I've been wanting to improve the horn on my BMW touring bike from a meep-meep to something commanding attention with an authoritative presence like the Stebel Nautilus that I shoe-horned into my GTV 10+ years ago.
I was just going to go buy another Stebel Nautilus but decided to do a bit of research on options. I'm glad I did. The Stebel was not the bst choice to my ears.
I had three criteria for horn selection:
1. Its got to be hidden under the bike's fairing (and there's not a lot of room under there)
2. Its gotta be loud. I know horn loudness or even using a horn at all is controversial with some members but I use my horn liberally. I always give people who can pull into my path and aren't looking at me a little toot. I sometimes get a little wave acknowledging me and sometimes a look that says, "I see you asshole". But I'd rather get a scornful look than get hit.
3. Its gotta have a rather pleasant sound, and that usually means multiple horns with sounds that blend harmonically. Most car, truck and train horns, for example, usually have 2 or more horns.
After reading a bunch of specifications for specific horns and listening on-line, I realized I wouldn't be satisfied till I could listen to them all live in the same afternoon. Fortunately, Amazon provides free returns through Kohl Stores and there's one about a mile from my house. So I bought a bunch of horns to test.
The horns fell into two categories:
o Diaphragm horns that creates air movement with a speaker-like membrane. Most cars and small trucks use these types of horns.
o Air horns that blow air past a reed like a clarinet or a saxophone. Trains and large trucks use air horns.
Both horn styles usually have a trumpet-like bell that shapes the sound characteristics and focuses the energy in a forward direction. While there's a lot to be said about the acoustical physics of horn design, I'll leave it there.
A note on sound and perception: These horns all operate between 300 and 500 Hz which describes the fundamental pitch. Orchestras tune at 440 Hz just to give you a sense of the range we're talking about. Car horns are in that same range. Train and large truck horns tend to be a bit lower. Meep-meep style scooter and motorcycle horns tend to be a bit higher.
The first picture below shows the horns I auditioned. I'll describe each of them starting in the upper left corner with the Fiamm AMS80
o Fiamm AMS80S Dual Horn system: This kit consists of two diaphragm horns with a snail-looking bell, virtually identical to the Fiamm Freeway Blaster horns shown below the AMS80S box. Its two horns are described as "Low" and "Hi" and centered at 400 Hz and 500 Hz. They are quite loud. Fiamm sells another kit called the AMS80SX. As far as I can tell, the two kits are identical.
o Fiamm Freeway Blasters 72012, 72112 and 72102 horns. These are all individual horns. Fiamm didn't provide much description of these horns so I just bought them realizing I could return them after the fact. The 72102 is identical to the Low horn in the kit and operates at 400 Hz and the 72012 and 72112 are identical to the High horn in the kit operating at 500 Hz. I don't know why they have two model numbers for it. Once I realized the single horns were identical to the horns in the kit, I ignored them for the rest of the tests. Had Fiamm's website been more descriptive, I would have known I didn't need to purchase them. But you'll see the 500 Hz horn played an important role later.
o PIAA Sports Horn consist of two diaphragm horns operating at 400 and 500 Hz. They are a bit higher quality in the hand than the Fiamm horns but are virtually the same design. They are a bit louder than the Fiamm kit horns and have about the same pitch, as you'd expect.
o PIAA Superior Bass Horn consists of two diaphragm horns operating at 330 and 400 Hz. It has a lower sounding pitch than the PIAA Sports Horn and I liked the sound better than the Sports Horn.
o Stebel Nautilus: This seems to be the go-to loud horn on MV so it had to be part of the test. It is an air horn and the silver cylinder is an air compressor. It has two horn frequencies of 400 Hz and 500 Hz.
o The Wolo Horn is virutually identical to the Stebel but about 2/3rds the cost. They sound nearly identical tho the Stebel was about 2x heavier. Not sure why.
Surprisingly, the diaphragm horns are louder, smaller, lighter and probably easier to mount than the air horns, so I decided to stick with the diaphragm horns.
I liked the PIAA Bass Horn sound best because it sounded more like a train or large truck and less like like a car horn.
Finally, I tried combining the PIAA Bass Horn kit at 330 Hz and 400 Hz with the Fiamm 72102 operating at 500 Hz. The sound of all three together was incredible and definitely had a very large presence.So that's the way I'm going. I just need to figure out how to mount the three horns but I'm working that. It will require that I run a seperate 20-30 amp circuit but that's pretty easy (for me). You have to do this becuase the stock circuit on the BMW, similar to the Vespa, cannot supply the power for the horns. It will blow the fuse.
I tested the horns by setting up a work bench (plywood on saw horses) next to my car which has a 260 amp-hour battery (this a large and powerful battery). I set up a sound pressure meter on my iPhone and measured the freuqency spectrum for each test about 8 feet away. Its not worth the time to post the spectra of each horn. I used it to verify what my ears were telling me. I wore ear protection during all testing. I ran the horns directly from the battery but on a 20 amp fused circuit.
I'll be returning all the horns tomorrow. All told I think I had about $275 in horns on my work bench. There are other horns out there but I think I had a good sampling and, unless something comes up that's really compelling, I have found my horn setup. I hope to have it completed by next week.
My next step is to figure out the horn mounting which will require removing the fairing on my bike and puttting in the auxiliary electrical circuit for the horn. I'll do a follow up once I get the horns installed and will provide and A/B sound comparison.
Hope this helps someone!!
---------Update with video------------
Last edited by Miguel on Mon Dec 30, 2019 10:34 pm; edited 6 times in total