LDODD Posted April 27, 2007 Posted April 27, 2007 Hi All Bit random this one.... Am currently updating all our spec sheets and had a request from one of our German Customers. They asked me to add the noise level of the cooling fan in one of our units.Not a problem, I thought - so I proceeded to trake the PSU to bits and get the part code of the fan.Searched on tinternet and found the manufacturer spec, which stated 28dBA. Fine - I added this to the spec and sent it to Germany for proofing. Response = Hi Luke, the datasheets look good form e, Mr. H**** is very glad about them. The only thing he mentioned: LD216, Fan Noise – there is no distance noted for the db. Have a nice weekend! Regards Karen Other than the obvious scathing comments, 1) Does this sound like a reasonable request?2) Is it something that is remotely recordable (ambient noise levels, acoustics etc)3) Is it like specifying Lux levels, not source Lumens in lighting?4) Any other constructive comments? Thanks in advance!
Bryson Posted April 27, 2007 Posted April 27, 2007 Well, technically, he has a point. It should be noted as 28dB @ distance.
WiLL Posted April 27, 2007 Posted April 27, 2007 Well, technically, he has a point. It should be noted as 28dB @ distance. pardon me for being a sound-noob, but surely that should be a standard distance of say 1 metre? after all, my car has a noise output of 0dB@ 2000 miles. Is there not a fixed distance if a product only says '28dB'? otherwise some kind of sliding scale graph would be needed.
Simon Lewis Posted April 27, 2007 Posted April 27, 2007 Other than the obvious scathing comments, 1) Does this sound like a reasonable request?2) Is it something that is remotely recordable (ambient noise levels, acoustics etc)3) Is it like specifying Lux levels, not source Lumens in lighting?4) Any other constructive comments? 1) Yes - I wish that more manufacturers would provide fan nose levels! 2) It's difficult to measure properly. You've mentioned two important areas - background noise and the acoustics of the measurement space. Other issues include the directivity of the source.3) Sort of. Sound Pressure Level is a log ratio of the sound pressure at that point to a reference sound pressure. It will be affected by the room etc., so stating the fan's dB(A) isn't that helpful. In your case, you have provided the manufacturer's SPL figure, but this may change (for better or worse) when it is mounted in a case, and as your customer points out, you really need to know at what distance the measurement was taken. Many devices could be 28dB(A) if measured far enough away! Therefore, don't feel that your customer is being picky - it's quite a reasonable request.4) The better way of providing information of a devices intrinsic acoustic output is to measure its Sound Power Level. This isn't as easy to do, but it does give a figure that isn't influenced by the immediate environment.
LDODD Posted April 27, 2007 Author Posted April 27, 2007 Agreed Have been web-researching and there is little note anywhere of distance and dBA - other than a few bods making the same point as above. Given that the fan comes from a Taiwanese manufacturer, I guess I'll never know unless I test it myself.... 1 site suggests that many manufacturers test at 1m in a controlled environment. Any other thoughts?
Bryson Posted April 27, 2007 Posted April 27, 2007 Here's an Anechoic Chamber for hire. Quite reasonable, actually. I was expecting far more!
LDODD Posted April 27, 2007 Author Posted April 27, 2007 Anechoic Chamber cost seems more than reasonnable!Think I'll look into it.
Simon Lewis Posted April 27, 2007 Posted April 27, 2007 Anechoic Chamber cost seems more than reasonnable!Think I'll look into it. If you do, try measuring SWL using the hemispherical survey method.
LDODD Posted April 27, 2007 Author Posted April 27, 2007 okay. Now I'm lost - but I'll ask! (Google tells me that I'm not a short wave radio listner) Thanks for the help here folks. Seems like the confusion was justified and that I'm not as big a numpty as I thought. I think there must be - or certainly needs to be some kind of test standard that is lacking at the moment. Again - I'm no expert though.
Rob_Beech Posted April 27, 2007 Posted April 27, 2007 after all, my car has a noise output of 0dB@ 2000 miles. Is that right.....
LDODD Posted April 27, 2007 Author Posted April 27, 2007 "if a tree falls in a dessolate forest, does it make a sound?" ...but lets not go there...
Simon Lewis Posted April 27, 2007 Posted April 27, 2007 I think there must be - or certainly needs to be some kind of test standard that is lacking at the moment. Again - I'm no expert though. OK... you could just measure sound pressure level (SPL) at 1m in your anechoic chamber. Measure both linear and A weighted. I should point out that there are several methods for measuring SPL in different environments - have a look at British Standards online. If you want to obtain the Sound Power Level (SWL) then a quick survey method utilising SPL measurements can be found in BS EN ISO 3746:1996 "Acoustics - Determination of sound power levels of noise sources using sound pressure - Survey method using an enveloping measurement surface over a reflecting plane." (catchy title ;-) Sound Pressure may be considered analogous to temperature - it's relative to the surroundings and the source. A 1kW fire might make a small, well insulated room feel warm, but in a large warehouse the temperature may not change at all. If you were to measure the power output of the fire, it would be the same in either location.
Simon Lewis Posted April 30, 2007 Posted April 30, 2007 A small postscript.... I was reading through this article, and a non related "sidebar" at the bottom was telling of manufacturers who quote only "xdB" as a noise rating.... They too suggest using Lw.
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