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Subject: FAQ: rec.audio.* Wire 2/99 (part 8 of 13)
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Summary: Answers to common questions about audio equipment, selecting,
  buying, set-up, tuning, use, repair, developments, and philosophy.
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Archive-name: AudioFAQ/part8
Last-modified: 2000/4/12
Version: 2.15

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 experimental, double-blind sense)
    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 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). Try to arrange it so you can trial such cables; at
    several hundred dollars per set, experiments can be expensive.

    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 operate at very low impedances, so that 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 are very good speaker
    terminals.  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.

COPYRIGHT NOTICE
The information contained here is collectively copyrighted by the
authors. The right to reproduce this is hereby given, provided it is
copied intact, with the text of sections 1 through 8, inclusive.
However, the authors explicitly prohibit selling this document, any
of its parts, or any document which contains parts of this document.

--
Bob Neidorff; Texas Instruments     |  Internet: [e-mail]
50 Phillippe Cote St.               |  Voice   : (US) 603-222-8541
Manchester, NH  03101 USA

Note: Texas Instruments has openings for Analog and Mixed
Signal Design Engineers in Manchester, New Hampshire.  If
interested, please send resume in confidence to address above.