Acoustic Considerations

The Room:
The acoustic of the room is at the same time the most important factor to be considered, and unfortunately, is the least likely to receive much forethought and attention.

Typically, to produce a feeling of warmth and intimacy, many clubs install quite low ceilings, especially, for some unknown reason, in the stage area. Rooms tend to be small enough and live enough to have serious resonance modes in the fundamental vowel range (250 100011/.).

Sound reflections off such objects as hard wall panels and large- glass areas wreak havoc with the reverberant response of the room.

Another acoustic problem area is the speaker-to-front-seat / speaker-to-rear-seat distance ratio of the room, which is often so imbalanccd that it is extremely difficult to distribute direct sound evenly. Exposed low ceiling beams can compound the problem.

For aesthetic design reasons there may not be very much the soundman can do to alter the resonance and reverberation conditions that exist in the room. However, where the management is negotiable on these points, the empirical and tactical use of drapes, carpets and curtains will certainly improve these acoustic characteristics.

Even though it is all too obvious, we should all be reminded that a full house (versus a room without an audience) also helps to reduce room resonances… in addition to its beneficial effect on the proprietor’s financial problems.

In dealing with the uneven sound distribution problem it has been found that most high frequency speakers suitable for club applications are short throw devices, quite different from those used in large concert halls or outdoors.

In order to optimize the pattern of these short-throw speakers and overcome the direct sound distribution problem, the high frequency speakers should always be located as high up as possible, and aimed or angled downward toward the audience.

The Stage:
The stage acoustic seldom, if ever, gets any attention. It has however, the governing effect on the performer’s sense of tonal balance, particularly in the middle and high frequency range with amplified rock bands.

It has often been the case that the high frequency energy from the percussion will bounce around the stage-area, causing a ringing effect. This multiple reflection, when uncontrolled, causes intense sound pressure levels in the higher end of the audio spectrum, which can and does cause hearing threshold shift.

A cycle of events then develops where the soundman and musicians not hearing enough highs boosts the high frequency equalization, this in turn causes further acoustic trauma, with the resultant at tempt to boost the highs even further.

Threshold shift is another way of saying that the ear and brain become desensitized to a sound. It is the result of fatigue, especially after exposure to high frequency, high energy sound, where the shift causes a loss of perceived highs.

Threshold shift is usually temporary, although with prolonged or extreme exposure it can be permanent. Tonal balance is judged from what you hear: as a sound mixer you may be in a club working a loud rock and roll act for some time and generally you detect that the bass is muddy and there aren’t enough highs so you boost the EQ and the level until it sounds right again.

Actually the problem may have been simply that your hearing over a period of time has lost the highs, due to threshold shift. When someone walks in from the street, he may perceive the sound as terribly shrill. His hearing hasn’t been affected yet.

But if he stays around for a couple of hours, his hearing may be just as affected as yours. After working one of these shows, as you drive home you sometimes can’t hear the engine in your car quite right. The motor may sound funny because you can’t hear the highs.

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