Rule 8 - Connecting cables
Select and integrate audiophile-quality connecting cables
The integrity of an audio signal is dependent on the quality of the connecting cables. Therefore, they should be carefully chosen to carry the delicate signal along the pathway with absolute fidelity beginning from its source to the loudspeakers.
The lifeblood of an audio system
All electrical cables have electrical properties that would interact with their source and load thereby making them somewhat reactive to the host equipment. An audio cable is characterized by its impedance and the velocity of signal propagation. Therefore, a cable cannot be said to be a passive actor in this respect. Though sonic differences between well-designed and quality cables are generally subtle, suffice it to say, for high-resolution audio playback every little nuance matters. The different shades of grey in music are what every audiophile can distinguish and appreciate.
Burdens of a cable
Connecting cables may include analog signal interconnects, digital cable interfaces, and loudspeaker cables, i.e., any conduit that carries an audio or digital signal. The cable must be a transporter and it needs to do this quickly, without carrying excessive baggage (‘noise’ in the case of analog and ‘jitter’ in the case of digital). Moreover, it needs to ensure that it does not lose or contaminate any of the cargo that it is supposed to haul. The output properties of the source, the properties of the cable, and the input properties of the host component or loudspeaker together as a whole would determine the eventual voice of the system.
Problems with cables
When subjected to mechanical force i.e., sharp bends or kinks witting or unwittingly made may alter the electrical properties of a cable causing it to behave differently.
If the environment is prone to RF or EMI interferences, a single-ended interconnect, poorly shielded cables or a loudspeaker cable becomes vulnerable to the threat.
If a loudspeaker cable has too much twisting or is coiled into a bundle, it will create a magnetic field around them that may cause certain amplifiers to oscillate.
Long runs of a small gauge loudspeaker cable may overheat and have more resistance causing signal drop and distortion when used with a high-current amplifier. That means cable resistance affects signal transfer.
The copper or silver conductors in cables may oxidize over time and introduce distortion adding more cable resistance and poor conductance.
A digital interface cable requiring a 75ohm connector should also see a 75ohm cable, otherwise, there would be bandwidth limitations.
If the loudspeaker cable is coiled when in use, and if it's too long, will cause a drop in the output, the lower the impedance at the load the greater the drop. The worry is that the losses may affect the frequency response of the signal arriving at the load which should ideally remain linear.
It is said that some older amplifiers rely on the loudspeaker cable’s inductance properties to remain stable.
DC Resistance – A high-resistance cable will oppose the flow of current, the higher the resistance the more it will resist current flow. This behavior is not frequency dependent; therefore, possible signal losses affect all frequencies. Loudspeaker cables should have a minimum size of 14-gauge especially when running amplifiers with high-current demand as there may be 20-30 amps gushing through the cable in some instances. As the loudspeaker’s impedance drops, a heavier gauge wire is needed to prevent degradation of the damping factor (a measure of the amplifier's control over the position of the voice coil). A commonly held view is that a loudspeaker cable will start to have an audible effect (depending on the hearing ability of the listener) when the resistance of the cable reaches about 5% of the loudspeaker’s impedance, yet others like loudspeaker designer Harley Lovegrove believe that it should not be more than 1%.
Note: The American Wire Gauge (AWG) uses a numbering system where a smaller number is a larger wire size with more conductors. Conversely, a larger number is used for a smaller wire size with fewer conductors
Inductance – This describes the amount of energy stored in a magnetic field. For example, a coiled wire such as the ones found in a loudspeaker crossover has inductance properties that are used as an ‘equalizer’ to filter certain frequencies that run through it. Parallel cables have certain inductance properties. Too much inductance will cause a cable to experience high-frequency losses.
Capacitance – This describes the ability of a cable to hold an electrical charge (stored energy). As the frequency increases the capacitance goes down, too much capacitance introduces low-frequency losses (however, the short runs in audio may not be an issue here). A cable’s shield increases the capacitance of a cable.
Other cable characteristics
Skin effect – High-Frequencies that travel through the conductors tend to migrate on the outside perimeter of the conductor. Low frequencies instead travel within the center core. Skin effect is contingent on the thickness of a cable, the thicker the greater the effect. Therefore, a solid core cable design may alleviate this problem. It is said that another solution to reduce the skin effect is to plate the copper strands with silver – because silver has lesser resistance.
