Anti-Phase (180°)

Anti-phase conditions are one of the most destructive problems in sound reinforcement. When two loudspeakers reproduce the same signal but one is wired with reversed polarity, their outputs are anti-phase. At the listener position, the positive pressure from one speaker arrives simultaneously with the negative pressure from the other, and the two cancel. Perfect cancellation only occurs when both signals have identical amplitude and exactly 180-degree phase offset. In practice, the cancellation is frequency-dependent because the path lengths from two speakers to a listener differ, creating a phase relationship that varies with frequency. Low frequencies with long wavelengths are most affected because the path-length difference is small relative to the wavelength. Common causes of anti-phase problems include reversed speaker polarity (swapped positive and negative terminals), incorrectly wired XLR cables, and phase-inverted processing in a signal chain. Subwoofer-to-main alignment issues frequently create partial anti-phase conditions in the crossover region, causing a pronounced dip. SonaVyx detects anti-phase conditions through its polarity checker in the Problem Detection suite and through transfer function phase analysis. The transfer function measurement shows the phase relationship between the reference signal and the measured output, making it easy to identify frequency ranges where destructive interference occurs. The fix is usually simple: correct the polarity of the reversed source, adjust delay timing, or apply polarity inversion in the processor. SonaVyx's before/after comparison confirms the correction.