intelligibility. Count silently to yourself. Move around the room and repeat as needed.
It’s not uncommon to hear both echo and reverberation. When you easily hear both, it usually indicates that the T60 is under 2 seconds, but greater than 1 second. If this is the case, treatment solutions may need to focus on absorption, diffusion, or both.
One more comment about excess reverberation: It’s fairly common for reverb to mask flutter echoes. When you treat a room to reduce the T60, you often will “uncover” residual flutter echoes. Keep an eye on the parallel walls when applying treatment. If possible install some of your absorptive or diffusive materials on at least one of each pair of parallel walls.
Two Talker. This assessment requires two people and is used to evaluate speech intelligibility and clarity, room noise, direct-to-reflected (D/R) ratio, and perhaps even the need for amplified sound reinforcement.
The procedure goes like this: Two people face each other, spaced an arm’s length distance apart. The beginning location is not overly critical, but let’s use the front row in a church sanctuary for our example. One person faces the back wall, the other faces the chancel, stage or platform. Begin a conversation at a normal speaking volume and maintain the same volume throughout the test.
