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Re: Quietest cars on the market?

> > No - 3 dB is a marginal increase in perceived volume but a doubling
> > of power, while 10 dB is twice the volume requiring 10 times the power.
> > 
> > - Lawrence Cheng
> >   lcheng@watson.ibm.com
> > 
> Can someone explain in more detail?
> Noise is the sound pressure waves arriving at your ear?
> dba is a measurement of this pressure.
> Are you saying takes ten times the pressure to 'hear' a doubling of
> the noise? Or that the 'item' making the noise needs ten times the power
> to double the sound pressure?

Time for Mr. Wizard to step in.

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 measured pressure.

Doubling the pressure does not double the perceived volume of a
sound. Volume is a highly subjective measurement that depends on
acuity, frequency, and the current volume. 3 dB is often referred
to as a JND (just noticeable difference), a psychological term
that idicates the minimum difference an "average" person can
perceive under "average" circumstances.


Andrew L. Duane (JOT-7)  w:(603)-884-5873	duane@aosg.gsf.dec.com
Digital Equipment Corporation
ALPHA Open Systems Group
M/S GSF1-1/K13
5 Wentworth Drive
Hudson, NH   03051

Only my cat shares my opinions, and she's too heavy to care.