[Boatanchors] decibels (was Microphone Output)

[Al Klase]

"Logarithmic" is the important word.  In audio and radio we're generally 
dealing with large dynamic ranges.

Trivia: A decibel (dB) in one tenth of a Bell (one order of magnitude, a 
factor of 10 times) named for Alexander Graham Bell who researched 
hearing before moving on to the telephone.
(Your ears have a dynamic range of about 120 dB.  That a trillion to one 
ratio!)

Power ratio in dB = 10 * log (P1/P2)

Voltage ration in dB = 20 * log (V1/V2)

Change of 10 dB = 10 * power, 20 dB = 100 * power, 30 db = 1000 * power etc.

1 dB is a barely audible change.

3 dB is twice the power.  -3db is half the power,  Not a big change in 
audibility.

6 dB is twice the voltage etc.

ENOUGH ALREADY!  Sorry, I freaked out.

Al


On 1/11/2013 11:39 AM, David Stinson wrote:
> "dB" is the unit of measure of a relative logarithmic ratio,
> usually involving power or amplitude.
> It needs a suffix to define a point of reference to which the reading 
> is relative.
>
> A few examples of these units are:
> dBm = power relative to 1 mW dissipated in 600 ohms.
> dBW = power relative to 1 W regardless of load impedance.
> dBi =  gain of an antenna relative to an isotropic radiator.
> dBd = gain of an antenna relative to a dipole in free space.
> dBV =  voltage relative to 1 volt, regardless of impedance.
>
> A chart of the ratios and more info than you want is at:
> http://en.wikipedia.org/wiki/Decibel
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/