Dear Jim and All, Isn't it sad that there are many people � indeed whole industries � who choose their units in such a way that the end result is confusion and conflict.
Could it be that obfuscation is their original goal? Cheers, Pat Naughtin LCAMS Geelong, Australia on 2003-02-11 13.05, James R. Frysinger at [EMAIL PROTECTED] wrote: > Interesting. I would have interpreted those figures somewhat > differently, as noted below... > >> kilopascal wrote: >> >> 2003-02-09 >> >> What a weird mess! >> >> I too was confused by the awkward use of decibels until I went to >> Rowlett's page and found that there are many different decibels. I >> have highlighted the definition of the two decibel units seen on the >> package in red. >> >> I would interpret the "106 dB spl/mW +/-4 dB" to mean that for each >> milliwatt of power applied to the speaker, there is 4 Pa (2.5 - 6.3 >> Pa) of pressure applied to the ear drum or produced by the speaker >> diaphragm. I found this by setting 106 = 100 + 20�log10(P/2) and >> solving for P. The decibels are positive because the pressure is >> greater then the 20 ?Pa reference. > > Here, John, I would have taken the +/-4 dB as applying to the first > figure, thus in a slightly different format: > SPL(re 20 �Pa) = (106 4) dB at 1 mW input power. > It cannot be SPL/mW = [etc.] since doubling input power would raise the > SPL (sound pressure level) by 6 dB; it would *not* double it to 212 dB > of course! > > Likewise, I would interpret the next figure for microphone sensitivity > as being > L_V(re 1 V) = (-39 � 5) dB at 1 Pa SPL. > Of course, that would be better written as > L_V(re 1 V) = (-19.5 �- 2.5) dNp at 1 Pa SPL > since voltage comparisons call for the use of napiers while power > comparisons call for the use of bels. (Read L_V as "L sub V".) There is > some information on this in IEEE std 260.1 which is about to be put to > ballot. > > The above comments may not be the most elegant way to put things, but I > think that they are closer to what was meant. But, of course, I'm > guessing, so I could be wrong about that. > > Jim
