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In Reply to: RE: Very interesting post, Dr Evil ... sorry, Dr Chaos!! :-)) ... posted by andyr on July 04, 2010 at 05:46:47
"...IM distortion happening when 2 drivers share the same sheet of mylar and the drivers are not clamped off from each other..."
Magnepan doesn't exactly crank out new products at breakneck speed. That doesn't mean that the engineering department takes 10 year coffee breaks. I suspect their products spend years in development. Is it possible that such concerns as you mention in the above quote are considerations Magnepan addressed in those years in the lab? Is it lunacy to imagine that their crossovers are worked out such that their speakers present their best behavior?
I ask this as one who has been led down the rabbit hole. I don't imagine I'm that different from the majority of inmates here in that much has changed over the years - equipment comes and goes and some gets modified and so it goes and goes. I recently spent a few hours alone with a pair of bone stock 3.6s and they delivered the goods in a way I've never experienced. I keep gushing because they were that good - right from Magnepan, as their creator intended them.
I didn't just fall off the turnip truck; I have no doubt that some improvements can be made. Even when producing a Maggie that sells at around $5,000, compromises are unavoidable. They certainly can't use hardwood for their frames, but I have a suspicion that much care goes into the design of their products - products honed by long development phases.
(Uh oh, did I just hear a snap?)
"Jazz is not dead - it just smells funny" FZ
Follow Ups:
The first compromise is that, because of the external/internal XO construction (left over from the III), the signal to the ribbon has to go through the 200uF mid-panel HP filter, before it enters the 17.1uF ribbon HP cap.
You would get better sound from the ribbon if the big cap was used just for the mid panel (probably with a lesser value) and the signal to the ribbon only went through the one 17.1uF cap. But then the speaker wire connection for the ribbon would have to be in the external XO box.
(I think someone posted a tweak about this?)
Secondly, in terms of: " Is it lunacy to imagine that their crossovers are worked out such that their speakers present their best behavior ?" ... this has got nothing to do with IM distortion between 2 drivers sharing the one piece of mylar.
Regards,
Andy
IM is probably the dominant form of distortion for any loudspeaker. I thought, maybe incorrectly (wouldn't be anything new), that crossover design is largely a balancing act between better temporal response (1st order) and better IM control (with a higher order) - points and slopes impact many aspects of a loudspeaker's performance, no?
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"Jazz is not dead - it just smells funny" FZ
While, yes, IM distortion is present all the time, it becomes more objectionable at higher frequencies when, say, the sheet of mylar which is producing 5KHz has 50Hz superimposed on it.
This is barely changed by whatever XO regime you happen to have, at the XO frequency in the middle.
Crossover design is a balancing act between better phase response (with 1st order being the best) and, with higher order slopes:
* better control over driver behaviour
* less smearing from having the 2 drivers (with different dynamics/mass) produce the same notes ... ie. those between the -3dB frequencies.
Regards,
Andy
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