Planar Speaker Asylum

I'll have a go at explaining.

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This Post Has Been Edited by the Author

In Reply to: RE: Correct. :-)) ... posted by andyr on August 09, 2010 at 22:41:54

Hi Randy,
Its is very confusing I know and I have recently bought a pair of 3.3Rs from a shop where they had them wired up like this too for a demo, - thats how they thought you wried them up . In fact this was even worse as they didn't even have the external crossover boxes at all and didn't realise they were even needed, - they had one amp running directly into the bass panel inputs (so the bass panel was reproducing a full range signal!!) and the other into the internal crossover for the mid/treble, - both wrong of course! And of course the sound was appaling!
I don't understand crossover lingo either!, - let me me try to explain it as I see it. Hopefully you will understand.

It confusing as you are right, the internal crossover does divide the mid/treble, but what were not getting is that the signal you were feeding into this internal crossover needs to initially be filtered of some low freqneucies (by a particular section in the external box) first before it reaches there. Its an obivious mistake to make. You were feeding the internal crossover a full range signal directly from the one the power amps instead missing out the first stage that cut off the low feqnecuies, - this is not correct, and like Andy says its why the mid fuse was blowing.
Some Magnepan external (passive speaker level) crossover boxes have two sets of inputs for biwiring/biamping, - your model does not unfortunately! This might seem like an unfortunate pain, and it true that yes you would have more felxibility to immediately passive biamp the speakers if you had an external crossover with two sets of inputs instead of one but you can get better results anyway I would have thought by mimiking what the external crossover box does for the mid/treble branch of the signal at line level instead of speaker level, - you can use a capacitor at line level between preamp and the power amp (the power amp you are using for the mid/tweeter section) that will give you a bass cut signal BEFORE actually reaching that the power amp ( not after the power amp as it usually does), - this bass cut signal from the power amp then does onto the internal crossover of the speaker and is correct as its a bass cut signal entering there. The advanatge of doing the first stage of filtering needed for the mid/treble at line level is you can use a high quality and much cheaper/smaller voltage popypropylene capacitor for line level rather than the much bigger/more expensive ones used at speaker level.
This is of course what the line level XO-1 (the black box) crossover does, - just some line level comopoenets inside that box, but you might as well do it yourself for much cheaper (if you can solder etc) , - you can also choose a capacitor tailor suited for your power amp's input impedance too.
So yeah Andy is right the reason the fuse was blowing is because the signal entering the internal crossover is unfiltered of bass frequencies and contains too much current, - its a good job the fuse was there protecting the midrange panel. Send the internal crossover a signal filtered of bass freqneucies (either from an active crososver or a line level passive crossover as explained above) and there will not be a problem, - the fuse will not blow as there is less current in the signal.
Hope I have not confused you more. Let me know if you get it now. If not I'll try to explain again!
Cheers,
Colin

Edits: 08/10/10

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