Re: Amplitude Decibel conversion problem

On Oct 8, 2:33=A0pm, Jerry Avins <j...@[EMAIL PROTECTED]
> wrote:
> c...@[EMAIL PROTECTED]
 wrote:
> > On Oct 8, 1:44 pm, Jerry Avins <j...@[EMAIL PROTECTED]
> wrote:
> >> c...@[EMAIL PROTECTED]
 wrote:
>
> >> =A0 =A0...
>
> >>> As I alluded to earlier 100 dB SPL being 0.946 watts per square
meter
> >>> is the resulting experimental value that corresponds to 0 dB being
th=
e
> >>> threshold of human detection. So if I say a sound has a level of
> >>> 100dB, I'm not talking about a signal in a wire or such. I'm talking
> >>> about the strength of the acoustic vibrations in the atmosphere at
> >>> STP. The reason I bring this up is this is the case where we don't
> >>> need to use a reference since sound is perceptual and therefore the
> >>> reference is humans.
> >> With regret, no. the reference is the sound power level at which 50$
o=
g
> >> the test subjects become aware of the sound. Your 100 dB is still a
> >> ratio: 10^10 times the reference.
>
> =A0 =A0...
>
> > I said it corresponds to not is equal to. That's why there is an
> > offset of 100dB. I didn't imply that 0.946 watts/meter^2 is 0dB, it is
> > 100dB. I'm sorry if my poor wording made matters confusing. 0 dB is
> > 0.946E-10 watts/meter^2 If you figure the average eardrum to have an
> > area of about 0.5*10E-4 m^2, then at 0 dB, the energy captured by the
> > ear at the threshold of detection is down in the femtowatt range -
> > damn sensitive!!! This turns out to be not very far from the noise
> > floor in the ear due to brownian motion and turbulant bloodflow.
>
> I evidently smeared egg on my face by not reading carefully. It
> nevertheless remains true that SPL given in dB remains a ratio, which
> was my point.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
>
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> ** Posted fromhttp://www.teranews.com**-
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I agree that there is an implicit ratio since a log(0) raises issues
in terms of doing some kind of measurement. I was trying to get at the
fact that we don't put an additional letter to denote the reference
such as the case with dBm and dBw.

Clay