Magnepan 20R vs 20.1Rs

No problemo, Bb. I hang with Maggie owners and we all know the 'code'. My bad.
The pole piece is what holds the magnets. The panels therefore are NOT the same on each side.
Side one.......You can easily see the mylar with the wires or ribbon glued on. The ribbon is the source of the marketing term....'Quasi-ribbon'.
Side two.......The pole piece side has a bunch vertical slots in it to let the sound out and not create backpressure on the mylar.

Thus, the speaker is NOT perfectly symetrical. EXCEPT for the 20.1 which has a pole piece on EACH side of the mylar.
Original maggies were oriented so the pole piece faced the listener when the speaker bananas were in back, and out of site, as intended. My original MG-1s were also marked 'left' / 'right'.
Sometime in the 90's, Magnepan changed and began putting the pole piece side in BACK with the wiring connections and fuse.
To ME, it sounds a little hotter and beamier. I flipped my MG1.6s around and listen to the 'wrong' side. This gives me a wider image, better dispersion and a wider sweet spot.

Bbro, do a search for HP's Absolute Sound review of the 20.1, it's available online and he compares the two versions.

Hi Magfan, they said in a review at the time (of the 3.3? whenever they flipped it) that they flipped the pole piece to the back to get better high frequency response. JBen did some measurements of the MMG's from both sides, and with the MMG's anyway there's a bit of a peak above 10 kHz followed by rolloff from above 15 kHz from the pole piece side. But I think it's a matter of preference, with my MMG's anyway I think the imaging is better from the pole piece side, but that the top octave is better from the front.

Last week, perhaps after reading your post, Josh, I got out the SPL meter.
I put it on a tripod, sideways, so sitting a couple feet to the side, I could read the meter.
I put on a Rives disk, which is 'calibrated' to the RatShack analogue meter.
I ran to zero db (80db ref) at 1khz. Far enough above the xover of my 1.6s to be a good place, I hope.
With the pole pieces TO me, at higher frequencies the cogging was awful. I could move my head a couple inches and be in or out of the sound field. My meter confirmed huge SPL differences in a matter of <1 foot.

I'm thinking this over before I do anything rash....however, music still sounds right and moving my head l/r makes no audible difference.

I think my plan of action will be to 1. shut off sub until mains are right.
2. Flip 'em back around and l/r to put them mylar front with tweeters IN.
3. Repeat measurments.

If this works and I still perceive them as too hot, I may have to resort to a resistor until I can work on the room, starting with behind the speaker diffusion.
Until I have more data, I'm officially puzzled:

That's interesting. Maybe you're measuring interference between the holes? There's also going to be some lobing at the crossover point. I haven't heard the effect either, maybe it's just because the brain is accustomed to comb filter effects at the highest frequencies. Anyway, it's the ear that counts. I tried the experiment you mentioned, flipping them around, but didn't think to measure them.

That's what I was thinking. To verify, I have to flip 'em back around and try again.
I'm simply to un-motivated and since it sounds fine, I won't worry myself over that.
Also, using the Rives disk, I couldn't measure anything over maybe 12 or 14 k. Zip. Nada. I'm still mulling THAT over, too. Fuse confirmed good by meter.
How high does the radioshackup meter go?
Did you like the sound of rotated? No? Oh, well....I fixed my issues, so until I can fix the room and try again, it'll stay.