# Re: More cable talk

"ptooner" <someguy@xxxxxxxxx> writes:

"Jim Carr" <newsgroups@xxxxxxxxxxxxxx> wrote in message
news:L_zgi.86191\$2K1.11495@xxxxxxxxxxxxxxx
"Todd H." <bmiawmb@xxxxxxxxx> wrote in message
news:841wfxrwun.fsf@xxxxxxxxxxxx

Bell used it for audio power _ratios_ though, not SPL. Hence the 10
in the power equation for decible 10*log(P / Preference).

So the point remains: the original and modern decibel was/is just a
ratio just was the decibel is a ratio.

I don't believe Bell the man used it.

http://www.sae.org/technical/papers/2005-01-2549
"Decibels were originally developed in the 1920s by the telephone industry
(AT&T and Bell Labs). Initially the unit was the bel, derived from the
name of Bell Labs and defined as the logarithm to the base 10 of the
transmission loss of electrical power in telephone lines. It was also used
for voice signals in telephones where the preferred unit became a tenth of
a bel or decibel."

But the point remains that its origin was not in SPLs.

Okay, I made an offhand comment about what I thought was a silly expression.
to wit:

Quote: "Very cool. The only thing that struck me is the following
statement: "A
0.4dB voltage loss at the frequency where the speaker resistance drops to
3 Ohm may be noticeable in an ABX test."

ME: Hmm, I don't think db is a measure of voltage. My memory could be
deceiving
me, but I think voltage is only measured in ---- Wait for it ----- VOLTS.

I thought that was self evident. Firstly, I've never heard voltage measured
in db. Now after reading the entire quoted article above, it does make
sense in their context. Further see:
http://www.sizes.com/units/decibel.htm you will see that late in the
article it says it is indeed correct to use db as a voltage ratio, although
the figure in that case is 20 times the common logarithm vs the normal 10
times.

Yeah. The 2x factor between the two happens when using dB to compare
amplitudes of voltage or current. Power was the original use, and
power involves the square of current or the square of voltage. In
logarithm land, exponents (the square) become factors (2x), and voila.

Anyway, although we commonly get into long discussions about minor
things, this one is too nit picking for even me. If I indeed
started it with the offhand comment above, I'm sorry.

Happily accepted. And there was peace in the land.

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
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X Promoting good netiquette | http://triplethreatband.com/
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.

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