15.0 Wire
        More than any other topic, speaker cables and equipment
        interconnects seem to use up rec.audio.* bandwidth echoing
        the same theoretical arguments, testimonials, and opinions.  
        Controversy can be stimulating, educational, and also amusing.  
        Please try to keep postings aimed at one of those three goals,
        and avoid the insults and emotion.  Also, try to avoid
        echoing a common position or principle, as described below.

15.1 Do speaker cables matter?
        To avoid confusion and repetition, here is some terminology,
        thanks to Steve Lampen of Belden Wire & Cable Co.

        A wire is a single conductor made up of one or more conducting
        elements, but all configured (as in a stranded design) to act
        as a single conductor.  Mostly, this is coated or covered by
        plastic, rubber, enamel or similar insulators.

        Groups of wires are called cables.  So zip cord is a cable,
        because it contains more than one insulated conducting
        element.  Coaxial cable is also cable.

        Cables can introduce noise into the signal, act as a filter
        (and thus change the frequency response of the system),
        attenuate the signal (change the amplitude), and provide
        nonlinearities from oxidized or otherwise poor connections.
        Nonlinearities can distort the signal which add harmonics.
        Nonlinearities can also rectify or demodulate higher frequency
        signals into audible signals.

        It is quite scientifically conceivable that some cables do
        cause a difference in sound, because of the differences in DC
        resistance, interconductor capacitance, and connector attachment
        alone.  The effects of exotic conductor weaving and materials
        are not so well established.  In general, these effects (once
        we eliminate DC resistance), seem to be small. However, if your
        system is at least fairly good, then some folks have observed
        (although not in an objective, double-blind experiment)
        significant differences in system performance with different
        cables. The effects are said to be quite system specific; the
        only real guideline is to try them and see which ones seem to
        sound better to you, in your system.

        Roughly speaking, the price ranges for speaker cables is low
        (under $1/ft), medium (under $6-8/ft), and high (up to $100/ft
        and more).  Experiments can be expensive, so don't commit your
        money unless the seller has a practical money-back guarantee.

        In any system or experiment, it is essential that the
        differences between cables be separated from the
        differences between connectors.

        You should have an EXTREMELY solid connection between cable and
        speaker.  Speakers carry high peak currents, so bad connections
        will create significant artifacts or signal losses at any power
        level.  For example, if the connection has a linear resistance
        of just 1 ohm, the speaker damping factor may be changed, and
        the bass may suffer. If the connection contains imperfect metal
        oxides, then a slightly rectifying junction will block the signal,
        producing compression, distortion, and other non-linear effects.

        There are many magazine articles on cables with various
        perspectives which are worth reading, including:
                "Speaker Cables: Testing for Audibility"
                        Fred E. Davis
                        Audio, July 1993, pgs. 34-43

15.2 What speaker cables are available and how good are they?
        There is a wide range of speaker wire available, ranging from
        30ga zip cord (~$.10/ft) to exotic wires costing over $300/ft.
        The material used ranges from copper to oxygen-free copper
        (OFC) to silver. (There are a bunch of others as well.)

        Oxygen-free copper is probably NOT any different from common
        copper in sound.  If you hear a difference between two cables,
        it is not a difference between oxygen-free and common copper.

        Resistance may be significant for speaker cables.  The higher
        the resistance, the more the cable will affect the sound, all
        else equal.  The resistance characteristic of metals is called
        resistivity.  The resistivity of copper is 1.7 microohm-cm.
        Silver is very slightly lower, 1.6.  Gold is a bit higher, 2.4.

        Silver and gold are different from copper in other ways than
        resistivity.  Gold does not oxidize in normal environments,
        so gold contacts will not need periodic cleaning and will not
        create rectifying junctions.  Silver will oxidize, but the
        oxide of silver is conductive, so oxidized silver will still
        make good contact.  Copper oxide is a bad conductor.  Oxidized
        copper contacts may insulate, may conduct, or may rectify.
        Copper is a bad material for cable terminals, but this may or
        may not mean anything for the conductor itself.

