AV cables: hype and science
AV cables: hype and science. When choosing interconnects and speaker cables, we really want brands that don’t promote expensive pseudoscience or make semi-scientific statements. With a background in science and engineering (Master of Electronic Engineering) Bart is a strong advocate of provable engineering principles . He believes that unscientific claims do not have a place in any sales environment, including AV and with that AV cables. Especially not when it is spread by companies who are knowingly trying to make money out of ordinary people like you and me, spending their hard-earned bucks on something they feel passionate about.
Yes, we know that we will rub some people the wrong way with this statement. It is by no means our intention to upset people. We do however believe that as a supplier who often hands out expert information, we have a responsibility to ensure accurate information that is backed up by science is provided.
Here goes:
The truth is it doesn’t take a lot to make quality cables and there are plenty of articles out there that define what makes a quality cable. Cables should only represent a very small percentage of total system budget so if you spent $10k on your equipment, you shouldn’t spend much more than $500 for the interconnects and speaker cables. That’s it.
We have been receiving numerous emails about how one should budget their spending on interconnects and speaker cables. This has prompted us to write a guide for home theatre wiring applications.
As a rule of thumb, we recommend spending no more than 5-7% of your total system cost into cables and interconnects. We recommend you prioritise as follows:
- HDMI and Component Video Interconnects (75 ohm, shielded coax)
- Analog interconnects (low capacitance, twisted pair / Coax-shielded when needed)
- Speaker Cables (Low DC resistance and inductance, short runs when possible)
- Digital Interconnects (75 ohm, shielded coax preferred, or toslink for short runs)
Let’s explain some further:
1. Video cables
Video cables may be the most sensitive cables in your visual/video system as the signals that are passed through these cables (especially when dealing with HDTV) are in the Megahertz range. The higher in frequency your transport, the more critical it is to use cables that have a proper characteristic impedance (usually 75ohm for video), adequate shielding, and solid terminations.
It’s even more critical to choose quality HDMI cables with low gauge (24AWG or lower, depending on the distance). Remember that the biggest enemy to HDMI cables is length. The longer the cable, the higher quality it needs to be.
The other thing to pay attention to is future proofing. These days, you want an HDMI cable that is tested to resolutions up to 4k or HDMI 2.0 spec.
With long HDMI runs, a RedMere cable can be a life-saver. RedMere is an active technology that uses power from the HDMI port to transmit signals over distance using much thinner cables. With a traditional cable you may have needed to use a much higher gauge conductor. In other words, a thick, heavy cable that would be difficult to bend around tight corners and could put a lot of strain on the HDMI port of your projector. A RedMere cable allows you to use a thinner, smaller gauge wire making the whole cable thinner, lighter, and easier to bend around corners, which is great when you’re crawling around a hot attic with fiberglass in your ears.
With all that said, it’s good to remember that a quality HDMI cable is not necessary the same as an expensive HDMI cable. You want to pay for a quality signal carrier, not extra-shiny connector, the pretty-coloured net jacket, or the fancy name on the packet.
Applications: TV, DVD, HDTV Decoder, Monitor Output of Receiver/Preamp.
Analogue interconnects are also quite important since they interface high impedance connections, usually greater than 10kohms for amplifiers, preamps, etc. It is important to choose twisted pair cables or shielded coax which provide reasonably low capacitance, good shielding, and solid terminations.
It should be relatively easy to find low capacitance, twisted pair interconnects for a reasonable price that will provide frequency response beyond the limits of your hearing and equipment abilities.
Shielded Coax with RCA terminations are also a great option, since they usually provide lower capacitance and sometimes better shielding than twisted pair shielded cables, but can sometimes be more costly. Additionally, coax cables with solid centre core wires are less flexible making them more difficult to route in tight places. You may wish to consider shielded coax with a stranded wire centre terminated with RCA plugs, much like a good quality video cable, for this application, especially if your runs are quite lengthy or subjected to many adjacent disturbers (IE. power cables, audio/video cables).
A quick mention of balanced (3 wires per cable) versus unbalanced (two wires per cable) systems is in place. We have spoken about a balanced system and cables before in an earlier blog (here)
Most home audio systems are fully unbalanced. The main argument for opting for a balanced system is to ensure a system that works virtually hum and buzz-free. One could argue that due to their small nature, short cable runs and 2-conductor AC line cords hum and buzz is not very often an issue even in unbalanced systems.
Hum and buzz is caused by the shield acting as an antenna for radio frequency (RF) interference. However, with digital technology increasing, the possibility of RF problems definitely grows.
