Common Noise Levels and Typical Reactions
Below is a useful comparative table of noise levels. But
what does Apparent
Loudness mean?
Alright, it is a bit
complicated!
Let us start at a noise level of 70 db.
We experience this sound because a certain level of noise energy is reaching our
ears. Now suppose we double the energy reaching our ears. A noise meter will
tell us that the noise level is now 73 db (a rise of 3 db in noise measured on
the meter is always due to a doubling of the noise energy level in the air
around us, e.g. 43 db has twice the noise energy of 40 db, 63 db has double the
noise energy of 6o db and so on) . But the sense of sound in our brain does not
react to the noise energy level in the same ratio. A rise from 70 db to 73 db
does not feel to us like a doubling of the noise, it sounds like much
less. For us to think that the
noise has doubled, the noise energy level outside has to increase TEN
times (which a noise meter will register as an increase of
10 db)!
So if we start at 40 db and increase the noise to 50 db, the real
noise energy outside has increased 10 times, but our ears tell us that it has
only increased 2 times i.e. the apparent loudness has doubled.
If we increase
further to 60 db, the real noise is now 100 times greater but our ears tell us
that it has increased 2 times from 40 to 50 db, and another two times from 50 to
60 db or 2 x 2, or 4 times altogether. Increase the noise once more from 60 to
70 db (the noise outside has now gone up 1000 times more than at 40 db); our
ears tell us it has gone up 2 x 2 x 2 or 8 times compared to 40 db.
Finally
increase the noise outside another 10 times. A meter will record an increase
from 70 to 80 db; the actual noise energy has now increased 10,000 times but our
ears tell us it has gone up 2 x 2 x 2 x 2 or 16 times greater than it was at 40
db.
So there you
are!
Let me summarise:
40 db Reference level
-----------Real Noise Level ----------APPARENT
LOUDNESS
50 db -----increased by 10-------------- increased by
2
60 db -----increased by 100------------ increased by
4
70 db -----increased by 1000 -----------increased by
8
80 db -----increased by 10000 ---------increased by
16
************(compared to the levels at 40
db)**********
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