Things to know about horns ... Big cars sound similar because they too have two horns ... one blows a high note and the other blows a low note. For both horns to work together and not sound out of tune, they are tuned to blow a middle note that is not out of pitch. When a car has a small sounding horn, it is probably because it has one horn. If so equipped, the one horn will be a high pitched horn. Also, 2 horns working together are twice as loud as one horn.

On a GL1800, the high horn is on the left and the low horn is on the right. If one inspects the horns, one horn is stamped "high" and the other "low."

For louder horns that would mount similar to what GL1800's have, one might get something from the light truck world. However, I believe the horns on my GL1800 are louder then the ones on my 2017 Toyota Tacoma. But maybe a Ford, Dodge, or GMC pu have louder ones.