Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!cbnewsh!europa
From: europa@cbnewsh.att.com (r.j.capik)
Newsgroups: sci.electronics
Subject: Re: electronics fog horn
Message-ID: <1990Jul23.223744.11581@cbnewsh.att.com>
Date: 23 Jul 90 22:37:44 GMT
References: <1990Jul18.172626.29473@ariel.unm.edu>
Distribution: usa
Organization: AT&T Bell Laboratories
Lines: 38

From article <1990Jul18.172626.29473@ariel.unm.edu>, by ee5391aa@hydra.unm.edu (Duke McMullan n5gax):
> In article <1990Jul16.220245.6545@mtcchi.uucp> cas@mtcchi.uucp
> (2668-Charles A Sherwood(Z550900)0000) writes:
>>My brother is interested in a fog horn for his boat.
>>Does anyone have a circuit that produces a fog horn like sound??
>>How about an idea as what frequencies a fog horn puts out?
> 
> Chuck, the frequency characteristic of the sound isn't the big thing: power is.

This is not correct.
The sound power level and frequency range are fixed by both
National and International regulations (typically 72 COLREGS), and
depend on vessel size.
In international waters for vessels less than 75 meters in length
the fundamental frequency should be in the 250-700 Hz range.
Minimum sound power levels also differ by vessel size. For vessels
less than 20 meters in length the sound pressure level at one meter
should be no less than 120 db (0.5 nautical mile range), and for
vessels more than 20 and less than 70 meters the spl should be
no less than 130 db at 1 meter (1 nautical mile range).
The specifics are slightly different for inland waters.
Sound signals in restricted visibility (ie: fog), should be sounded
as one prolonged blast at intervals of not more than two minutes.

> 
> 
> Unless I've missed a bet somewhere, an electronic foghorn of equivalent power
> to an acoustical horn is gonna cost huge bucks.
> 

OK, I'll buy that. However, small vessels only need a 0.5 nautical mile
audibility range (90% probability of being heard on axis, in still air,
with a ~63 db background level). I think you can get that range with a
typical boom-box.  


Ron Capik
homxa!lotus@ATT.COM