15.3 What can I use for budget speaker cables?
        First, a few words on terminology.  Wire is sized by AWG or BS
        gauge number.  Larger numbers represent smaller wire.  AWG 40
        (also called 40 gauge) is as fine as human hair.  AWG 12 is 2mm
        or .081" diameter.  If you reduce the AWG number by 3 (such as
        from 29 to 26) then the wire cross-sectional area increases by
        a factor of 2 and the series resistance drops by a factor of 2.

        Some wire is classified as solid, because it contains one
        strand per conductor.  Other wire is called stranded, because
        it consists of many strands per conductor.  Stranded wire is
        far more flexible than solid wire.  Most wire is made from
        drawn copper.  Some wire is sold that is claimed to be made
        with a process that produces oxygen-free copper.  Oxygen-free
        copper has a different metallurgical structure than common
        copper and may or may not conduct current better.

        Some critical listeners have reported excellent sound from large
        diameter solid copper wire, such as home wiring "Romex 12-2".
        At least one expert has said that common 18-gauge solid copper
        hook-up wire sold by Radio Shack also works very well.  Also
        recommended on a budget is Sound King wire, a 12 gauge oxygen
        free copper stranded cable.  This is available from MCM
        Electronics for $.39/ft.

        Scientifically, thinner wire has more resistance than fatter
        wire, so fatter wire will have less resistance-related effects.
        Resistance effects can be eliminated by using at least 12
        gauge wire, particularly for long runs.  Of course, shorter
        runs are always preferred, because they come much closer to
        the ideal zero-length wire, with no resistance, no
        capacitance, no inductance, and no change in signal.

15.4 What can I use for budget speaker connectors?
        The worst connectors are push-down, or spring terminals.  Screw
        terminals with solid copper wire are much better.  Gold-plated
        binding posts and gold spade lugs are inexpensive by audiophile
        standards and are extremely stable.  Binding posts with spade
        lugs can be tightened to get a very good mechanical joint, and
        may offer the lowest electrical resistance of any connector.

        Gold plated banana plugs and jacks can be very good speaker
        terminals, depending on construction.  Some banana plugs
        have weak springs and fall out rather than staying in place.
        Good ones are more expensive than gold spade lugs, however, they
        also provide a bigger area of contact, and are more convenient
        when you must frequently reconfigure the system.  Banana plugs
        should be periodically monitored for corrosion and loss of
        spring tension.  Monster offers a banana-plug connector with
        an expanding center pin that forms an even better connection
        than common gold banana plugs.  At approximately $25 per pair,
        the Monster banana plugs aren't a budget connector.

        All else equal, connectors with gold surfaces are better than
        connectors with any other surface.  This is for two reasons.  
        First, gold is extremely inert, meaning that unless gold is
        exposed to very harsh chemicals or harsh vapors, it will not
        corrode or oxidize.  It will remain a pure, low-resistance
        conductor.  Second, gold is quite soft, so that if a
        gold-plated connector is squeezed between two metal
        surfaces, it will deform slightly to fill scratches and
        voids, giving a very broad, low-resistance contact area.

        Corrosion of connectors is often a problem.  Gold-plated
        terminals and connectors somewhat avoid this problem;
        problems with other connectors can be mitigated by
        unplugging and replugging the connector on a regular basis,
        cleaning the contact areas with a pencil eraser, or by
        using a contact enhancer such as Cramolin or Tweek.  When
        you use a contact enhancer, be very sure to follow the
        directions, and avoid spreading enhancer about your equipment.

15.5 What about interconnects, such as the cable between tuner and amp?
        Line-level interconnects conduct smaller signals than speaker
        cables; the typical signal ranges from -2V to +2V (the CD
        output standard) with currents in the microamps (the
        corresponding values for speaker cables attached to a largish
        power amp might be -70V to +70V and currents of many amps).  
        Line-level interconnects can be divided into single-ended (or
        unbalanced), and balanced interconnects.  Home audio is almost
        always single-ended interconnects.

