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In Reply to: RE: Crossovers posted by airtime on June 04, 2015 at 16:28:54
I once changed the iron core coils in a set of IMF Studio 2 speakers for air cores. We matched the resistance by using larger wire in the air cores. Many prefer air core coils. By the way we found we had to drop the air cores to the bottom of the transmission line away from the crossover because the larger field of the air cores interacted with the rest of the cross over.
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Location and orientation of inductors are important considerations. Also, I use brass screws in the vicinity of inductors.
You do have magnetic field lines you have to deal with. The coil winding directions must be rotated 90 degrees from each other. otherwise they interact magnetically with each other AND the other components. Found that out with an oscilloscope one day.
Some 25 years ago, a local audio shop had a pair of original B&W 801 Matrix speakers, and Jim the owner was experimenting with passive bi-amping. At one point, he was testing out the woofer section alone and heard this weird "pocka-pocka" sound coming from the unconnected midrange driver. He opened up the crossover and found that the main iron-core coil in the lowpass filter was mounted nose-to-butt with a cored coil in the bandpass filter, and the mutual inductance was sufficient for some of the signal going to the woofer to creep into the midrange circuit. B&W apparently got enough complaints from dealers and techs that they corrected the board layout in subsequent editions.
I had a friend who produced a speaker with a passive crossover in a single box for both channels. The speaker had very large air core coils, one for each channel parallel to each other. Another friend took the coils out and hooked them up to long connectors and as the spacing between the coils increased we could hear the sound improve. Air core coils are the worst at this with their large external fields. Iron cores are not as bad.
Makes sense that air cores would emit a more diffuse magnetic field, while iron cores concentrate that field in the core. Another very good reason NOT to mount iron cores nose-to-butt the way B&W did.
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