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RE: Satie, thanks for the picture

Hi Randy,
I am sure Satie will confirm but you are right on all that I think, - if you want to use the Threshold on the mid/tweeter section and avoid passing DC you could build this box consisting of the 60 uf capacitor and 3.5 mH coil which would be place after the Threshold. The box would then go on feed your mid/tweeter internal crossover, and you would not need to use the stock wodden sides external crossover at all if you used an active crososver for the bass amp/panel to do biamping (a great cheap option is of course the DCX2496 everyone keeps mentioning). The only other way to achieve biamping would be to buy an XO-1 or build a line level passive crososver for the bass section (same thing as the XO-1 anyway). But of course actively driving the bass section in a biamp setup (with the mid/treble driven passively at speaker level) would give you a big leap in performacen over using an XO1 and also protect your mid/tweeter from DC.

But I've just realsied there is something you can very simply do here to achieve part active/part passive biamping and not have to build a box with the 60 uf capacitor and 3.5 mH coil yourself! Its very simple, - if you look at the IIIa crossver box on this schematic (section on the left) the 60 uf cap and 3.5 coil are of course already there to use for your mid tweeter barch befor entering the internal crossover of the speaker.
http://www.integracoustics.com/MUG/MUG/tweaks/stranger/MG-IIIa_Crossover.htm

The problem you are having now is there is no way to phsycailly access these two componenets in a biamp setup (only if you are using a single amp). BUT if you buy an active crossover for the bass the problem is sorted!, - use the active crossover and other amp on the bass panel, - thats one side of the biamp setup sorted, and simply run the other side going from the Threshold into the inputs of the external crossover box (which are now free to use) and then use the mid/tweeter output on it feeding your mid/treble input on the speakers. The bass output from the crossover box is of course not used - all sorted, no need at all to build another box wih that cap and inductor in at all. If you wire up the external crossover box like this with the bass output on it not used the bass components of the crossover in that box are not being used.

This is a pretty simple solution I think, - a bit of volume matching to do and fiddling about setting up the active crossover but thats it!. All you have to do is buy an active crossover that can do the right slope (3rd order I think it is) and right crossover point.

I don't have the external crososver boxes (they was missing) for my 3.3R so I can't do this unless I buy them from Magnepan. However after reaisling how simple this makes it to run a part active/part passive biamp setup I might well now buy external crossover boxes. I could use a line level equivalent instead using caps and inductors for the mid/treble (putting them between preamp and power amp) but that would involve changing values etc for use with different power amps and using the speaker level components protect the speaker from DC and that is a nice advantage and I like that. You are still getting the benefit of active operation of the bass panel, - far more efficient drive of it, - I'm sure it woudl be a big improvement.

Hope this helps. Satie if you reading this can you comfrim this is sound (I am pretty sure it is though despite not being very technical!)

Cheers,
Colin


Edits: 08/14/10
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