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Biamping Maggie 20.1s: Amps and Xover Frequencies

I am trying to optimize the sound from a pair of 20.1’s – currently driven by a pair of VTL 450 signature monoblocks (450 watts into 4 ohms). You’d figure that is plenty for the Maggies, but I am not totally wowed in the dynamics and openness category. I’ve heard that biamping makes them more dynamic and open, and want to try that route. To that effect, I’ve just ordered a Marchand XM-44 active Xover with 0.5 db attenuators, and am currently selecting modules. I’m also selecting an amplifier to drive the low frequency drivers. I don’t want to invest a ton in trying out this approach, but I want to make sure I am getting a sense of what it can do. So – my questions relate to amplifier selection for the bottom end and Xover frequencies.

For amplifiers, my price range is $2k-$4k, but I’d really like to stay near the $2k level for now and maybe upgrade later if warranted. Here is my current working list of amplifiers in approximate order of ascending price:

Bryston 4BSST
Bryston 7BSST
Innersound (not sure which model to consider)
H2O 250 Monoblocks
Parasound JC-1
McCormack DNA-500
Pass labs x350
Edge NL10
Pass Labs x600

I think I’d like to go with the Bryston 4BSST to start, but would like comments and other suggestions. The VTL’s would power the mids and highs. A digital amp would be great for power consumption considerations, and I know they do well on the bass (I’ve owned PS Audio), but still find myself hesitating a bit. More comments?

As for Xover frequencies, my review online indicates the following:

Stock high-pass (HP) is 6dB (first order) with a -3dB point at 230Hz
Stock low-pass (LP) is 18dB (third order) with a -3dB point of 116Hz

Recommendations include:

Increase LP to 140Hz (same 18dB slope)
Increase HP to 250Hz (same 6dB slope)

The second recommendation also included moving the LP to 110Hz instead of 116Hz, but I can’t imagine that 6Hz is audible in this case.

The Marchand Xover modules aren’t too pricey, so I intend to get the stock settings (230/6 and 116/18) along with a 140/18 and maybe a 250/6. Are there any other combinations out there worthy of trying? If I took a shotgun approach, should I stick with the specified slopes of the HP and LP units and just try different Xover frequencies? How much of a change is significant for both the LP and the HP (e.g. 10%).

Thanks Very Much, Peter S.
peter_s
peter_s OP
1,327 posts
 
This from the 20.1 manual:

"Set the high pass section at 200-300 Hz, 6dB per octave. Due to standing waves at the crossover frequency, the low pass section may require adjustment from as low as 90Hz (12dB Bessel) to 150Hz (15dB Butterworth). Typical settings are in the middle of this range. Optimization of the low pass can be done by ear (with music) or spectrum analysis."

Should I experiment with 2nd order for the LP, as suggested above?
peter_s OP
1,327 posts
 
Also, and thoughts on the Parasound HCA-3500? Seems similar to the Rotel, but reviewed as having greater bass control...
loontoon
301 posts
 
I can't emphasise enough the that amps on bass make a huge difference in sound, they control the pace. I learned this long ago when I subbed in a B&K amp for a Muse 160II during an all night session with an old freind. He's a music buff but no audiophool.

When the B&K went in I heard it right off but said nothing, it took him maybe a minute to ask me what just happened to the music.

When I moved up from the Muse to a Threshold there was again an increase in bass quality and speed but nothing like from the B&K to the Muse.

BTW this is all on Maggies.

As for X/O slopes, get a RANE 22, it's adjustable, not the cleanest audiophoolish device out there, but they can be had on the open market for about 1-200. Use it to find the settings you seek then swap for the Marchand unit, then------ sorry but find a used Bryston 10B. Yeah you'll hear it, the problem with maggies, is you hear freakin everything. I wouldn't rush to find a Bryston but keep you eye out for one a good price.

I'm not as keep on the Bryston amps as I am the 10B X/O.

das loon
rathbone
22 posts
 
Yes, you will get more dynamics and openess by bi-amping, but musicality and the balancing act of the speaker often suffers (badly). I assume that you picked 20.1's over other speakers because you were willing to suffer some of their trade-offs/weaknesses. Maybe you are not.

The Absolute Sound's review of the 20.1 and Pass Labs active XO summs things up pretty well. Magnepan's stock passive XO's get a bad rap, but they are not all that bad, and VERY difficult to copy or improve on using an electronic XO. It takes time and patience (plus the modules will probably sound horrible to start out with and take time to burn-in, so be prepared). Many have claimed victory and are happy with active bi-amping, but victory is always short-lived in audio (always on to the next tweak/component). Things are not going to be automatically better just because the stock passive is out of the way.

It will be a fun and great learning experience however, so best of luck!
peter_s OP
1,327 posts
 
Rathbone - what are your thoughts on amps that are right for running through the stock passive? I don't think the VTL450 is enough, even though the TAS article said it was.

Loontoon - any $2k amps you can recommend?

Best, Peter
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