Bill Putney wrote:

> Ted Mittelstaedt wrote:
>
>> However the problem is that if you use the wrong notes, like A & D, you
>> create I think it's called a dissonant chord, which doesen't sound right.
>> Basically the 2 notes aren't harmonics of each other,...
>
>
> Is that what's intentionally used on fire trucks?
>

Probably. There's also a certain amount of debate as to whether or not a
major or minor chord is more attention-getting. Railroad companies have
often specified one vs. the other for their locomotives (google for
'Nathan Airchime' and 'Leslie air horn' for more info on train horns and
chords).

One thing I'm convinced of is that the goofy little "buzzer" horns found
on a lot of imports are completely useless.