The Truth About Power Cords and there "Real" Price to Performance

It is not a Zobel network, though it looks the same, it performs a much different function.

A Zobel network is placed, typically across the woofer, so that as the impedance of the woofer goes up, the Zobel network simulates a constant impedance. That constant impedance allows the crossover to work properly. These were used in speakers well before Polk.


Polk patented putting an RC-damper/snubber across the speaker terminals. The purpose of this was to dampen high frequency oscillations.

turnbowm50 posts11-20-2019 2:14pm
atdavid432 posts11-20-2019 10:10am"Originally patented by Polk 30ish years ago."

Matt Polk did indeed patent the use of Zobel networks in loudspeakers. That was in response to power amps self-destructing when using Polk’s high-capacitance Cobra speaker cables.

The concept of Zobel networks, however, was developed by Otto Zobel of Bell Labs in 1923.

atdavid,

How is the series R-C network (Zobel) that is used to provide a constant impedance different from the series R-C circuit used by Polk to dampen power amp oscillations? To me, they serve a dual purpose.

I thought you might find this excerpt from Nelson Pass's discussion of speaker cables to be of interest. ...

"After a period of confusion, Matt Polk and I realized independently tahat the lack of a characteristic termination was causing the problem. Polk developed and patented a "damper" consisting of a .047uF capacitor and 6 ohm resistor in series placed across the loudspeaker, while I used the same network but with .1uF and 5 ohms. The results of this network are seen in Fig. 8 where the resonance in the pulsed waveform is damped out, restoring stability to an otherwise oscillating amplifier. Since Polk's commercial introduction of the damper circuit we have found it cures oscillation problems caused by the other exotic low inductance cables. It is necessary whenever a reasonably long length (>3 feet) of low inductance cable is mated with any wide bandwidth amplifier. It interacts unfavorably with twin lead conductors (Fig. 8) which require higher impedance values (say, .01uF, 60(2); however, twin lead's higher characteristic impedance and resonant frequencies are in any case unlikely to induce oscillation in amplifiers now available."  
https://www.passlabs.com/press/speaker-cables-science-or-snake-oil

For the same reason an RC-snubber across a diode or FET is not a Zobel network ....

atdavid438 posts11-20-2019 1:00pm"For the same reason an RC-snubber across a diode or FET is not a Zobel network ...."

They both have a resistor in series with a capacitor. To me, that makes them the same except for the name. I guess we'll have to agree to disagree.

One point about high end cables: they all look a whole lot better than zip cord and Romex!