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In Reply to: Interconnects and Cables in General posted by Gary Jacobson on April 26, 1999 at 23:33:54:

In response to your post on system configuration, there is no doubt that in theory, a long interconnect would be preferable. But the real world dictates otherwise in many cases, so many, that it would be difficult to state unequivocally that it is THE way to go.
The many exceptions are more prevalent than you might think. Besides tube preamps, and the others listed, many modern preamps do not have the capability to drive lonmg runs of interconnect. SO many of the integrated circuit based preamps will not drive anything but a 1-2M cable with good fidelity. This is because many of the IC's are unstable driving capacitvie loads that exceed several hundred pF. It is not just the output Z and the potential for HF roll off, but a matter of avboiding oscilitory and unstable behavior. Even using low capacitance cables, some preamps would not be capable of driving over 10 feet of interconnect cleanly.
In some cases, it may be possible to insert an additional series resistor of another hundred ohms or so, and alleviate this instability, without incurring too much in the way of HF roll off problems.
There are several op-amps (when used with the proper topology and designs) that can adeqautely drive more than a few hundred pF. The old standby 5532/34 can do OK, at least it does not completely lose it with a capacitive load. The OPA -2604 can handle a decent amount of capacitance, as can several others. many of the cheaper op-amps, or super high bandwidth ones may have problems driving UNTERMINATED capacitive loads. The super bandwidth op-amps originally designed for video use need a 75 ohm build-out AND 75 ohm termination in order to operate properly in the face of capacitive loading.
Some of the beefier preamps that have discrete output styages, and resemble a small power amp output (Bryston comes to mind readily), can not onlyu drive a capacitive load that would bring even acceptable IC based preamps to their knees, can also drive into a fairly low load. If yuou terminate the load end of an audio cable, you greatly reduce the effects of energy storage, and render the dielectric qualities less of an issue. This also brings up the sensitivity to the conductor purity and materials, but as long as it is bare copper or pure silver, this should not be as much of an issue, and the overall situation should be improved.
For something as hearty as the Brystonl a 600 ohm load resistor should do the trick, for 5532/34 or OPA-2604 based units, a 1K resistor should do the trick. Loading the input (load end of cable) should greatly reduce the effects of the dielectric. Those with the right gear, try it out, and see what you think. There is also a method of staggered loading involving capacitors, which is more suited for preamps with less drive capability, and I am experimenting with that.
I offer this incomplete note as a source for further discussion on the subject of cables. Enjoy

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Cable Esoterica
preliminary note 4-28-99 Jon M. Risch
Characteristic impedance vs. frequency
usually much higher at low audio frequencies, around 1000 ohms, dropping toward 75 ohms above 1 MHz, and still around 100-200 ohms at 20 kHz.
For those interested in a graph depicting this, see:
http://www.belden.com/products/ciocahalf.htm, almost at the end of the article.

Dielectric constant vs. frequency
More properly called a dielectric coefficient, the multiplier used to show the amplifying effect of the dielectric over the properties of a vacuum (or air). As an aside, it is important to note that this is truly an amplification of the capacitors charge, and as such, the dielectric material is acting as a charge amplifier. Many of the distortions that you can conceive of regarding power amps have their analog in the distorted amplification of the capacitors dielectric coefficient. Why make the distinction between dielectric coefficient and dielectric constant? Because many of the common dielectrics are not constant across the audio band.
For instance, PVC can vary from around 6.3 at 100 Hz, down to around 3.5 or 4 at 20 kHz. Polyethylene and teflon are constant across the audio band, at around 2.3 and 2.1 respectively.
Ready for a stunning revealation? The COLOR of the PVC will affect the dielectric coefficient! Black colored PVC is worse than white colored!
So when certain people try to make light of audio cable construction details and materials concerns, and they start talking about the color of the wire having an effect, well, litle do they know how true it is!
The proof for this is at:
http://www.belden.com/products/ciocahalf.htm, about half way down the page.
For more information on how the dielectric in a cable can be a problematic capacitor, see:
http://www.capacitors.com/pickcap/pickcap.htm
and for information on how dielectric absorption can affect signal pulses, see:
http://www.nsc.com/rap/Application/0,1570,28,00.html
ETP copper vs. OFHC copper
The most common conductor for audio cables is copper. While copper is a fine and cost effective material, it has it's problems. When cast, and drawn through a die, it tends to form more numerous and fragmented crystals, with lesser purity materials incuring more crystal formation. See:
http://microstructure.copper.org/coppers.htm
Note the differences between the OFHC copper, and the ETP coppers (you must take into account the scale factor of the various microphotographs, use a graphics program to resize and place the pictures on an equal footing before judging relative crystal sizes).
Note that the OFHC has crystals that are literally tens of times larger than the ETP copper. This means that there are less boundaries for the signal to pass through on it's way from one end of the wire to the other.
Some of the audio cable companies make claims for the purity or crystalline structure of their copper, with AudioQuest, TARA and Harmonic Tech being the prime examples.
Harmonic Technologies has microphtographs of OFHC vs. their OCC copper at:
http://www.harmonictech.com/techgraph.htm
Once again, the difference in the size and number of crystal domains is easily seen.
The effect of the signal having to jump many more crystal boundaries would not necessarily show up as a change in the DCR, or even the AC impedance, but might manifest as a grainy sonic signature, one that would be the difference between a completely silent and clear backdrop for the music, and one that was not as clearly defined and obvious.

