On Oct 8, 4:41=A0pm, Randy Yates <ya...@[EMAIL PROTECTED]
> wrote:
> c...@[EMAIL PROTECTED]
writes:
> > [...]
> > 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.
>
> Hi Clay,
>
> I don't know why you would assert such a thing. I don't agree.
>
> There are multiple reference levels, even within the context of
> acoustics, and even within the context of acoustics for humans.
>
> In both cases, the expression determining dB is
>
> =A0 dB =3D 20 * log_10 (p / p_ref),
>
> The first reference level is dB SPL, which is mentioned in other posts,
> in which p_ref =3D 0.0002 microbar (2E-5 newton/m^2). This also
> corresponds to an intensity of 10^(-12) W/m^2.
>
> The second does not have a special acronym or identification
> but it is p_ref =3D 1 microbar.
>
> I quote these from Baranek.
>
> Baranek concludes the paragraph with the statement
>
> =A0 "The reference pressure must always be stated explicitly."
>
> Unless I'm misunderstanding you, this would seem to diametrically
> contradict your assertion.
>
> --Randy
>
> @[EMAIL PROTECTED]
> =A0 title =3D "Acoustics",
> =A0 author =3D "{Leo L. Baranek}",
> =A0 publisher =3D "McGraw-Hill",
> =A0 year =3D "1954"}
>
> --
> % =A0Randy Yates =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0% "Maybe one day
I'll=
feel her cold embrace,
> %% Fuquay-Varina, NC =A0 =A0 =A0 =A0 =A0 =A0% =A0 =A0 =A0 =A0 =A0 =A0
=A0=
=A0 =A0 =A0and kiss her interface,
> %%% 919-577-9882 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0% =A0 =A0 =A0 =A0 =A0
=A0=
til then, I'll leave her alone."
> %%%% <ya...@[EMAIL PROTECTED]
> =A0 =A0 =A0 =A0 =A0 % =A0 =A0 =A0 =A0'Yours Truly,
=
2095', *Time*, ELO =A0http://www.digitalsignallabs.com
Certainly, the plethora of difference refernce values, would indicate
one should state which reference he is using. When I get back to the
farm, I have an old book, "The Science of Measurement," which has a
couple of chapters on sound measurements. I'll review it and see how
its author denotes the different reference values. This book is good
about giving the historical basis behind various units and how they
sometimes get redefined over time. Sometimes they get rounded to some
nearest convenient value. A kT TNT energy equivalent is one such
example. It is taken to be 10^12 calories which is a value very close
to experimental values for TNT. I'll re****t what I find out about
the sound measurements.
Clay
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