Re: [Phys-l] decibels

[chuck britton <cvbritton@mac.com>]

http://en.wikipedia.org/wiki/Line_level

Here's a bit more on dB's in the audio world - specifically the 
mismatch between 'Professional' and 'Consumer' reference levels.

Similar to the marketing world using 'peak' wattage for specifying 
power capabilities.

Check out vacuum cleaners and you will find that the advertised 
wattage (horsepower) will invariably exceed the volts x amps. Same 
with audio amplifiers. (Consumer specs - the Pro's won't put up with 
such cr*p)
.
At 3:59 PM -0400 8/28/11, Kyle Forinash wrote:
> Hi;
>
> Decibels for acoustic applications are always positive numbers,
> basically because the log of the ratio is intensity (W/m^2) to a very
> small reference intensity (10^-12 W/m^2) and ambient sound is always
> greater than this reference so the ln is positive.
>
> I'm a little confused about what ratio of reference power or voltage is
> used in electronics/engineering (where the dB scale is usually a set of
> negative numbers). In particular, electrical engineers seem to come up
> with this negative scale even when the circuit is measuring input from a
> microphone. Can anyone point me to a reference that makes the connection
> between the acoustic scale and the electrical engineering scale?