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High-frequency Foghorns

Because low-frequency sound waves aren't very directional.
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I live in a city with major ties to sea travel, shipping, and Navy. Right now, a fog has engulfed our area. I was just outside, listening to the deep drones of the foghorns. The ships are all around, but I can’t quite localize them.

This made me wonder: Why do large ships use such deep horns? It is well known that low frequencies aren’t very directional, while higher frequencies are easier to pinpoint. This is why in a home theater system, subwoofer placement is flexible, but precise speaker placement is important.

Because the purpose of foghorns is to help identify ships in low visibility situations, I propose high pitched omnidirectional sound emitters be used instead of the current low pitched horns.

[New category suggestion- Public:Marine]

JRandMoby, Mar 17 2003

Sound propagation http://www.sfu.ca/s...nd_Propagation.html
High frequencies attenuate more in cold, damp air. [8th of 7, Oct 21 2004]

See the Gamewell Diaphone http://www.big-horn.com/diagram.html
The Kahlenberg S-6 would be neat on my bicycle (apart from the weight) [Ling, Oct 21 2004]

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       I think it's a propagation effect; low frequency sounds propagate better than high frequency.
8th of 7, Mar 18 2003
  

       You could have a dual-frequency device with a low frequency horn followed/accompanied by a high frequency localizer pulse train.   

       Personally, I've always wondered why lighthouses don't use colored lights (like an airfield tower beacon). Color is good because:   

       (1) You can include information like WHITE:RED means rocks, WHITE:BLUE means harbor mouth, RED:BLUE:RED means rocks and current   

       (2) You can better localize the beacon. At a long distance and in fog, a lighthouse might cause a big, diffuse blob of light. With a dual color beacon, for a brief moment, two arcs of fog on each side will be different colors. The point of intersection being the location of the beacon
FloridaManatee, Mar 18 2003
  

       Some navigational marks do use sectors of colours to give you information about how you relate to thier position. From memory, the marks at either side of the entrance to Portsmouth harbour in the UK are like that. They are conventional IALA marks except when viewed from a certain bearing when they act as leading lights for vessels entering the port.
oneoffdave, Mar 18 2003
  

       Loud high pitched noises might injure the crews hearing.
GeorgeF, May 16 2004
  

       how about using ultrahigh frequencies that could be only picked up by a device on the ship. because it uses radio waves, we could call it a "radio Transmitter"....   

       I think a high pitched sound would be really annoying. It would probably wake up the locals more than a foghorn.
schematics, May 16 2004
  

       Do SHIPS have foghorns? I thought foghorns were generally land-based. And low frequency sounds do propagate much further than high-frequency ones. A foghorn might not let a ship know exactly where land is, but it's still better than nothing.
supercat, May 16 2004
  

       I think ships have foghorns to let other ships know where they are in the fog. I live a thousand miles from any ship, but that's my guess.
schematics, May 16 2004
  

       I disagree that low frequency sounds are not very directional... I think that's an illusion perpetuated by the room that your stereo is in. Out in the open, (without walls), low frequency sound is just as directional as any other.   

       As an aside, one way to quiet aircraft is to raise the frequency of the aircraft's noise... it prevents it from reaching the ground in many cases. The difference in distance for a given sound pressure is astonishing.
zigness, May 17 2004
  

       I think this idea needs a clear problem statement. If you are trying to alert another ship of your presence, sound is good - any sound. If you want them to know your exact location, any kind of sound pales in comparison to radar and electronic means of communication.   

       Oh, and if high pitched sound is so directional why can I never find my cell phone in the middle of the night when it's letting out it's out-of-battery high pitched dying screams?
Worldgineer, May 17 2004
  

       //Oh, and if high pitched sound is so directional why can I never find my cell phone in the middle of the night when it's letting out it's out-of-battery high pitched dying screams?//   

       There is a range of sound frequencies where the ear and brain can provide good directional sense. Above this frequency, wavelengths are sufficiently short that phase relationships between the two ears become effectively random. Below this range, phase relationships are too slight to be very noticeable.
supercat, May 18 2004
  

       I agree: sound may be directional, but you cannot always perceive which direction it comes from. Especially if you stand near reflecting objects.
I think a fog-horn might be a warning that something is nearby - be careful!
Link for BIG horns. Don't ever cut this guy up!
Ling, May 18 2004
  
      
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