When used with a Presonus StudioLive 312AI, 315AI, or 328AI, the Presonus StudioLive 18sAI subwoofer forms a true four-way system. But the Presonus StudioLive 18sAI is flexible enough to work great with other powered loudspeakers, too!
With most 4-way systems, leaving frequency content below 100 Hz in the full-range loudspeaker can introduce cancellation and reinforcement with the highest frequencies that are reproduced by the PreSonus subwoofer. Some frequencies will be exaggerated (reinforced) while others are weakened (cancellation).
PreSonus StudioLive AI loudspeakers avoid this problem when combined with an 18sAI subwoofer. For applications where a frequency overlap at 100 Hz is beneficial, you can achieve bigger bass sound without any extra effort. For applications that require a more linear (“flat”) frequency response between the subwoofer and full-range speaker, simply engage the highpass filter on the full-range PreSonus StudioLive AI loudspeaker. This will also readjust the phase and time-alignment to keep the full-range system in phase with the 18sAI subwoofer, enabling you to create the best four-way system for your application.
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 PreSonus 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 PreSonus 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 PreSonus StudioLive 18sAI’s alignment-delay presets provide compensation 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 on stage, 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.
In this way, you can keep your subwoofer in alignment with your full-range system for the most common speaker configurations without any extra gear. You’ll experience tighter bass response and a more cohesive sound, which means better intelligibility and bigger sound without more volume.