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[KSTR]

IHMO that cable is a perfect example how to "sound" a cable (that is, the complete system of amp+cable+loudpeaker) under a given speciific condition.

This RC, when it sits at the speaker end of the cable, can function (if properly designed and the speaker doesn't spoil it) as a RF termination of the cable. An unterminated cable happens to be sort of a "chaotic" impededance at RF as it cycles from inductive to capacitive behaviour all the time above a certain frequency -- and the capacitive part is the problem, the equivalent peak value can be much higher that the lumped capacitance value of the cable. Now some HiFi-Amps don't like capacitance at their output and if you have bad luck then just a certain length of the cable will load the amp capacitvely at frequencies where it doesn't like that at all, putting the amp on the edge of oscillation, which might indeed affect the sound of the amp. With that RC installed the amps sees a benign RF load and may sound different. Of course the real problem is the amp's construction, but the effect as it manifests itself to the user is that this amp will sound different with certain cables.

This was discussed at DIYaudio.com:
 http://www.diyaudio.com/forums/showthread.php?postid=1343565 #post1343565
The topic continues over the next few pages, with occasional breaks as the original thread topic was different, my main contribution is the following post:
 http://www.diyaudio.com/forums/showthread.php?postid=1345824 #post1345824
For non-DIYaudio members I attach the plot I've shown there.

- Klaus

[Barry Hufker]

Klaus,

For people such as myself, would you explain what is being shown in the graph?

Thank you,

Barry

[John Roberts {JR}]

KSTR wrote on Sat, 11 July 2009 19:45

IHMO that cable is a perfect example how to "sound" a cable (that is, the complete system of amp+cable+loudpeaker) under a given speciific condition. This RC, when it sits at the speaker end of the cable, can function (if properly designed and the speaker doesn't spoil it) as a RF termination of the cable. An unterminated cable happens to be sort of a "chaotic" impededance at RF as it cycles from inductive to capacitive behaviour all the time above a certain frequency -- and the capacitive part is the problem, the equivalent peak value can be much higher that the lumped capacitance value of the cable. Now some HiFi-Amps don't like capacitance at their output and if you have bad luck then just a certain length of the cable will load the amp capacitvely at frequencies where it doesn't like that at all, putting the amp on the edge of oscillation, which might indeed affect the sound of the amp. With that RC installed the amps sees a benign RF load and may sound different. Of course the real problem is the amp's construction, but the effect as it manifests itself to the user is that this amp will sound different with certain cables. Klaus

If I understand your post.. This wire treatment to properly terminate speaker wire at RF, is to mitigate the (capacitive) loading impact on amp designs that are unstable at those RF.

Having some exposure to amplifier design, if an amp sounds different with different speaker wire, IMO the amp is defective (Same goes for line cords, etc).  Prudent amplifier designers routinely bench test amps with capacitive (and inductive) loads well in excess of that expected from good loads and wire. For the last couple decades we also test for what we might encounter from oddball speaker wire and even poorly designed speaker crossovers.

JR

PS: Thanks for the links it was nice to see Bob Cordell is still active. He is (IMO) also worth listening to (and reading).

[KSTR]

Hi,

Barry Hufker wrote on Sat, 11 July 2009 23:06

Klaus, For people such as myself, would you explain what is being shown in the graph?

The green trace in the top plot is the key point. It shows the varying "capacitance" that the amp sees vs. frequency with an unterminated cable of this specific lenght, which is not accounted for if one only does "lumped element" analysis, using the cable's LCR paramters (C would be 0.5nF/m which gives 5nf total for that 10m length). BTW I'm not sure if that simulation is really correct in absolute (quantities) terms (I even cannot recreate now the values I seemed to read from the plots, so much said ), but with an RF impedance analyzer one will see what's really going on which surely would be close -- and that has been done by people.

@John:
One problem that can still arise with bench testing is that one can happen to miss that specific problematic capacitance, unless you have close enough spacing between the tested values. A 1-3-10 or 1-2-5-10 ratio sequence could easlily miss that critical values. This is a place where simulations can come handy and today's delevopers ususally have pretty good sims of their amps generated and optimized by "iterative feedback" from sims-vs.-measurements cycles.

Of course I completely agree that any amp shall not be sensitive to any reasonable cable parameters, but in "HiEnd" realms this is not always the case.

- Klaus

[John Roberts {JR}]

KSTR wrote on Sun, 12 July 2009 11:05

@John: One problem that can still arise with bench testing is that one can happen to miss that specific problematic capacitance, unless you have close enough spacing between the tested values. A 1-3-10 or 1-2-5-10 ratio sequence could easlily miss that critical values. This is a place where simulations can come handy and today's delevopers ususally have pretty good sims of their amps generated and optimized by "iterative feedback" from sims-vs.-measurements cycles. Of course I completely agree that any amp shall not be sensitive to any reasonable cable parameters, but in "HiEnd" realms this is not always the case. - Klaus

Another reason I have avoided audio esoterica for decades.

Many high power amplifiers include an inductor in series with the output to isolate load capacitance from the amplifier's HF feedback path.

Another real issue is to protect amplifiers from speaker wires acting like antennas and pumping RF back onto the amplifier via the output end of the feedback network. Again this is known to those skilled in amplifier design. As long as we avoid rectification there are no audible artifacts.

JR

[Barry Hufker]

KSTR wrote on Sun, 12 July 2009 11:05

Hi, Barry Hufker wrote on Sat, 11 July 2009 23:06 Klaus, For people such as myself, would you explain what is being shown in the graph? The green trace in the top plot is the key point. It shows the varying "capacitance" that the amp sees vs. frequency with an unterminated cable of this specific lenght, which is not accounted for if one only does "lumped element" analysis, using the cable's LCR paramters (C would be 0.5nF/m which gives 5nf total for that 10m length). BTW I'm not sure if that simulation is really correct in absolute (quantities) terms (I even cannot recreate now the values I seemed to read from the plots, so much said ), but with an RF impedance analyzer one will see what's really going on which surely would be close -- and that has been done by people. @John: One problem that can still arise with bench testing is that one can happen to miss that specific problematic capacitance, unless you have close enough spacing between the tested values. A 1-3-10 or 1-2-5-10 ratio sequence could easlily miss that critical values. This is a place where simulations can come handy and today's delevopers ususally have pretty good sims of their amps generated and optimized by "iterative feedback" from sims-vs.-measurements cycles. Of course I completely agree that any amp shall not be sensitive to any reasonable cable parameters, but in "HiEnd" realms this is not always the case. - Klaus

Thank you Klaus. Most (if not all)of the people participating in this thread are capable of a much deeper discussion than I.  I appreciate the education and the possibility of keeping up with what's being said.

Barry