Posted by SteveBrown [ 4.224.210.187 ] on September 23, 2006 at 07:10:01:
I tried a fun experiment last night that I thought I'd post here for comments, and I've got a couple questions. Over the years I've accumulated a half dozen similar 12" Electro Voice vintage high efficiency speakers (TRXBs and SP-12's). These also have a fairly high Qt (around 0.65), so I keep thinking about them in an Open Baffle. I have tried just one SP-12 in a small OB with promising results - nice vocal tone, but lacking a bit in the mid bass (150 to 300hz).
So last night I tried something new - I put two 12" EVs (TRXBs), in parallel, in an open back box to help extend the bass, then put a third EV (SP-12) on top, Open Baffle, running full range. It sounds really good. I crossed the lower two with a 0.7 mh coil so they don't interfere with the top end, but reinforce the bottom where everything falls off fast. If anything there is a bit too much around 200hz (about +4db). Maybe I could try a 1 mh or something to even it out? According to specs, these run around 97db. Measurements in room with my RS SPL last night gave me pretty darn flat to 40 hz, and down about 7db at 30.
So I am open to ideas to enhance this even further. I'm also wondering about how this whole mess looks from a power distribution perspective, so help me out. The two TRXBs being used for bass are 8 ohm and the SP12 on the top is 16. I hooked the lower in parallel, making a combined 4 ohms, so do they take on 4x the energy of the SP12? Or would it be the other way around? I'm having to pad down the SP12 about 1/2 on an Lpad. So wondering if putting the two bottom speakers in series would even things out a bit.I guess that would alter my crossover coil too, making it 4x as large? I only have one channel built, tempted to knock out the second one today.
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