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Subject: FAQ: rec.audio.* Wire 7/07 (part 8 of 13)
This article was archived around: 15 Jan 2009 06:01:56 GMT
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
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.
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: email@example.com
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.