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In Reply to: RE: Replace 3.7i's with 20.7's? posted by Satie on September 27, 2016 at 07:47:17
Biamp v triamp: I was planning only to biamp but did the model for triamp just for completeness -- the mid LP and treble HP filters could be ignored for biamping and the speaker level crossover for the high end left intact. Interestingly the translation from the parallel speaker level crossover to the ALLXO requires 2nd order filters not 1st order. There seems to be a problem with my installed version of Librecalc so at this time I cannot pull up the spreadsheet and Bode diagrams. IIRC I could flatten the hump but then there was too much deviation from the OEM which is not what I wanted. I am of the opinion that the active XO should closely emulate the OEM so the voicing is unchanged from the manufacturers goal.
I married the perfect woman. The downside is everything that goes wrong is my fault.
Follow Ups:
I am guessing that the parallel setup you were trying is with inverse polarities, while the OEM is (guessing again, did not go and check) with the same polarity. I am guessing that is why the summations are different - i don't find the 90 deg difference in driver phase at the XO to be that bothersome. In my biamping setup with the high freq tweeter high pass it comes off much better than having the classic 1st order XO with inverted phase. Most notably in not having a narrow sweet spot.
Thanks so much for everyone's feedback. I very much appreciate the depth of knowledge and experience among this group of inmates! After digesting some of this (I have a very limited understanding of electrical engineering), I'm tempted to try pair of the 20.7's with just the JL7's. These amps are beasts and seem to far outperform their specs. It might just work great without having to biamp, which sort of scares me because I've got no idea at all about how to build or set up an external crossover.
I'm thinking of calling the local Maggie dealer who sold me the 3.7i's and see if they might have a demo pair of 20.7's I could borrow for a couple of days. Trying them may be the only way to know for sure. I might be able to spread the 20.7's another 12" or 18" but if I just couldn't get the speaker locations dialed in or if the 20.7's overpowered the room, I could put back the 3.7i's and rest in peace knowing that they were a better fit for that room. But the odds of finding a demo pair seems pretty slim. I'll let you know what happens. Thanks again!
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