Air Horns

[Rams]

Anyone know anything about air horns?   How they work or more specifically, how is the tone/note or pitch of the horn set?

I'm adding an compressor driven air horn to a piece of equipment and would like to lower the tone/pitch to a lower note.

I don't have a clue as to how this might be accomplished and am not willing to just take the one I already have and attempt to adjust it with out any background information.   No, I don't want an electric horn, I already have the air horn.   I assume that the compressed air is forced through some kind of orifice producing the note but, I'm guessing.   If that "guess" is correct, can that orifice be altered?  Anyone?

Rams

[..]

Isn't there a screw to turn to alter the pitch?

[Rams]

Isn't there a screw to turn to alter the pitch?

Well, if there is, I don't see one.   Then again, when it comes to this kind of thing I'm kind of like the Cowardly Lion of Wizard of Oz fame.   I generally destroy things that I take apart trying to figure out how they work.

Assuming such and adjustment screw existed on the air horn, any suggestion on where it might be?
Everything I'm looking at appears to hold the unit together and not an adjustment type screw.

[Rams]

Just found the answer.

https://en.wikipedia.org/wiki/Air_horn

How it works


Diagram of a typical locomotive air horn power chamber, showing operation
An air horn consists of a flaring metal or plastic horn or trumpet (called the "bell") attached to a small air chamber containing a metal reed or diaphragm in the throat of the horn. Compressed air flows from an inlet line through a narrow opening past the reed or diaphragm, causing it to vibrate, which creates sound waves. The flaring horn serves as an acoustic "transformer" to improve the transfer of sound energy from the diaphragm to the open air, making the sound louder. In most horns it also determines the pitch of the sound. When vibrated by the diaphragm, the column of air in the horn vibrates in standing waves. The length of the horn determines the wavelength of the sound waves generated, and thus the fundamental frequency (pitch) of the note produced by the horn. The longer the horn, the lower the pitch.

Larger air horns used on ships and foghorns function similarly to a whistle; instead of a diaphragm the air escapes from a closed cylindrical resonator chamber through a precisely shaped slit directed against a knife edge (fipple). The air blowing past the knife edge oscillates, creating sound waves. The oscillations excite standing waves in the resonator chamber, so the length of the chamber determines the pitch of the note produced.

Well, that answers that.   Obviously, I didn't know that.   Never took band in school.   Makes me have a better idea of how a trombone works.  Was hoping it would be more like a trumpet. 
It's a chrome horn (bell) and I'm not about to screw that up. Oh well. Thanks for the responses.

Rams

[Bigwolf]

Ron,

I believe the pitch of an air horn is set by the diameter and length of the trumpet part of the horn. 

Jerry

I see you found the answer before I was able to post it.

[¿spoom]

Just found the answer.

https://en.wikipedia.org/wiki/Air_horn

How it works


Diagram of a typical locomotive air horn power chamber, showing operation
An air horn consists of a flaring metal or plastic horn or trumpet (called the "bell") attached to a small air chamber containing a metal reed or diaphragm in the throat of the horn. Compressed air flows from an inlet line through a narrow opening past the reed or diaphragm, causing it to vibrate, which creates sound waves. The flaring horn serves as an acoustic "transformer" to improve the transfer of sound energy from the diaphragm to the open air, making the sound louder. In most horns it also determines the pitch of the sound. When vibrated by the diaphragm, the column of air in the horn vibrates in standing waves. The length of the horn determines the wavelength of the sound waves generated, and thus the fundamental frequency (pitch) of the note produced by the horn. The longer the horn, the lower the pitch.

Larger air horns used on ships and foghorns function similarly to a whistle; instead of a diaphragm the air escapes from a closed cylindrical resonator chamber through a precisely shaped slit directed against a knife edge (fipple). The air blowing past the knife edge oscillates, creating sound waves. The oscillations excite standing waves in the resonator chamber, so the length of the chamber determines the pitch of the note produced.

Well, that answers that.   Obviously, I didn't know that.   Never took band in school.   Makes me have a better idea of how a trombone works.  Was hoping it would be more like a trumpet. 
It's a chrome horn (bell) and I'm not about to screw that up. Oh well. Thanks for the responses.

Rams

Yeah, that's why the deeper sounding ones are usually the coiled up ones, because it's the only way to get say, a 12" long horn in an 8" package.

[Rams]

Ron,

I believe the pitch of an air horn is set by the diameter and length of the trumpet part of the horn. 