        Single-ended interconnects almost always use a form of the
        RCA connector (or phono plug). RCA plugs form fair to poor
        connections that degrade with time as corrosion works into the
        metal-metal contact and as the spring tension of the connectors
        relax.  Gold-plating reduces the effect of corrosion and locking
        RCA connectors solve most of the mechanical problems.  However,
        these premium phono connectors are rare and expensive.  For
        example, a gold-plated Vampire locking RCA plug costs
        approximately $23/pair.  If RCA connectors weren't a de facto
        standard, we'd recommend against them.

        Unbalanced interconnect wires vary in geometry, material and
        price.  Cheaper wires have a single conductor (normally
        stranded) and a shield and cost $.20-$2/ft. Medium (complexity
        and price) wires have two conductors (often arranged as a
        twisted pair) surrounded by a shield and cost from about
        $3-$20/ft.  Exotic wires have all sorts of geometries and
        materials (such as stranded silver conductors, or ribbon cable
        braided around a core, or in one extreme case, a tube filled
        with mercury!).  Prices may be as high as $200-$300/ft.

        Balanced interconnects have three conductors: two for the signal
        one for ground, and additionally a shield.  The standard
        connector for balanced cable is the ITT/Cannon XLR connector,
        which is quite good mechanically (they lock).  Equivalent
        connectors are also available from Switchcraft, Neutrik, and
        other vendors.  If you have to run cables longer than 12 feet or
        4 meters, the greater noise immunity of balanced interconnects
        is often a good idea. For this reason, balanced connectors are
        standard equipment in professional installations such as
        studios, public address systems, and broadcast stations.  There
        is not much variation in balanced cables.  The three brands
        mentioned above are known to be rugged, high quality and
        moderately priced. Slightly weaker imported connectors are
        available, but they aren't dramatically cheaper. Better
        connectors are also easier to assemble and have a more durable
        cord strain-relief.

        For most systems, the most important aspect of a cable are
        the mechanical reliability of the connectors; in particular,
        the joint between connector and wire, and the joint between
        connector and socket. Typically, interconnect cables are
        short.  It is worth getting just the right length; cables
        often come in .5 meter increments.  With quite good systems,
        some people observe differences in sound between various
        interconnects. This is quite system-specific and the same
        advice as given above applies: try several brands.  Most
        good dealers will loan interconnects for home evaluation.

        In cables where the shield does not carry the signal or ground,
        the shield is normally only connected to ground at one end.
        In systems where there are significant differences between
        ground levels on various components, it may make a difference
        which way such cables are connected.  Typically, the end where
        the shield is grounded should be at the source of the signal.  
        Often, such cable has arrows on it pointing in the direction of
        the signal flow.  In any case, try both orientations.

        There are many objective reasons why cables might cause
        differences in sound by interacting with the drivers in the
        signal sources as well as by providing non-linear effects in the
        RCA connector.  Most of these effects are again related to
        interconductor capacitance and resistance, and the quality of
        the shielding provided by the "shield" conductor.  In balanced
        cables the quality of the "twisted pair" inside the shield is
        also important.  One might note that a shield protects from only
        capacitively coupled interference, and not from any magnetic
        field interference.  The twisted pair in a balanced line provide
        some magnetic rejection, as does steel conduit.  However, steel
        conduit has other characteristics which make it undesirable for
        audio in general.

15.6 What about Phono Interconnects:
        Phono interconnects are part of the link between a cartridge on
        a turntable and a preamp (or head amp or receiver). They are a
        special case of line-level interconnects because the signal is
        much lower, typically 1 to 50 millivolts.  They are also
        intended to operate into a higher impedance, typically 47K ohms,
        and form part of the capacitive load for the cartridge.

        The low signal levels mean that the shielding of the cable, and
        the presence of a separate drain/shield are more important, as
        is a good ground.  A separate solid ground should come along
        with the cable as a separate lead co-routed with the cable.

