SPEAKERS.net

Most loudspeakers have two wires that must be connected to the source of the signal (the audio amplifier or receiver). This is usually accomplished by five-way binding posts or spring wire clips provided on the back of the enclosure. Most professional speakers (except studio monitors) use 1 or more 1/4" phone plugs (in case of being bi-amplified), or a single Speakon connector, when the speaker enclosure is Bi or Tri-amplified. Some speakers have an input and an output to connect directly to another speaker.

Correct signal polarity (phase) must be observed. If both sets of wires for left and right (in a stereo setup) are not connected in phase, the speakers will be out of phase from each other and destructive interference in the sound waves will occur. In this case, any motion one cone makes will be opposite to the other. This type of wiring error creates inverse sound waves that partially cancel out the sound of the other speaker. This does not cause silence, because reflections from surfaces diminish the effect somewhat, but results in a major loss of sound quality. The most prominent effect to the untrained ear is a loss of bass response. The second most noticed is an unsettling feeling.

A similar effect is used in noise-cancelling headphones. The headphones produce the inverse sound waves of the external noise. The inverse sound waves and external noise cancel each other out and produce near silence.