I just picked up four of the Eminence Beta 8's that Madisound has on sale to try with a pair of NIB Heil (ESS) AMT's and other divers I already have. I was thinking maybe I'd try them in an MTM configuration with the Beta 8's playing down to around 250 Hz where I'd let a bass driver (either a JBL 2226 or Acoustic Elegance IB-15) take over to bridge between the Beta 8's and my GR Research Triple Threat open baffle servo subs using either an active crossover (I have Rane AC-23 and Ashly 2001 ) or MiniDSP 2X4 HD to get transitions between drivers sorted out..
My question is...for the baffle area where the MTM will be situated, what might be the best way to locate the drivers on the baffle and what might I consider for wings? I owned GR Research x-Statiks at one time and those configure the MTM with no offset for the tweeter or mids and use no wings on a narrow baffle. Danny says the issues that this configuration typically will create (dipole hump and baffle edge artifacts, I assume) are compensated for in the networks...but that with models like the NX-Otica and NX-Treme, the use of side wings largely negates the need for electronic compensation. But I still wonder how he avoids the baffle edge artifacts with a centered tweeter. Is it because he uses a waveguide...which I assume controls dispersion and directs energy away from the baffle edge? And if so, would it be the same for the Heil AMT since it has a sort of waveguide in its design?
A second question is about driver spacing. I'm a bit of a newbie with this stuff, but my understanding is that in a D'Apolitto array, the center to center distance between mid drivers should not exceed the wave length at crossover frequency. So if I have a pair of 8" drivers and the height of the Heil AMT is 6", that's around 14-15" with drivers clustered together as tightly as is physically possible...which would necessitate a crossover frequency in the 900-975 Hz range
..which is a bit lower than I was hoping for. Hopefully someone will point out that my calculations are wrong and I can push that crossover frequency up a bit higher, lol.
As I said, I'm a bit of a newbie with speaker DIY, but have built a few open baffles before including a PAP Trio clone using Tang Band 1808 and Alpha 15a's, and my first OB build used Beta 12LTA and BG Neo3 on top of Alpha 15a in an H-frame...so I'm not flying totally blind. I'm a fairly competent woodworker and my listening space is large and very well treated for acoustics. Really, I'm just wanting to have some fun and maybe wind up with something noteworthy I can call my own creation.
