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In Reply to: Cable resistance will not make the amps work harder. posted by Al Sekela on March 19, 2007 at 14:42:12:
AlActually I was referring to Active Shielded speaker wires, but now you have two points I would ask about.
1) my speaker cables are both passive and Active Shielded speaker wires (http://www.synergisticresearch.com/index.php?PageID=70) -- do you think this "active" charge really helps reduce RFI introduction into the cables - or is this a gimic ?? Would not the transformer that plugs into the wall seperately near the origin of the wires from the amp end not create more RFI in the air around the system ??
2) "If you mean active crossovers, I don't have experience with them, but distrust them because of the extra gain stages, power supplies, and connection points they require. They will increase RF noise and susceptibility to RF noise degradation. "
Most seem to really disreguard the passive crossovers of all maggie lines and suggest adding the active crossover. One of my thoughts with this has also been what about the added wires to, inside, and out of the active system ... Are they as good of quality as the 20.1s passives ?? From what I have read, I guess getting the crossover "parts" in the system BEFORE the amp can improve the amp / speaker interaction ?? (in my layman's terms). Any thoughts ??
Also, the active crossover is needed to balance the gain if two different amps are used.
Thanks
Follow Ups:
Sorry I did not think about active shielded speaker cables. What I know about this is mostly second-hand, as a good friend of mine designs and makes his own active cables. My own speaker cables are damped with carbon fiber, which is a weak sort of shielding, and with dynamic loading. I do use actively-shielded power cords.The DC bias in active cables makes the wire insulation more linear as a dielectric, but also can make it microphonic. The shield electrode supports the DC bias as well as shields against external noise. The problem with the shield is that it supports RF resonance modes of its own and with the internal conductors. These resonances can make RF noise problems worse unless the cable design includes damping mechanisms. I don't know if Synergistic Research cables include damping mechanisms in their designs.
Shielding also increases the total capacitance of the cables. This might present a problem with some amps, where it could drive them into instability. The shielding is not likely to be effective against magnetic fields. Therefore, its main use in speaker cables appears to be to support DC bias to make the insulation behave more like a perfect dielectric. If you have ever compared PVC to Teflon insulation, you will know that this is not a small benefit.
You are correct that a wall-wart bias supply is a possible entry path for RF noise. I don't think you can use batteries with these cables. The power connection and feed wires for the bias supply have to be designed with care to suppress RF noise carried on the house power wiring.
As for active crossovers, the main benefit is to allow direct coupling of the amps to the speaker elements. The direct-coupled amps will damp the speaker elements outside their operating ranges, while some of the Magnepan passive crossover designs prevent adequate out-of-band damping. I modified my MG-20 passive crossovers to include R-C shunt elements at the outputs of the bass panel low-pass filters, and this made a definite improvement. The stock design has a series inductor at the output, so higher frequency resonances in the bass panel cannot be damped by the amplifier.
The main draw-back, as I said before, is the additional active electronics and cabling required to implement the crossover. Magnepans can be tweaked to be very revealing speakers, and would easily reveal the distortion and noise added by the active crossover, IMO. Proponents of active crossovers always wave this argument away. I simply don't know if an active setup can be made to be as natural-sounding as a teaked passive setup.
hello Al Sekela,thanks for your great work.
I need help about RC network and you are the expert.
can you mail me please (impossible for me with your optinal E-mail Preference )Thanks,best regards,
:)
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