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Old 20th June 2007, 03:04 PM   #11
...truth seeker...
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Default OS Worksheet

I can provide an excel worksheet (size~35k) which allows the display of any variety of profiles based on the oblate spheroid formula. JoshK did most of the work to get it to the current state. That includes a roundover transition to the baffle. I'd be glad to e-mail it by request and/or send it to someone who could provide a "host" site for it.

A question for Earl: In this worksheet the roundover is a circular arc that is tangent with the WG and the baffle. Is there a better shape (maybe a segment of a spiral) for the transition from the waveguide to the baffle?
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Old 20th June 2007, 03:18 PM   #12
Hennie is online now Hennie  South Africa
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Quote:
Originally posted by gedlee

For extreme accuracy, which appears to be important, one wants the initial angle and radius of the wavegiude to match the exit angle and radius of the driver.
Dr Geddes,

I'm still quite new with regard to waveguide and compression driver concepts, but what is the exit angle of the compression driver? Is it a physical property determined by the phase plug geometry or is it wavefront curvature at the compression driver exit?

And just out of curiosity, will the new speaker series use a new compression driver with a plane wave or is it not worth the additional effort?
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Old 20th June 2007, 03:39 PM   #13
gedlee is offline gedlee  United States
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Quote:
Originally posted by Hennie


Dr Geddes,

I'm still quite new with regard to waveguide and compression driver concepts, but what is the exit angle of the compression driver? Is it a physical property determined by the phase plug geometry or is it wavefront curvature at the compression driver exit?

And just out of curiosity, will the new speaker series use a new compression driver with a plane wave or is it not worth the additional effort?

Compression drivers have exit "tubes" which flare outward. The most typical is 6.5 degree, which is what almost all B&C drivers are. For a particular driover you may need to get this from the manufacturer as there is no standard.

For our initial release we will use the B&C drivers that I have ghad so much success with. I believe that the improvement in a compression driver from using a modified phase plug may well be worth the effsrt, but initially I simply don't have the time to put in that effort. We are not big enough to get a major manufacturers attention to make these design changes for us. It will happen, just when I don't know.
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Old 20th June 2007, 03:41 PM   #14
gedlee is offline gedlee  United States
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Default Re: OS Worksheet

Quote:
Originally posted by Ed LaFontaine
A question for Earl: In this worksheet the roundover is a circular arc that is tangent with the WG and the baffle. Is there a better shape (maybe a segment of a spiral) for the transition from the waveguide to the baffle?
If you send me a copy I'll check on the math.

I just use a "fillet" tangent to the waveguide and the baffle as you suggest.
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Old 20th June 2007, 04:14 PM   #15
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Earl and Randy, you've got mail
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Old 20th June 2007, 05:05 PM   #16
Jazr is offline Jazr  United States
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Default Earl, Have you looked at BMS

I wonder how the use of a ring radiator based compression driver affects the formation of HOMs? Here is a link to a gentleman who tested dome tweeters loaded by conical waveguides and found advantages to using an XT-25 ring radiator.
http://www.aeronet.com.au/waveguide.htm
The BMS 4552 has a following for sure.
http://www.bmspro.info/index.php?sho...10278&id=54364

The real question is if a ringradiator produces a wavefront that is less disturbed by an OS waveguide.
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Old 20th June 2007, 05:29 PM   #17
gedlee is offline gedlee  United States
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Ed

The math that you sent is great for the baffle radius, but neglects the finese at the throat. Your waveguide has a slope of zero at the throat, but the exit of the compression driver has a slope of 6.5 degrees. This mismatch in slopes will cause more HOM. You want to match the input of the waveguide radius and slope to the same on the exit of the driver, otherwise there is a mismatch. This math is tricky, but it can be done with a cut and try approach.

Preliminary data of ours suggests that the throat is very sensitive to small perturbations of the wavefront and that the transition from the driver to the waveguide must be as smooth as possible. We actually fill in the small cracks here with clay so that the transition is seamless. No real hard data on this but the "soft" data suggests that smoother is measurably better.
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Old 20th June 2007, 05:40 PM   #18
gedlee is offline gedlee  United States
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Default Re: Earl, Have you looked at BMS

Quote:
Originally posted by Jazr
I wonder how the use of a ring radiator based compression driver affects the formation of HOMs? Here is a link to a gentleman who tested dome tweeters loaded by conical waveguides and found advantages to using an XT-25 ring radiator.
http://www.aeronet.com.au/waveguide.htm
Well first off I disgree with his terminology. I first used the term "waveguide" to differentiate it from a "horn" - the two things use different equations and approaches and should go by different names. Then he calls an exponetial horn a waveguide, which, by my deffinition it is not. This made me sceptical.

His measurements look way better than measurements that I get, and well, I trust mine, how he got his is not clear. If his measurements are correct then it appears that using just about any form of "waveguide" on almost anything works pretty good. This has not been my experience.

I would not have expected a ring radiator to have worked very well, but I suspect that all of his waveguides are very short wide devices, yet he still seems to show high directivity. Very curiuos.
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Old 20th June 2007, 07:55 PM   #19
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Posted by gedlee:
Quote:
Your waveguide has a slope of zero at the throat, but the exit of the compression driver has a slope of 6.5 degrees. This mismatch in slopes will cause more HOM. You want to match the input of the waveguide radius and slope to the same on the exit of the driver, otherwise there is a mismatch. This math is tricky, but it can be done with a cut and try approach.
Cut and try it will be. I think you reference the B&C driver. So, for another driver I assume the angle could be different from 6.5 degrees.

Thanks for all.
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Old 20th June 2007, 09:07 PM   #20
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Does the physical shape of the waveguide get modified to accommodate the 0.25- 0.5 thickness of plastic foam glued along the inside waveguide wall for HOM reduction?
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