What you need to do is take a note of the pitches you require. 

I suggest you do this by ear, or using google. I'd use a piano. When you have ascertained that you have the right series of notes (you may need to take a few sets to bits), you can then go about building your own. 

What you'll need to do is the following. Take the manifold off the pump and then wire it up to a battery. Note the amount of time it takes the disk (mark it clearly and the body of the pump) to make 10 revolutions. You can then work out what the duration of the note is (how wide your holes need to be IN DEGREES). As the inner bit goes slower than the outer, like a wheel, the outer holes need to be bigger in order to sound the same duration note as the inner. 

What I suggest you do next is to build yourself a model with a big piece of paper. Draw a big circle which will be the model width of your control disc. Then draw another "n" circles which represent the positions of the air take off holes for each horn (each horn is clearly at a different radius). 

Now is the difficult part. It's not quite as simple as everything starting at 12 o clock, each horn has a seemingly random position in relation to the first horn. It follows that each horn has it's own start point. If you imagine cucaracha, you have 1113-5- 1113-5- 4433221. 

1 horn (lowest pitch goes) 111gap gap 111 gap gap gg gg gg 1. That starts at 12 o clock. 

Lets say horn 3 starts at 9 o clock it goes ggg 3 gap ggg 3 gap gg 33 gg gap. The pattern starts at 12 o clock, BUT IS RETARDED BY 90 derees. 



If it was me, I'd draw a bar chart with left to right bars and figure out what notes are sounding and for how long (notice that notes do not overlap - it doesn't do chords!!) I'd then transpose this to a circle and cut out the individual notes and rotate them accordingly so they're in the right position. For instance -90 degree for our 3 horn above. 

I'd then cut out the holes I'd marked and enjoy my unique horn!

Nope, notes would play in the same sequence but at a lower pitch (as heard by subject).

 ...but as you drove past the subject, by your logic, the song would play backwards.

I hope it's not some Black Sabbath tune Alex is thinking of !

You might wanna just have one horn and vary your speed for each note then the doppler effect would change pitch for you. Then you just have to figger out what speed you need to go for each note. 

"Self Preservation So-Ci-e-ty !"

There used to be a company called Happy Horn.  They had about 250 tunes back when I got mine.  I got the U.W ( on Wisconsin ) and Dixie tunes.  I dont know if they are around yet.

This one is supposed to be air horn based: //www.horntones.com/

This one appears a more conventional loud horn (and is considerably cheaper): //www.autobarn.net/wolo-programmable-musical-car-horn-wol336.html

I searched on google (in USA) with the words: programmable musical air horns

Title says it all really - I'm thinking about investing in a 6-trumpet air horn (one more than normal) as there is a specific tune I would like to be able to blast out which isn't commercially available.

Has anyone every attempted to reprogramme an air horn ?
Based on installing a few for people over the years, I'm guessing that there must be either a rotating disc or a programmed set of solenoids inside the compressor unit.

I'm loathed to shell out (and get shipped from the USA) on something that might not be possible though...