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RE: Wendell's answer

No sooner had I begun to uncover one MMG than my wife warned we had visitors on their way Sunday afternoon. So, it all got moved up, again. However, I kept thinking that I must have saved my early measurements, at least the ones that I needed for the PLLXO-based bi-amp calculations.

TaDahhh! I just found them and I also rechecked the impedances from outside each MMG. They match what I measured long ago. At the time, years ago:
a. Both tweeters measured 2.61 ohms. This was 6 runs, 38 inches long each + 7 inches in bottom traces to the terminals. Aprox total=235+ inches.
b. The mid/bass panels measured 4.1 & 4.14 ohms, respectively. There are 24 runs, of which 14 are double. Therefore, the equivalent of 38 runs, each 37.75 inches long (extending 38" when as twin loops). There are about 16.25 inches of additional connecting traces at the bottom. In total, roughly 1451+ inches.

The actual lengths are probably just slightly longer because I don't think I added the short horizontals at each end. I do remember measuring at the looping (U) center between two mid/bass panel traces, that should be close enough.

In fact, I did a quick proportional extrapolation with the numbers that Tom_G supplied earlier about the 12s. Tom is not clear if he included the traces to the terminals but there's enough thoroughness to suggest he would not have missed it. Electrically, the mid-panel numbers are right on. Using his figures backwards, mine should be 4.1~4.16 ohms, which is a virtual match.

The tweeters are also close enough. Backing up from Tom's numbers I get that my tweeters would have been 2.64 ohms, I measure 2.61 ohms...so yeah, ballpark.

Therefore, it seems that my old MMGs and Tom's 12s are made of the very same type of wire and foil.

The newer MMGs probably are, as well. If so, it then means that their longer tweeter runs (vs old MMGs) would have around 3.5 ohms impedance, close to the 12s. OTOH, the newer MMGs mid/bass would be able to match the old MMGs impedance by using 22 rows of wire, 16 of them doubled for a total of 38. Is this the row count? If it is, you should see around 4.1 ohms there.

In other words:
- New MMGs with 8 tweeter runs and 22(38) mid/bass runs?
- Old MMGs with 6 tweeter runs and 24(38) mid/bass runs

Curiously, it appears that the 12s use less wire for mid/bass than the MMGs.

Anyway, for QR on my mid/bass panels, it looks like I'd have enough "run length" for 24 runs of 38 inches (plus about 16" for horizontal & terminal runs). Using the same tweeter QR material, I would get a total impedance of about 10.5 ohms. Should I just thank God that I bi-amp at line-level or are we getting more suitable QR strips from Magnepan?




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