Stereophile has this article on the subject:
http://www.stereophile.com/asweseeit/190/index3.html
Here are a few excerpts from this very long article:
External cables:
Still less welcome to the engineering establishment is the discovery that audio cables vary in their subjective accuracy; rather less than amplifiers, it must be immediately noted, but nevertheless in ways which can be described and ranked on merit.
With the finest of today's systems the best cable is fortunately close to invisibility in audio termsâ€â€the ideal condition. The results from cable reviewing suggest that the use of poor or inappropriate cabling leads to a loss of up to 30% in performance in a state-of-the-art system.
Detailed comparative tests made on audio cables have brought to light a diversity of previously unsuspected and therefore neglected factors which have subjective consequences:
• Dielectric: A good correlation has been observed between dielectric loss and sound quality. A vacuum insulator shows the lowest loss, followed by air, and then by a range of dielectric materials commonly used for cables of all classes. The subjective ranking correlates with their dielectric properties. Thus, foamed or predominantly air-spaced types with PTFE, polypropylene, and polyethylene dielectrics score highly, while higher-loss materials such as PVC are distinctly inferior, even to the point of generating identifiable colorations and changes in timbre.
Associated with the subjective performance of the cable dielectric is the insulating thickness, this often related to the manufacturer's voltage rating. Better sound often follows higher ratings. Solid dielectrics are common and include those plastics mentioned above, as well as higher-molecular-weight polymers, ceramic powder, silicone rubber, and resin-impregnated glass fiber. Natural thread such as cotton or silk has been tried, plus various grades of carbon-based rubber. Every dielectric can be shown to have its own distinctive sound, even when used in a line-level interconnect application of just 1m in length.
• Metallurgy: Many establishment audio engineers consider that Ohm's Law is wholly sufficient to describe current flow in a wire, and that all metallic conductors must sound the same owing to the fundamental property of free electron mobility in this class of material. However, there is now strong evidence to indicate that the choice of element or alloy for a conductor, its metallurgical history, and its absolute purity all affect the sound quality. This finding, unwelcome for those working in this field, cannot be ignored. It seems a cruel twist of fate that of the many conducting materials tried, high-purity silver sounds the most accurate, as it costs approximately 100 times as much as the substantially effective and most widely used material available: copper.
Some physicists approached on this subject have invoked quantum theory to analyze the behavior of metallic conductors in varying states of practical purity, particularly with respect to the boundaries between metallic crystals.
• Geometry: The physical design of a cable is a variable which affects sound quality. There is a strong association between a balanced symmetrical twisted pair or twisted quad construction and a sound quality that is judged to be superior to a coaxial construction. The form of the conductor also mattersâ€â€whether it is solid-core or stranded. Generally, the single strand is preferable unless the wire is of unusually high purity, and the strands are bound in intimate electrical contact.
Cable assessment:
For cable assessment, the reference should be taken to be an absence of cable in that particular link, achieved by positioning the program source very close to the next unit and joining them by pure silver wire links barely 20mm long. The cables under test are substituted for this near-perfect link and their negative sound-quality characteristics assessed. In a recent test (footnote 5), 50 interconnect cables were successfully analyzed subjectively by using the single presentation method. Occasional return to the reference helped refresh the memory, while repeats constituted 25% of all the tests and gave reasonable confidence in the reliability of the judgments.
Conclusions:
This article has barely touched on the wide scope of the judgment of sound quality of audio components for review. While it is readily acknowledged that the bulk of the listening tests mentioned are not based on established "scientific" procedure, control methods have been used as far as is possible, However, if "scientific" methodologies had been adopted, many of these results would not have been observedâ€â€not, as the cynics would have you believe, because the differences do not exist, but because rigorous subjective testing requires an inordinate time scale, often imposing sufficient stress to desensitize the subjects.
In one well-researched case, however, a pair of good-performing, extensively measured amplifiers was found to be easy to differentiate by ear under normal review conditions, one being clearly more accurate than the other (footnote 6). A single presentation test was subsequently devised for a meeting of the London AES, where a large number of listeners (90 or so) participated in a controlled listening experiment to see a) whether two amplifiers could be differentiated, and b) whether one was preferred to the other. The judgment method required that the audience score each presentation as a new trial, this constituting the database. On first publication of the results (footnote 7), some colleagues helpfully pointed out certain analytical weaknesses (footnote
.
Sufficiently good data were obtained, however, for a statistician to confirm the validity of the test and find that while the aural sensitivity of the unscreened AES members under the difficult conditions of a public meeting was not very good, they nonetheless were able to collectively discriminate, and moreover did prefer one amplifier to the other. This agreed with the original review findings. The test was exhaustively researched with regard to load matching, absolute level, and the like. CD was the program source, and no switch box was involved.
Good hi-fi reviewing has moved beyond the basic framework of a comprehensive lab test and engineering analysis coupled with descriptions of finish, facilities, and ergonomics and a cursory listening check to make sure all is in order. Extensive listening work using consistent and methodical techniques, especially numerical scoring, has shown that many engineering factors are responsible for audible changes in reproduced sound quality, not least in absolute merit. Many of these factors are at present dismissed by the electronic and acoustic establishment.
Subjective assessment is a learned skill, one which is greatly helped by a familiarity with and an understanding of music. Frequent acquaintance with live, natural sound is also vital. Such a skill may be used routinely to judge fidelity, without persistent calls to statistically prove the results.
Personally I do believe that better inner-connects and speaker cables do exist. But spending $3,000.00 on a pure silver cable to gain a 1-3% improvement is pretty rediculous in my book if that same amount of money will buy you a better source with a bigger overall improvement...
Wed Aug 29, 2007 9:38 pm 
