Acoustic Horn Design – The Easy Way (Ath4)

Maybe something like this? (Still just a basic sketch.)

The beams could be made longer to suppress a possible diffraction there, perhaps?
 

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Ro808

Member
2010-03-27 4:25 pm
P. Bateman posted some interesting comments and quotes from Tom Danley on the diycaraudioforum about phaseplugs producing either a converging wave front at the exit, a plane wave, or a diverging wave front.
According to Tom Danley, a diverging wavefront (as emitted by drivers with annular diaphragms) is preferred for conical horns.
 
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Sure, a diverging spherical wavefront of the corresponding radius is actually the perfect match for a conical waveguide (and the only one), even better than a flat wavefront is for an OS waveguide. There is no doubt about that. That's the reason I would like to try this out. Now I'm searching for any drawbacks. There must be some as I don't see this being done - actually I have never seen this done like that. Either it is too brilliant or too dumb :)
 
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If you had a pulsating spherical cap as a source you would not need any phase plug. The above might be a way how to shape the sound wave produced by axially oscillating dome to be approximately spherical. The question is if it would be any better in the end than a flat wavefront (as produced by majority of CDs) fed to na OS waveguide. Or if it would work as intended at all.
 
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Sure, a diverging spherical wavefront of the corresponding radius is actually the perfect match for a conical waveguide (and the only one), even better than a flat wavefront is for an OS waveguide. There is no doubt about that. That's the reason I would like to try this out. Now I'm searching for any drawbacks. There must be some as I don't see this being done - actually I have never seen this done like that. Either it is too brilliant or too dumb :)

A converging wave front at the exit, a plane wave, or a diverging wave front can all be made by varying the path lengths in the phase plug from inner and outer portions of the diaphragm, regardless of whether the diaphragm is annular or dome shaped.

Drawbacks to your “in horn” rather than “in driver” phase plug proposal:

1)The level of machining (fractions of a millimeter) to make a good high frequency phase plug is such that incorporating it into the horn itself would not be cost effective for manufacturing.
2) Each different pattern horn would require a complete redesign of the phase plug portion.
3) Each section of the phase plug as illustrated is a “beamy” very high frequency horn, and as such would have HF “fingering” as multi-cell horns do.
4) Diffraction effects would be worse than standard phase plugs, as the slit exit dimensions are larger and spaced further apart.

Dave Gunness 2005 AES Convention paper “Improving Loudspeaker Transient Response with Digital Signal Processing”

https://web.archive.org/web/2012051...m/info/EAW/Technical_Papers/NT_Whitepaper.pdf

section 3.1 gives some insight into problems inherent in phase plug design.

Art
 
I agree with Art that I do see these proposals as being ones that integrate the phase plug into the whole waveguide design. I argued in one of my patents that this should be done and could be easily accommodated with replaceable phase plugs. To Art's points I would say:

1) If the phase plug were separated from the waveguide and replaceable then this is not an issue. With the way its being approached here it would be.
2)Absolutely true, but not really all that complex to achieve.
3) "as illustrated" perhaps, but if done correctly then this is not an issue.
4) This need not be the case, although it could be if things were not done correctly. However, again, if done correctly this is also not an issue.
 
Thanks. That actually doesn't sound that discouraging. By drawbacks I meant mostly the acoustic flaws. This is DIY after all, much of what would be impractical or expensive in a serial production is almost a norm here.

So far I haven't thought much about any mounting or dividing into actual parts, this is to be left as the final step. I have some ideas though.

I suppose none of you are willing to disclose here what "done correctly" means and I guess I really should figure that out myself - just let me ask one quick question: Should the slits have straight sides?
 

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