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SUBJECTIVE RESONANCE

The Application of “Subjective Resonance” in the design of multiple diameter silver cables
By Dr R Bews

Within this paper I will discuss the concept of “Subjective Resonance” and its application in the design of audio cable using silver conductors of different diameters.

Subjective Resonance

Subjective resonance is a term that the author has invented to describe abnormalities that listeners appear to perceive when listening to reproduced music. Unfortunately the rudimentary test procedures currently performed on audio equipment are woefully inadequate in defining the subjective impression perceived by the listener. Essentially, the test results produced by the engineer DO NOT correlate with the listening experience. I am not saying that better and more sophisticated testing could not be employed to give us a better understanding of how we hear sounds within music. In fact the simple tests currently employed, probably give us a reasonable understanding of how we perceive simple CONTINOUS signals, unfortunately music is far more complicated. I urge the reader to consult papers on the subject of psycho-acoustic modelling of hearing, to get a better understanding of some of the interesting experiments that have been carried out to understand the physical nature of the hearing system. I can say with confidence that the test procedures and test equipment employed in the evaluation of audio equipment currently, have little relevance to the perceived quality of reproduced music, by an experience human listener. Therefore an alternative way to understand what we perceive sounds during a listening experience must be sort. The author proposes that it may be more convenient to evaluate equipment from the perspective of subjective evaluation, not engineering competence. Over the years it has become apparent that the Audiophile community have created a set of descriptions that describe the errors that are perceived when listening to music. Such words as: “bright”, “slow bass”, “clinical”, etc are regularly used. To formalise these subjective terms, it is proposed that all of these words and phases be viewed as different types of SUBECTIVE RESONANCE. The use of resonance is deliberate, since there is similarly to mechanical and electrical resonances. The subjective errors that occur during the reproduction of music can be described by a simple set of pseudo engineering terms: “frequency response” and “time response”. As an example, “slow bass” is really describing a mild irregularity in the subjective frequency response located in the lower frequencies, typically with a time response (impulse response) that extends in time for too long. This concept is not as far fetched as might first appear, since the most important part of the hearing system is the basilar membrane, located in the inner ear. The neural impulses received by the brain are produced by the hair cells on the basilar membrane. The basilar membrane is like a tuning fork, with many resonances. This occurs because the basilar membrane changes in cross sectional area as you proceed down its length. Therefore when a signal is received at its base, the signal then travels along the membrane physically exciting motion within the membrane. For a SINGLE excitation frequency, more motion will be seen at a particular region of the basilar membrane due to the physical stiffness in that region and the fact that a standing wave has been produced. This region of excitement occurs at different points along the basilar membrane determined by the excitation frequency. Essentially the thick stiff region of the basilar membrane is excited the most, by higher frequencies. As a consequence, the basilar membrane will perform a crude frequency analysis of any signal that is received by the ear. Timing information is also gathered, since the brain will know at what time various parts of the membrane are excited. Remember that this system is fairly crude from an engineering viewpoint, but human evolution has made it very sensitive to particular waveforms and waveform changes. So the human hearing system may appear to be very insensitive to particular types of lower order harmonic distortion, but quite sensitive to some transient distortions. Do not under-estimate the human hearing system, when it comes to complex signals, it has to be good at analysing these types of signals, since in past times, it is of great benefit for human survival to hear a lion in the long grass.

