[OT] Decibels and the ear [was: Re: [plug] Hot and bothered CPU hankers for cool breeze]

[James Devenish]

Hi,

In message <Pine.LNX.4.58.0312171304110.28723 at ob.golden.wattle.id.au>
on Wed, Dec 17, 2003 at 01:13:28PM +0800, Mike Holland wrote:
> Amongst the interesting technical comments, I think the simple answer was
> lost. 400 fans are 400x louder.

Well no. This is what I was saying (but I didn't realise Cameron had
beat me to it). 400 fans produce 400 times the noise. But whether that
is 400x *louder* is a consequence of our physiology (or physio-
pathology). The "rule of thumb" (that Cameron provided) implies that
increasing the intensity 400-fold would cause a 2.6-fold increase in
loudness. Derek's experience would seem to indicate that 400 machines
were not 400 times louder than one machine.

> Its more sensible to humans to talk in dB, but then its wrong to speak
> of multiples. 100dB is NOT double 50dB.

Exactly.

> It just doesnt make any sense to talk about multiples (e.g. doubling) on
> an open-ended logarithmic scale with an arbitrarty zero point.

There are "units", such as phons and sones, that are determined
empirically to describe the relationships between the physical
phenomenon of sound and its perceptual consequences at different
frequencies and intensities.