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 From: Hudson, Alan [mailto:alan.hud...@amsjv.com] Sent: Thursday, January 23, 2003 2:15 AM To: EMC-pstc (E-mail) Subject: RE: Acoustic noise calculations for multiple shelves John Woodgate wrote: > The noises are uncorrelated (largely), so you add 3 dB, not 6. Now I'm confused! I always thought it was noise *level* (similar to voltage level) not noise *power*, and hence it was 20*log(ratio) not 10*log(ratio). So I've been using 6dB for doubling noise, not 3dB. I'll need to consult some basic texts, methinks. Regards, Alan -- Remove ".paper-bag" from address if replying by email. ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** 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" 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"
