Re: [Phys-l] decibels

[chuck britton <cvbritton@mac.com>]

http://en.wikipedia.org/wiki/Decibel#Suffixes_and_reference_levels

seems to cover as much as you might want to know.
I'm sure that others will chime in if there are errors or further 
clarifications available.

Audio dB's use a somewhat arbitrarily defined 'Quietest Noise Humanly Hearable'
whereas EE's choose a specific power of voltage level.

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?