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Magnepan Active Bi-Amping

I’m wondering if anyone else has tried this, but also if there is a better unit or a better method out there to achieve similar or better improvements in sound quality.

I’ve inserted a dbx Driverack 260 speaker management unit into my system. It provides the means to employ an amp for my Magnepan 3.6R’s low frequency panels, and a separate amp for the mids and tweeters (the internal crossovers between mids and highs are still in use). The dbx has been set up to provide a close approximation - only slightly tweaked - of the Maggie’s manufacturer-listed crossover points and slopes. It does the same job for the Martin Logan Descent i sub that accompanies them. I’ve spent about a week making adjustments and have honed in on what I think is close to the ideal, at least as far as my ear can discern, although no measurements of this configuration have been taken yet. I can list the specific crossover frequencies and slopes if anyone finds it necessary for the purpose of this discussion.

Before I get to the benefits, I’d like to highlight what I believe are the drawbacks. First, inserting this unit into the signal path creates another A-D/D-A conversion. Second, I’m not sure of the quality of the internals of the dbx unit. They may fall well short of the higher standard typically seen in audiophile components. Given the unit’s price ($700) and its typical use, not to mention the added connection points, I find it entirely possible that some signal degradation is happening. But to what degree and to what detriment, I can’t tell from listening. It's possible that I'm still just mesmerized by the speakers' increased liveliness and therefore missing any possible degradation. 

The benefits of this configuration are what I perceive to be a greater authority of the amps over the speakers. The sound seems to be more dynamic, lively and, well, effortless. The Maggie’s 86dB/watt/m efficiency has always been a weak point for me. I believe this configuration goes a long way towards alleviating that drawback. But could it be mitigated with a more powerful amp? The image the speakers present is slightly more pin-point, and maintains that quality across a wider portion of the soundstage. Could this improvement be happening because the stock passive crossovers are being bypassed? Magnepan's crossovers are so often faulted as a weak link, but I have nothing to compare mine to. Has anyone gone to the trouble of having a custom crossover made, and if so, by whom?

I think I've done this a bit "on the cheap," which concerns me a bit. I don't want to be stifling the potential for even better sound quality by using the dbx unit. I would rather spend more money on a better crossover (active or passive) and, if necessary, a more powerful amp (or set of amps) as long as I can be reasonably assured that the results will meet or exceed what I'm getting now in this active crossover/bi-amp configuration. But I feel woefully uninformed as to what equipment to seek out, especially in regards to the potential crossover upgrade.  

It might be worth mentioning that the subwoofer’s integration is so much more precise using the dbx than it ever was with the Descent i’s controls and careful subwoofer placement by themselves. I’ve set what I feel is the best crossover frequency, slope and phase for the sub in its current location. But arguably more important than a flat response in subwoofer integration is the timing. I’m using a delay in the signal going to the mains in order to align the wave from the sub with that of the Magnepans at the crossover frequency. I’ve done all this by ear and with the use of an adjustable sine wave tone generator, so some adjustments might still be necessary after measurements are taken.

So to recap, has anyone seen improvements in their Magnepans by using:
- a speaker management unit or other active crossover and bi-amp configuration, and if so, which one(s), 
- a significantly powerful amp (or pair of amps), and/or
- a custom-made passive crossover network of higher quality than stock? 

(edited for clarity - I hope)
sixfour3
terry9
2,333 posts
 
Yes. I first used an ARC electronic crossover in the 70’s to power a tube top end and SS bottom end on Tympani 1a’s. Huge improvement: dynamics, clarity, sweetness.

Then I used a custom analogue unit for another Magnepan system, and then decided to upgrade. The choice was Magnepan plus active crossover plus three channels per speaker, or ESL with only one channel per speaker. I chose the latter for audio.

For home theatre, MP is ideal. But I still upgrade the crossover components from mediocre to superior, and get similar improvements, but not as pronounced. Best amp for Magnepan I know is Bryston - I use one for the MP woofer and the sub. I would avoid a digital crossover unless it's a really really good one, like Classe used to make.

