Unbalanced | Balanced
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Unbalanced connections have two conductors, one at ground potential
and the other carrying signal. Equipment operating at -10 dBv invariably
uses unbalanced connections.
Balanced connections use two conductors, each which carries the same
signal but with the polarity of one reversed with respect to the other.
Balanced connections may or may not be referred to ground. If not, they
are referred to as floating connections. A balanced connection referred
to ground requires three conductors, the third having ground potential.
Why use balanced connections?
In sound reinforcment and recording evironments, balanced connections
are preferable to unbalanced because they are far less susceptible to interference.
Also many feel that the redundancy of two signal conductors carrying audio
yields better quality audio.
Good cables and connectors
- Not all cables and connectors are the same. Good connectors will have
low contact resistance and well supported strain relief. Products like
Whirlwind, Switchcraft and Neutric have been the industry standard for
years. All brands offer quality products for equipment interfacing.
- So what about cables? Cables can play a big roll on the quality of
your audio signal. Even if the diameter, wire gauge, and general construction
are similar, two cables may have significantly different electrical and
physical properties such as resistance, capacitance between conductors,
inductance between conductors, over all flexibility, shielding density,
durability, ability to withstand crushing or sharp bends, tensile strength,
jacket friction, and so forth.
- The best shielding you can use is foil shield, but such cables are
not particulary strong and the shielding can deteriorate if they are flexed
too much. Foil shielding is most often used in permanent installs and within
racks where cable movement is minimal. Braided and wrapped cable is most
often used for mic and instrument cables. Braided is preferred over wrapped
because wrapped tends to open when flexing. This only degrades the shielding
density and can also cause microphone noise.
- If the cable capacitance changes when you flex it, this can change
the induced noise level, and the cable is said to be microphonic. This
can be a big problem with phantom power in mic cables, it can happen in
any cable though. Avoid this problem by using cables with stable dielectric
(insulating) material, and with a tightly braided shield that is well-trapped
by the outer jacket so the shield itself doesn't open up as the cable is
flexed.
Unshielded cable
- Shielding adds capacitance, bulk, weight, and cost to a cable, but
never consider using unshielded cable for instruments or microphones.
- Speaker signal is different. The signal level is so high in speaker
cables that electromagnetic noise is insignifcant in comparison so unshielded
cable is fine. In fact, the higher reactance of shielded speaker cables
can induce deleterious parasitc oscillation.
Written by Devin DeVore
additional infomation provided by Yamaha
© TSC/TRINITY
SOUND COMPANY
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