On Tue, Feb 27, 2007 at 10:40:46PM +0100, Arnold Krille wrote: > We are talking about music-production for the mainstream and PA, not > musicians amps. :-) But you said "or with a professional PA". Surely you know that commonly installed public address systems are capable of far more than my puny 800 watt bass amp with its two 12" speakers? A typical 300 capacity club here in NY will have 5000 watts or so driving a 3-way system with the midrange drivers less than a meter from the closest audience members. 120 dB at 1 meter would be about 108 dB at 4 meters, still plenty dangerous... > I haven't seen anyone firing his home equipment to have 120dB and > sitting 1m or less away from it... You never said anything about distance :-) and i see that every time I go out to a club. > <snip> > >120 dB dynamic range is an incredible amount, it corresponds roughly > >to the difference between whispering and a rifle fired at 1 meter. > >Even the humble CD can capture the difference between whispering and a > >chainsaw. > > 120dB is the difference between just loud enough to be heard by your > ear (1dB) and the loudness when the bones in your ear bow to protect > it. At higher levels (>120dB) your ear aches but it will recover if > the noise isn't permanent. At least thats the definition I learned... I got my numbers from http://en.wikipedia.org/wiki/Decibel#Safety but obviously their numbers represent some sort of typical examples; I been in a number of discotheques (here in the US we can't pronounce that so we just say "clubs") that had sound levels far above 100 dB. The amount of time the ear can be exposed to a given sound pressure level before sustaining permanent damange clearly varies a lot from person to person. But government standards are probably a good guideline to start with, eg. OSHA table G-16: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9735 TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1) ______________________________________________________________ | Duration per day, hours | Sound level dBA slow response ____________________________|_________________________________ | 8...........................| 90 6...........................| 92 4...........................| 95 3...........................| 97 2...........................| 100 1 1/2 ......................| 102 1...........................| 105 1/2 ........................| 110 1/4 or less................| 115 ____________________________|________________________________ Footnote(1) When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each. If the sum of the following fractions: C(1)/T(1) + C(2)/T(2) C(n)/T(n) exceeds unity, then, the mixed exposure should be considered to exceed the limit value. Cn indicates the total time of exposure at a specified noise level, and Tn indicates the total time of exposure permitted at that level. Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level. -- Paul Winkler http://www.slinkp.com
