Sound Calcs
Sound Calcs
(OP)
I have a large room with an ambient sound of 87 dBA. I wish to sound an alarm that is heard at 15dBA above ambient (or 102dBA) throughout.
If I have a speaker that can output 104dBA at 10', how do I calculate the spacing of the speakers.
If I have a speaker that can output 104dBA at 10', how do I calculate the spacing of the speakers.





RE: Sound Calcs
Two non coherent sound sources of 104 dB SPL when mixed will produce 107 dB SPL (mixing two equal level sources that are not in phase results in an increase of 3 dB SPL).
If at 10' the signal is 104 dB SPL, at 20' it would be 98 dB SPL (doubling distance results in a 6 dB decrease from point sources).
If two of your speakers were 40' apart, and you stood equa-distance between them, the level would be 101 dB SPL, assuming there was no other noise in the equation.
Because you have a background noise of 87 dB, the overall level measured will be higher by a bit - that math is somewhat more complicated.
For a good reference, see "The New Audiocyclopedia".
Regards,
Andy
Andy Somers
Myndex Technologies Inc.
RE: Sound Calcs
are you familiar with noise at work regs? - PPE, risk assessment...
RE: Sound Calcs
Thanks for the responses.
RE: Sound Calcs
RE: Sound Calcs
RE: Sound Calcs
RE: Sound Calcs
If there were a situation where the ambient is over 105 (such as an active generator room), the fire inspector is more flexible.
RE: Sound Calcs
Does it have to be a speaker?
Couldn't one or several of these mechanical sirenes do the job?
They are usually a lot more energy efficient too.
RE: Sound Calcs
RE: Sound Calcs
As an undergrad (decades ago) I worked for a sound installation company. I used what I had learned in CALC 201 and came up with essentially the same answer the boss got from a cheap cardboard slipstick. IIRC, that little tool came from J.W.Davis as well...and is probably a collectable all these years later.
I remain,
The Old Soldering Gunslinger