I'm currently using two SVS 25-31PC+ subs along with the 950/ICBM for HT and music (no SACD or DVD-A just yet). The ICBM is installed between the 950 and the amplifier.

Note that the subs have variable phase controls (0 - 180), and they're setup to work in stereo, not mono, using the ICBM. Also, each sub is located near its corresponding L/R main speaker. Main speaks are away from side and rear walls.

Does anyone have advice on the best method (using the old Avia disc and a Radio Shack SPL meter) for calibrating the phase and output levels for the subs relative to their corresponding mains?

Thanks in advance.

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).]

Thanks for the response. I'll get a test-tone CD and give it a try!

Bestbang4thebuck,

I noticed in one of the other threads that you also are using stereo subs with the ICBM.

I'm curious about the calibration steps that you followed to get the subs integrated well with your mains.

Thanks in advance.

I use an Outlaw ICBM to integrate and operate two powered subwoofers in my system in a stereo configuration. The ICBM is wired between the 950 and the amplifier in order to provide bass management for any source used, with or without processing, by the 950. I configure the 950 for "large" speakers everywhere, letting the ICBM handle all the crossover work. Each sub has its own input level adjustment. The subs are slightly elevated from the floor and placed almost directly underneath the left and right speakers. I have a relatively small room, so the fronts and subs are near corners, about one foot from the side wall and three feet from the front wall. I initially set up this way:

- I setup the subwoofer phasing first.
- Per the instructions for the 950, I perform channel calibration with a SPL meter for all channels except the subwoofer. I note the settings for the front left and right. As an example, let’s say that the front left setting is “4” and the front right is “3.”
- Without changing the main volume, I go to the subwoofer channel calibration and set it to “4,” agreeing with the front left setting. At this point the subwoofer output of the 950 is providing low frequency noise.
- I unplug the front left channel input cable from the ICBM and connect the cable carrying the LF noise to the front left input of the ICBM. The ICBM sends very little of this signal to the amp for the main speakers, but directs this LF noise to the ICBM left sub output.
- I adjust the level of the left subwoofer until the SPL meter reads about two dB lower than the calibrated reading of the main speaker. I do this because I know the meter I have reads very low frequencies about two dB lower than they actually are.
- I change the ICBM cable connections so that the front right ICBM input is now receiving the LF noise from the 950. I adjust the subwoofer channel calibration to “3,” agreeing with the front right setting.
- I adjust the level of the right subwoofer until the SPL meter reads about two dB lower than the calibrated reading of the main speaker.
- I restore the cabling on the ICBM to normal.
- I turn the LFE level control knob on the ICBM to the LFE calibration position.
- I adjust the 950’s subwoofer channel calibration while watching the SPL meter, again seeking a reading about two dB below the main speaker level meter reading.
- I return the LFE level control on the ICBM to its normal position of -10dB.

This is my preliminary set up. Further minor refinement may follow based on test signals generated from DVD and/or computer software. Additionally I listen to familiar passages. For instance, if one knows what an electric bass sounds like in regard to fundamental low frequencies mixed with somewhat higher harmonics of the strings in some styles of play, listen to make sure the low fundamentals are present and strong in the right places, but such that they are in the proper ratio to the higher harmonics coming from the main speakers – not so strong as to muddy the tightness of certain electric bass or drum playing. I have found that “refinement” adjusting with only one particular musical passage ends up giving me my favorite “system tuning” for that piece, and this may not be good for another piece of music. On one piece of music, I am boosting bass, on another piece, I am lowering the sub levels. I almost always end up being the happiest overall with the preliminary settings I obtain in the first place, or just slightly less than these settings.* So my recommendation is to be very “gentle” in varying the setup “to taste” after following the steps above.

I hope this helps. It may at least be a method with which to experiment.

*The reason I usually end up working "down" from these settings, is because I suspect producers of some recent music may be pushing the very low end of their mix mildly upwards in amplitude, or using some kind of "add a lower octave" processor to get a "low end feel" when playing back on normal consumer equipment, for home or vehicle, that rolls off more significantly at the low end than on the equipment belonging to those of us who seek frequency extension beyond the directly audible. Even within one CD, such as Bare by Annie Lennox, there are cuts which sound great with my initial sub settings, and other cuts with extended low end that overpower the rest of the music when played back on my main system. If I lower the subwoofer output level on the ICBM to bring the bass on the "extended low" cuts into line, then other music ends up without sufficient low end. This part is subjective, of course, but, after all, it's the end result sought is the best listening possible ... and "best listening" involves the subjective, doesn't it?

Enjoy the journey!


[This message has been edited by bestbang4thebuck (edited February 06, 2004).]