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Magnepan 20.7 and Subs

I've been reading about supplementing my Magnepan 20.7s with a sub, the general preference being REL.  However in room I'm getting fairly deep bass with the 20.7's, so my sense is that I would put the crossover on the REL pretty low, probably at 30Hz, leaving only sub 30Hz material porting "also" to the sub to augment the natural deep bass of the Magnepans.  I'm just wondering since there's precious little info in the 15hz to 25hz range, do I really need a PAIR of RELs, or could I get by with just one?  And shouldn't that one be capable of going REALLY low, like the G1, or what's the point?  Any advice would be appreciated.  Thanks.
pwhinson
mijostyn's avatar
mijostyn
8,178 posts
 
I love 20.7s. Great speaker. They do bass better than most dipoles but still suffer a bit below 40 Hz. The cross overs are at about 450 and 3500 Hz and they are usually pretty slow. 12 db/oct. Putting subwoofers in will clean them up a bit and increase impact. You will need at least two subs and ideally 4. I would cross at 24 db/oct  100 Hz. I think the JL Audio f112s would be wonderful as a pair. But if you want the ultimate in powerful performances 4 all right up against the front wall with two in the corner and the other two equally spaced along the front wall. With the 20.7 driven by proper 200 watt or better mono amps you will be rocking for sure. 
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mijostyn's avatar
mijostyn
8,178 posts
 
Elizabeth, that bassiness you describe can be adjusted by moving the speakers away from the wall which in an attached condo might be a problem due to room. The bass that is annoying you is between 150 and 50 Hz. If you have a test record with frequency tracks you can hear exactly where the problem is. Now interestingly enough if you get two subwoofers and cross them just a little higher 125-150 Hz you will have more control of your bass just by turning the subwoofer volume down and get the advantage of further cleaning up an already clean loudspeaker. The longer bass excursions doppler distort the higher frequencies, it modulates them. It is one of the most important reasons for using subwoofers with planar dipoles.

Mike
jafant
18,804 posts
 
pwhinson
any new developments on this thread? Hope you are well and enjoying Summer.  Give us an update as your Maggies continue to bloom and settle into your room/system.
Happy Listening!
don_c55
1,025 posts
 
The 20.7 will go down to 25Hz in a good room with proper setup and a decent power amp.

There is a noticeable sonic transition to subs with tall Magnepan’s, because Magnepan’s have tall bass waves, and subs have short bass waves.

Some do not like planar bass, with it’s natural sound for acoustic instruments, they like punchy, dry bass, that box speakers put out with with rock ((since rock bass is played mostly through boxes.

I have Magnepan IIIas and 3.6s and guests always ask me where the sub woofers are?
There are none! I know how to setup Magnepan’s in an appropriate room.
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