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In Reply to: Re: I think I answered my own question... posted by neolith on November 18, 2006 at 07:51:14:
I'm using a Dahlquist LP-1 active crossover which has 18dB low pass and 6dB high pass crossover points. I already rewired the internal wiring with magnet wire, removed the midrange fuse and rebuilt the mid/high crossover outboard and replaced all the binding posts. I already had the midrange wired out of phase with the ribbon and the bass panel per AndyR's suggestions--this was running the panels in their stock configuration.So now that I've reversed the panels, I wired the ribbon opposite of stock as AndyR recommended and I've reversed all the amplifiers + and - connections to the system. It sounds pretty good right now--much more detail but the mids sound a bit recessed. It would seem to me the mid should still be out of phase with the bass and ribbon since the crossover network hasn't changed. I guess I don't understand why the ribbon wires should be reversed.
Thanks,
steve
Follow Ups:
After more listening, it turns out the bass was what was really light, so I reveresed the bass amps polarity to the panels back to the same (+ to + and - to -) and the bass sounds much better now. This still leaves the mid/hi amp out of phase with the outboard crossover. Is this correct or not?
Thanks,
steve
Your goal is to have the bass and treble in correct (+) polarity and the mid in reverse (-) polarity. IME it is better to have the bass in + polarity which is what you also found. If I understand you correctly at this point the mid and treble are in reverse polarity which is what you want (mid + and treble -). However, you may find it advantageous now to reverse the speaker connection to the mid-treble thus making the mid (-) and the treble (+). The result will be (+),(-),(+) which is where you were before all the swapping.It is important that the mid and treble have reverse polarity because the mid-treble crossover (low and high pass) are 2nd order. The low pass and high pass 2nd order filters are 180 degrees out-of-phase and thus will cancel creating a big sonic hole at crossover point. By wiring them with reverse polarity, you end up with the phase angle being zero - this is called phase aligned or phase corrected.
This polarity stuff gives me a headache.
I may be an egoist but at least I don't talk about other people.
I think that's what I have now. What threw me off was wiring the tweeter in reverse when I switched the panels. I've tried it all three ways now and it definitely sounds best this way. Thanks for you help. This did give me a headache. It was worth it though. Reversing the panels is definitely an upgrade in detail, slam and clarity with the IIIA's. It's a no brainer why Magnepan went this direction with the 3 series.
steve
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