        In addition, the low signal levels make a good solid connection
        to and through the connectors MUCH more important, because of
        the greater sensitivity to low-level nonlinearities.

        Wire capacitance is often ignored in line-level interconnects;
        however, in a phono interconnect, it may constitute half of the
        total capacitive load of the cartridge. Obviously, then, two
        cables with significantly different capacitances should sound
        differently.  In this sense, the "right" cable for one cartridge
        may be too low or high in capacitance for another cartridge.

        For low-impedance cartridges (most moving coil cartridges),
        the wire must have low resistance to prevent cartridge unloading
        and frequency-dependent signal loss. In addition, as the
        signal levels are quite low, shielding is important.

        Unfortunately, copper shields do not block stray magnetic
        fields, so in the case of phono cables, careful routing may be
        even more effective at reducing hum than special wire.

15.7 Is there really a difference in digital interconnects?
        There are now three kinds of digital interconnects that connect
        transports to D/A converters: coax, plastic fiber (Toslink) and
        glass fiber (AT&T ST).  In theory, these should sound EXACTLY
        the same (bits are bits).  However, this assumes good circuit
        design (in particular, the clock recovery circuits of the DAC,
        and careful consideration of electronic noise) which may be
        compromised because of cost considerations or ignorance.  Note:
        different signaling schemes are used on plastic and glass fiber.

        In any case, some people claim to hear a difference;
        of those who do, most seem to prefer the glass fiber.  
        However, the technology of fast digital data transmission
        in consumer electronics is evolving very quickly now.  
        Any specific recommendation should be treated with
        suspicion until the industry matures.

15.8 Can I make very good interconnects myself?
        Yes.  You will need to be the judge of whether or not they
        are as good as $100 interconnects, but it is easy to make
        interconnects that are better than the $2.00 set which comes
        with new equipment.

        There are two necessary ingredients: two-conductor shielded
        cable and RCA connectors.  There is a lot of debate over what
        is the best cable, but in general, the lower the capacitance
        per foot, the better.  Choice of insulation is harder.  There
        may be an advantage to polypropylene or teflon over polyester
        or rubber, but even that is debatable.  If you are buying wire
        from an electronics distributor, some have successfully used
        Belden 1192A microphone cable.  It is rubber insulated, so very
        flexible.  Another recommended cable is Belden 8451.  This is
        a polypropylene cable with foil shield.  Finally, consider
        Belden 89182.  This is foamed teflon insulated, so very low
        capacitance, and foil shielded.  If you plan to make a long
        cable, this low capacitance cable may be the best choice.

        There is also a variety of RCA connectors available.  A
        good connector would be gold plated and machined to tight
        tolerances.  A poorer connector will not fit as well, will
        make poorer contact as the connecting surface oxides, and
        will lose its springiness with use.  

        When wiring the cable to the connector, use one wire for
        signal, (the tip of the RCA connector) and one wire for
        ground (the shell or outer conductor of the RCA connector).  

        Some cables use a foil shield which is difficult to solder.  
        These cables typically have a drain wire parallel to the foil
        which can be used for soldering.  Others use a braided shield.

        Regardless of which type of wire you have, connect the shield
        or the shield drain wire to ground on only ONE SIDE.  This will
        stop noise picked up by the shield from causing ground noise.

        It can be a touchy job soldering RCA connectors.  Before
        you use your new cables, check with an ohmmeter or
        a continuity tester to make sure that you have not
        accidentally sorted the signal and ground leads together,
        either with a stray drop of solder or a loose wire strand.

15.9 Is there a standard for wiring balanced XLR-3 cables?
        Yes.  Connect pin 1 to ground/green, pin 2 to white, and
        pin 3 to black.  Herb Hamilton suggests that you remember
        "George Washington Bridge" and then use the first letter
        of each word (GWB) to help you remember Green=1, White=2,
        and Black=3.  This same wiring convention works for
        balanced line level signals and balanced microphone cables.

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--
Bob Neidorff; Texas Instruments     |  Internet: neido...@ti.com
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