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Wave guide 'mouth' cut off frequency?

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Sam Bass View Drop Down
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    Posted: 10 May 2016 at 8:34pm
Hi, couple of quick questions.

In essence I would like to load a 10" driver onto a short wave guide; as a 'directional aid' if you will. 

I would like to understand if this arrangement is subject to the same laws that horn theory displays with its LF cut off frequencies direct relationship to the circumference of the horn mouth (As I currently understand it with no compression at the throat this arrangement becomes a waveguide opposed to a horn?) 

If I was to load my 10" driver into a sealed rear chamber of adequate size attached to a (for instance) 150mm long waveguide much like the following very rough sketch:



Would the total circumference of the mouth govern the LF cut off?

And at what point will my wave guide become directional, at a 1/4, 1/2 or whole wave length?

Also is there, in anyones experience, any reasons I should steer away from this idea?


Edited by Sam Bass - 10 May 2016 at 10:32pm
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smoore View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smoore Quote  Post ReplyReply Direct Link To This Post Posted: 11 May 2016 at 9:59am
Seems to me that you have the right idea. Should aid directionality in all 1/4 1/2 and whole wavelengths. 

 Another thing to consider is that though mouth circumference is a big factor overall, each dimension (width vs height) will affect the horizontal and vertical dispersion. ie a smaller vertical height will increase control over dispersion in higher frequencies but reduce control over lower frequencies. The angle of the dispersion is normally controlled by the first 2/3rds of the horn length
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 11 May 2016 at 11:02am
Have a read - http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20%281975-05%20AES%20Preprint%29%20-%20Whats%20So%20Sacred%20Exp%20Horns.pdf

A lot of your answers are in there, or at least some very similar theory you can draw conclusions from. Pay attention to the figures.

Technically I'd say what you have drawn there is a horn in at least the x-axis, as it has a continually expanding cross sectional area from throat to mouth. A horn does not necessarily require a compression chamber.
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