s buckley-jones Posted January 20, 2015 Share Posted January 20, 2015 wonder if you can help to put these Db levels in to context for me . Two roof mounted fan with attenuators fitted are spec to give the following levels at 70% duty cycle. 64dB at 63 Hz, 57dB at 125 Hz, 43dB at 250 Hz, 30dB at 500 Hz, 13dB at 1 kHz, 10dB at 2 kHz, 12dB at 4 kHz, 19dB at 8 kHz.. automatic start up on co2 and heat . 210 seated . little acoustic damping eg hard wall and . ? would this been seen as a performance issue for the spoken word . I have done more work on this data from classroom acoustics give this information . window air con 62-- 67-- 63-- 60 --- 56--50-- 40.. background noise 57--42--32--24--16--10--6. distance from vent over stage 9 meter to head hight over seat area " 2 levels" 8 meters. a first glance ? Link to comment Share on other sites More sharing options...
Oldradiohand Posted January 20, 2015 Share Posted January 20, 2015 Db referenced to what and at what distance? And if it's at 70% duty cycle is this an averaged figure? Assuming a 20 micropascal 0bB level this looks a bit loud to me. My source of reference for this sort of thing is here:- http://downloads.bbc.co.uk/rd/pubs/reports/1980-08.pdf. I don't think theatres would be much different but there must be some published recommended figures for performance spaces. Link to comment Share on other sites More sharing options...
Simon Lewis Posted January 20, 2015 Share Posted January 20, 2015 ... would this been seen as a performance issue for the spoken word . If spoken word was purely acoustic, yes. 60dB is around conversational speech level at 1m. The fans have a reasonable level of low frequency noise at a a similar level (but not all in the same frequency band) as speech. They will present a certain degree of masking to acoustic speech and may be perceived as an annoying background distractor.If the speech is amplified you would get a better signal to noise ratio, but depending upon the audience's tolerance to noise, the level of the reverberant sound field and any directivity characteristic from the noise source itself, it may detract from amplified speech too. Is it possible to find something with better low frequency attenuation? Link to comment Share on other sites More sharing options...
Jivemaster Posted January 20, 2015 Share Posted January 20, 2015 Add to that that the fans may/will be on together so there will be an additive effect, ( +3dB ? )I'd keep looking, or find some low and mid band damping. Link to comment Share on other sites More sharing options...
Simon Lewis Posted January 21, 2015 Share Posted January 21, 2015 Do you have a link to the fan data? It would be useful to see if there are any more clues to how these figures were arrived at. On the one hand, by the time the (presumably Z weighted) octave band figures are A weighted and added to give a single figure, that may not look too bad, but on the other, there may be many other factors (conservative measurement, duct noise, structure borne vibration etc.) that will make them more intrusive. Link to comment Share on other sites More sharing options...
MarkPAman Posted January 21, 2015 Share Posted January 21, 2015 Having fitted a small fan at home recently, I had a data sheet with a noise figure on it. Mine claims to be 62 dB(A) @ 3m. Doesn't mean they're all measured like that though does it. :( Link to comment Share on other sites More sharing options...
Bobbsy Posted January 21, 2015 Share Posted January 21, 2015 The trouble with specs like that is that (assuming it was properly measured) it still doesn't necessarily tell the whole story. A slightly loose screw, a bit of thin ply around, etc. can all set up extra resonances at certain frequencies. The OP's measurements sound loud enough to be an annoyance to me but pure numbers aren't the whole story. How does it sound when the auditorium is full and somebody is speaking normally on stage? Link to comment Share on other sites More sharing options...
s buckley-jones Posted January 21, 2015 Author Share Posted January 21, 2015 I agree that there are a lot of factors that I do not have data for . The levels given for the fans come from our M/E engineer . mid range levels do seem to be bordering on being a problem, drama /conference and children's performance being the ones that come to light . fine you get the A grade fan if not . I would rather not wait till we open again to find out there is a problem. Link to comment Share on other sites More sharing options...
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