Ahh...the Magnepan. Quite a popular speaker. My dad has an old set...quite nice.
There are some great things about the Magnepans. They throw a HUGE image, mainly due to the immence surface area of the drivers. Instead of the piano sound coming through a 4" midrange and a 6.5" mid woofer, it has a few square FEET of driver to be reproduced on. A lot of people like the sound of the planars, they tend to sound nice, crisp, and tight. Another cool thing is the dipole radiation. That helps them make a huge soundstage. Once you get them set up properly with the backwave reflection going just right, it's magical. A wall of sound.
The bad...
Magnepans eat amps for lunch. Seriously. The MG20.1s are insane power hogs. I've heard of people biamping EACH speaker with a pair of Bryston 7BSSTs (900W into 4 ohm monoblocks). Yeah, they draw that much power. The efficiency of course is ultra low. Another problem is with placement. The sweet spot is fairly small, and you really can't move too much from it. And until you go for the 3.6R or 20.1, they don't have much bass response. And even in that range, if you drive them too hard, the panels bottom out and sound like arse. So if you have Magnepans, you're going to need a sub, probably crossed around 60Hz. Velodynes usually make a good match because they tend to be "fast" subs (matching the sonic qualities of the planar drivers).
Planars are of course different from ESL (Electrostatic Loudspeakers) like Martin Logans. ESLs use two electrified grids with thousands of volts between them that, when fed a signal, move the membrane inside. These speakers require a big transformer and have to be plugged in. The Quad speakers that you asked about earlier are also ESLs. But unlike the Martin Logans, the Quad's are designed to act as a near perfect point-source speaker (as opposed to the line source Magnepan), meaning all the sound radiates from one point on the panel outward, like the ripples on a pond after you toss a stone in. This helps make them more forgiving on placement.
ESLs tend to also be full range, or mostly full range. This means the ESL (minus the Woofer if it's a Martin Logan) takes care of all the treble and midrange. The Magnepans, on the other hand, are 2 and 3 way designs with a crossover. They have a bass panel, and then a mid panel and ribbon tweeter, or a quasi-ribbon mid-tweet panel. Only the 3.6R and MG20.1 are 3 way designs, the rest being 2-Way Quasi-Ribbon models.
Were you thinking of trying out the Magnepans? If so, order a pair of the MG's straight from Magnepan (only $500) and see how you like them. Make sure not to feed them too much bass. Use a good sub if you can. And of course, get a beefy amp to power them. You'll need it. A receiver will NOT, repeat NOT cut it with Magnepans.
Good luck!
Edit: I didnt' really explain the difference between the magnepan and a conventional cone speaker. Here goes....
Conventional cone speakers are composed of the cone that is attached to a former (tube). Around the former is wrapped a coil of wire, the voice coil. When the speaker is fed power, the magnetic flux in the air gap between the permanent magnet and the voice coil changes and causes the voice coil to move, moving the cone with it (not the best/most correct explanation, but it works). Magnepans use superthin mylar panels and strips. Ah heck, just look at their explanation
here. It's much better than I can do.
