chapter  3
22 Pages

Measuring noise

Although some noise sources seem to be emitting steady noise levels, in practice it

is normally found that the level is fluctuating to some extent. Some noise sources

vary in level very obviously and by a great deal in a short time. The changes in

level may contain important information, but they make it very difficult to

measure because of the rapidly changing meter display. Two standard ap-

proaches were developed to allow readings to be made in a way that would give

consistent results when used in different noise environments. One used a slow

time constant of 1 s. This means that level fluctuations over periods of around a

second would be smoothed out and an essentially steady noise source would

generate a steady reading on a sound level meter. The fast time constant of 1/8 s,

on the other hand, would allow a sound level meter to respond much more

quickly to level changes although it would never be useful if a steady reading

were required. Slow time constant was the more useful of the two when investi-

gating workplace noise.