Good luck.



sixfour3 OP
21 posts
 
Thanks @terry9 

I can see how upgrading the Magnepans' passive crossovers could benefit the imaging and clarity.  But I'm reluctant to dive into spec-ing out and buying new crossover components and breaking out the soldering iron.  For one, the level of technical know-how to choose such items is beyond me and also intimidating.  Assuming for the moment that I could find a way to upgrade the crossovers, the downside that remains is that I'd probably be missing these newfound dynamics and punch that the bi-amping configuration is bringing forth, which is just so very engaging.  That said, if there's anyone reputable out there who offers that service, I'd like to know who they are, if only at the very least to have a chat with them about pricing and what to expect from the upgrade. 

Listening at higher levels yesterday rendered an annoying harshness or "glare" that I didn't hear that first week when the volume was lower.  It seems that when the music's loud the dbx is introducing this harshness and essentially killing any benefit I get from the PS Audio Directstream DAC that is situated upstream of it.  (The DAC also serves as the preamp.)  It's likely happening at lower volume, too, but so far seems to be significantly less noticeable.  So, based on that, my preference is to keep the signal analog downstream of the DAC.  But I suppose that if there is a DSP-based device out there that can retain the analog-like sweetness of my DAC, I'm not entirely opposed to it. Does such a thing exist?

I don't envision a magic bullet presenting itself anytime soon. A compromise will have to be found based on these competing factors. I should admit that retiring the Magnepans for speakers with a 92+dB/watt/m spec has crossed my mind. But I'd like to chase this a little further down the rabbit hole before I seriously consider that option.
  
terry9
2,333 posts
 

I do not recommend re-engineering your crossover, but rather repackaging it. You could get a tech to identify the components, their values, and their specifications. Then order better quality ones and put them in a box. This drives the different zones of the speakers. Add a factory refurbished Bryston 4B SST and you have a fine setup. Not quite as good as tri-amping with a low-distortion analogue electronic crossover, but very good. IMO.

I did this for a neighbour with his bookshelf speakers when he felt the itch, and the results were dramatic. You can also tune your system this way. Begin with film and foil caps, always film and foil; you already have metallized. Polypropylene makes a warmer but less precise sound than teflon or styrene, Teflon makes a precise but slightly harsh sound (I find Relcap and Solen teflons to be least harsh), and styrene quite neutral (MIT RTX is a good choice). Inductors should be made of ribbon with an air core (like Goertz), and resistors should be non-inductive wire wound such as Mills.

I like the sound of planar speakers, so I would not change. To my mind, there is no substitute. But your mind is what counts in your system, and YMMV.

I too hear an unpleasant glare from digital systems. With really high quality ones, it’s tolerable, but not for classical music (Classe’s processor was expensive and also legendary; the SSP 800 is available used for about 3K, but it can be buggy IME). But since I know little about the state of the digital art, other than I don’t expect to like it, my opinion isn’t worth much.

You might want to check out analogue crossovers. ARC used to make them, maybe you could find one of those (EC-4, I believe). Or Levinson.
Good Luck.
sixfour3 OP
21 posts
 
Excellent information re: the capacitors in the crossover and the process by which it should be upgraded. This is exactly the type of information I need to know should I choose to go that route. Thank you! 

I see that Bryston is offering an active speaker system. Unfortunately, their active crossover unit seems to be exclusively intended for their speaker systems. 

I'm having trouble finding options for higher quality active crossovers. The Pass Labs XVR-1 and the First Watt B5 seem to be about the best units available, except that they aren't available. Anywhere. And everything new that isn't a MiniDSP is more geared towards the professional audio/sound reinforcement market. 

In other forums it has been suggested that high end audio manufacturers don't generally go the route of offering this type of product. The theory goes that they don't need to; their crossover networks are a high enough grade as to make such things superfluous. Perhaps Magnepan is unique in this hobby in that their speakers seem to benefit tremendously from bi-amping (where available), potentially due to their lack of efficiency, and their crossovers are just suspect enough to make them a common upgrade. Going the active crossover route allows for gains to be realized in both areas.

I absolutely love these Maggies. I truly do. And this newfound dynamicism is absolutely outstanding, but at the cost of the added digital harshness from the speaker management unit. I'm still asking myself if I should continue with the Magnepans and accept that they will always have these limitations, then just upgrade the crossovers, or if I should start the search for new speakers. 

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