OB Center channel design

[arc2v]

Okay, the DDR (also known disturbingly as Dankinis ) thread got me thinking about OB speakers again.

I have a Magnepan home theater now. I really enjoy the dipole sound, but I have never had a center channel speaker. When I'm in the middle of the room, the imaging is superb, the soundstage wide, and the sound is, well, effortless. Really cool and I would miss it if it were gone.

However, sit off to the side, even just a bit, and the soundstage collapses to one of the speakers. It still sounds open and airy, but coming from whichever speaker is closest to you. Not good.

Now the MG center comes in around $1k, and I could probably get $600 for my other four speakers, so I got to thinking that for under $2k, I could probably build some open baffle speakers and tailor them more to HT than music.

Okay, enough about the background. How about the design:
OB's have wide horizontal and narrow vertical dispersion patterns -- great for a center speaker b/c it eliminates the combing effect from floor and ceiling reflections and is wide enough to anchor the sound to the screen from the side seats.

I'm thinking MTM with a ribbon tweeter (BG Neo3 or Neo8), and sticking with a home theater "standard" of around 80Hz for the -3dB cutoff.

For the center, I was also thinking about curving the baffle a bit, mostly to "sharpen" the beam a bit so that it just fills in the middle and doesn't overwhelm the LRs.

Potential Problems:
Most projects I have read about had little luck with OB centers. Problems integrating with the soundfield, mostly.

Power: inefficient, but I already have Maggies, so I'm used to that


I guess what I want most is feedback from OB experts, especially anyone who has tried this before. I'll post actual designs in here to get some feedback.

Thanks for any inputs:
AC

[badman]

Hi:

I would consider a primary goal of the OB center to be: as small as possible. I'd want to mount it in free space, probably above the gear, and align listening distances carefully, using a metal framework of some sort so it's free on all sides to allow dipole cancellation. Of course, you'll need to use similar drivers, and deal with the processing somehow....

[arc2v]

Size isn't really a restriction as this will be under a 92" screen.

My buddy and I had an idea: since OBs are so simple to mock up (scrap MDF, circle jig, and spare crossover parts).

So I'm going to buy a neo3 driver, maybe a neo8, and a couple suitable mid-woofs and throw some ideas together. I have a Behringer ECM8000 and Room EQ wizard, so I should be able to get some good measurements. It won't be anechoic, but I can baseline against it.

1st is a traditional MTM vertical.
2nd would be an MTM with the Neo 8. We're expecting some comb effect in the mid freq's due to the farther spacing to acomodate the larger Neo8, which leads to idea 3
3rd will be an offset MTM, with the tweeter section set to the side a bit so the woofs can be closer.

Those would be for the LR and surrounds.

For the center, once we decide on which tweeter to use, I'll play around with designs here.

1st: sideways MTM with the tweeter vertical
2nd: same arrangement but the M's are curved in a bit
3rd: same, but M's curved out

I'm basing those ideas on the fact that the Martin Logan center is curved in and the Magnepan center is curved out, so both of them saw something in the dispersion pattern that they liked.

So it looks like this is going to be a research project before it's a speaker system . . .

Now to buy a lab coat