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From the "meep meep" of the smallest scooter to the "BLLLAAAAAGGGGGHHH" of the largest seagoing container vessel, vehicles seem to have horn sounds that, in an auditory way, seem to indicate their mass. Of course, nothing prevents a designer from putting a "large" sounding semi truck horn into a mini automobile, it seems one would only do this for a joke and indeed, I can imagine it would make people laugh because of the unexpected mismatch between the vehicle and its warning sound.

Are there actual engineering guidelines that drive such design decisions? Presumably, from a psychological acceptability standpoint or from safety or general human-machine interface principles?

Note to audience: I tried my best to find the most appropriate SE mini-site. We have "Sound Design" which seems to relate to music; and "User Experience" which doesn't say so but seems 100% related to software design.

Note to site moderators: A tag for usability engineering or human machine interface design would be helpful.

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    $\begingroup$ Yep. IMO Requirements (ColRegs) for Marine Sound Signalling (Kahlenberg UK Ltd) $\endgroup$ – Phil Sweet Jun 9 '18 at 12:52
  • $\begingroup$ And some physics of why we do it the way we do - physics.stackexchange.com/questions/87751/… $\endgroup$ – Phil Sweet Jun 9 '18 at 12:55
  • $\begingroup$ There was an edit proposal to add the "acoustics" tag. Since I am asking for design guidelines and not anything about the generation or propagation of the sounds... I have rejected the tag proposal. $\endgroup$ – Douglas Held Jun 9 '18 at 23:15
  • $\begingroup$ Wow, thanks @Phil Sweet. That's a great reference. I wonder what there is for land vehicles. $\endgroup$ – Douglas Held Jun 10 '18 at 0:42
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    $\begingroup$ Human-machine interface falls under ergonomics, and engineering of the environment (making the environment more comfortable/understandable for those working in it). Surprisingly, we didn't have an ergonomics tag before. From a control alarms perspective, it's usually done with simplicity in mind - a single oscillator circuit to generate a single pitch that can be heard is relatively easy and has less parts that can fail in case of emergency. But I haven't dealt with cars. $\endgroup$ – Mark Jun 11 '18 at 16:50
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Ships have loud horns because they need to be heard from far away. Because they can't stop abruptly. For cars it is less so, for scooters even less.

A car's engine isn't powerful enough to drive a shiphorn, a scooter not powerful enough to power a car horn. You can go a louder than standard, but regulations prevent manufacturers from doing so, and fines prevent people from fitting loud horns to their vehicles.

Usually horns with alternating tones are also forbidden. Very boring indeed.

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  • $\begingroup$ I hear horns with multiple tones all the time. Most notably on trains but also on American midsize cars. Isn't a minor third interval fairly common? $\endgroup$ – Douglas Held Jun 10 '18 at 0:46
  • $\begingroup$ @DouglasHeld It may not be forbidden everywhere, but here it is, at least for cars. With multiple tone i mean one tone after another, not at the same time, which usually is legal. $\endgroup$ – Bart Jun 10 '18 at 11:12
  • $\begingroup$ Perhaps edit your answer to describe this as "Usually horns which change tone e.g by alternating notes or playing a tune"? $\endgroup$ – Jonathan R Swift Jun 11 '18 at 16:59
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the mismatch between the horn sound and the size of the vehicle is a very useful way to gain attention. My Suzuki GS1000 carries a pair (!) of Italian sports car horns, tuned to two different notes, which sound like those horns used on large diesel trucks. VERY effective!

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Needs to be heard (volume) within vehicle stopping distance.

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  • $\begingroup$ That's very sensible requirement, yet I've never heard of a vehicle design that lowers the horn frequency in line with the vehicle's speed. $\endgroup$ – Douglas Held Jun 10 '18 at 0:44
  • $\begingroup$ This answer should be improved by providing some examples, and possibly showing real-life engineers who made these decisions. $\endgroup$ – Mark Jun 11 '18 at 16:46
  • $\begingroup$ @Mark It was the first answer. Pretty simple logic. If I vehicle cannot stop in time and can't be heard to know to get out of the way then Houston we have a problem. $\endgroup$ – paparazzo Jun 11 '18 at 16:54
  • $\begingroup$ @paparazzo - no questions there. Just curious if you could point to a model in use today (such as an ASME code). If so, you'd get a +1 from me. $\endgroup$ – Mark Jun 11 '18 at 16:55
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    $\begingroup$ @Mark I suspect ships have guidelines. $\endgroup$ – paparazzo Jun 11 '18 at 16:57

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