Subwoofer Alignment

Subwoofer-to-main alignment is one of the highest-impact optimizations in live sound. At a crossover of 100 Hz (wavelength 3.43 m), a timing error of just 5 ms (1.72 m path difference) produces complete cancellation. Even 2 ms of misalignment causes a 4 dB dip at crossover. Given that subwoofers and mains are often physically separated by several meters, achieving alignment requires careful measurement and delay adjustment. The standard alignment procedure: (1) Measure the mains alone to establish their arrival time and level at the measurement position. (2) Measure the subwoofers alone at the same position. (3) Compare the phase of both systems at the crossover frequency. (4) Add delay to the earlier-arriving system until the phases match at crossover. (5) Check polarity — if the sub and main are 180° apart, flipping sub polarity is faster than adding half-wavelength delay. The complication is that subwoofer delay depends on the crossover filter type and order. A 4th-order Linkwitz-Riley crossover at 100 Hz adds about 3.2 ms of group delay to the subwoofer signal (the low-pass section delays more than the high-pass section). This filter delay adds to the acoustic propagation delay and must be compensated. Physical placement also matters. Subwoofers on the ground benefit from half-space loading (+6 dB from ground reflection), but the ground reflection path creates a comb filter effect at higher frequencies. This is one reason subwoofers are crossed over below 120 Hz — it keeps them below the first comb filter null from the ground bounce. Cardioid subwoofer arrays (end-fire, gradient) require individual driver delays for pattern control. These delays interact with the sub-to-main alignment and must be set first, then the overall sub array aligned to the mains. SonaVyx facilitates sub alignment through its transfer function mode, showing phase and coherence at the crossover frequency.