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In Reply to: RE: ? posted by Duster on December 05, 2016 at 13:08:43
The subwoofer high level input is a high impedance input buffer, likely 10k ohms or greater. That's 3-4 orders of magnitude greater than a typical loudspeaker impedance, so the presence of the subwoofer connection is effectively "invisible" to both the amp and speaker.
Also, a typical speaker cable resistance is 0.01-0.1 ohms, which is 5-6 orders of magnitude less than the input impedance of the subwoofer. And the cable reactance is insignificant at very low frequencies. So the subwoofer response is far, far less affected by the cable impedance than the loudspeaker response.
Regarding back-EMF, on second thought I think you're right. I was thinking that since amplifier damping factor is usually highest at low frequencies, back-EMF wouldn't be as much of a problem. But I neglected to consider that loudspeaker resonances are typically strongest in the bass, and in a typical small two-way + sub combination the port resonance of the loudspeaker is going to be within the transition band of the sub's crossover.
Follow Ups:
I measured the speaker (high level) input impedance of three different sub Plate amps I have and the input impedance measured from 5600 Ohms to 21500 Ohms
One of the Plate amps (The one with the lowest impedance) has a High Level High Pass output (Series inductor followed by parallel capacitor) which effects the DC and AC impedance measurement.
I personally prefer all the bass management to be done at the low level (high impedance (RCA or Balanced) level. More control, Less RF and Hum likelihood.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
5-6 orders of magnitude , not 5-6 times
Cable impedance of 0.01-0.1 ohms, subwoofer input impedance of 5600 to 21500 ohms, that's 5-6 orders of magnitude, right?
I agree with you that high level is preferable and arguably better.
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