Here ya go .... No hype or sales pitch , just REAL scientific research ... Read it if you REALLY want to learn....
The Science of Cable Design
Measuring Cable Performance &
Correlating Results with the Listening Experience
technical article by TARA Labs designer Matthew Bond.
There is an increased awareness among audiophiles as to the importance of cables in the sound of an audio system. It is a subject that has been surrounded by controversy, in part because many feel the differences to be either too subtle to be audible, or too system-dependent to hold any universal truth for buyers of audio equipment.
In fact, it is possible to make measurements of different audio cable conductor designs that will correlate with audible differences in the cables' performance. Moreover, with these measurements as a learning tool, one can begin to distinguish conductor designs which are linear and accurate as opposed to designs which soften, brighten or otherwise color the sound.
In 1988 TARA Labs developed Constant Current Impedance Testing TM (CCZT), a testing method which has been used in advanced university engineering studies to measure cable performance. These measurements provide reliable predictions about the sound to be heard from the changes of cable conductor design and configuration. With CCZT, we have been able to reliably and repeatable correlate the listening experience to the test-bench experience CCZT measures impedance vs. frequency or linearity with frequency. This is both a necessary and important criterion of cable performance because it directly relates to rise time and phase coherency. These two elements, more than any other, correlate directly to one's perception of a cable's sound as either alive,; or reproduced.
In CCZT testing we use conductor runs of equal mass (i.e. same D.C. resistance) but varying conductor shape and arrangement. They are set up in a test jig having the same parallel configuration between the send and return lines. This methodology accurately compares the design qualities of the conductors themselves while keeping all other factors identical.
The results of the tests are shown in the graph. Listening tests of the cables generate results as might be expected from examination of the graph.
· Single 2mm (14 gauge) round conductor: Upper bass and mid-range are warm. Treble is soft and rolled off.
·· Two 1mm (14 gauge) round conductors: Upper bass and mid-range are cleaner, with better definition. Sound is more natural and coherent. Less roll-off in high frequencies.
= Two 1mm (14 gauge ) rectangular conductors: Upper bass and mid-range are more vivid, palpable and live sounding. The sound through the mid treble and upper frequencies is extremely coherent and natural. Overall, the natural Harmanic structure of the music is more accurately revealed.
With even a rudimentary under-standing of the principles of cable design it's possible to make good predictions about the sound of a cable just by examining its internal structure. In Part Two, we'll examine why various conductor configurations yield the differences in frequency linearity (and therefore, sound) demonstrated here, and what to look for when comparing cable designs.
The testing methodology for CCZT is relatively simple to duplicate. Contact SARA Labs for detailed instructions on seeing up a test jig and sample data from TARA Labs in-house testing.
How Conductor Size and Shape Affect Performance; What to Look for
In Part 1, we measured the frequency linearity of various cable designs using TARA Labs' Constant Current Impedance Testing (CCZT).
Why do different conductor types of the same mass yield such different results? In a few words: electromagnetic flux linkage.
Referring to the graph of the CCZT results, we see that the single 2 mm2 (14 gauge) conductor shows the least linearity with frequency. This is because in a larger single conductor there is more electromagnetic flux, which increases in density towards the center of the conductor. This crowding, or density of the electromagnetic lines of force at the center of the conductor effectively chokes off higher frequencies and forces them to travel towards the outside of the conductor.
Any compact or uniform shape increases the tendency of the whole conductor to have greater density in the coupling or linkage of electro-magnetic flux. In this diagram, a stranded conductor shows the same tendered to roll off high frequencies as a single solid conductor of the same mass.
An important note: this is true whether the conductor is a single solid-core or a stranded conductor of the same conductive mass or DC resistance. A large diameter conductor, whether solid-core or stranded, will have the same impedance vs. frequency curve for a given diameter and mass. In other words, the closely bundled small conductors in a multi-strand conductor approximate a single large solid-core conductor, so nothing is gained by stranding many smaller conductors.'
In the second trace, we have split the single conductor into two smaller ones. Combined, they have the same mass, but the frequency linearity is improved because of their smaller individual diameters and lower electromagnetic flux linkage. Although the conductors are subject to flux linkage because of proximity, they have the greater frequency linearity that goes with a smaller diameter. This is the principle behind many of TARA Labs' Prism TM Series solid-core cable designs.
In the third trace, the Rectangular Solid Core conductors still have the same mass but their frequency linearity is improved further. This is because the rectangular conductor has less coupling of electromagnetic flux at the center of the conductor. Due to its shape, there is effectively no "center" to speak of.
What to look for, then, when choosing cables? A design with thinner conductors in a more open configuration will yield cleaner, clearer and more frequency-linear sound. One with a single, large conductor or a bundle of smaller conductors will yield sound that is smoother and rolled off.
These guidelines hold true regardless of variations on these design themes and account for most of an audio cable's sound. Other elements, such as dielectric and conductor material and treatments, are the icing on the cake of cable design, having a lesser effect on cable performance than good, solid design principles. In the next article, we'll begin to examine those issues to shed some light on their relevance to audio cable performance.
All designs have the same conductive mass, but frequency linearity (i.e. a cleaner, clearer sound) will improve from left to right due to conductor size, shape S arrangement.
The Sonic Differences Between Conductor and Dielectric Materials and Treatments.
In Part 2, we discussed the conductor's own inductive reactance and its effect on the sound in an audio cable. In this installment, we'll examine conductor materials and treatments, as well as dielectric materials
D = Diameter of conductor
u = Permeability of material
f = Frequency at which HF attenuation Occurs
p = Specific Resistivity of material (micro m cm)
and their effect on the sound. Although it's important to note that these factors have a lesser effect on the sound than the design of the conductors themselves, when the conductor is more linear with frequency, these minor differences in materials do become more apparent.
The two most common conductor materials today are copper and silver. Is one inherently better than the other? Not necessarily. So much depends on the purity and treatment of the raw conductor material. The treatment process known as annealing softens and purifies the conductor material, affecting its specific resistivity. Proper annealing of copper conductors increases conductivity (lowers specific resistivity) by increasing the length and size of the crystals within the material. This results in fewer electrical discontinuities in the conductor, removing the distortion, brightness, or hashiness from the sound.
