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Old 17th November 2008, 05:57 PM   #1
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Default Determining Xover Point with Waveguide

I was wondering which parameters determine the xover point with a waveguide in terms of directivity. I am using a 15-inch OB design with a B&C DE250 in a 10.6-inch 90 degree DDS waveguide.

From everything I have read the 15-inch narrows significantly around 800-900 Hz and the DDS loses directivity around 1K - 1.2 Khz. Given that I am using extremely steep slopes (48 dB, LR active) what might be the optimum compromise for a xover point? I am currently set at 957 Hz.
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Old 17th November 2008, 06:56 PM   #2
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I've been fooling around with the same issue as of late, though with a different set of drivers/ horn...

My conclusion was that there's no textbook answer, and that the only way to figure out the best crossover point in terms of matching directivity is to get out the measuring equipment and knock out a series of on- & off-axis measurements. For me, I found what was actually going on in terms of directivity to be a bit suprising, and not what I was expecting at all (of course, that could be just because of my lack of experience).

Regards,
John
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Old 17th November 2008, 11:46 PM   #3
BHTX is offline BHTX  United States
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That DDS waveguide would most likely be best used with an 8" mid driver, 10" at the most.. crossed somewhere between 1.5 - 2 KHz. I have three pro 12's that I bought with the intention of using them with this DDS waveguide (never bought them tho), but put the project off for a number of reasons, including this. It just seems to me like anything near or above about 1 KHz from larger cone drivers (8" or 10" and above?) quickly turns into screaming.
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Old 18th November 2008, 12:06 AM   #4
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Which 15" woofer are you using btw? Just curious.
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Old 18th November 2008, 12:10 AM   #5
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Eminence Alpha 15. Cloning the Emerald Physics CS2. Running the Alpha to 1K is no problem but I would like to xover as low as possible (800 Hz).
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Old 18th November 2008, 12:51 AM   #6
sqlkev is offline sqlkev  United States
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can you do some measurements to this set up?

how does it sound so far?
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Old 18th November 2008, 08:36 PM   #7
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I am setting up TrueRTA with a PC right now. I will post some screen shots when I can.
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Old 18th November 2008, 08:53 PM   #8
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I get pretty good pattern matching in the horizontal plane by overlapping my 12" woofer with the DDS waveguide somewhat, with both of them shelved down a bit. The tradeoff is lobing in the vertical plane, but in my opinion that's not as bad as an anomaly in the horizontal plane, and nobody has ever noticed it. Accomplishing the shelved overlap calls for some tweaking of the crossover, and isn't something that's readily do-able with an off-the-shelf steep-slope active crossover. That's why I prefer a passive crossover - I can usually make it do what I want.

Also, the 12" woofer I'm using has better off-axis characteristics than most (AE Speakers Lambda series TD-12M). I wouldn't try to match up the DDS with the Alpha 15.

My suggestion: Get the big Geddes waveguides if you want to use the Alpha 15.

Duke

edit - Horizons, if you didn't get an e-mail from me, shoot me one at: audiokinesis at yahoo dot com.
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Old 18th November 2008, 10:28 PM   #9
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>>overlapping my 12" woofer with the DDS waveguide somewhat, with both of them shelved down a bit.

I think I could kludge that with the DCX2496 by overlapping a bit and adding a small Q parametric dip near the overlap point on both sides of the xover.

I still don't know where to do this though... Does anyone know where the DDS starts to lose directivity? 1.2 K or thereabouts?
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Old 18th November 2008, 10:53 PM   #10
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BMS 4552ND + DDS ENG 1-90 Pro
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File Type: jpg 4552nd + dds.jpg (94.5 KB, 270 views)
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