Phase (cancellation, interference)
Running two inputs 180° out-of-phase puts the peaks and valleys of the sine wave so that they null each other out when summed (see the middle picture below). This has a tendency to cancel out both inputs, and is quite pronounced in the "far" field, but negligible in the "near" field. Normally phase cancellation is undesirable, but when you know what you want (and in this case, what you don't want) then you do it deliberately.
Use this category for articles that reference this concept.
Phase cancellation occurs when two signals of the same frequency are out of phase with each other resulting in either a boost or cut in the overall level of the combined signal. -- Phase at the Zen Audio Project
If you are suffering from some or all of these, you could be experiencing Phase Interference
- "Hot" and "cold" spots in the audience area
- Tonal coloration
- Poor speech intelligibility
- Lack of music clarity
- Poor gain-before-feedback
- Poor imaging