Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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Here's a clue............

Posted by yaukui (A) on March 20, 2008 at 12:47:59

...................... to why cables can change the sound in various combinations and configurations with different amplifiers, from a man that has been designing and building amplifiers for over 25 years (cable naysayers should look away now as none of this is going to change their minds anyway);

[quote="Mike Creek"]You may wonder how I can measure the distortion contribution of wire? Well, I simply drive a sine wave signal into a resistive dummy load with an amplifier (any amplifier). I then measure the difference from one end of the cable to the other. In other words I am not measuring the amplifier's distortion, but the contribution of the cable. This technique was introduced to me by Creek's former chief engineer, Alex Nikitin, who had no particular axe to grind but wanted to debunk the many cable related myths that existed and find the source of missing musical information. We applied those findings to our choice of interconnects and believe it or not, power cords, which we tested in large numbers to find a suitable make/type to supply with our equipment at the time.

Interestingly, solid wire has much lower distortion than flexible wire at all frequencies. Needless to say, with all cables, there are many other factors that affect sound quality. Not the least is the effect of capacitance, (proximity of conductors to each other) and inductance. These 'components' in the system critically affect how the amplifier will work into a given load (loudspeaker) that is outside the control of the designer of the individual equipment.

So, I prefer to use the simplest cables, as they present the least inductance and capacitance. Resistance is not so important, but should be kept within reason. Shielding is sometimes an issue, depending on the environment surrounding the system in use, but the lack of shielding helps to reduce the capacitance that would otherwise create an unwanted filter in the circuit to the speaker and together with inductance caused by winding a cables or just inherent in flexible wire, causes a phase change to the amplifier's feedback circuitry, that could under extreme circumstances create instability that will at the very least make for poor sonic performance and in the worst case break the amplifier.


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Regards
Mike Creek[/quote]

In discovering and reading Mr. Creek's theory, I did some quick measurements in my shop using a Sound Technology ST1700A distortion analyser (SigGen output at 1kHz), Dale/Vishay 8 0hm precision dummy load, and an old Bryston 2B power amplifier which is part of an audio test rig. The test itself is very simple, and I could probably teach just about anybody¹ how to do it and how to interpret the findings. I tested various cables that I had around, power cords, speaker cables, interconnects, and just for fun, test leads, scope probe leads, various other test equipment "patch" cables, and some scrap wire from the bin. Well, Mr. Creek is not wrong. Each of the "samples" measured contributed different amounts of added distortion. Some were negligible trace measurements, some were astonishing in that the wire's contribution was as much as 3 times the base distortion level of the Bryston. There seems to be no real pattern to the results at this time, based on my afternoon of messing around, however, Mr. Creek is correct about solid core wire having a lower distortion contribution than stranded wire as the solid core samples I tested exhibited the lowest numbers. One thing is for sure, regardless that some people believe that all cables sound the same, they certainly don't measure the same, and this is demonstrable. At some point I will set some time aside to study this further and attempt to put some sort of a matrix together.

In the meantime, I came away from this with some thoughts;

Even if a particular amplifier has a superb (ie: low) THD spec from its manufacturer, this spec can be made worse (but not better) by adding the requisite cables necessary to make it work. An amplifier with no captive cables requires a minimum of 1 pair of interconnects at its input, one set of speaker cables at its output, and 1 power cable in order to have it operate and make sound. Each of the 3 cable sets can add its own distortion contribution to the system, and the aggregate contribution can far exceed the amplifier's rated THD which it is now added to. Can this have an effect on the sound?

Apart from solid core exhibiting lower distortion numbers than stranded, no other conclusions can be drawn at this time relative to cost/performance within the context of this test. Distortion measurements of quality spendy wire was all over the place, as it was for cheaper examples. No construction model was consistently better than other construction models.

No conclusions can be made as to which cable will offer the best sound in a given position in a particular system. Will the highest distortion example sound better than the lowest distortion one, can't say. On what day in what city with which system with whose ears?

So what's the conclusion? Distortion matters, otherwise designers wouldn't attempt to reduce or eliminate it. Distortion is measurable, full stop. Distortion is not only relevant in audio equipment. Every electronic measurement device I own has noise and distortion specs and adjustment controls to re-calibrate to spec if need be, and most of these devices have nothing to do with measuring audio. Keeping the distortion level as low as possible makes sense, as a lack thereof would eliminate it as a target of blame. If you had a medical condition that your doctor knew could be blamed on the existence of a particular substance in your blood, and a blood test confirmed that the substance in question didn't exist in your blood, then more tests would have to be performed. On the flip side, if you change a cable in your system and hear a [i]difference[/i], have you by chance changed the total system distortion by substituting a cable with a higher distortion contribution for one with a lower distortion contribution, or vice-versa. Does the [i]difference[/i] you hear sound better to you one way vs the other?

More on this as I find the time to do some more tests and interpret the results.

One more thing. I checked the Creek website and confirmed that they do not manufacture and/or sell cables, so Mr. Creek's theory is not in support of a product he is pushing. In fact, I believe that he has laid bare one of the problems that he and all other audio designers have to live with, which is, that one of his products can be rendered substandard by something that is out of his control, the end-users choice of cables.

¹Just [i]about[/i] anybody (subject to the confirmation of an open mind) .

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