new guy, 2 questions.

So I have a build style picked, and I’m hoping soon I can start. I have these questions…

  1. what differences should I expect between using a smaller diameter vs. a larger diameter. Ie. Louder, deeper, uses more air volume to function, etc.

  2. Do I have to use a cone, or can I run straight tube, (mine will be hidden, and don’t need to be pretty)

oh, it’ll be a pvc build as well, not sure if you need that info or not.

So you’re building a PVC train horn? I would check out this guy’s Youtube channel.

Knowing space is often a problem, if you did want to make a PVC horn, you would want to aim for making it shorter. To achieve a D# at 311hz on one of my PVC horns it was 17.5 inches long even with a cone. Both longer length and larger diameter contribute to lower pitch. Since the cones flare out to a much larger diameter, they are much more efficient as reducing pitch without having an extremely long length. If you do opt for a straight pipe though, it would be wise to have a larger pipe diameter if space is a problem. Cones and larger diameter throats also allow for the sound to amplify better. This doesn’t effect air consumption though.

Air inlets shouldn’t be any larger than 1/8" if you want to keep air consumption efficient. Larger air inlets do in fact lower pitch as well, but if you ever heard of the Nathan M5, which had 3/8" or 5/8" inlets, they drain a 5 gallon tank around three times as fast as a K5LA. PVC diaphragms also need to be kept at lower pressures. They work best at 120psi.

I would also check out DozerBoyMiller’s PVC horn plans.

I’m planning on running my horns along the frame rail of my truck, doing this, I can run at least 2 decent sized horns. I was considering using 2" pipe, however long I need, up to 10 feet, (I think.) It’s an old truck with pretty straight frame, not a lot of bends and curves.

Okay. My PVC horns had 1" pipe, and still were quite powerful. The video link below is the demonstration of what I had.

With that much room, you could have a low frequency three chime ship horn. Depends on what you want of course. I certainly would go for three horns upwards if you want a really commanding sound. The notes D#, F# and A# are my personal favorite, and they mimic that of a Cadillac horn or Burlington Northern/CN/CP locomotive. Again though, entirely your choice. Try to avoid anything a half step apart though, such as D and D#. That’s how you get that wailing elephant sound, or whatever you call it.

I’m curious, is there a way to cover the opening of the horn to keep mud and debris from getting in there?

When it’s under the car, I don’t believe anything will really stop it completely unless you face the horns backwards and let the sound bounce of the the rest of the metal under your car. I used screen door netting for mine, but a lot of dirt still went in. A lot of people try and face them straight down in front of the radiator for that reason, however, I doubt you’d have enough room with PVC unless you used a straight pipe with a small flared funnel attached to the end. Unfortunately putting horns underneath the car does come with a lot of issues, and they’re not likely to last very long unless you’re out in the desert. It can be done with a full shield in front and under the horn, but the only thing that does is prevent the sound from projecting forward.

True, but with pvc, its cheap enough to replace I guess. lol now to just figure out my onboard air system requirements.