danny@garnet.berkeley.edu (Danny Lee) (05/31/91)
Ok, stupid question of the day/week/month . . . Why is the decibal scale expressed in negative numbers? Or should I say, why is 0db louder than -45db? Also, is t here a differance in acoustic db and electrical db's? Idiot question I know but hey, I can't get a straight answer from anyone around here. Thanx in advance. -- Danny Lee danny@garnet.berkeley.edu 415.548.2173
wlsmith@valve.heart.rri.uwo.ca (Wayne L. Smith) (05/31/91)
In article <1991May31.001234.7155@agate.berkeley.edu> danny@garnet.berkeley.edu (Danny Lee) writes: > > Ok, stupid question of the day/week/month . . . Why is the decibal >scale expressed in negative numbers? Or should I say, why is 0db louder than >-45db? Also, is there a differance in acoustic db and electrical db's? >Thanx in advance. This should be asked in sci.electronics, but... Db is a log scale of measured intensity versus an absolute reference. If you send a 1V signal through a box and get 50V output, the output is 10 x LOG (50/1) = 17 db higher than the input. If the output is 0.003 V, then the output is 10 x LOG (.003/1) = -25 db. A negative db measurement indicates a loss or reduction, and a positive db indicates a gain. Acoustic db's relate so sound `pressure' (a physical phenomena), while electrical db's can be signal voltage or power. I don't know what the 0 db reference is for sound, but 120 db (ie 1x10E12) above that reference is, I think, either the threshold of pain, or a jet engine at 10 ft.