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Old 21st June 2007, 01:32 PM   #41
gedlee is offline gedlee  United States
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Quote:
Originally posted by Paul W


The larger drivers roll off at HF but I understood response on a plane wave tube to be equivalent to power response...or the same as a "perfect" CD waveguide. Why greater rolloff on a CD waveguide than a plane wave tube?

Not looking into your question in depth, I believe that a plane wave tube is the power response (there are some caveats here at the upper end), but nobody that I know publishes plane wave tube data. Data is always taken on a horn, and ususlly one that is not CD. This gives them a "better looking response".

A true CD waveguide does not have a very flat response when unequalized and would not make for a very imperessive curve on a data sheet.
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Old 21st June 2007, 02:02 PM   #42
MBK is offline MBK  Singapore
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Earl,

The design and the polar measurements of my WG prototype are all linked in post #38 of this thread. Here is the main link again to the curves in the "Large midrange for OB" thread:

Post #293 Large midrange for OB

It's not professional grade data but should be ok for a first appreciation. Post #292 has the measurement setup.
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Old 21st June 2007, 02:52 PM   #43
Salas is online now Salas  Greece
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Quote:
Originally posted by gedlee



I've never called them a "phase plug". I called them a "refractive index absorber" in the patent, but thats a bit complex. Nothing really comes to mind.

What about 'HOMLESS' ?
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Old 21st June 2007, 04:08 PM   #44
gedlee is offline gedlee  United States
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Quote:
Originally posted by salas



What about 'HOMLESS' ?

I love it!
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Old 21st June 2007, 04:10 PM   #45
gedlee is offline gedlee  United States
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Quote:
Originally posted by MBK
Earl,

The design and the polar measurements of my WG prototype are all linked in post #38 of this thread. Here is the main link again to the curves in the "Large midrange for OB" thread:

Post #293 Large midrange for OB

It's not professional grade data but should be ok for a first appreciation. Post #292 has the measurement setup.

Its not really very CD, but the data is kind of course and hard to tell what is really going on. I use 7.5 degree increments as a minimum to really see the field.
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Old 21st June 2007, 04:30 PM   #46
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Dr. Geddes,

I'm not ready to graduate to compression drivers, so I use wide rangers in my WG's (just a simple 90 square conical). This seems to really help balance the off axis response. Some of my wide rangers require assistance above 5-10khz and those with good high end extension need the top end replaced by a tweeter. Would it be a good idea to put a tweeter inside the same WG, or is that just begging for more problems?
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Old 21st June 2007, 04:35 PM   #47
MBK is offline MBK  Singapore
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Yes this first test was a bit limited. I used 75 cm measurement distance to keep it well over the dimensions of the WG, but this did not help my outdoors S/N ratio and made a 3 ms window necessary to get rid of the floor reflection. And this in turn limits the frequency resolution. I'll just have to find a better setup.

Which measurement distances, windowing and excitation signal would you recommend to measure this WG?
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Old 21st June 2007, 06:11 PM   #48
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Quote:
Originally posted by gedlee

but nobody that I know publishes plane wave tube data. Data is always taken on a horn, and ususlly one that is not CD. This gives them a "better looking response".

I know a little company called JBL that publishes plane wave tube data on their compression drivers.

http://www.jblpro.com/pages/pub/components/2426.pdf
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Old 21st June 2007, 08:21 PM   #49
Pano is offline Pano  United States
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Quote:
Originally posted by Tom Brennan
I know a little company called JBL that publishes plane wave tube data on their compression drivers.
Yep.. So does Selenium. They show specs on horns and plane wave guides.
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Old 21st June 2007, 08:43 PM   #50
gedlee is offline gedlee  United States
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Quote:
Originally posted by johninCR
Dr. Geddes,

I'm not ready to graduate to compression drivers, so I use wide rangers in my WG's (just a simple 90 square conical). This seems to really help balance the off axis response. Some of my wide rangers require assistance above 5-10khz and those with good high end extension need the top end replaced by a tweeter. Would it be a good idea to put a tweeter inside the same WG, or is that just begging for more problems?

Compression drivers have so many advantages over small tweeters you really should check them out.

I don't use JBL drivers as they are not cost effective, and I wasn't aware of seleniums data sheets. I wish more companies did this as I like seeing both sets of data.

As for measurements its always the greatest distance that wins, but this is always difficult. get as far away as your situation will allow. I used to use my cathedral ceiling living room for reasonable data, but not the factory has a very high ceiling so we get real far away - like 3 meters.
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