Planar Speaker Asylum

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RE: Here's a reason for belonging to the 'ASYLUM', Magnepan corrundrum (long story)

Posted by UncleMeat on February 9, 2025 at 11:39:38:
OK, back to square one.

Now, I've been completely put to shame by an old school audio test record.

Played the Shure "Audio Obstacle Course" and it has a phase test. The phase test resulted in 'out of phase' even though I thought everything was in phase/fixed. Totally confused because the sound was really good, with audio image 'everywhere'. But that's also a problem with out of phase because while the mono sound is canceled, the stereo sound is not so you're left with only a stereo signal and very little L+R center information.

So went back, soldered the right mid and left tweeter back to their original phase. Now the image was flat, and all the sound was back at the front wall again. UGH

Started playing with the phase again, but only with wires to speakers, not soldering. I figured if I mix up the phase, maybe it would 'balance' and improve overall L+R while maintaining the image. So I put left front Mid/Ribbon out of phase, and right rear low-mid out. Yes it seemed to improve image and center was 'acceptable'. But there was one big problem, L/R image was reversed, so I would need to swap L/R amp outputs for it to 'work'. Also L/R balance was off-axis. Seems like a lot of strange tweaking to get it where it -should- be.

So just before going to bed, (2AM now) I thought what if I'm only partially fixing the problem by putting one front speaker out of phase with one rear? So let's try putting both rears out of phase and see if that is better. YES, absolutely was better, everything balanced, image came forward (except for low notes) image was correct L/R. So it appears that all of the L/R phase tweaking was only partially fixing the real problem, which is front/back phase error because the rear speakers are about 6' behind the fronts. I thought I had tested/checked for this initially but maybe I didn't hear the improvement on the tracks I had selected to listen for it, it seems that some songs don't 'bloom' like others do in this configuration.

So, apologies are in order to Magnepan, past and present. The phase of the speaker drivers are/were correct. However, the T-IV mids did have a factory flaw of being installed backwards (magnets facing rear) but they didn't reverse the input phase to correct it. This was probably the main reason for weak midrange, the overlap between low/mid and mid/tweeter were cancelling instead of summing in their roll-off regions.