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RE: Crossover Assistance on 3.3R Please

Posted by Davy (A) on August 8, 2014 at 06:49:50

In Reply to: Crossover Assistance on 3.3R Please posted by plschlesinger@aol.com on July 31, 2014 at 03:28:46:

Congrats on the purchase. Just thought I’d throw a few thoughts around here.

The 3.3Rs are nice speakers, certainly in terms of the quality of the ribbon tweeter and the panels. Have a set myself. I've tried the stock crossover with them and also several other different XO setups. There are several options if you don't have the stock external crossovers boxes. Don't use the speakers without an external crossover as the sound/FR will be completely (and I mean completely) wrong and feeding the mid/tweeter section with a full range signal is not a good idea.

Although the stock 3.3R crossover sounds nice and coherent I found it to be problematic in other ways, largely as it has a sucked out midrange, which is a deliberate part of the design. It’s called an "audiophile dip". I was personally not keen on this at all as it makes the midrange sound too distant in my opinion. The stock XO also sounded a bit foggy and phasey to me, which might be partly due to the slopes used but perhaps in part because to achieve that dip there is a 50 uF electrolytic cap on the midrange in the 3.3R internal XO which is not ideal. This position cap a better quality lower value mylar film cap in the earlier model Maggies.

I settled on a quite different crossover setup to stock but that involved altering the internal crossover (as well as external) to something simpler with less components (based quite closely on the older MGIII crossover design). This gives a flatter response without the midrange dip. You say you aren't a techie but if you ever want the details sometime with the future just ask me for info. If you know someone handy with a soldering iron its worth doing in my opinion.

So that’s my long term advice but I think your cheapest solution to get up and running (unless you have spare power amps knocking around) would simply be to get someone to build you a copy of the stock 3.3R external crossovers as Sbrians suggest, using similar quality components (i.e. Iron core inductors and electrolytic caps on the bass, mylar caps on the mid/tweeter part). The iron core inductors and electrolytic caps are not sonically ideal but you could get a functional crossover built for a reasonable price. Probably Around $150 I would have thought (maybe less). Like Neo says, to upgrade both the internal and external stock crossover with better parts (i.e. using air core inductors and film caps) would cost a lot of money (probably near to $1000). I would personally not recommend doing this with the stock 3.3R crossover values anyway due to the issues I’ve explained above (as the FR will be the same with the same midrange dip).

Your other option is active biamping though this involves having another power amp available, and and buying an active crossover. Most people recommended this over stock single amp passive drive, but I am personally not so keen on it. Active biamping certainly does improves the sound over stock in terms of detail and transparency,lower distortion and greater output capability but I personally don’t think it sounds as coherent as single amp drive.

I would say from my experience that the most Maggies stock passive crossovers (using single amp drive) are better matched for phase alignment between the panels than you can achieve with a external typical analogue active biamp setup and standard off the shelf active crossover unless you get a custom expensive active XO made for the job. Magnepan take a lot of care with their stock crossover design in terms of the values used matching the phase of the panels up. As well as the coherency issue I had trouble with active biamp setups sounding too thin in the lower midrange, which was probably a phase issue. Although the stock 3.3R crossover had the midrange dip I didn’t like the sound was much fuller the lower midrange and it was more coherent sounding. Using a digital active crossover that‘s more phase adjustable (than just + or -) than an analogue crossover etc might be a way around this problem but it can be complicated and pricey to do and I still not completely sure you would get the coherence of single amp drive.

If you try the active biamping option see how you get on. If it sounds likes the speaker is not blending together very well I would personally try using a single amp solution and stock crossover setup for starters (then consider changing the values later on).

Like I say I use a crossover similar to the MGIII crossover, with good quality polypropylenes film caps on the external mid/tweeter high pass section. However I am still using rather rubbish electrolytic caps and iron core inductors on the bass LP section. Need to upgrade that eventually, though it’s a pricey job. I’m committed to single amp drive so I’ll do it eventually.

One other thing to mention is that unless the 3.3Rs have been serviced there is quite a fair chance they have some delamination at the end of the panels and the wires might have lifted up (particularity in the bass section),due to the 3M spray adhesive and Miloxane adhesive failing over time. If you ever hear the speakers buzzing on bass notes this is the cause. To repair it is a possible DIY job and although time consuming is not too difficult if you read up a lot on it first. With the 3.3R you will actually be able to see if the wires have lifted at the top and bottom of the bass panel if you look closely at the back of the speaker through the sock in the light.

Edits: 08/08/14 08/08/14 08/08/14

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