If you don't already own an inexpensive SPL (sound pressure level) meter, get one.
These meters can be had for twenty bucks or so and are quite durable in my experiences. I have personally owned a variety of meters for close to 20 years now and as long as you remember to keep a fresh battery (usually a single 9 volt) in them...they appear to last forever.
Here is one I recently purchased to test out and it appears to use the same microphone element as the tried and true Radio Shack meters.
This is a good thing as the Radio Shack meters have been tested quite thoroughly. They are reasonably accurate and there are plenty of "compensation charts" available for the deep bass range where this SPL meter tends to "roll off" a bit. For example, add the following to this meter's readout...@20hz add 7dB, @25hz, add 5dB, @31hz add 3dB, and from 40hz to 80hz add about 2dB. This will give you very accurate measurements. Also, since most subwoofer calibration tones produced by AV Receivers are limited to the 40-80hz range add about 2dB here too.
Back in the 1990s having a SPL meter was mandatory for accurate system calibration. Today, most AV Receivers and processors have some sort of "automatic speaker/system calibration feature. Even so, having a SPL meter handy will still allow to double check the accuracy of the channel level settings. You can check peak output levels of your favorite action oriented DVDs at your seating positions. And having a SPL meter will allow you to troubleshoot "weak" channels, improper phase(or distance) settings, and other potential gremlins that may pop up in your home audio system(s). You can even take the SPL meter along the next time you travel to a professional sporting event like a NFL football game. This will allow you to see how your team's fans compare to Seattle's fans.http://espn.go.com/nfl/story/_/id/10071653/seattle-seahawks-fans-set-stadium-noise-record
If you do purchase a different model SPL meter be sure it has a "C weighting" option. Some meters only have "A weighting" which will not give you accurate measurements in the bass frequency range.
If you already have a meter, dust it off and check your channel calibrations. Even if the receiver has an "automatic speaker setup" feature it may or may not be accurate. And even if it did a good job things may change. Changing the room environment can change things a bit. And if your have experienced a power outage, even for a few seconds, your system may "reset" with incorrect menu options/settings. Never hurts to double check and it only takes a few minutes.
Power Sound Audio