I bought Dozerboy’s manual and built a few horns. Several out of 3" chambers with 3/4" tube and one of those with as long as pipe as I could make work ~ 5’. It sounded ok but not so low . An 8’ pipe just blew it away literally. Then I thought perhaps the static pressure was too high so I went to 4" chambers and 1.25" pipe. It again sounded good at 5’ and even 7’ long but the frequency was still fairly high. Kinda like a truck horn. So I just wondered if anyone here can help with the idea of it all so I don’t have to keep experimenting I just don’t want to reinvent the wheel. Perhaps you can only do so much with diaphragms designs to get the frequency so low. I have read about diaphone’s which are a more technical device used in fog horns. Kinda like a piston. But was hoping for simple way to make something low and a little loud for a different application.
Here’s a vid of the latest 5’ horn with 4" chamber. It got harsh on the first slow blow but sounds clean, for what it is, on the 2nd one. This is really as low as I can I get at this time. If anyone can help me with understanding design limits or how to achieve what I want, I really be thankful!!
Well I work with some very inventive people and their thoughts were to use a more flexible diaphrams to allow free flow but again the physics of this is a mystery to me. I made a 3" power chamber with 2 foot 3/4" diameter tube that sounded about the same as that last vid. Seems you can just make that tube longer and longer and the Hz doesn’t get much lower. Maybe a little but it seems really logarithmic so to speak. Just hoping there is techno geak here. There was a story once when I was a kid about being in a huge tunnel and there was this huge echo resonating from each end where both were open. I think the air pressure in the tunnel was a bit different from the world at each end so sound bounced off of the ends of the tunnel. I think maybe horns have an issue regarding this with different designs and of course, power chamber design is huge here as well.
It’s going to be hard to do with the PVC, but lowering the frequency will be achieved through a very gradual taper on the horn- not just with a long tube and a bigger diaphragm. Apparently a horn area growth rate of 30% per foot will allow reproduction down to about 30 Hz.
Also DBO, can you point me to math? I’m looking on my own but wondering how long it would be at 30% per foot. My guess is pretty long. Although I really don’t need 30 hz. 60 might be fine.
I just don’t want to reinvent the wheel. Perhaps you can only do so much with diaphragms designs to get the frequency so low. I have read about diaphone’s which are a more technical device used in fog horns. Kinda like a piston. But was hoping for simple way to make something low and a little loud for a different application.