Understanding the “Wires”
Thereby Knowing the System
Part One
It is probably the easiest place to start the nitty
gritty of the Celtic Harp Amplification Series, right
down to the wire, in order to understand how a system
is created. Different cables have different jobs and
are built differently as a result. If you understand
the cabling you understand a lot of the “why’s”
as to why things are done the way they are. I will describe
the construction of cables on this page and their uses
in Part
Two. The bold phrases
have complete definitions below.
I will describe a simple
scenario of a sound system signal
path. A microphone transduces an audible sound
into an audio signal, which follows a path through the
gear and then to the speakers. Along this path the voltage
levels of the signal are changed to suit various requirements.
The original microphone
signal is carried at mic level
by an XLR mic cable from
the microphone output to a pre-amplifier input. The
signal is converted to professional
audio line level signal by the pre-amp which
is then routed to an amplifier using either a balanced
XLR cable or an unbalanced TS
phone jack. The amplifier amplifies the professional
line level signal to speaker
levels, which is then transmitted along speaker
wires to power the speakers. Line level (balanced or
unbalanced) inputs and outputs may be used to connect
numerous processors and other mic inputs in the signal
path prior to amplification.
The same can be said
for your home stereo with a signal path being from a
CD player output to a pre-amp input then to an amplifier
then to speakers along speaker wires. The consumer standard
RCA line level interconnects
however are of a different (lower) voltage compared
to professional line level and are not easily interchangeable
with pro audio standard gear.
An XLR
(mic) cable consists of two fine insulated wires twisted
around each other with a braided third wire surrounding
the first two as an audio signal electrical shield
or ground. The two fine
wires are considered balanced as they carry identical
currents (“hot” send leg and “cold”
return leg) in opposite directions
A TS
(1/4”, phone, jack) cable is considered unbalanced
as it has a single fine internal wire (“hot”
send leg) which is insulated from a surrounding wire
braid shield which acts both as ground and a “cold”
return leg
A speaker wire is simply
2 parallel wires either 12, 14 or 16 gauge with the
legs simply referred to as “+” positive
(hot) and “-“ negative (ground)
A 120V mains wire is
simply 3 parallel wires either 12, 14 or 16 gauge with
the legs simply referred to as positive (hot leg), negative
(cold return leg) and the electrical earth (ground)
A Few Definitions
Direct from the InSync Archives
Take the time to read
these and figure out the nuances, as this knowledge
is fundamental to understanding audio systems and how
to amplify Celtic harp music in any meaningful way.
Signal
Path - |
Simply
the route a particular signal takes through a
chain of equipment and/or electronic components
on the way to its destination. When we think of
signal paths in audio we are usually thinking
about connecting different pieces of equipment
together and routing some signal(s) through them.
An example of this would be something like a microphone
to mixer to speaker or recorder setup. The signal
path has the signal from the microphone pass from
the microphone through those (and potentially
other) devices on the way to being recorded or
amplified (or both). But there is also a signal
path inside each piece of equipment. A mixer may
be configured to route signals in different ways
internally bypassing or utilizing different gain
stages along the way to achieve different results.
|
Ground - |
In electricity
an electrical path to ground is provided by code
at all electrical outlets for safety. In the event
of a failure or circumstance that might normally
cause the operator (or anyone coming in to electrical
contact with connected equipment) to be the return
path for the electrical current the ground can
shunt this current away safely and return it to
earth, which is
where it is trying to go anyway. The alternative
of the operator being the return path can cause
electrocution.
In audio, ground usually refers to either the
electrical ground mentioned above, or to an audio
shield. An audio shield is not always a
ground and should never be used as a safety ground.
That they are often at ground potential is a function
of how they may be connected to other equipment.
Many audio devices have the ability to disconnect
their signal paths entirely from electrical ground
as a way to prevent hum or ground loop problems.
|
Shield - |
In electronic
terms, a shield is a conductive enclosure, protecting
its contents from magnetic and electrostatic fields.
Since audio conductors and circuits tend to be
extremely sensitive to such fields, shields are
very important to us! In cabling, shields often
consist of braided copper strands wrapped around
the signal conductors. The amount of coverage
the shield provides is directly related to the
noise and hum performance of the cable. Some cables
offer a shield consisting of a thin wrap of metallic
sheeting, which can offer complete coverage of
the encased signal conductors. Quality shielding,
while more expensive, makes a tremendous difference
in the noise performance of a cable - skimping
on cables is never a good idea!
|
Line Level
- |
The average
voltage of an electronic audio signal. There are
two line level references in use today: Balanced
"pro" gear (XLR) runs at around
+4 dBm (1.23 volts), while unbalanced
"semi-pro" consumer gear (RCA/Phono
Jacks) operates at approximately .316 volts
(-10 dBV). The two operating levels must not be
interconnected directly. The important thing is
to match the levels of the gear you are using
so that -10 equipment isn't directly feeding +4
equipment, and vice versa. If you use gear of
both levels, there are various level matching
devices on the market to properly interface the
items.
|
Mic Level
- |
The level (or
voltage) of signal generated by a microphone.