Insulator – This is the casing that surrounds the conductor. Many materials are used as an insulator with a characteristic called the die-electric constant. The die-electric constant is a measure of the Velocity of Propagation (VOP) i.e., the speed at which the signal travels through the cable. PVC material used in cheap cables has a VOP of 5 (55%), whereas, PE (Polyethylene) has a VOP of 2.5 (65%), and PTFE (Teflon) has a VOP of 2.1 (70%). An insulator with a lower die-electric constant is said to be a more efficient transporter for an audio signal.
Conductor Quality
There are different materials used as conductors such as copper, silver, silver plated, rhodium plating and carbon, etc. The best high-end audio conductors readily available would-be pure silver followed by pure copper for their superior conductivity. Plating such as Rhodium is tonally neutral as compared to gold or silver and it does resist corrosion better than silver plating. Rhodium is a good conductor of electricity but not as good as copper, gold, or silver. Gold is too expensive and not practical for audio use; Silver is price prohibitive; therefore, copper becomes the conductor of choice for the mainstream audiophile community. However, copper will eventually oxidize and coat the surface with a thin layer of copper oxide creating a high resistance barrier where the connection takes place. It is said that the more ‘air space’ available inside the copper, the more susceptible the copper is to oxidation whose impurities interfere with the signal flow.
Pure silver has the lowest DC resistance than copper and may therefore be used in relatively smaller gauges. It’s a commonly held belief among audiophiles that pure silver sounds a little aggressive at the top end. I think this may be due to the silver oxide formed in between the silver grains, similarly silver-plated copper also suffers from oxide forming between the silver plate and the copper. Pure silver cables are significantly more expensive than pure copper cables even one with a lower gauge. Copper cables come in different grades making it abundantly clear that sound quality is related to the purity of copper. Oxygen-free copper (OFC) has a higher conductivity index with almost no crystal boundaries, it is said that an audio signal is no longer impeded by impurities while moving down the copper stream with potentially more speed and information delivery integrity.
Copper grades
Oxygen-Free Copper (OFC) – Developed in Japan around 1975, OFC is produced through an extrusion process that takes place in an oxygen-free-inert-gas atmosphere which leads to the reduced oxygen content in the copper that is 99.99% pure (aka 4N) thereby improving conductivity.
Linear Crystal Copper (LC-OFC) – Hitachi's patented process after extrusion, the copper wire is re-heated, or annealed, which reduces impurities between the crystal boundaries as the copper crystal formation grows and leads to a long grain length.
Ohno Continuous Cast Copper (OCC) – This unique patented casting process was developed by Professor Ohno to help defeat annealing issues and virtually eliminate all grain boundaries in copper with a continuous crystal formation that is 99.999% pure (aka 5N) copper.
Types of conductors
Stranded wires - made up of multiple strands of copper wire that are not insulated from each other in the conductor pair; it is flexible and also easier to strip, crimp to connectors, and work with by hand. The copper oxide may form between the strands encouraging non-linear conduction.
Solid core - only has a single conductor for each pair; difficult to bend and curve without the risk of breaking, harder to make connections with, and is said to reduce skin effect.
Types of cable geometry
Geometry is said to be the most important factor in a cable design; even more important than the conducting material type. Many differing conductor sizes and electrical lengths can impact the signal arrival times across the audio band-based physical conductor size and lengths. A loudspeaker cable is also most sensitive to geometry because it carries a high current. The late Max Townshend of Townshend Audio believes loudspeaker cables may show a variety of tonal discrepancies which are due to multiple reflections caused by a mismatch between the cable’s characteristic impedance and the impedance of the load. He goes on to say that cable geometry is a critical factor when it comes to cable design, if the positive and negative conductors are spaced further apart, it would negatively impact the flat frequency response i.e., the further apart, the worse the response curve.
Parallel - the most common type with 2 conductors running alongside each other. This geometry offers a higher inductance and may not reject EMI and RF interferences.
2. Twisted - this is also a common design and offers good noise rejection because of its 45-degree angle twist. Closely twisted pairs are good at rejecting EMI but offer higher capacitance.
