I would further amplify on this comment. It is not just a 10 log vs. 20 log calculation. Sound power is the quantity of interest, so by definition it is a 10 log relationship . But someone said add 3 dB for each added component. That is incorrect. You only add 3 dB for the second component. The issue is that the sound pressure level (exclusive of localized interference effects) adds as the square root of the sum of the squares. And that is what you get when you use 10 log(number of units).
>From: "Luttrell, Lyle" <lluttr...@peakstor.com> >To: "'Gandler, Mark'" <mgand...@ciena.com>, emc-p...@majordomo.ieee.org >Subject: RE: Acoustic noise calculations for multiple shelves >Date: Wed, Jan 22, 2003, 9:23 AM > > > Mark, > You need to know what type of level you are working with. > Sound power level (re 1pW) of multiple sources is straightforward: 10*log(n) > = 13 dB for n=20. This is essentially independent of measurement > environment. > Sound pressure level (re 20uPa) depends on the sound power level plus the > environment (measurement distance and room conditions). If you have a sound > pressure level of a unit measured in free space conditions at a distance, > the level due to multiple identical sources in the same environment will > typically be no more than 10*log(n) because the distance to the acoustic > centers of all sources will not be identical. > > Lyle F. Luttrell, PE > PeAk Storage Solutions, Div of MaxOptix > 303-664-8286 fax 303-664-8299 > lluttr...@peakstor.com > > -----Original Message----- > From: Gandler, Mark [mailto:mgand...@ciena.com] > Sent: Tuesday, January 21, 2003 4:31 PM > To: emc-p...@majordomo.ieee.org > Subject: Acoustic noise calculations for multiple shelves > > > Hello Group! > Imagine you are going to install 20 small chassis (shelves) in one rack in > Central Office. > If you know your acoustic noise level from one chassis, is it any way to > calculate total noise? > Sorry, if it is not the smartest question. > Please reply!!! Need an answer!!! > Thanks, > Mark Gandler > Ciena > > ------------------------------------------- > 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" > 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"
