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  #1  
Old 06-24-2011
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Post Signal Horns - Boring Tech Questions

In a nutshell, we have a 41 foot sailboat. Going to mount signal horns on the mizzen mast. The regulations are hard to find - but I found them. (Electronic Code of Federal Regulations:)

I looked for the regulations because the specifications by manufacturers do not always tell you such things as "Complies with regulations for vessels up to X meters"

You can take a look at the chart in the link above.

The first two headings: Length of vessel in meters and Fundamental frequency range (Hz) are perfectly understandable as is the last: Audibility range in nautical miles .

But the other two headings are a bit obtuse:
For measured frequencies (Hz) and 1/3-octave band level at 1 meter in dB referred to 2×10−5N/m2

Any audio engineers out there can explain this?

The reason I ask is I am trying to decide if dual horns are enough more effective to spend the extra money on. Is that column which says "For measured frequencies" which has two sets of frequencies listed for each length category have anything to do with the dual horns?

Have I bored you enough? Hello, are you still awake?
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Old 06-24-2011
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they make an electronic control that will automatically sound your horn with appropriate fog or other signal with out having to push a button every few minutes. I know that is not what you asked but I keep looking at them at the boat show and would like one. I have not been grounded or caught in the fog to need one yet. just a thought, and thanks for the sound link.
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Old 06-24-2011
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Mechanical horns and "wind" instruments normally do not produce a single pure tone the way an electronically synthesized tone would be generated. They produce a range of tones.

In this case the regulation appears to be calling for a uniform level of loudness, across a range of tones that span 1/3 of an octave centered about the primary tone of the "horn".

An octave is defined as ". A series of eight notes occupying the interval between two notes, one having twice or half the frequency of vibration of the other." So if one tone is 440Hz, one octave up from it would be 880 Hz and one octave down would be 220 Hz. The regulation appears to call for a minimum volume level across 1/3 of that spread, i.e. if your horn was centered at 440Hz the volume might be measured 75 Hz lower (down to 365 Hz) or 146 Hz higher (586Hz). Assuming that's how they figure 1/3 of the "octave" range on either side.

If the manufacturer can't state that the unit complies with regulations, you can assume that it DOES NOT on any reliable basis. Save the math, unless you also plan to go out and conduct test measurements on the horn after it has been installed.
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Old 06-24-2011
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I honestly didn't know there were regulations about this (duh, there are regulations about every known thing in the universe these days). I understand that you are trying to install horns that meet the regs, but if the little hand held air horns meet the requirement then you might be overthinking this a bit?
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Old 06-24-2011
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In layman's terms, horns for vessels 40 ft to 65 ft LOA should produce 115 dB near or just below middle C. The other gobbledy-goop is the definition of how the sound pressure level is to be measured and referenced.
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Old 06-24-2011
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The size vessel (41 ft) you have, A set of 12v air horns from an Auto parts store will fit your vessel just find. They come with their own air compressor, 12v and easy to install.
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Old 06-24-2011
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I don't live in the US so extensive research of the regs doesn't interest me but I did read the one on Larry's link and although it waxes lyrical about what the "whistle" should sound like, I never saw anywhere that said you have to have one.

So if having one isn't a requirement, how can the sound of the one you have be a requirement? Another beauraucratic screw-up, IMHO.
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Old 06-24-2011
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WOW! Thanks for all the input. One can always count on Sailnet!

badsanta - I've seen that device - don't like the price.

hellosailor - Thank you so much for an understandable explanation!

jrd22 - You're right, I'm probably overthinking - but I've had a couple of instances where I needed the horn right away - and somebody had carelessly, carefully put it away. A button at the helm would be nice - and the horns 30 feet above wouldn't bust the eardrums and can probably be heard farther. Maybe.

MikeWhy - Sometimes I just like getting into the gobbledygook - I hate being a layman.

Boasun - I'll check out the autoparts store - good idea. I'm always for saving a few bux.

Omatako - At least here in the US, ya gotta have one - even if it's just a handheld.
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Old 06-24-2011
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Larry, I'm not an acoustical engineer, but the definition should still bore you to tears. The column heading of "dB referred to 2×10−5N/m2" means standard sound pressure level referenced to human threshold of hearing (20 micro-pascals). The "1/3-octave band" refers to specified 450-800 hertz (first harmonic of the fundamental tone).

Taken all together, it means what I wrote earlier: a properly calibrated meter placed one meter in front of the horn of your compliant whistle should read 115 dB or higher. It doesn't tell you anything more, or whether dual tone carries farther or better. Personally, I think dual tone horns sound fuller and more melodic.

So, bottom line, the horn should be slightly higher in pitch than middle C (not lower, as I wrote earlier), and pretty dang loud, but doesn't need to be painfully loud.
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Old 06-24-2011
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Have you ever heard or been given a blast by a large commercial vessel? That is what you want for your 41 footer!
I got the 5 horn blast salute from a 100'+ motor yacht down in Annapolis harbor a few weeks ago. The commercial vessels give better horn.

Then again there is probably a regulation stating that you cannot make your horn sound like a 1,000 ton freighter if it is a 41' sailboat. There are regulations for everything after all.
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