Hello everybody,
I want to have a go at Hoffman's Law in a DIY project, and that means it must involve something exotic.
My current idea is to use a modulated compressed air stream. Not a new idea, but nowadays you can buy miniature electrically controlled proportional pneumatic control valves with a bandwidth above 100 Hz. Unfortunately I don't know much about pneumatics.
There still are lost of design choices to make, I hope you can help with some ideas.
For instance, how much air do I actually need related to sound pressure? And what about impedance matching. How to avoid parasitic noise (hissing etc)
My current idea is to use an air amplifier like this: . Would that work for higher frequencies?
Luke
I want to have a go at Hoffman's Law in a DIY project, and that means it must involve something exotic.
My current idea is to use a modulated compressed air stream. Not a new idea, but nowadays you can buy miniature electrically controlled proportional pneumatic control valves with a bandwidth above 100 Hz. Unfortunately I don't know much about pneumatics.
There still are lost of design choices to make, I hope you can help with some ideas.
For instance, how much air do I actually need related to sound pressure? And what about impedance matching. How to avoid parasitic noise (hissing etc)
My current idea is to use an air amplifier like this: . Would that work for higher frequencies?
Luke
Rotary screw compressors are a lot quieter then piston compressors. A turbine like that used for hvlp paint spraying might also be an option. Still need to be in a separate room from the listening space.
43 dba compressors are readily available (300 euro) and it can be placed in another room. So I'm not worried about compressor sound. The question is how much air do I need? anybody know how to calculate this.
Im trying to understand how that venturi intensifier is going to do anything but hiss from the turbulence.
I would think a very large air pump and a tuned horn would be the way to go...
http://www.spencerturbine.com/wp-content/uploads/2014/11/OrgobloForPipeOrgans.pdf
I would think a very large air pump and a tuned horn would be the way to go...
http://www.spencerturbine.com/wp-content/uploads/2014/11/OrgobloForPipeOrgans.pdf
It is not venturi but the Coanda effect. This works thanks to laminar flow that 'sticks' to the surface and drags the air along with it. So no turbulance at work here. Look at this video where you can see how smooth the air is: https://www.youtube.com/watch?v=4WNcjkZ6d0w
Well that's for an organ and such a pipe (tuned horn) produces only one tone. Not usefull for a speaker.
Although a large air pump produces low presure and high flow (what you want) it also means the proportional valve is going to be a challange and it is going to be big, if we can go big, we might as well build a normal sub.
What about keeping distortion low enough? Except for sub-sub-sonic tones, might be hard to get the pieces of a pneumatic speaker to act linearly enough, even by the lax standards of Rice-Kellogg* (cone) drivers. I think I'd address that requirement early in the R&D.
Ben
*amusing how those two inventors names sound like a breakfast cereal
Ben
*amusing how those two inventors names sound like a breakfast cereal
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