RE: Acoustic noise calculations for multiple shelves
>FROM A PREVIOUS EPISODE OF "AS THE DB TURNS" But in the end it doesn't matter, does it? A dB is a dB. An increase in SPL of 6 dB is the same as an increase in sound power of 6 dB. Just like a 6dB change in voltage results in a 6dB change in power. Wonderful things, those dB's.. Careful...It does matter. They aren't as wonderful as you think!!! Take an analogy from electronics A 6dB increase in voltage will not necessarily result in a 6dB increase in power. You would have to make a bunch of assumptions, such as a constant resistive load.. What if the load was non-linear? Power is the product of voltage and current. If you have a 6dB voltage increase with no current increase, then you only have a 3dB power increase. Going back to sound An increase in sound pressure level may not necessarily translate to the same increase in noise power. This problem isn't so bad because most sound measurements are made assuming that air is the "resistance" or transmissions medium. However; the reference level is different. If we assume air as the transmission medium, a sound intensity of 0 dB (referenced to 1pW/m^^2) is not produced by a sound pressure level of 0 dB (referenced to 1 x10^^-5 lb/in^^2). The person who originally started this thread wanted to estimate the sound increase from adding multiple cards to a shelf. If those cards had been characterized to have x dBpW/m^^2 of noise; then adding 6dB for each factor of two would result in an extremely high estimate.On the other hand; if those cards had been characterized to have x dBlb/in^^2; then adding 3dB for each factor of two would result in an extremely low estimate. Even worse, if the standard assumes dB pW/in^^2; and he was working in dBa or dB lb/in^2; his answer would be wrong before he even put pen to paper. I know that I'm beating a dead horse; but how else would you know how it died :-) I'm not participating in this thread to prove anybody right or wrong; I just want to make sure that one of our colleagues doesn't add apples to oranges and end up with fruit salad. Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | 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"
RE: Acoustic noise calculations for multiple shelves
But in the end it doesn't matter, does it? A dB is a dB. An increase in SPL of 6 dB is the same as an increase in sound power of 6 dB. Just like a 6dB change in voltage results in a 6dB change in power. Wonderful things, those dB's.. Dave Cuthbert Micron Technology From: drcuthbert [mailto:drcuthb...@micron.com] Sent: Thursday, January 23, 2003 8:51 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 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" 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"
RE: Acoustic noise calculations for multiple shelves
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"
RE: Acoustic noise calculations for multiple shelves
Hi Alan, Your confusion over 3 and 6dB is understandable. Sometimes "sound intensity" and "sound pressure" are improperly used interchangeably. Intensity is proportional to the square of pressure. If the intensity is doubled, one would say that there is a 3dB increase in sound intensity; 10*log(2I/I). However, if the pressure is doubled there is a 6dB increase in sound pressure; 10*log(2p/p)^2. Also, when doubling (or halving) the DISTANCE between source and receiver, one would subtract (or add) 6dB when dealing with a point source. However, for a cylindrical source there is a 3dB difference when doubling/halving distances. Good luck, Paul Hare From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Hudson, Alan Sent: Thursday, January 23, 2003 4:15 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"
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 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"
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"
RE: Acoustic noise calculations for multiple shelves
Quite right for uncorrelated noise. To add to this discussing we can think about the response of the human ear to sound level. A 3 dB increase in SPL does not sound twice as loud. If I remember correctly it takes a 6-8 dB increase to "sound" twice as loud. So is the goal to meet a standard or for operator comfort? Dave Cuthbert Micron Tech From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, January 22, 2003 10:56 AM To: Luttrell, Lyle; 'Gandler, Mark'; emc-p...@majordomo.ieee.org Subject: Re: Acoustic noise calculations for multiple shelves 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). 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"
RE: Acoustic noise calculations for multiple shelves (Correction)
Ahhh! Guilty! Thanks Ken. >From my posting below, the part about "3dB for each shelf" is WRONG!!. Hopefully, I didn't corrupt any innocent minds. It would be more correct to say 3dB for each factor of two, 1 to 2, 2 to 4... I'm glad that I wasn't designing any airplanes today! SNIP >>For sound, the worst case would be to add 3dB for each shelf. However, in the real world, the >>noise probably won't all add together (there will be power/phase/frequency differences). SNIP Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | > -Original Message- > From: Ken Javor [SMTP:ken.ja...@emccompliance.com] > Sent: Wednesday, January 22, 2003 12:56 PM > To: Luttrell, Lyle; 'Gandler, Mark'; emc-p...@majordomo.ieee.org > Subject: Re: Acoustic noise calculations for multiple shelves > > > 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). > > > 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"
Re: Acoustic noise calculations for multiple shelves
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" >To: "'Gandler, Mark'" , 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"
RE: Acoustic noise calculations for multiple shelves
Lyle and Everybody How answered my question!!! Thank you very much for the fast and clear responses! It is great to have this forum. Mark Gandler Ciena From: Luttrell, Lyle [mailto:lluttr...@peakstor.com] Sent: Wednesday, January 22, 2003 7:24 AM To: Gandler, Mark; emc-p...@majordomo.ieee.org Subject: RE: Acoustic noise calculations for multiple shelves 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 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"
RE: Acoustic noise calculations for multiple shelves
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 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"
RE: Acoustic noise calculations for multiple shelves
I saw a posting which said add 6dB for a factor of 2. That is incorrect; when you are dealing with sound. My apologies to this poster; no disrespect intended. When dealing with sound and power, add 3dB for a factor of two. A factor of two only works out to 6dB if you are dealing with voltage, field strength (and possibly some other measurements). There was a long thread which went into the gory mathematical details about a year ago. I'll spare everyone the details; but I'd be glad to explain to anyone who contacts me offline. For sound, the worst case would be to add 3dB for each shelf. However, in the real world, the noise probably won't all add together (there will be power/phase/frequency differences). I saw Paul Hare's response which said to add 13dB for 20 chassis. That "sounds" about right to me ;-) Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | 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"
Re: Acoustic noise calculations for multiple shelves
I read in !emc-pstc that Neil Helsby wrote (in <20030122.8281...@mis.configured.host>) about 'Acoustic noise calculations for multiple shelves' on Wed, 22 Jan 2003: >The simple answer is that the result will be logarithmic – double the >noise and you add 6 dB. The noises are uncorrelated (largely), so you add 3 dB, not 6. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! 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"
Re: Acoustic noise calculations for multiple shelves
The simple answer is that the result will be logarithmic – double the noise and you add 6 dB. In practice it probably isn't and neither will the on-site result when compared to your office measurements unless all conditions are identical. We measure the audio noise (mainly from fans) from our products in a studio environment. Noise is directional and over the length of a product noise from one end has little effect on the noise measurement from the other end. Studio finish absorbs much of the noise but it is not acoustically dead. Now take the product into a metal lined room and, due to reflections, the measurement levels increase. Not much help I'm afraid but hope it gives food for thought. Neil Helsby ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ** 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"
RE: Acoustic noise calculations for multiple shelves
Hi Mark, If you understand the fact that adding two sources of the same level gives you a 3dB increase, you can do some quick addition. Let's say one of your small chassis has a noise level of 75dB. If you add a second one you would get a total noise level of 78dB. (Of course this does not consider cancellation due to superposition, but at least this is a worst case scenario.) If you add another pair of chassis (i.e. total of four), you get to 81 dB. And so on and so on... When the noise levels are different, then it becomes a little more difficult. Without going into great detail here, you should add 13dB to the level of a single chassis to get the noise level for 20 chassis... Hope this helps... Paul Hare From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Gandler, Mark Sent: Tuesday, January 21, 2003 6:31 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"
