Bi-amping Maggies

**garylkoh** · 08-30-2011, 09:14 AM

Originally Posted by fas42

This is a nice echo of the discussion in "How much is too much?": overly complicated and expensive system failing miserably by all accounts. But why did it sound so bad? Was it audibly distorting, or was the speaker designer in you just too aware that the drivers weren't presenting a coherent, integrated picture?

Frank

It was much more than a lack of coherence or integration, it was an ugly, jarring sound.

**garylkoh** · 08-30-2011, 09:42 AM

Hi Don, Sorry - I was away from the forum for too long - first finishing off a series of new loudspeakers, then a 3-week vacation. Now I recall that in another thread you were looking for a HPF for the main amp to the Maggies. Yes, that makes sense if you are looking to relieve the amp (and more importantly the panel) of the low frequency load for better high-frequency clarity.

I've got a pair of 3.6's and they do sound better biamped using the dual inputs on the stock MG crossover even when I have a crossover. I haven't tried a HPF on the low-frequency input, but my latest experiments having a pair of 1440W prototype amps into each input certainly belies the "truth" that Maggies can't play softly with dynamics. If I do find the time to build one and tweak it, I can certainly send it to you after I'm done with it.

**DonH50** · 08-30-2011, 12:20 PM

No worries! And yes, I am wanting to relieve the panel, much more so than the amp. Once you start down the crossover path, it quickly turns into "anything worth doing is worth overdoing" and so I started thinking about full bi-amping again. And so it goes...

I have a theory that, despite their avowed "ease" of driving, in fact the panels need very good amp control (high broadband damping factor) to control secondary "ripples" in the panels during operation. That would explain why they sound better (cleaner, anyway) with higher-power amps even when the power is not needed. Of course, since they are like 82 dB/W/m, a little extra power doesn't hurt, either...

Hey, if you build something you like and can part with, I'd love to play with it! - Don

**mep** · 08-30-2011, 01:41 PM

Originally Posted by DonH50

Well, shoot, the price is right, ship it to me! Let me know the cost and I will drop you a check for the shipping. My plan is to use it as a HPF for the amps driving my Magnepans, getting the very LF stuff out of the panels (they are full-range now, I am using the subs' built-in LPFs but not touching the Maggies). They are a little happier that way, at least measurably. I am still not sure the difference I heard was real or wishful thinking, but I figure what the heck. I already have 1/4" TRS to RCA, just need to pick up XLR to RCA. I may even have some of those in my bag, though I got rid of most of my patch cables when I (pretty much) quit doing live sound.

As a two-way, that also prevents me from running out and buying another amp to bi-amp the Maggies immediately; a good thing the way college costs have shot up! This way I can try out the unit and see how it sounds to me before deciding the next step.

Thanks! - Don

Don-PM with your address and I will get it shipped out to you.

Mark

**DonH50** · 09-01-2011, 08:37 PM

So I did the math... The stock MG-IIIa external crossover is LPF = 300 Hz, 18 dB/oct (3rd-order) and HPF = 500 Hz, 12 dB/oct (2nd-order). The asymmetry imparts about a +1 dB hump around 220 Hz and about -1 dB dip around 450 Hz. This is for the electrical transfer function, of course, so there is no guarantee the acoustic output exactly matches, but we'll run with it for now.

The filters are 6 dB down around 380 Hz, so a 4th-order Linkwitz-Riley crossover centered at 400 Hz is pretty close to providing the same effective input power band and results in no ripple across the band. I might post pictures later but have not exported them out of my analysis program. So, if I want to bi-amp, I need a 400 Hz 4th-order L-R crossover to do the trick.

Plus the subwoofer filter, of course, which I was planning to be around 50 Hz. That would be -6 dB at 50 Hz with a 4th-order L-R, and about 10 dB down at 40 Hz, so I might move it down a little (the panels are rated -3 dB at 35 Hz but I would like them to not work so hard down there). Moving the sub crossover to 45 Hz puts the panels down 6 dB at 45 Hz and 10 dB around 38 Hz, probably close enough. The advantage of the higher-order filters are that I can get less overlap and move the crossover down a little to help avoid the usual integration issues between planar panels and the dynamic sub.

Onwards - Don

**DonH50** · 09-21-2011, 11:59 AM

Update: I installed the dbx crossover Mark graciously provided last weekend. Unfortunately, not a lot of listening, story of my life. The crossover is a stereo two-way unit, and I set it at 50 Hz to cross from my main MG-IIIa's (driven by an Emotiva XPA-2) to my subs (a stereo pair of Rythmik F12's co-located with the Maggies). The goal was to off-load the very lowest frequencies to the sub and away from the panels, reducing their excursion and thus improving their linearity and increasing their effective dynamic range.

After hooking everything up (a much bigger chore than I anticipated, for various reasons), I did not hear a lot of difference. This was not unexpected; I listened mainly to music which has less very deep bass than some movies. I did not hear any added noise or distortion, a very good thing. I can convince myself I heard improvment on some of the loud drum licks but without a DBT who knows. In the past I was able to measure lower distortion using a similar setup with these same Maggies, but even back then it was often difficult to hear unless I knew exactly what and when to listen. I need to get some good piano and organ music on CD… I also plan to try a movie or two this weekend; that is more likely to demonstrate audible improvements.

Other things in Life have put bi-amping them, the next step, on the back burner for now. Just found out the house needs a new roof, so the funds for a new amp are going towards a new roof instead…

I may play around with the crossover, though in the past found 50 Hz was a good compromise for me so am in no hurry. I had to mount the crossover behind my center speaker, making it less accessible than I would have hoped. OTOH, it’s not something that gets tweaked after the initial setup.

Thanks again Mark! - Don

p.s. Less anyone misunderstand my excitement, with 24 dB/oct filters the input into the Maggies is down 6 dB at 50 Hz and ~24 dB down at 25 Hz. This is a major reduction in LF energy and should really improve the low-end performance of the system. A lack of listening coupled with our (humans') relatively low sensitivity to LF distortion makes it less audible than higher-frequency effects, but the benefits are real and I have, in the past, measured substantial reduction in distortion.