[LAD] twice as loud

fons at kokkinizita.net fons at kokkinizita.net
Fri Jul 23 16:57:47 UTC 2010


On Fri, Jul 23, 2010 at 02:20:02PM +0200, Arnold Krille wrote:

> But if two people talking is power because their talking is uncorrelated (even 
> if they speak about the same thing:), then making a PA louder (twice as loud 
> as before) would be an amplitude thing as it is correlated. No?

Assuming you can find some gain factor that your test listeners
would agree on to call 'double', then that will correspond to
some amplitude ratio R and a power ratio R^2. It doesn't matter
wich one you use. The important thing here is that your test is
measuring the subjective loudness effect of playing back the
*same* sound at different levels, as opposed to increasing the
level by adding other sounds. 

I guess that if you ask people to adjust the levels of two
similar sounds until one seems 'double as loud' as the other,
what they do is choose some ratio that they feel comfortable
with calling 'double' in everyday parlance. I doubt very much
if such a choice would be consistent with their choice for
other (bigger) loudness ratios.

For example if you find that for the your listeners 'twice
as loud' means +10dB, and then you'd play two sounds with a
difference of 40dB, would they experience that as '16 times
as loud' ? I doubt if they would even be able say if it is
8 or 32 times. 

There is another consequence of calling some dB difference
'twice as loud'. If the result is consistent (in the above
sense), it means that our perception of loudness is *not*
logarithmic as it is often described to be: if it were,
a change of a fixed number of dB would correspond to a 
constant subjective *difference*, and not to a constant
ratio such as 2:1. For example, the classical +10dB for
double loudness means that L = c * P^0.3, L = loudness,
P sound power, and c some constant. This is a power law,
not a logarithmic one.

If 'twice as loud' would correspond to +6dB, that would
actually mean that loudness is a *linear* function of
sound pressure...
 
All this makes me think that the whole concept of 'twice
as loud' is meaningless, and where it has been used it
is a bad name for something else. 

Ciao,

-- 
FA

There are three of them, and Alleline.




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