Cable Budget Guidelines

We have been receiving numerous emails about how one should budget their spending on interconnects and speaker cables. Thus this has inspired us to write practical Cable Budget Guidelines for home theater applications.

As a rule of thumb, we recommend spending as little as you can to get the job done right, but no more than 5-7% of your total system cost into cables and interconnects, with the following priorities:

1. Video cables

Video cables may be the most important cables in your system as the signals that are being 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 that are well shielded, low gauge (24AWG or lower) and are tested to resolutions up to 1080p. 

Applications: TV, DVD, HDTV Decoder, Monitor Output of Receiver/Preamp.

Check out the Component Video Cable Definitive Guide for more details.

Check out the HDMI & DVI Video Connections and HDMI Considerations for more details.

2. Analog Interconnects

Analog 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. An excellent example of a cable well suited for audio applications is a shielded twister pair used for microphones such as the Belden #8422.

If we assume the output impedance of your source component (IE. CD player) is around a hundred ohms up to several kiloohms, then you can get away with an interconnect of up to a few hundred picofarads of capacitance and still yield a 3dB point well above 100kHz, or flat within the audio bandwidth 20Hz to 20kHz, based on the relationship of: frequency = 1 / [2*pi*(R*C)^1/2].

However, capacitance should be kept to a minimum on interconnects to avoid any possibilities of amplifier/driver stability compromises or premature roll-off. Older tube preamp designs tended to go unstable when driving high capacitive loads. This isn't much of a problem these days with solid state devices. In fact, most decent op-amp devices are capable of driving capacitive loads in the nanofarad range in shunt with a high input impedance without causing stability or noticeable overshoot problems.

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, is 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 center 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 center 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).

Applications: Preamp, Power Amp, CD Player, Subwoofer.

3. Speaker Cables

Despite all the myths and engineering fallacies surrounding speaker cables, these cables are not as critical as many cable companies would have you believe. In fact, 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 Multistranded 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 50ft) connected to low impedance speakers (4 ohms or less). In these cases, speaker cables with lower DCR and inductance may be more optimal to achieve the fullest potential of the system.

12 AWG OFMC has low enough DCR for runs up to about 50ft 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 50ft or so, compared to the actual impedance properties of your loudspeakers and the 20kHz bandwidth in question. The majority of users running speaker cables of this length are usually doing so for surround sound applications. In most cases, these speakers are usually so far off axis with respect to the listener that the attenuation and phase change due to increased cable impedance is a secondary concern. For the ESL case driven by esoteric tube amps or amplifiers with higher than usual output impedances, it is usually recommended to shorten your cable runs by placing each amplifier as closely to each speaker as possible.

If you consider that even most high end loudspeakers are internally wired with 14-16 AWG copper wire, and the terminations of most power amps / receivers and loudspeakers are soldered onto binding posts, then ask yourself, how could these "exotic" cables make such an audible difference?

What is important in speaker cables 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. For that, I recommend either spades or banana plugs. Despite the fact that Spades generally have greater surface area contact than banana plugs, I have found that banana plugs usually make for a better connection to most commercial binding posts found on loudspeakers and amplifiers. 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.

If you cannot avoid running speaker wires in parallel with power cords, and /or your system is prone to RFI ingress, shielded twisted pair speaker cables may also be a great option. Many manufacturers offer this option for only a small additional cost. I suggest reviewing the excellent article written by Dan Banquer title "Bulletproofing Your System from Interference" for tips in combating noisy environments.

Applications: Loudspeakers.

4. Digital Cables

Digital cables, particularly coax, are not quite as critical as video since S/PDIF bandwidth is less than NTSC and the rise/fall times are not quite that stringent. The purpose of these cables is to pass a 44.1-48kHz sampled bitstream for PCM, DD /DTS. Should you choose to use coax type cables for your digital connections, I recommend using 75 ohm compatible shielded RCA cables, even good video cables will work just fine, 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, is 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 and for long runs compression and rarefractions can occur, especially if the cable excessively flexes or bends. I recommend selecting toslink cables that have a decent locking mechanism to avoid these mechanical issues.

What can make a difference in the sound of digital signal ?
There are two things which can cause differences between the sound of digital interfaces:

1. Jitter (clock phase noise)
This 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, so the jitter is not so big problem nowadays that it used to be.

2. Errors
This usually causes very significant changes in the sound, often loud popping noises but occasionally less offensive effects. Any data loss or errors in either are a sign of a very broken link which is probably intermittently dropping out altogether.

S/PDIF signals defined
The signal on the digital output of a CD/DVD player looks like almost perfect square-wave, with an amplitude of about 1Vpp and a frequency bandwidth of almost 3 MHz.

For each sample, two 32-bit words are transmitted, which results in a bit-rate of:

• 2.8224 Mbit/s (44.1 kHz sampling rate, CD, DAT)
• 3.072 Mbit/s (48 kHz sampling rate, DAT, DVD)
• 2.048 Mbit/s (32 kHz sampling rate, for satellite purposes)

The output impedance is standard 75 ohm, so ordinary coaxial cable designed for video applications can be used. The minimal input level of S/PDIF interface is 200 mVrms which allows some cable losses. There is no real need for special quality cable as long as the cable is made of 75 ohm coaxial cable (a good video accessory cable works also as good S/PDIF cable). Newer formats such as

DVD-Audio and SACD are now starting to come with proprietary digital outputs for passing the high resolution signals in the digital domain. We will come back to this application when hardware vendor support of these interfaces becomes more common place.

Applications: CD / DVD Player, DAT, Cable Box.

Bottom Line

Use common sense when purchasing cables and interconnects for your system. Don't run out and spend $1000 on a pair of "exotic" speaker cables for your $500 loudspeakers. The $1000 wasted on those "so called" exotic speaker cables may be better utilized on upgrading your $500 loudspeakers to a better set of $1500 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.

For more details about cable arrangement, please refer to our Connection Tips 101 article. For additional reading about cables, please visit our Cable Principles section.

Enjoy the music!

updated 1/26/03 - Expanded Speaker Cable Section regarding long cable runs.
updated 2/14/03 - Added links for cable related articles and updated digital cable section.
updated 2/20/03 - Included coax cable option for Analog IC's.