A frequently suggested solution to hum and buzz problems without going down the road of a full balanced system involves disconnecting one end of the shield.
Applications: Preamp, Power Amp, CD Player, Subwoofer.
Again, we want to be clear that it’s not our intention to patronise. We are all entitled to our opinions and I believe that as an engineer, and scientist, it needs to be backed up by science. In that context, I really want to debunk some of the marketing stories some companies have been selling and be clear on what is the single most important aspect of speaker cables – resistance.
Anytime you are driving power into a low impedance load such as a loudspeaker, the dominant metric of concern is DC resistance (measure of restriction of conductivity in a circuit).
Sure, there are secondary concerns which are also important such as inductance, and capacitance. But the thing is that if you cannot first select a cable with low enough DC resistance, the losses will be so great between the amplifier and loudspeaker that all other cable parameters will become insignificant. So, what we are talking about is choosing the right wire gauge (AWG) for your installation to ensure you realize the maximum potential of your setup.
Many of these cable companies are simply marketing Snake Oil in fancy packages, and selling them to you for outrageous prices.
The truth of the matter is, standard 10 or 12 AWG Oxygen Free Multi-stranded Cable (OFMC) is fine for most applications except for maybe the extreme scenario of a particularly difficult Electrostatic Loudspeaker (ESL) system driven by tube amplifiers, or extremely long runs (greater than 15m) connected to low impedance speakers (4 ohms or less). In these cases, speaker cables with lower DC resistance and inductance may be more optimal to achieve the fullest potential of the system.
10-12 AWG OFMC has low enough DC resistance for runs up to about 15m to not cause any deleterious effects on system performance. Dealing with relatively low frequencies (IE. 20kHz bandwidth) into low impedance loads (typically 4/ 8 ohms), it is very difficult for RF to ingress in your speaker cables. In addition, the inductance and capacitance of these cables is insignificant for runs up to even 15m or so, compared to the actual impedance properties of your loudspeakers and the 20kHz bandwidth in question.
You will find tables with recommended speaker cable gauge for various lengths and speaker loads. Remember that these are guidelines only. In case you’re choosing between two cable gauges, We usually recommend going for the lower one (all other things being equal) to be on the safe side.
The other thing to pay attention to when it comes to speaker cable is how you terminate them. You want to ensure that you have the tightest connection of the cable to your amp and loudspeaker to minimize contact resistance.
Always remember to keep you speaker cable runs as short as possible and not to loop excessive cables as this may slightly increase cable inductance. You will want to avoid running speaker wires in parallel with power cords, but if you have to, stay 60cm away and cross them under an angle of 90 degrees.
While these fairly simple rules of thumb are important. Many other claims surrounding speaker cable are not.
We mentioned earlier how pseudoscience marketing tries to justify the sale of exuberantly priced speaker cable. The truth is that as soon as you subject these claims to some solid scientific calculations, they go flat on their bums. We’re aware that his is a very, very controversial topic on forums. Some companies can sound very convincing. The thing is: I don’t buy into the ‘You can’t measure it or argue its benefits in a scientific way, but you can hear it!’ claims made by those audio cable companies. Until they can actually really proove it, I’m out.
Some speaker cable myths debunked:
- Fancy speaker cable suppliers like to talk about skin effect. What is Skin effect and how relevant is it in speaker cables? Skin Effect is a real-world problem in high frequency applications such as RF Power and Transmission, however it is negligible at audio frequencies. Skin effect refers to the tendency of alternating current to flow near the surface of a conductor (as opposed over the entire diameter). In doing that it is restricting the current to a small part of the total cross-sectional area and increasing the resistance to the flow of current. Some proper calculations on how big an issue skin effect is for cable wire have been done. The increase in resistance for signals at 20,000 Hz is under 3%, in the range of a few milliohms (!) for the common home stereo system; this is absolutely negligible. It’s like saying you need an umbrella because rain will make you wet, while living in a desert.
- Beware of any cable suppliers that try to tell you their product is so much better because itis a solid core wire (as opposed to a cheaper stranded speaker cable) The claim is that it is superior because it avoids ‘strand jumping’ (Current in stranded cable supposedly ‘jumps’ constantly from strand to strand to stay on the outside of the cable, increasing skin effect) Here’s the science: strand jumping doesn’t exist. There is no scientific base to the claim. None! As a consequence, there is also no increase in skin effect. And while we are at it: it’s good to know that solid core speaker cable is less flexible during the installation process which comes with its own annoyances and risks. Do you still want to spend the extra dollars?
