Let’s say you normally mount your full-range PA speakers directly atop your subwoofer using the custom designed SP1BK sub pole. Whether with a StudioLive AI speaker or Brand X, with this configuration, your full-range system and subwoofer should be time-aligned for practical purposes, so you can leave the StudioLive 18sAI’s alignment setting at 0M (no delay).
But what if your sub can’t be set up directly beneath your full-range StudioLive loudspeaker? If the same low frequencies are reproduced by two sound sources that are set some distance apart, you’ll have problems with cancellation and reinforcement. Low frequencies in the crossover region between full-range and subwoofer have wavelengths that are several feet long (the wavelength of a 150 Hz wave is about 7.5 ft!), and reinforcement and cancellation will occur as the waves interact in the room.
The StudioLive 18sAI’s alignment delay presets compensate for this effect. For instance, if your full-range speaker is on a tripod stand adjacent to your subwoofer, the two speakers are typically about one meter apart. Choosing the 1M setting will delay the signal to the subwoofer’s onboard amp by about 2.9 ms, which compensates for that 1 meter offset.
If your full-range system is onstage, and the subwoofer is on the floor, assuming a typical stage, the two will probably be about two meters apart. The 2M setting adds about 5.9 ms of delay the signal going to the subwoofer amp, which compensates for a 2 meter offset.