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Reviewers: Marja Vanderloo & Henk Boot
Sources: Acoustic Signature Mambo, Acoustic Signature Final Tool MkII, Kuzma Stogi, Benz Micro Glider [all in for review], CEC TL5100, Metronome Kalista [in for review], Hifidelio Pro 160/Olive Symphony music server [in for review], Philips DVP 5500S SACD/DVD player
Preamp/integrated: Acoustic Signature Tango phonostage [in for review[, Greatech MuVac 1-watt integrated [in for review], TacT RCS 2.0 room control system; modified Audio Note Meishuwith AVVT, JJ or KR Audio 300B output tubes
Speakers: Avantgarde Acoustic Duo internally wired with silver; Avantgarde Acoustic Solo; Audio Note AN/Jsp silver-wired
Cables: Audio Note AN/Vx interconnects; Siltech Paris interconnects; Gizmo silver interconnect; Qunex 75 reference interconnect; Crystal Cable CrystalConnect Reference interconnect, CrystalDigit S/PDIF RCA/RCA and RCA/BNC, Y-cable, Crystal Cable Piccolo iPod to XLR, CrystalPower Reference AC-Eur/IEC; CrystalSpeak Reference, Audio Note AN-L, Gizmo silver LS cable.
Power line conditioning: Omtec PowerControllers, PS Audio P1000 [in for review]
Sundry accessoires: IAR carbon CD damper; Denson demagnetizer CD; Nespa #1; TacT RCS calibrated microphone and software; Exact Audio Copy software; Compaq server w/Windows Server 2003 and XP; wood, brass and aluminum cones and pyramids; Xitel surround processor; Manley Skipjack.
Room treatment: complete set of Acoustic System Resonators; Gizmo's Harley Davidson cap
Review Component Retail: 300 - 6000 euros
|Assembling a satisfying audio system is no easy task. After a thorough background check based on reviews in various audio print and web 'zines like 6moons, one visits a dealer for a personal listening session. In many cases, even a visit to an audio show can be helpful to identify prospective components. Finally the hard choice is made and the various kit all stacks up neatly in a rack ready to rock. Alas, before music can fill the room, these components need to all be connected - via power cords to the grid, with speaker cables and interconnects between each other.
Contrary to components where technical specifications can give an indication of expected behavior, cable specifications cannot. Each and every cable sounds different. Worse yet, the same cable sounds different when used in combination with other equipment, even if just a single component were changed. Any skeptic better follow this link and enjoy his or her zip cord or lamp wire.
Wire is wire, cable is cable. Too bad this statement is invalid. It's all the more reason to dive into this matter a little deeper and attempt to understand what factors contribute to these audible if not always measurable differences.
Cables -- and thus the species of interconnects we shall focus on in our listening tests here -- are all susceptible to the laws of nature. This is where electrical, magnetic and mechanical values play their roles. Most of the time, an interconnect consists of a pair of cables where each leg handles a discrete channel. The need for both legs to be absolutely identical should be evident.
|The only thing an interested layperson ever sees of an interconnect cable is its outside. Every supplier dresses -- or better yet, cloaks -- their cables in the most beautiful or at least most impressive looking mantles. The ends are terminated in various RCA or XLR plugs whose insides are often potted. The remaining available observation concerns the girth of the cable. This can range from just a millimeter to several centimeters. What is going on inside the fancy cable cover remains a closed book (safe for a few makes who publish cross-sectional graphics or photographs). As far as we know, there has never been a review written wherein the reviewer followed CSI and performed a cable autopsy to study the innards. [Corey Greenberg's infamous hacksaw job on an MIT terminator box comes to mind as a singular attempt to pry into some of these secrets - Ed.]
Suppose we performed an autopsy on an arbitrary cable. The following is what we can expect to see. Our first cut is lengthwise to open the outer mantle. Depending on the type of cable, we might reveal a shield or the so-called dielectric, the electrical insulation material. If a shield, it could be a wire mesh or foil. Examples of the former are coaxial cables like digital interlinks or cable TV leads. Beneath the shield, we should expect dielectric. We say "should" - every cable maker uses a different recipe.
