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-   -   What would happen if I took a 1" exit compression driver... (http://www.diyaudio.com/forums/multi-way/242431-what-would-happen-if-i-took-1-exit-compression-driver.html)

dumptruck 12th September 2013 11:35 PM

What would happen if I took a 1" exit compression driver...
 
...and mounted it flush in the middle of a big disc pointing up, and then I had a matching disc in above that, 0.25"-ish away so that the cross section at the exit is the same as in the exit? I get 360 of... what?

kenpeter 13th September 2013 12:27 AM

Smith horn...

I would worry the reflection back down the throat from the
sudden discontinuity at the outer edge, uniformly the same
distance all around. You might get better results to put the
driver off-center, or cut some scallops into the upper plate
like JBL Aquarius...

gedlee 13th September 2013 01:18 AM

Lots of standing waves, but almost Omni radiation - with a lot of coloration from the standing waves. You could reduce the coloration with some randomness as suggested above, but then you would also get some random directivity. It would have a hugely "spacious" sound as a result.

dumptruck 13th September 2013 01:21 AM

Standing waves from the edges, or from in front of the driver, or both? It's not so much that I think this is a good idea as I want to understand how bad it is. I was also wondering about doing this with a round planar, or two opposing ones. I suppose I could just try it and measure for myself, hardly the most difficult thing to build.

whgeiger 13th September 2013 01:30 AM

Example
 
Quote:

Originally Posted by dumptruck (Post 3630011)
...and mounted it flush in the middle of a big disc pointing up, and then I had a matching disc in above that, 0.25"-ish away so that the cross section at the exit is the same as in the exit? I get 360 of... what?

https://www.google.com/patents/US4496021

Regards,

WHG

dumptruck 13th September 2013 01:47 AM

Sure, I can imagine all kinds of things like that (and some of them are commercial products), but I'm more interested in just how bad it is to do it the easy way. The easy way definitely can't involve any kind of phase plugs not already attached to the driver, nor any kind of expansion different than that already provided by the circles. Just two flat pieces, and a half- or quarter-circle roundover at the exit.

kenpeter 13th September 2013 05:38 AM

Your standing waves are from the driver to the edge of the plates.
Simultaneously too wide and too narrow to support other internal
modes. There are also room modes to worry. But in this plan, the
horn's length (and harmonics of length) will dominate.

If you can equalize the exiting sound (the big if), corrections will
apply equally in every direction. That's constant directivity for you.

whgeiger 13th September 2013 06:27 AM

?
 
Quote:

Originally Posted by dumptruck (Post 3630118)
Sure, I can imagine all kinds of things like that (and some of them are commercial products), but I'm more interested in just how bad it is to do it the easy way. The easy way definitely can't involve any kind of phase plugs not already attached to the driver, nor any kind of expansion different than that already provided by the circles. Just two flat pieces, and a half- or quarter-circle roundover at the exit.

If it is so easy to build, then do that and observe the results to determine which of the imagined shortcomings are important and which ones are not; otherwise, simply settle for conjecture to avoid that effort. The difference between your imagined design and the example provided are most likely what is important to make the effort a success.

WHG

gedlee 13th September 2013 12:08 PM

Agreed - with things like this best is to just build one and try it.

As far as standing waves, I see two main ones. Diaphragm to top plate and diaphragm to open edge. There could also be radial standing waves in the gap. Lots of possibilities.

badman 13th September 2013 04:09 PM

I'd expect a lot of standing waves as described- a much gentler transition from driver into the "ring" a la duvel and others would be a much better solution but also much harder to build.


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