Although part of the audio range,
loudspeaker wiring is very different and needs a little
consideration. Little loudspeakers in equipment may be wired up
using almost any wire, as may intercom type circuits and so on.
Hi-fi loudspeaker cabling and In-Car
Entertainment speaker wiring is much more critical. It is very
easy to drop a significant part of the output of an audio
amplifier over a medium to long run of inadequate but inexpensive
speaker cable. Many people automatically use a thin figure of
eight “Zip” wire for speaker connections but for any amplifier
delivering over a few Watts, a thicker and more substantial cable
is needed for a quality reproduction of sound without burning part
of your output as heat and having to have the volume higher to
achieve the same volume at lower quality.
Look at heavy duty and Hi-fi loudspeaker
cables or, if the increased bulk of those is a problem, there are
several special flat variants that will go under the carpet
easily. Silver plated and oxygen free copper are also available
and provide a very clean transfer of power to your loudspeakers.
The first thing to consider with an RF
cable is impedance. Impedance is a combination of DC resistance as
well as capacitive and inductive effects in the cable. It may be
considered as the effective resistance of a cable to an AC signal.
Most RF equipment is designed to work with
a cable of a specific impedance. TV’s, video recorders and
satellite equipment are designed to use 75 Ohm cables, whereas
radio transmitters and some receivers are designed to use 50 Ohm
cable. It is important to select a cable with the correct
impedance for the job, otherwise a bad match will be made between
the equipment and signal will be lost, resulting in poor
reception. In the case of transmitters, it is possible that this
will cause the output stages to heat up in use, or even burn out.
The other associated figure to look at when
choosing an RF cable is attenuation. Attenuation is a measure of
how much signal you will lose over a given length of cable at a
stated frequency, expressed in Decibels. The explanation of both
impedance and attenuation is beyond the scope of this guide, but
suffice it to say that a cable of the correct impedance for the
application, with the lowest attenuation figure at the frequency
range to be used, will give the very best results, although the
voltage rating of the cable is also important at very high
transmitter output levels.
Impedance is also important for some
professional audio uses, such as the use of balanced microphones
in studio or stage situations. Check the impedance rating of the
equipment and use the correct cable and connectors for the job.
Networking connections that use the BNC
connector are designed to use 50 Ohm RF cable to interconnect
computer equipment. Newer networking connections tend to be made
using special multi-way twisted pair cables that help to reduce
both radiation of the very sharp edged RF data signals as well as
reducing the likelihood of pick up of interference from other
There are various standards for these
data cables (Category 5 for example) and it is always best to
check the instructions supplied with each unit before choosing a
If you intend to do a lot of cabling, there
are a number of special cable stripping tools that will make the
job a lot easier.
Many connectors need soldering onto the
cables and sharp cutters, a craft knife and small screwdriver for
any screw-fixed connectors will be needed.
A multimeter or continuity tester is ideal
for reassuring you that your completed cable and connector
assembly really does connect as you think it does, with no open or
short circuits that could cause damage or other problems later.
Consider the use of conduits or trunking to
box up, hide and protect long cable runs. Wiring inside equipment
may be secured by using cable ties, lacing cord or spiral
wrapping. There is a large range of different cable clips that
will also help tidy your wiring and keep it in place after
If your cables or wires have many different
terminations, you may wish to use coloured or numbered sleeving at
each end of each wire to aid later fault finding or rewiring. Heat
shrink sleeving will allow you to join cables in places where no
connectors are required, and then shrink the sleeving over the
individual joins to remake the insulating layer, or just provide
an additional protective layer for a cable in a vulnerable
Cable glands and grommets will allow you to
make neat entry to boxes or through panels, and will prevent the
cable chafing on metal edges.
It is never ideal to run a cable across the
floor but, if you have no alternative, consider using a cable
protector, which is a heavy rubber strip the cable lies protected
inside on the floor, shaped to minimise tripping over it.
It seems fairly obvious that the ends of
your cable will somehow need to be securely attached to the
equipment, either by directly soldering each conductor to a
terminal or tag, or by screw or clamp terminals, or via a suitable
set of connectors. Check before choosing connectors that their
current and voltage rating is sufficient and safe for the job in
RF cables must be properly connected and
joined by suitable RF connectors of the same impedance. Use of the
wrong connector, or a hard wired soldered or screw terminal joint,
may result in a break in the smooth transfer of RF energy that may
result in the signal being reflected back up the cable instead of
passing through it.
Note that, especially for RF, a soldered
connector is usually far better than a screwed one, and that TV
aerial and distribution wiring should always be soldered for best
long term results.
We hope that this guide to cables has
helped you to think about what you need from your cables and
wiring, and that you now feel ready to make your choice.