Over the last dozen years or so of my 47 years in this hobby I've owned over 30 "premium" stand mounted speakers retailing for > $1500/pr., plus assorted floor standers and cheaper standmounts.
Among them PSB Platinum M2, Volent Paragon VL-2, VMPS 626R, Totem Model 1 Signature, Thiel PCS, Talon Khite, Spendor LS3/5a, Silverline SR11, Sequerra Met 7.7 mk V, Selah Tempesta, Selah SSR, Selah RAAL/revelator monitor, Revel M20, Paradigm Active 20, Paradigm ref 40, Onix Ref 1 MK 2 ninja, Nohr 9.0 Mini w/ dennis murphy xover, Morel Renaissance, Monitor audio GR10, merlin tsm-m and MME, Joseph audio RM7si mkii, GMA Rio, Event Opal studio monitor, Escalante Juniper, Buggtussel Cingulate, Aerial Acoustics 5, ACI Sapphire III, AAD silver 1, AAD 2001, and Paragon Jubilee.
In terms of overall quality in my rooms and by my taste, Selah Tempesta, Volent VL-2, Selah "mini-Verita" Scanspeak/RAAL monitors, Event Opal, Selah SSR, Merlin TSM-MME, Buggtusel Cingulate, AAD silver, AAD 2001 and Revel M20 were in my top 10, in roughly that order of preference.
The Revel M20, which I owned about 13 yeas ago, was one of only 5 of these (Tempesta, Volent, Opal, Cingulate and M20) that had enough deep, powerful bass to sound balanced in my lossy living room system without a sub. They are very neutral and offer a fast, dynamic, transparent, wide range soundstage. They are very well built and measure about as well as any speaker out there. http://www.stereophile.com/content/revel-performa-m20-loudspeaker-measurementshttp://www.soundstagemagazine.com/measurements/revel_performa_m20/
Stereophile ranked them class A, IIRC. I liked them quite a lot, but I did feel the tweeter didn't integrate fully with the woofer, despite virtually perfect measurements. I could always hear the tweeter as a separate driver, and it had a bit of metal dome sound.
About a dozen years ago I bought a pair of Thiel 3.6s, which besides being much larger were better integrated and had better soundstaging. They also had a metal dome, but it was better behaved and integrated. I sold the M20s, but have fond memories of them.
I had read an AC posting about modding a pair of F30s, Revel's floorstanding counterpart to the M20, which I have also owned (and didn't like as well overall, feeling that there was a lower midrange integration issue). Perhaps if I had modded my pair I would have liked them better.http://www.audiocircle.com/index.php?topic=46327.msg415105#msg415105
Crossover parts and cabinet damping upgrades such as are described there are something I've done a lot, so I thought I might see if the M20 could be similarly improved. Now days the used prices of M20s has dropped to a level below that of other competitive speakers, and I consider them a bargain, so they would seem to be a promising candidate for a project.
I bought a near mint pair recently to kick it off:
I decided to keep it simple- I lined the cabinet with No-Rez damping sheets, removed a third of the stock fiberglass stuffing, and replaced the generic looking film tweeter caps with Sonicaps, bypassing the larger of the two with Sonicap Gen 2. The woofer circuit uses large electrolytic shunt caps; for now I decided to leave them alone. Wiring is large guage and looks like ok quality, so I decided to leave that alone as well.
I've run them for ~20 hours, probably not enough to fully burn in the caps, but the overall sound is probably stable.
First off, these mods have not changed the overall nature of the sound, but have increased the overall focus from top to bottom in a pretty notable way. The lower midrange is much clearer and more focused and the bass is tighter and better focused as well without losing the great extension that is so special.
The top end is also similarly improved- it is smoother, grain-free and more finely detailed, and it now integrates better with the woofer than it did before. The metal dome signature is pretty much gone too, and I don't hear it separately from the woofer nearly as much as I had before the mods.
So an already good speaker is very nicely improved, essentially transformed, but there is still an asterisk here. While the top end is notably cleaner and clearer, it still has a signature, in that the tonality still sounds tipped up a bit. The clearest example is listening to Joshua Bell in the Red Violin. Compared to my Daedalus speakers (Eton soft dome) or my Selah stand mounts (RAAL ribbon), the violin, while squeaky clean and clear, seems to favor the upper harmonics over the lower body tone by just a bit, making the violin sound a little thinner and smaller. The effect is to make the overall sound a little cooler. Not huge, and not a show stopper for me, but it does define some of the sonic nature of the speaker.
So- here's my verdict. For the price of the speakers ($500-800 depending on condition) plus about $150 for parts, you get a very fine, nearly full range standmount that is very fast and clean, with excellent transparency and a large soundstage. It is built properly, with quality drivers, a state of the art conventional crossover design and a solidly built cabinet. Often ignored elements like mounting hardware, connectors and switches are executed very well, making them quite easy to work on. They are very flexible in use, having enough bass to supplant small floorstanders in medium sized rooms, yet able to be used against the wall or in a cabinet at the flip of a switch.
For me, they have cracked my top 5 list, moving ahead of the Event Opals, which have a trace of metal dome emphasis and a tad less clarity in the lower mids, and they are knocking on the door of the Volent VL-2 in overall quality, trading some of the VL-2s fine detail and soundstage depth for superior balance. While still not up to my Daedalus DA-RMA v2s (which favor the mids and "power" range), principally in richness of tonality and soundstage dimensionality, I could live with them permanently in my main system now.
The only caveat is that one should prefer or at least tolerate a squeaky clean presentation and a slightly cool, dry overall sound that showcases the upper range, and use appropriately matched front end and cabling. I've done that and I think they are great speakers for my bedroom system (the position matching selector on the rear works very well for small rooms and close wall placement).
I consider the simple mods I performed successfully got the lowest hanging fruit. I suspect replacing the woofer 'lytics, wiring, using better replacement caps and resistors should extract even more from these chestnuts, for much more effort and 2x+ the parts cost.
So- if you have a pair of M20s, in my opinion this is a pretty easy, inexpensive and worthwhile upgrade. If you're looking for a very good smallish speaker for under a grand and are a little bit handy, this might be a very good option for you.
Over the years many speakers have been put up as "giant killers", sub $1000 speakers that play with the high priced options.
Spending the weekend listening to these in all 3 of my systems leads me to believe this is truly one of them. I didn't consider the M20 to be Class A in their original form, but I think they are with these simple mods.
I don't know of any under $1k stand mount speaker that will outperform it overall, new or used, and Revel builds their speakers to last a long time, so a majority of their useful lifetime is still ahead in most cases.
The M20 is one speaker entering its "golden years" that truly deserves a new lease on life.