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Although Webster’s English Dictionary expands on the definition of sound and noise, in general, the word “sound” denotes a positive or neutral experience while “noise” denotes a negative experience. But who defines what is sound and what is noise? The answer is: it depends. Let’s examine a community example first. Consider a neighborhood that backs up to an elementary school. While the kids are outside for recess, the parents of those children probably enjoy listening to the sounds of children at play. The 3rd shift worker who is trying to sleep could be bothered by the noise. This is a rather obvious example that illustrates how the sound, situation, and listener determine if what is heard is desirable sound or distracting noise.
How about mechanical system sources? Is it sound or noise when the HVAC system is audible? Designers have the impression that all spaces should be very quiet. While this can be true, the generality gets applied with too broad a brush. The background level should be extremely quiet in a recording studio so that recordings don’t accidentally pick up the sound of the HVAC system. But if an office building were that quiet, most occupants would find it uncomfortable. Spaces that are seldom or only briefly occupied, for example, a computer server room, can tolerate much louder levels because there are rarely human occupants. A meeting space as loud as a server room could potentially cause mental fatigue and make it hard to hold a conversation. Somewhere in the middle lies a design goal where the background level is not so quiet you can hear a pin drop, but not so loud it affect speech intelligibility.
It is the job of the acoustical consultant to carefully consider the situation, occupants, and goals to determine the level of background noise. And further, to decide if the potentially audible signals are positive sounds or less desirable noises. The next time you hear something, before dismissing it consider: is it sound or noise? And would others categorize that perception the same way?