Re: Quietest cars on the market?

["C.B. MORTON" <bmorton@uwovax.uwo.ca>]

>Sound pressure is measured in "bels", which is a unit of air pressure
>variation. For convenience, we generally use "decibels", which are 1/10th of
>a "bel". 1 bel doubles the sound pressure, hence 10 decibels doubles the 
>sounds pressure. "power" does not enter in to this, just the measure pressure.

Not exactly -- the decibel scale is a logarithmic scale. A decibel is defined
as (20 log P) where P is a sound-pressure unit (defined as 2 x 10 E-05 N/sq.m).
An average conversation is 1000 P. log 1000 is 3, so the decibel conversion
is 60 dB. Loud music might have a pressure value of 10 000 P. log 10 000 is
4; conversion is 80 dB. So every 20 dB increase translates to a 10-fold 
increase in sound pressure.

The height of the sound wave indicates the total pressure exerted by the
molecules of air (or another medium) as they move back and forth, which is
referred to as the sound's amplitude or intensity and corresponds to what we
hear as the sound's loudness. The frequency of the sound waves is what we
hear as the sound's pitch.

(All logs are base 10, obviously).

-- Brent
bmorton@hydra.uwo.ca