And it's something that was recently brought up on the Great Church Sound Techs Facebook group.
The venerable 1/4" (6.35mm) phone plug has been with us for a long time – since 1878!
Something that has been around that long is bound to have a lot of different uses associated with it.
Yes, it's called a "phone" plug because...
As it relates to audio and professional live sound systems, the 1/4" plug is used for 5 primary functions:
- Stereo cables (headphones)
- Unbalanced cables (guitars)
- Balanced pro audio cables (console outputs)
- Insert patch cables (side-chain effects like reverb or compression)
- Speaker cables (monitors & mains)
The first four cables may look exactly the same, but they have different uses for the signal conductors in the cable.
The last one (speaker cables) can cause huge problems if you use the wrong cable in the wrong place!
Even though the connector can be the same shape and size for each of the five applications, you need to pay special attention to the cable configuration and how it relates to your equipment.
It may be helpful to see how this works in respect to the connector segments.
(There's a nice overview and discussion about this in the the book and the Church Sound Basics video training course if you're interested in learning more.)
The important thing is that you need to pay attention to what your audio OUTPUT jacks are configured to deliver and compare that to what your audio INPUT jacks are expecting to receive.
Then use the right cable and connector type for the job.
If your gear sends out a left/right unbalanced stereo signal, don't plug it into a piece of gear expecting a balanced mono input. You'll loose half of your audio signal (the right channel most of the time), and you could cause some other system anomalies and noise.
If you're unsure about the gear, jacks, and signal types you're working with, read the manual or do a quick Google search. You can generally find the details pretty quickly.
Hopefully that helps clear up a little confusion!
(Check out this Wikipedia entry for more history on the phone plug.)