3. Braided, weave or woven - this design uses litz-type conductors with a proprietary braid that reduces inductance and associated capacitance and is said to be good at rejecting EMI and RF interferences.
4. Coaxial - uses a solid core conductor as the positive side and a braided shield surrounding the solid core as the negative side of the conductor. The rejection of EMI is quite good, not recommended for audio but for carrying digital data and video use.
5. Litz-wire - each conductor is insulated from the others in a multi-strand conductor held in a particular pattern like a weave design. A Litz design is said to reduce skin and proximity effects.
6. Ribbon – the conductors are placed together on top of each other or side by side with just a thin strip of insulation in between. It is said to achieve a close impedance match with the loudspeaker in this regard.
Shielding
Shielding may apply to interconnects to guard against noise from EMI and RF interferences. However, the braided shield found in some interconnects will not cover the entire area and therefore remain vulnerable to leaks, conductive plastic wrap (foil) affords a better shield in this respect. However, braid and foils are limited to high-frequency shielding. It is pertinent to note that cheap cables (stock) have poor shielding properties.
Audio interconnects are available in 2 formats. The common type is the Single-Ended aka RCA cables which as the name suggests use RCA termination pins. Single-ended cables are the cheapest method that consists of only 2 conductors (positive and negative sides, including the shield which covers them both – triaxial design). You should not even consider an interconnect with the shield used as the negative side, i.e., coaxial - only one conductor in the middle, the shield being the other. Single-ended (unbalanced) – has no galvanic separation i.e., no transformer/circuits to isolate the spurious signals. Single-ended is notorious for causing ground loops. Therefore, keep them as short as possible and away from power cables to avoid the risk of interference.
Balance cables on the other hand are widely used in the pro-audio industry. Balanced interconnects are terminated with XLR pins and they provide double the voltage as the single-ended type which is desirable for longer runs. However, manufacturers also provide Pseudo-Balanced cables. They look the same and use the same term “Balanced” but are configured differently and don’t enjoy the benefit of noise cancelation. They must be true balance i.e., there should be 2 amplifier stages for each conductor when the signal arrives inside the chassis. The design provides separate circuits for each conductor, doubling the cost of the electronic parts. The noise traveling through both cables will cancel out each other (common mode rejection) because one of the 2 circuits will be out of phase. Balanced cables are therefore excellent for long runs and defend against ground loops and spurious signals. However, the cable is still susceptible to EMI and RF interferences depending on the quality of the shield. Though the balanced system in the electronics will try to address this, it is also dependent on the complimentary filtering circuits around the design. It is said that prevention is better than cure, therefore you will be wise to get a balanced cable with superior shielding which usually costs more.
Terminations
Terminations are an integral part of the cable’s performance. Cables may be terminated by either crimp, solder, cold-welded, or by a direct mechanical joint. Depending on how it is soldered, a cold solder may fail over time or provide a higher resistance at the solder point or if the conductor is not touching the object surface, then you have a piece of solder in the audio signal path which is truly a worst-case scenario. This is also the case when you tint the wire with solder and mechanically join the cable to the loudspeaker terminal.
On the mechanical part of the plug termination, they should have high-contact pressure i.e., fit tightly, better still if they have a locking mechanism for a secure fit. Whatever connections are made should guarantee a robust contact otherwise, sparking, and increased resistance due to poor contact will introduce distortion. Remember, the terminations at the ends of cables and interconnects are part of the transmission path. Therefore, audiophile-quality cables are preferred because they provide better quality materials, well-conceived design construction, and ensure the integrity of the terminations with machined connectors and split center pins ensuring a more reliable connection than more conventional designs.