Application of Subjective Resonance in the design of audio cables

It is generally agreed by Audiophiles, that audio cables sound different because construction and materials employed in a particular cable differ so much. Although there is minimal or NO changes in the technical performance of well designed audio electronics, when different cables are used, consistent subjective characteristics of audio cables are observed. Which means that our test procedures are NOT sufficiently good enough to uncover the subjective problems exhibited by a simple piece of interconnect or loudspeaker wire. Remember that electronic engineers normally assume that our current set of test measurements are sufficient to describe an audio system. I however, do not believe this assertion, for two simple reasons: the test signals are dissimilar to music and the test equipment is very unlike the hearing system. I do believe, that if a better set of test signals was developed and the test equipment was designed to mimick the aural system better, NEW engineering characterisations of audio systems may be created to enable us to understand the subjective inaccuracies present.
Firstly, I suggest that an audio cable should be manufactured from very pure conductor materials, since over the years I have found empirical evidence that lower purity conductors seem to give rise to subjective deficiencies such as “grain” and loss of “transparency”. The construction geometry and dielectric properties chosen for a cable also have a big impact on the subjective behavior of an audio cable. I generally prefer continuous cast silver of at least 5 nines pure, however I do not believe purity of the silver (or copper) beyond  6 nines pure has any benefit. General experimentation (listening tests) shows that a given diameter of silver (or copper) produces  a subjective “frequency response” that is NOT flat across the whole aural frequency band of 20hz to 20kHz.  Unfortunately I have no technical explanation of why this appears to occur, except that the electromagnetic radial field structure (gives rise to skin effect) within the conductor when a current flows, may be responsible. Please refer  to some articles printed in Hifi News by Prof Malcolm Hawksford relating to the propagation of the Electromagnetic wave within transmission lines (cables), http://www.essex.ac.uk/ese/research/audio_lab/malcolms_publications.html section G9. The subjective “frequency response” of a single conductor appears to be a sharp bandpass filter, i.e. it has a peak at a defined frequency and rolls off either side of this frequency. The peak frequency (or center frequency) progressively lowers in frequency as the diameter increases. This is why certain diameters are chosen for single strand cables; i.e. for interconnect cable: 0.6mm diameter for copper and 0.9mm diameter for silver. I must emphasis that the dielectric surrounding the conductors, the material used for the outer jacket and exact crystal structure of the conductor, influence the sound as well. Through subjective evaluation, I have established that when many single strand conductors of the SAME diameter are put together to form a conventional multistrand cable. The subjective frequency response is widened relative to the frequency response of the single strand. This would suggest that multistrand cables are therefore more preferable to single strand cables, However, I have not talked about the subjective “time response” of single strand and  multistrand cables. Unfortunately, it appears that a single strand cable seems to “ring” at a particular frequency (related to its diameter) and has a fast decay. Whereas conventional mulistrand cables on the other hand, again “ring” at a particular frequency (related  to the diameter of the strands), but the ringing is much longer in duration. I believe that neither cable solution is correct, since the fast decay of single strands tends to lead to subjective comments: tight, fast sound, but not rich or warm. Whereas a multistand cable can often sound: warm, slow with  some smearing. I must point out that copper is much easier to work with, since its subjective “frequency response”  is wider than that of silver, for a comparable single strand conductor. That is why many silver cables appear to sound NOT quite right, sometimes they might be a little bright or coloured.
Over the past 7 years I have been experimenting with different diameters of silver, which form a multistrand conductor. Although this method has been tried with copper, e.g. Cardas, Van den Hul, and others, I believe that silver is better, because it possess better sonic purity and transparency compared to copper. Essentially the composition and number of different diameters of silver within the multistrand give rise to the overall subjective “frequency response” and “time response”. I suggest you think of each different diameter of silver as a bandpass filter, and the overall response is formed from the combination of each of the separate filters. The trick is to make sure that the overlapping between successive filters is correct, which subsequently dictates the exact diameter of each strand of silver chosen. As the experimentation progressed, it became apparent that the sound became better as the number of diameters increased, which dictated that the difference between each of the diameters reduced. This is a very labour intensive job, but now we have a formula to determine the size of each strand within the multistrand. If this experiment, only enabled the manufacture of neutral sounding cables, then really it would be a waste of time and money. But what seems to happen subjectively, as the number of strands increases, is that more detail is revealed in a very natural manner, because time smearing seems to be greatly reduced, so giving greater separation of instruments and vocals. At the present moment our best cable uses 23 strands of silver possessing 23 different diameters. I must point out at this point, that this theory may well be applicable to copper conductors, however the actual implementations will be very different, due to the fact that the “frequency response” and “time response” of single strand conductors of copper and silver differ widely.
In the design of our reference interconnect cable using different diameter of silver, the dielectric and outer jacket materials have NOT been discussed. These are very important considerations in the overall design of the cable. After many years of subjective evaluation, our top range silver interconnect cables utilize a silicon dielectric and polyethylene outer jacket.
 


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