Jerry

Yeah, apparently, like other things in life, satisfaction is based on the shape and length.
Guess I'm stuck with what I've got. 

[¿spoom]

Ron,

I believe the pitch of an air horn is set by the diameter and length of the trumpet part of the horn. 

Jerry

Yeah, apparently, like other things in life, satisfaction is based on the shape and length.
Guess I'm stuck with what I've got. 

Take heart, few women would choose a coiled up one 

[Bigwolf]

Ron,

I believe the pitch of an air horn is set by the diameter and length of the trumpet part of the horn. 

Jerry

Yeah, apparently, like other things in life, satisfaction is based on the shape and length.
Guess I'm stuck with what I've got. 

Take heart, few women would choose a coiled up one 

Although, most women do have a way of straightening those things out.   

[Rams]

Ron,

I believe the pitch of an air horn is set by the diameter and length of the trumpet part of the horn. 

Jerry

Yeah, apparently, like other things in life, satisfaction is based on the shape and length.
Guess I'm stuck with what I've got. 

Take heart, few women would choose a coiled up one 

Although, most women do have a way of straightening those things out.   

Well, this appears to be getting out of hand................

[old2soon]

When I was still driving 18 wheeler a lot of the big trucks had bug covers? over the openings which may or may not have made a deeper tone. Maybe an in line pressur regyulator to adjust the air pressure to the horn itself? RIDE SAFE.

[MarkT]

Also the frequency the sound emitter vibrates at determines the note.  e.g. a bugle (also a trumpet) you change the tension on your lips to make them vibrate through the notes you want.  A diaphram horn is lower, deeper and louder than a reed horn.  Also it's self-cleaning.  I have a diaphram horn by Grover on Deerslayer.  They also make semi truck, fire truck, and train horns. This kind of horn you need compressed air in a tank, released by a solenoid - not powered by a vane compressor but piston. I have a train horn I was going to install then I found this one - it's a fire truck horn.  VERY loud.  And low note.  My bike with horn was featured in Nov '03 Motorcycle Cruiser magazine - this pic.

[Rams]

Also the frequency the sound emitter vibrates at determines the note.  e.g. a bugle (also a trumpet) you change the tension on your lips to make them vibrate through the notes you want.  A diaphram horn is lower, deeper and louder than a reed horn.  Also it's self-cleaning.  I have a diaphram horn by Grover on Deerslayer.  They also make semi truck, fire truck, and train horns. This kind of horn you need compressed air in a tank, released by a solenoid - not powered by a vane compressor but piston. I have a train horn I was going to install then I found this one - it's a fire truck horn.  VERY loud.  And low note.  My bike with horn was featured in Nov '03 Motorcycle Cruiser magazine - this pic.

No doubt, that's a dandy and most assuredly would get folks attention!!!   Might be just a hair over my budget limit though. 

[signart]

Here are the air horns on my swap meet parts hauler, a '70 Club Car Rat Rod. Has custom grill made from mesh gutter guard, headlights are '59 Chev truck turnsignal bezels. Notice behind the custom handmade windshield, a chrome LaFrance fire extinguisher which I converted to an air tank for the horns. Those horns will get your attention.

[Rams]

Here are the air horns on my swap meet parts hauler, a '70 Club Car Rat Rod. Has custom grill made from mesh gutter guard, headlights are '59 Chev truck turnsignal bezels. Notice behind the custom handmade windshield, a chrome LaFrance fire extinguisher which I converted to an air tank for the horns. Those horns will get you attention.

Another very cool ride!!!

[Leathel]

Some are pretty cheap from China

https://www.ebay.com/itm/12V-135DB-Super-Loud-Air-Horn-Chrome-Single-Trumpet-Car-Truck-Boat-Automobile-RO/291812528583?hash=item43f161d1c7:g:IUIAAOSw2xRYSLjN&vxp=mtr

I have the same horn driven by an air horn pump and its loud and deep

someone elses video of it in action

https://www.youtube.com/watch?v=zC4G9s7GO4o

[oldsmokey]

SOME, horns are adjustable by turning the bell. Very fine thread and little movement is needed. If I remember right the threaded end may just touch the diaphragm inside, therefore the note change.

[MarkT]

The adjustable Grovers are like that.  They have adjustable and non-adjustable models.

[Rams]

SOME, horns are adjustable by turning the bell. Very fine thread and little movement is needed. If I remember right the threaded end may just touch the diaphragm inside, therefore the note change.

So, what you’re saying is, if you have sufficient length over depth, there is a sweet spot?

[art]

Size matters