Checking The Hall
SIZING UP THE HALL Two halls may look very much alike, but one may have excellent acoustics and the other may be terrible. The single most important consideration which determines whether you will be successful in providing good sound is its REVERBERATION TIME. This is the number of seconds that it takes for a single sound to die away in a single hall. A hall with low reverberation time will be easy to sound. A hall with a high reverberation time will be difficult if not impossible to sound properly. To measure the reverb time, stand in the center of the empty hall and clap your hands. Count very carefully the seconds it takes for the sound to die away completely. If your watch has a second hand, use it; or you can count one thousand one, one thousand two, etc.
If the reverb time is more than three seconds the sound will not be good. With a music tempo of 120 beats per minute and a reverb time of two seconds, along with each music beat the dancers hear, they will also still be hearing the last three beats. This is what causes the music to run together and make it hard to distinguish the rhythm and the melody.
Let's look at the things that affect reverb time. Reverberation is caused by sound reflecting back and fourth from one flat surface to another. The harder and flatter the surface, the more reverb will be present. Conversely, soft and irregular surfaces tend to absorb sound and reduce the reverb time. A ceiling of acoustic tile or blown fiberglass will greatly reduce reverberation. Heavy velour drapes covering a hard surface will also reduce reverb. A wall covered with acoustic tile will not reflect sound and will reduce reverberation.
Here are some suggestions to help minimize reverberation. If there is one wall which reflects more sound than the others, never aim speakers at that wall. If there is one wall which absorbs more sound than the others, direct speakers towards that wall. Try to aim speakers downward, at the dancers, so the sound won't bounce directly off the opposite wall. Think of the sound as a beam of light, and aim it at the dancers, not at a surface from which it will bounce back. In a reverberant hall, the less volume you can use the better the sound will be; if your speakers are well above the dancers' heads you can reach the farthest dancers with less volume than if they are at head height or lower. There are things you can do with the volume and tone controls on your sound system which will be of some help in a reverberant hall; they will be discussed later.
Reverberation time is important. One and a half seconds or less is a good indication that a hall has good acoustics. If you don't have good sound in such a hall, either your sound system is inadequate or you are doing something wrong. Two seconds of reverb is usually acceptable. If you set up correctly and use care in operation of the sound system, your sound should be at least passable. If the reverb is three seconds or more it's unlikely any type of sound equipment or amount of expertise will produce truly good sound in this hall. Certain things can be done, as mentioned above, to make it less bad, but nothing short of acoustical treatment of the hall will produce good sound with such a reverb time.
If the reverb time is more than three seconds the sound will not be good. With a music tempo of 120 beats per minute and a reverb time of two seconds, along with each music beat the dancers hear, they will also still be hearing the last three beats. This is what causes the music to run together and make it hard to distinguish the rhythm and the melody.
Let's look at the things that affect reverb time. Reverberation is caused by sound reflecting back and fourth from one flat surface to another. The harder and flatter the surface, the more reverb will be present. Conversely, soft and irregular surfaces tend to absorb sound and reduce the reverb time. A ceiling of acoustic tile or blown fiberglass will greatly reduce reverberation. Heavy velour drapes covering a hard surface will also reduce reverb. A wall covered with acoustic tile will not reflect sound and will reduce reverberation.
Here are some suggestions to help minimize reverberation. If there is one wall which reflects more sound than the others, never aim speakers at that wall. If there is one wall which absorbs more sound than the others, direct speakers towards that wall. Try to aim speakers downward, at the dancers, so the sound won't bounce directly off the opposite wall. Think of the sound as a beam of light, and aim it at the dancers, not at a surface from which it will bounce back. In a reverberant hall, the less volume you can use the better the sound will be; if your speakers are well above the dancers' heads you can reach the farthest dancers with less volume than if they are at head height or lower. There are things you can do with the volume and tone controls on your sound system which will be of some help in a reverberant hall; they will be discussed later.
Reverberation time is important. One and a half seconds or less is a good indication that a hall has good acoustics. If you don't have good sound in such a hall, either your sound system is inadequate or you are doing something wrong. Two seconds of reverb is usually acceptable. If you set up correctly and use care in operation of the sound system, your sound should be at least passable. If the reverb is three seconds or more it's unlikely any type of sound equipment or amount of expertise will produce truly good sound in this hall. Certain things can be done, as mentioned above, to make it less bad, but nothing short of acoustical treatment of the hall will produce good sound with such a reverb time.