Resonances
It might seem that physical resonance of an audio cable would not have any bearing on the signal passing through it. This just goes to show how single-minded some of us have become in our thinking processes. A cable is not an isolated electrical device, with only text-book perfect L, C and R to be concerend with. Nor is it only of concern what the proper model of these far from perfect LCR parameters will do to the signal as it passes through the cable. There are many aspects to be concerned with.
One of those aspects is the physical resonance behavior of the cable. How in the world can that affect the signal? Let's look at some basic physics. There is a basic property of electromagnetic fields, one that allows our generators and motors to function. The basic property is: whenever a conductor is moved through a magnetic field, a current will be generated in that conductor. The converse of that is whenever a current carrying conductor is inside a magnetic field, a physical force is generated on that conductor. These are the basic principles behind motors and generators.
How will these basic properties of electromagnetism affect an audio cable? Well, for one, all audio cables carry some amount of current. In the case of speaker cables, it can be many amps, in the case of interconnects, it will be on the order of milliamps. If the audio signal consisted of a pure DC signal, then there would be no issues to address. However, audio is a constantly changing signal, and the current flow is constantly changing.
What happens when you pass a transient through a speaker cable?
A current pulse is generated, and as the current flows through the speaker cable, a magnetic field is present also. Since the current is changing, the magnetic field is changing also. If we look at a single wire, carrying one half of the audio signal, it will be exposed to varying magnetic fields from it's own current flow, and therefore will have a current generated inside of itself that is related to those magnetic fields. This current is opposite in polarity and a mirror image of the original current. This phenomenon is due to Lenz's law, and can be considered to be the mechanism behind self-inductance.
Since the single wire has the magnetic field it generates centered on itself, the net result is that of no appreciable physical torque or force on the wire. In isolation, the only ill that occurs is an increasing resistance to higher frequencies, due to the self inductance. This a linear effect, and does not assume the proportions of gross signal distortion. While there is loss of high frequecies, in theory, they could be restored via EQ or a complementary response tone control.
The problem occurs because we have two wires that are in close proximity, and they are carrying current in opposite directions. This causes a force to be developed that is pulling the two wires together. You might think that since the wires are covered in some sort of insulator, and may even be bonded together, or at the least, they are contained within a common jacket, that they would not be able to move at all. This would be true if either of two things were true:
if the cables were infinitely heavy, the sheer inertia would prevent them from moving, or if the cable materials were all infinitely rigid, then the two conductors could not move. If you have ever picked up a speaker cable, then the first item is not true, and if you have ever felt a speaker cable, then you know that often, very flexible materials are used in the construction of the cable. For zip cords, soft pliable vinyl is used, and for other constructions, the two wires may not even be twisted around one another, or bonded, such as with Romex.
Hence, even the most esoteric cables have the potential to move in reaction to a musical transient, and to generate a false signal is response to that transient. The false signal will be delayed in time, due to the mass and stifness of the cable conductors, and the stifness of the cable insulators, but there will be some minute amount of movement, that will generate a small signal. This is where the cables physical resonance will come into play. If a cable has a tendency to resonate physically, when the cable assembly is excited by a musical transient, it will be as if the cable wires were plucked and the physical resonace will now determine to some extent how the false signal will develop and how long it will continue past the transient. The false signal caused by the relative movement of the cable conductors will definitely have the resonant signature of the cable superimposed upon upon it, and this will further color and make noticable the false signal.
This motor/generator action within the cable is commonly refered to as magnetostriction. This is not exactly correct, as magnetostriction is the change in size of a material itself in response to a magnetic field, but it does describe what is happening within the cable as a system. Several cable companies go to great pains over cable resonance. Kimber uses different sized wire strands in its braided cables, and Cardas has a patent on using different sized wires, in a ratio known as Phi, to spread any tendency for the wires to want to resonate at the same frequency. Some motion or vibration inside the cable is inevitable, so why not make it as harmless as possible? Other cable companies also refer to resonance control or vibration control, with regard to the RCA plugs, the cable itself, or the cable assembly as a whole.
There is also the factor of the sound vibrations from the speakers themselves, moving the cable wires as they carry current. These vibrations are further delayed compared to the delayed vibrations from the signal the cable is carrying, as they had to travel through then air, and at a speed of approx. 1 mS for every 13 inches of travel, the delay is quite a bit greater than that of the physical inertia and resonance of the cable assembly. It is also likely that these false signals will be on the bass heavy side, as it is the bass which will be moving the cables the most, even more so than for the magnetostriction action.
The signals produced by these vibrations and current pulses are not up around the nominal signal level, they are down as much as 60 dB or so. This may sound like these false signals will be too far down to hear, or that they would be masked by the original signal. IF they were all occuring at the exact same time as the original signal, and IF they were ocuring one at a time, then this might be true. However, from my research into multitone test signals, which are more like music with it's complex harmonies and harmonic structures, I have found that when there are many distortion products occuring at the same time, the total amount of distortion is raised considerably. If there are 10 distortion products all at about the same levels, then the total level is 10 dB above the individual distortion products. For 100 products, the overall level is up 20 dB. This raises the effectivity of the motor/generator distortion to levels that are not as low as they might seem initially. The other factor is the amount of time delay, actually two distinct and separate amounts of time delay, that will cause transient signals to have delayed false signals. Once the false signals are not right underneath the original signals in the time domain, they are capable of a much easier exposure in terms of audibility.
So cable resonances are indeed a possible factor, and I think that anyone who has experimented with vibration control can relate to the kinds of improvements that can accrue. It would be relatively easy to place sand bags under and on top of the interconnects and speaker cables in most home systems to give it a listen, and see what you might hear from such an experiment.
Skin Effect
http://www.csolve.net/~add/system/trcskin.htm
Cable References, a non-ABX oriented listing.

