Magnepan 20R vs 20.1Rs

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.

IIRC, the Radio Shack meter goes all the way up, but it's not even roughly accurate towards the top. So you could see relative changes but not absolute ones. If you do a search on the Planar Asylum, you should be able to find JBen's measurements of his MMG's with mylar front and mylar back. They're close enough to the 1.6's that I suspect the results would be similar.

I actually liked them both ways. On balance, I preferred front, because getting the high end right was more important than the better imaging from the back, but I can see that that could depend on personal preferences and your room (mine was very live when I tried it, no furnishings at all).