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Multi-Way Conventional loudspeakers with crossovers

Thoughts on a unique OB setup
Thoughts on a unique OB setup
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Old 16th August 2017, 08:38 PM   #1
badman is offline badman  United States
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Default Thoughts on a unique OB setup

http://i.imgur.com/dxKxv8Z.jpg

http://i.imgur.com/e2eHeiL.jpg

http://i.imgur.com/r5alfGL.jpg

http://www.jblpro.com/ProductAttachm...328C_CT.v1.pdf

Front and rear coaxial 8"s (from JBL 328CT) on a sideless enclosure as shown- I'm currently running it as a front/back dipole (coaxes out of phase front and rear) but it's designed to allow for a "dipole/bipole" configuration where cancellation will be more like a pair of traditional open baffles firing front and rear. They are set up on top of subs rather than on the floor (as shown).

Dipole cancellation's pretty straightforward, either the "inside" of drivers cancel and the front and rear have an effective baffle width of the baffle width plus 1" (Added waveguide effective depth) plus 7.5" (1/2 the total system depth between baffles)

When run as "bipole dipole" effective baffle width is simply Baffle Width + .75 (1/2 of the 1.5" thick baffle) +1" (Added Waveguide effective depth)

I haven't had a chance to measure in the current setup, but I'm currently crossing at 140hz, which is probably an overly aggressive high-pass (could probably be lower), but I'd love to hear any thoughts people have on such a setup.

The coaxes are normally ceiling mounted with a shallow waveguide, my waveguide is somewhat improved, in that it closely tracks the cone profile and is slightly larger, deeper, and smoother than the JBL ceiling mount metal waveguide. This is important as the horn leverages the cone as the waveguide so that transition must be as smooth as possible.

I'd love to hear any thoughts- this is an experimenter system, regardless of the (rather ridiculous) effort required to create the waveguide. Naturally I have my own ideas for what might work in this highly configurable system, but I figure this is the best place for such conversations.
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Old 18th August 2017, 06:18 AM   #2
goodguys is offline goodguys  United Kingdom
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I have open baffle as well using the visaton b200 drivers, i found the darkstar thread very helpful
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Old 18th August 2017, 09:56 PM   #3
badman is offline badman  United States
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OB Coax Bi Di Sim Edge.png

Here's the response sim from the edge based on the modified dimensions for the setup with the numbers as-run (drivers out of electrical phase). -3@ 100, and it's probably flatter than the "idealized" setup due to all the randomizing elements, but if this is accurate from a peak perspective, a simple notch at 400 could let me run a 100hz XO very comfortably.
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Old 18th August 2017, 10:02 PM   #4
CharlieLaub is offline CharlieLaub  United States
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Thoughts on a unique OB setup
I believe those are back-to-back dipoles, which can be used to form a "second-order gradient" (cardioid at low frequencies) system. See:
Subwoofer positioning, orientation and calibration for large-scale sound reinforcement (PDF Download Available)
Second Order Gradients
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Old 18th August 2017, 10:22 PM   #5
badman is offline badman  United States
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Thanks Charlie- I think that because of the symmetry, cardioid operation is not the case on them as-set, but could be achieved with some additional manipulation. I'll plan to take some measurements over the weekend and see what exactly is happening- the 100-500hz range is where it's critical for me to see what's going on- it's in heavy cancellation below 100 and the baffle acts much like an infinite baffle above.
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