SPL meter subwoofer tuning

SPL meters can get you kindof close but it really takes tuning by ear. When "perfectly" flat response is acheived according to the SPL meter it usually sounds bad. There is a formula for correcting the RadioShack meter that can help (search archives). If you want to measure inroom response you will need a disc with worble tones. This plays a tone that varies within a small range continuously to eliminate the single tone building up and resonating within the room which would give a false reading.
Placement flexibility is the biggest obstacle though. Get a 10meter generic interconnect (less than $20) and place the sub in every livible location.

Good luck!

You'll need a test cd to generate various frequencies. The problem is unless you have an EQ you are only left with crossover frequency, volume, placement and probably phase.

How do the subs sound now? Why are you not satisfied?

There are MP3 pure test tones (from 10Hz to 300 Hz in 1 Hz increments) that can be downloaded from RealTraps website and which you can burn to make a test CD. The digital Ratshack meter is another essential tool with this approach. There is a plot that you can use too. As the 10 second pure tones maximize the room modal response, I suspect that it is best to eyeball the curve and concentrate on taming the broader "bumps" rather than trying to eliminate the inevitable sharp spikes/troughs that you get with a CD with single frequencies.

A PEQ, used sparingly, seems to be another essential tool in practice. (for example It may not be acceptable to install the significant amount of bass traps that might be needed to make an impact on a large room with significant modes below 60 HZ)