Interconnections
Cables are used to connect the various parts of our sound systems together. Those cables are made in different varieties for different applications. Some are used for "balanced" connections, while others are used for "unbalanced", and still others are used for speaker level connections.
Balanced connections are almost universally used for microphones since the electrical level out of a microphone is very low and balanced connections help reject interference from being picked up. The cable used for balanced connections is made with a pair of wires twisted together, and a wire or foil shield around the twisted pair.
The connectors used at each end of the cable are usually of the "XLR" style for microphone connections:
For other "line level" connections they may be XLR or 3 contact (Tip Ring Sleeve or TRS) 1/4" plugs:
Note that the same style of 3 contact 1/4" plugs are used for stereo headphones, but the cable and signal type are different. This is a potential source of mistaken connections since the same style connector is used commonly for at least two different applications (but with different cable types connected to it).
In most cases the use of balanced connections is enough to keep out interference, but GSM or Nextel cell phones and Blackberries have been able to inject mosquito like noises into condenser microphones. Neutrik has developed a special XLR type connector (NC3FXX-EMC) that if used in place of a standard XLR connector at the microphone, can in many cases greatly reduce the cell phone interference:
Unbalanced connections do not provide the rejection of interference available from balanced connections, and therefore should only be used for shorter connections (up to about 20'). They are generally made with a cable that has only one wire inside the shield:
Guitar cords are a very common sort of unbalanced connection, and usually have two contact (Tip Sleeve or TS) 1/4" plugs at each end:
Note that these plugs look very similar to the 3 contact variety used for balanced connection or stereo headphones, except they don't have the "Ring" contact, but only the "Tip" and "Sleeve" contacts.
Unbalanced instrument connections can be converted to balanced connections so they can plug into balanced microphone type inputs using a "direct box". A typical direct box will have two 1/4" jacks (one for the instrument and one to connect on to an optional instrument amp) and a XLR jack that outputs a balanced mic level signal:
Speaker connections are made with cable that generally does not have a shield, and has thicker copper in the wires to reduce loss of sound quality and level in the cable:
Speaker cable comes in several different physical constructions. The wires may run parallel to each other in a zip cord style:
Or they may be twisted like a balanced cable but without a shield:
Old style speaker connections were often made with the same sort of two contact (Tip Sleeve or TS) 1/4" plugs used for unbalanced connections:
This can easily lead to confusion and even blowing up equipment when incorrect connections are made. Since speaker wire is not shielded, this can result in hum and buzz if it is used by mistake for unbalanced connections. To reduce the chances of error a special connector type used only for speakers was developed called the "Speakon":
Many power amplifiers and loudspeakers today are using Speakon connections. Using a type of connector for speakers that is not used for anything else helps make our lives simpler and our systems more reliable.
Ray A. Rayburn
Ray@K2Audio.com
http://www.K2Audio.com/
Special thanks to Neutrik for the connector photos, to Belden for the wire drawings, and to Radial Engineering for the direct box photo.
