Adjustable phasing primarily addresses the time when both the main loudspeaker and the corresponding subwoofer are reproducing the same frequency. This is generally at the crossover frequency. With an ICBM between processor and amp, letting the ICBM handle the crossover point, not the subwoofer, I would adjust as follows:

1)To only one channel, send a single-frequency tone of the crossover frequency.
2)With the SPL meter at the usual listening position and
3)with the subwoofers off, find a volume level that is over extraneous noise but doesn’t cause things in the room to rattle – note the reading on the SPL meter.
4)Interrupt the tone without changing the level at which it will play.
5)With the main speaker off and only the corresponding subwoofer on, restore the tone and set the level for the subwoofer to match the same SPL as the main speaker provided.
6)Interrupt the tone without changing the level at which it will play.
7)Allow both the subwoofer and the main speaker to operate and restore the tone.
8)Adjusting the phase only should cause an level change at the SPL meter as the tone coming from the two slightly different locations arrives at the listening position interactively in either an additive or canceling manner – seek the maximum SPL. There may be, due to room considerations, more than one place throughout the phase adjustment that brings an increase in level at the listening position.
9)Repeat steps 3 – 8 enough to establish consistency without further adjustment.
10)Repeat the process for the other main channel.

This will not work over a range of frequencies, as the additive or canceling interaction will be different at different frequencies. For this reason, making phase adjustments at 100Hz does not mean you have attained proper phasing for setting your crossover to 40Hz. Also, should you move either main or sub to a different location, it will be time to phase adjust again!

This procedure does not necessarily determine the level at which your subwoofer will best perform with the rest of your system, it only provides for a phasing adjustment at the crossover frequency. After completing the phasing adjustment, then go through your normal subwoofer level setting procedure, which I assume uses a range of frequencies or pink noise, changing the subwoofer level without altering the phase adjustment.

I hope this helps.


[This message has been edited by bestbang4thebuck (edited January 23, 2004).]