- When we talk about conductors, we should also address materials. Copper is an excellent conductor. Compared to other materials it has very low resistance. Copper cladded aluminium cable is cheaper, but this is at the expense of higher resistance. Aluminium is also much more brittle and so be careful when you install. Some speaker cable suppliers will try and tell you that silver is superior to copper cable. The truth is that the difference in resistance between silver and copper is almost negligible. (The resistance of copper is 1.7 x 10-8, Ohms per metre at room temperature, for silver it is 1.6 x 10-8 Ohms per metre in the same conditions!) You may also be interested to know that silver has the downside of tarnishing, which can result in higher contact resistance. In other words: the difference over the length of a few metres between silver and copper is so small that you can’t possibly hear the difference between a silver or a copper cable of equal geometry and gauge. The difference in your wallet on the other hand will be very noticeable.
- Speaker cable is not directional. How can it be when an audio signal is AC and effectively random from a physical perspective? Nothing can align to a random signal.
- For the same reason speaker cables also don’t need a break in period. Cable sellers claim that the break-in has to do with the insulation or dielectric (not the wire), with insulation molecules aligning with a signal. Apart from the fact that it is kind of hard to align with a random signal, break-in in speaker cable has never been scientifically proven. The best guess is that it is just your ear getting adjusted to the new cable.
- Cable elevators to lift your speaker cable off the floor do not improve static electric fields.
Obviously, in the end, it is your money and you can spend it on whatever you desire (more or less). We just think it our job, to inform you to the best of our ability. If after that, you still want to spend the extra dollars for a great science-fiction story fuelled by certain companies riding on a marketing hype as opposed to real science, that’s ok by us. But before you do, you may want to think about the awesome speakers you could get with that money. A step-up in speakers could actually make a noticeable improvement to your set-up.
Applications: Loudspeakers.
4. Digital Cables
S/PDIF stands for Sony/Philips Digital interface and is a type of digital audio interconnect used in consumer audio equipment to output audio over reasonably short distances.
Because S/PDIF bandwidth is less than NTSC or PAL (video TV standards in the USA and rest of world respectively) digital cables, are not quite as critical as video cables. In the end, the purpose of these cables is to pass a 44.1-48kHz sampled bitstream for audio codecs like Dolby Digital, DTS or PCM.
The thing to take away is that there are some options here:
Should you choose to use coax type cables for your digital connections, we recommend using 75 ohm compatible shielded RCA cables. The ‘shielded’ is important to minimize coupling issues from adjacent cabling on long runs and/or potential RFI/EMI ingress, while also keeping losses to a minimum by proper impedance matching.
Toslink, or fiber optic cables, are another viable option with the advantage of not being disturbed by RFI/EMI, or ingress from adjacent cables carrying digital, analog, or power signals. The downsides are that some toslink cables may make a rather flimsy connection to the interface equipment which can be compromised when adjusting components in your rack or if the cable is weighed down by other cables in your system.
Also, for long runs compression and rare fractions can occur, especially if the cable excessively flexes or bends. We recommend selecting toslink cables that have a decent locking mechanism to avoid these mechanical issues.
Some trouble shooting:
There are two things which can cause differences between the sound of digital interfaces:
1. Jitter (clock phase noise)
A digital signal is sent in periodical intervals. A deviation from that ‘true’ periodicity is called ‘jitter’ and can cause ‘noise’. These days, this is no longer a big problem because it really only affects sound of the signal going directly to a DAC. Modern DACs in DVD/CD players typically have a small buffer and reclocking circuitry, making this largely an issue of the past.
2. Errors
A broken link can cause a loss of data. This usually causes very significant changes in the sound, often loud popping noises but occasionally less offensive effects. Sometimes it can be as bad as the system dropping out.
Applications: CD / DVD / Blu-ray/ UHD Player, Skybox.
Bottom Line – AV cables: hype and science
Use common sense when purchasing cables and interconnects for your system. Don’t run out and spend $2000 on a pair of “high-priced” speaker cables for your $1000 loudspeakers. The $2000 wasted on those “so called” high-priced speaker cables may be better utilized on upgrading your $1000 loudspeakers to a better set of $2500 speakers, with all things being equal.
Choose cables that are durable and built well while providing solid mechanical connections (terminations) with your hardware. Most importantly, arrange your cables in a logical and neat fashion to minimize any potential interference issues. And always future proof: pull a few extra wires and allow for flexible set-up. As always, give us a call to discuss, we are more than happy to help you out.
Sources: Audioholics, Radio-electronics, AVS-forum, Evaluation engineering