Ben Duncan, Loudspeaker cables, Case Proven, Proc. The Institute of Acoustics, UK, Nov '95.
Also published in Studio Sound & Broadcast Engineering (UK); and Stereophile (USA) - both Dec 95.
Ben Duncan, Modelling cable, Electronics World (UK), Feb 96.
Ben Duncan, Measuring speaker cable differences, Electronics World (UK), June/July '96.
Ben Duncan, Black Box (column), Hi-Fi News & Record Review (UK), June & July '96.
Malcolm Omar, Mawksford, The Essex Echo, Hi-Fi News, Aug '85; Aug & Oct '86 & Feb '87. Reprinted in Stereophile.

For cheap decent RCA plugs;
http://www.apature.com/connectors.html
See "14PP"
Jon Risch

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Follow Ups Full Thread

Topic - Interconnects and Cables in General - Gary Jacobson 23:33:54 04/26/99 (3)

Long and partially unrelated reply - Jon Risch 20:13:11 04/28/99 (0)

Re: Interconnects and Cables in General - Rod M 08:42:15 04/27/99 (1)

Re: Interconnects and Cables in General - Gary Jacobson 04:54:36 04/28/99 (0)

Follow Ups

Long and partially unrelated reply - Jon Risch 20:13:11 04/28/99 (0)

You can not post to an archived thread.