The next cut we make to our cable victim -- still no blood yet -- exposes the actual conductors. At this level inside a cable's guts, we should expect a variety of geometries. Forget standardized guidebooks or golden rules. Most conductors are made of a metal like aluminum, copper, silver, gold and palladium or a combination thereof which could be alloys (molecular mixes) or discrete layers (plating or cladding). No matter what we find, all metals exhibit clearly defined electric properties when it comes to electrical conductivity.
Upon taking a closer look at these conductors, we may find a single tiny wire or a bundle of complexly twisted, braided, layered, bundled or otherwise interwoven wires or wire groups wherein each conductor could be individually coated with insulation (Litz). We might find thousands of individual conductors in fact. At this level, anarchy rules and any imaginable geometry could be revealed.
To get a better insight into the actual geometry at hand, our next cut is crosswise. Now we might find an exquisite pattern resembling a picture made by the kind of spirographical tool once -- or perhaps still -- popular. Too bad so many manufacturers hide this beautiful aspect of their work and do not show it off with pride. One reason to play coy is of course the ever-alert competition and piracy.
|All in all, our post-mortem provided a complete insight into what hides beneath a cable's outer mantle. Now we take a look at the physical properties of the inner materials beneath the jacket. Let's begin with the conductor. The moment a conductor carrier an electrical current, it interacts with its environment. That environment could be the dielectric or an adjacent conductor. That magnitude of influence is reciprocally related to distance. Every material we come across here has a specific resistance expressed in ohm per meter (or foot). Besides resistance, a conductor also exhibits magnetic permeability. This relates to its capacity to conduct a magnetic field. Then we have to mention the relative dielectric constant, a property of the insulating material surrounding the conductor. Our three key physical properties are collected in the following table for some of the most popular materials we're likely to find in the construction of a common interconnect.
The resistance of a cable is dependent on the diameter of the aggregate conductor, conductor surface area and cable length. It should be clear that the thicker and longer the wire -- i.e. the larger its surface -- the lower the resistance; the thinner and shorter the wire, the higher its resistance. For ordinary plain copper, a length of 5 meters with a surface area of 0.5mm² works out to a resistance of 0.35 ohm. The same length with a surface of 4mm² exhibits a resistance of 0.045 ohm instead.
One effect of the magnetic field around a signal-carrying conductor is that at higher frequencies, more current will travel on the outside/surface of the conductor. This effect is aptly called skin effect and dependent on the specific resistance and magnetic permeability of the conductor at hand. Skin effect increases with rising frequency and wire diameter - the thicker the conductor, the higher the skin effect. In a 2mm thick wire, the skin effect will be noticeable only from above 10KHz. Even in thinner wire, the effect is still not entirely absent. Higher frequencies travel on the conductor surface and are thus influenced by conductor diameter. This also influences impedance.
Then there's capacitance which, in an interconnect, is responsible for the frequency-dependent resistance of the cable. Rising frequency equates to lowered resistance. Higher capacitance incurs premature HF rolloff. Capacitance should really be thought of as reactance since an audio signal is an alternating current.
A cable's capacitance is strongly dependent on the source and load impedance of the connected components. More on that later. A way to keep cable capacitance low is to use either very thick insulation or very thin conductor but the latter might result in increased self-induction and resistance.
Self-induction is the phenomenon whereby a current propagating through a conductor creates a magnetic field, which in turn generates a counter current in the conductor. A thicker conductor will lower self-inductance but raise cable capacitance.
Cable impedance is primarily of concern in digital interconnects where RCA/BNC terminations rely on exact 75-ohm impedance, AES/EBU variants on 110 ohms. Impedance offsets in such applications incur unwanted signal reflections inside the cable.
From our cursory overview of primary cable variables and electrical values, you might think that a great-sounding cable should be easy to make. Simply make sure your cable has low resistance by picking just the right conductor diameter. Use highly resistive dielectric and don't be stingy on insulation thickness. Not only does it make the cable appear more audiophile, it's better for its capacitance. Stick the whole affair inside a fancy jacket, terminate with your conductors of choice and proudly silk-screen your name anywhere you choose.