Thank you Frantz for your instructions. I have had a pair of 3.6Rs tri-amped with a pair of Velodyne subs using three Bryston 10B LRs and three pairs of Bryston 7BSTs...but I do like 20.1s in normal passive crossover setting better.
I did reposition my 20.1s from using long wall to short wall last night before reading your reply. I'll fine tune the setup following your instructions.
Thanks,
Ki
PMJI as I've owned MGIIIas (and major modded them) and reviewed the MG20s quite some time ago. My old room was a little weird (but sonically pretty amazing; the room was decently flat from 300 Hz to 15 K at which point started rolling off; below that, there were some spikes and dips due to dipolar cancellation effects) and the speakers were placed along the long wall so there was 8 feet or so from the side of each speaker to the room boundary; conversely, I sat close to the speaker so that also affected things sonically.
First the MGIIIs. One has not heard what the Maggie RIBBON or these speakers can do until the fuses are removed, the capacitors changed (at that time, they used a 12 uf mylar cap on the ribbon and a 160 uf electrolytic shunt for the bass; that was replaced with a bank of Rel polystyrenes for the ribbon and a bank of 10 uF Solen caps for the bass shunt-that surprisingly made a difference too), the xover is hardwired to the speaker, the chokes are replaced (the supplied chokes were Fe core; this was replaced with Solen 10 ga for the bass and 14 ga for the mid and ribbon -that at that time ran around $40 each and weighed a ton), the speaker rewired (at that time they used alpha wire and it was replaced with tripled up and specially wound MIT hook up cable from Michael Percy) and new binding posts added. At that time it probably cost me around $800 for the mods. Now I spoke to Wendell, etc. at Magnepan about coming out with a MGIIIa Super but they really didn't have any interest and it seems that Jim Winey is not a big believer in passive parts. Now the newer speakers employ better parts but I feel that the MGIIIs could still be improved - and conversely-a used pair rebuilt like the old Dynacos, might be one way to go for speakers.
I also had the MG20s (and my close friend had the 20.1 rebuilt the way I described above). The 20.1 can be amazing speakers but the one thing the can lack compared to a dynamic speaker is dynamics. One needs to hear a standup bass played back thru the 20s to really appreciate the speaker's low frequency resolution. There no smearing and the snap of the strings can almost fool one on occassion.
Now they were set up with the ribbons inside in all cases. My take is that these speakers -esp. the 20.1 - are best run biamped (and one needs to find the resistive value and not use the XO supplied box as that degrades the sound too). The problem is that the bass panel can slap if not properly controlled.
As far as amps, Maggies and tubes are a match made in heaven because of the Maggies easy and relatively constant 4 ohm load. Back in those days, I ran the Maggies with tube amps biamped horizontally eg. the left amps left channel was hooked up to the bass and the left amps right channel ran the mid/highs. That among other things improved the bass since there was less draw upon the amps power supply. I also ran a cj MV75A1 top/mid and a Perraux 2150 bass with nice results. (one amp though that didn't cut the mustard with the Maggies was the old Berning EA 2100.) The caveat is that because of the xover point and slope, one can hear the bass amps mid/upper mid characteristics; as such, if the amps on the bottom are bright, then that will add a hardness to the speaker. And as we know, that ribbon can be ruthlessly revealing as evidenced by the need for a selectable resistor for the ribbon.
If running with a single amp, I'd suggest a big wattage tube amp; my friends 220 wpc Rogue audio did a nice job and did a Premier 350 ss amp.
One of the room treatments I played with were ASC tube traps located between the speakers ( I don't remember how I set the absorptive/reflective strips any more). This markedly improved imaging and transparency but I felt it also compromised dynamics. Perhaps other rooms will respond differently.