Dave, What you say is absolutely true (see attached message)
>From Halliday and Resnick's "Fundamentals of Physics", a "decibel" is referenced to 1 picoWatt/square meter. Since I had used this book for three semesters of physics; I always assumed it was the "Bible". Alas, it is just another definition to add to the two that you have below. Maybe the acoustic guys should take a note from the EMC guys and always put the subscript after the dB. For instance, there is no doubt what a dBuV/m or dBmW refers to. (As long as you can tell that "uV/m" means "micro-Volt per meter") To be clear, I would have to say that was thinking in terms of dBpw/m^^2 :-) > -----Original Message----- > From: drcuthbert [SMTP:drcuthb...@micron.com] > Sent: Thursday, January 23, 2003 10:51 AM > To: 'Hudson, Alan'; EMC-pstc (E-mail) > Subject: RE: Acoustic noise calculations for multiple shelves > > > Alan, > > here is a definition of dBa: > dBa: Abbreviation for decibels adjusted. Weighted absolute noise power, > calculated in dB referenced to 3.16 picowatts (-85 dBm), which is 0 dBa. > (188) Note: The use of F1A-line or HA1-receiver weighting must be indicated > in parentheses as required. A one-milliwatt, 1000-Hz tone will read +85 dBa, > but the same power as white noise, randomly distributed over a 3-kHz band > (nominally 300 to 3300 Hz), will read +82 dBa, due to the frequency > weighting. Synonym dBrn adjusted. From this link: > http://www.its.bldrdoc.gov/fs-1037/dir-010/_1471.htm > > Now here is a definition of SPL: > Sound Pressure Level: > The sound pressure level at a point is measured in decibels (dB) and is > equal to 20 times the logarithm to the base 10 of the ratio of R.M.S. sound > pressure to the reference sound pressure. The reference sound pressure in > air is taken to be 2 * 10-5 Pa. From this link: > http://www.camets.com.au/info/glossary/spl.htm > > Is this where some of the confusion is coming from? Some are thinking of > sound pressure and others are thinking in terms of sound power. > > Dave Cuthbert > Micron Technology > > > > > > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
