sounds has the distractive qualities inherent in music or speech. But if they are not available, a slightly noisy ventilating system may be as effective. In many commercial buildings, masking noise is introduced electronically through a system of speakers distributed throughout. Any masking noise must be strong in the frequencies that predominate in the sound to be masked.
Quieting a Noisy Room Why are some restaurants so noisy that we have to shout to converse with our tablemates, whereas other restaurants are hushed and relaxed? A noisy restaurant is one with hard surfaces all around: plaster walls and ceiling and a bare floor. The first few diners that arrive for dinner are able to converse normally. When more people arrive and begin speaking, sound levels rise with the considerable assistance of sounds that are reflected from the surfaces of the room. As sound levels rise, everyone must speak more loudly in order to be understood. This creates a still higher level of noise, people have to speak louder still, and a vicious circle is established that reaches climax with everyone shouting amid a level of general noise that approximates that of an airport runway. If the same restaurant were to have acoustic panels on its ceiling, heavy curtains on the windows, deep upholstery on the chairs, and a thick, padded carpet on the floor, it would become a quiet restaurant. If you're seeking a quiet place for a meal, look for the carpet and acoustic panels and avoid restaurants with hard surfaces.
Creating Privacy If a building must create acoustical privacy—preventing conversations from being overheard—much the same strategies come into play: Construction must be airtight and heavy. Sound levels within the room can be lowered somewhat by the use of sound-absorbing materials. And masking noise can be invaluable. A barroom packed elbow to elbow with chattering people is in fact a very private environment for intimate conversation. There is simply so much noise generated in the frequency range of human speech that only the closest, most attentive listener can understand one's words. This is why, too, master spies and diplomats, whether fictional or real, turn up the radio or television before conducting discussions in a room that is suspected of being "bugged." Hearing, being heard, not hearing, and not being heard are important factors that we must consider in the design of buildings.
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