Typically around 2 millivolts. Compare this with
the two normal line levels (1.23 volts and .316
volts), and it becomes apparent just how much
amplification is going on in a microphone preamp,
and why it is essential that preamps be of as
high quality as possible!
|
Speaker
Level - |
The level to
which the line level is amplified to power the
speakers. This will vary from a few volts to 70
volts depending on the volumes selected and amplifiers
used. Speaker cables are unbalanced and usually
are 1/4” TS
phone jacks for smaller speakers and speakons
for larger speakers.
|
Mains Level
- |
120Volts (220V)
right out of the wall used to power the system.
Consists of a “hot” leg, a “cold”
leg and a ground all in 3 parallel wires. It is
important that the 3 wires are in “phase”
or electrocution may occur. All outlets should
be tested before use as a significant number are
defective or out of phase.
|
Unbalanced
Cables - |
A condition
where the two legs of the circuit are unbalanced
with respect to ground, usually because one leg
is kept at ground potential rather than as a discrete
return (cold) leg. An audio signal requires two
wires or conductors to function. In an unbalanced
situation, one of those conductors is used to
carry both signal (cold) and ground (shield).
Unbalanced circuits tend to be less expensive
to construct, but they are much more susceptible
to induced noise problems than their balanced
counterparts. This is because any induced noise
in one conductor is not cancelled by similar noise
in the other conductor (as in a balanced line)
and may be carried with signal into connected
equipment. In general, unbalanced lines should
be kept as short as possible (certainly under
25-30' maximum) to minimize potential noise problems.
|
Balanced
Cables - |
In audio, the
opposite of Unbalanced. Balanced refers to a type
of AC electrical signal having two "legs"
independent of ground. One is generally considered
positive (+) “hot” and the other negative
(-) “cold” in voltage and current
flow with respect to ground “shield”.
Unlike unbalanced audio lines there is no "signal"
carried in the shield or ground connection unless
there is a fault. The main benefit is that any
noise that gets induced into the line will be
common to both the positive and negative sides
and thus cancelled when it arrives at its destination,
assuming the destination is balanced. Balanced
lines are generally much better for long cable
runs due to their ability to reject induced noises.
XLR and TRS type cables are designed to transmit
balanced audio from one balanced device to another.
A standard 1/4-inch guitar cable is an example
of an unbalanced cable.
|
|
Circular 3-pin
connectors developed by Cannon. "XLR"
was originally nothing more than Cannon's part
designation for the connector. You'll also sometimes
see these connectors referred to as "Cannon"
connectors. XLR has since evolved into a generic
industry term, and many manufacturers now make
this style connector. In audio work, XLR connectors
are normally used for transmitting balanced mic
and line level signals. Pin 1 of an XLR connector
is always ground/shield. Either pin 2 or pin 3
may be hot (determined by the gear the connector
is plugged into), with the remaining pin being
cold.
|
Phone Plug -
|
A phone plug
refers to your standard, run-of-the-mill 1/4"
connector, jack
or TS (tip/sleeve)
plug. The name gets its origin in the old telephone
switchboards where the phone patching cords all
had this type of connector on them. While the
term phone plug is usually taken to refer to standard
1/4" tip sleeve connectors it has actually
come to refer to a family of connectors that are
all similar. A TRS
(tip/ring/sleeve) plug is a form of phone plug
sometimes called a stereo jack. The sleeve is
ground/return. The tip is hot and the ring can
remove the return function from the sleeve. TRS
connectors are used wherever it is desired to
have two conductors plus a ground (shield) in
one plug. Common uses are as a way to connect
balanced equipment (where the TRS plug has a positive,
negative, and ground connection), or stereo unbalanced
equipment (left and right are on the Tip and Ring,
with a common ground) like headphones.
|
|
A small inexpensive
coaxial connector used for interconnection of
many audio devices, especially consumer devices.
Not to be confused with the phone plug, which
was developed and used by Bell labs for telephone
patch cables, the phono plug was first used by
RCA to connect phonograph tonearms to their amplifiers,
hence the name Phono Plug.
As a result of it being common in RCA brand equipment,
it is also widely known as an RCA
plug. Phono plugs are not renowned for
their durability and longevity, but they are small
and easy to use. RCA plugs are unbalanced with
the center "hot" conductor being surrounded
by a “ground” connection.
|
|
A type of multi-pin
connector developed by Neutrik, which is now commonly
found on speakers and amplifiers, intended to
be used in high power mobile applications. They
have become popular because they offer a very
high quality reliable connection, can handle extremely
high power, are very durable, and are relatively
low cost compared to other similar connectors.
|
For a more in depth look at the wire connections inside
the cables, look at the top 10 illustrations in the
Spirit-Connections-Document.PDF.
I have used images, documents
and abridged definitions from the three following sites
and I do so unabashedly as I happily recommend you give
these highly regarded companies your custom.
Sweetwater.com/inSynch
- Excellent audio reference, good prices, very knowledgeable
staff.
Neutrik
Connectors - The only connector I will now buy
Spirit
by Soundcraft - Check out the "M Series"
- Great sound, value and very easy to use.
|||Part
Two - Continue further
as I bring you to an understanding of the uses of these
cables|||
Stephen
Vardy
Harpsound
Audio
[email protected]
|
