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FAQ: rec.audio.* Wire 7/07 (part 8 of 13)

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Archive-name: AudioFAQ/part8
Last-modified: 2007/07/12
Version: 2.17

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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.

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: neidorff@ti.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.

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