Audible differences in signal cables
Signal cables may be placed into three distinct categories; audio interconnects, digital cables, and loudspeaker cables. As for audio interconnects, differences between interconnects are subtle but for the areas of high frequencies and the midrange. As for digital cables; the SPDIF standard is best, AES/EBU connects are superior, followed by BNC, then the RCA equivalent, followed by the USB type B, and the Toslink is the worse sounding in this rank order. In the case of the USB interface, it is shared with the power requirements, and therefore subject to interference unless a special cable is used such as the one sold by ‘ifi’ that separates the audio and power. However, the USB interface is important because they are compatible with DSD and higher resolution formats, unlike single-ended RCA which usually offers limited support for hi-res audio. I found the sound differences of digital cables to be subtle but for pace and rhythm rather than the tonal balance. That means, one cable can sound slower and another faster with better dynamics. As for the loudspeakers, there appear to be more subtle changes such as fluidity in the treble, fullness of bass or lack thereof, overall warmth, and tightness during transient attacks. To hear these differences, your system should be finely tuned following all the rules as described in my foundational articles. In a high-resolution system, every little nuance will be heard.
A dozen recommended tips and tweaks
Loudspeaker cables are characterized as a low-voltage high current application, therefore you should keep the loudspeaker cable lengths as short as possible. You would want a higher gauge cable of at least 14 gauge or larger. Having a larger gauge cable is necessary for unusually long runs because resistance is proportional to the length or when using very low-impedance loudspeakers (under 4 ohms).
Subwoofers require low capacitance interconnects for runs exceeding 3 meters.
Interconnects should not be more than 1.5 meters, otherwise, consider balanced cables.
Do not coil excess loudspeaker cables (it creates a magnetic field) as this can create an inductance that reduces some
frequencies as a crossover do. Keep them straight and curved or better still cut them short. Do not run them parallel with power lines, if they should cross, cross them at right angles with a spacer between them. Give fresh cables some burn-in time for the cable to settle before you make any judgments on its performance.
The cable manufacturer or a professional technician should terminate cables if buying custom-made ones to ensure the
integrity of the connection rather than DIY. The cable lengths should also be equal on both channels (matched pair) so that they see the same resistance and the system will be better balanced.
The cable design should afford the lowest capacitance possible and the cable's dielectric to be the best quality possible.
7. Bi-wiring loudspeakers are strongly recommended if you have two sets of connections, one for low and the other for high frequencies. Prof. Malcom Hawkesford on the Maxwell effect found that different frequencies travel at different speeds through a piece of wire. The high and low crossover source signals should be connected at the amplifier end instead of the loudspeaker terminal end. You can use different cables to best suit the different frequency groups (e.g., solid core for the highs and heavy gauge multi-strand for the lows) for optimization however, make sure they are of the same length but may not necessarily be of the same gauge.
8. A good rule of thumb is to use balanced interconnects for longer runs, or ideally ‘balanced’ the entire system with a ‘true balanced’ system if your immediate environment is contaminated with radio frequencies. Neutrik connectors are highly recommended for balanced interconnecting cables.
9. Turntable interconnecting cables should be no more than 1.5 meters long to the phono stage, otherwise, they become vulnerable to noise interferences. The low voltage that they deliver will be attenuated, therefore they may not have sufficient voltage to feed the phono stage. They will add distortion because of the additional gain required to compensate for the loss.
10. Exposed copper wire can oxidize over time and create a poor connection. Cut and re-solder or change the connector after periodic inspection. The best connector is no connector, direct wire to loudspeaker terminals is best. Do not tint the wire's ends with solder because the solder is not a good conductor.
11. Loudspeaker wire terminals can become loose over time because of cabinet vibrations, and degrading sound quality. Check and tighten occasionally or replace with locking banana pins instead.
12. Digital interface cables should be of a 75-ohm variety (relevant makes and models such Mogami or Belden with dry crimped works best) and not be more than 1.5 meters in length and ideally with double-shield i.e., both foil and braid or double braid.
Conclusion
Most audio consumers except for the audiophile community don’t believe that cables can have an impact on sound quality. I agree with them, on their own they don’t, but once they see a load, the interactions on both opposite sides (source and load) will suggest to any logical person in assuming that the different electrical properties in cables will in some way interact, influence and affect the quality of the signal flow. Nonetheless, I believe the main performance concern in cables is the sin of commission instead of omission which is mainly triggered by the interactions of the source and the load. Suffice it to say, all cables “react” differently and should therefore be designed to offer the most benign interaction possible between the source and the load. Your choice of cables will eventually be limited to your preferred sound integration between two companion components. Connecting cables are the lifeblood of your audio system, choose wisely, otherwise, it will be your weakest link in the audio chain.