Setting The Subwoofer Level

The best succinct article I've read about properly calibrating a sub is by Tom Holman in the September 2001 issue of Digital TV magazine (which I've not been able to find online), so I'm paraphrasing it here. Because of the initial works of Fletcher and Munson in the 1930's (nowadays we use the updated ISO standard), we know that our perception of loudness is not very flat, and it takes more bass energy to sound equally as loud as the midrange. To get that extra headroom to achieve "equal" loudness, the LFE channel is "turned down" by 10dB in the medium and "turned back up" by the end user's equipment. Work by Eric Benjamin of Dolby Labs confirms that this 10dB amount is a good choice. However, since the bandwidth of the LFE channel is less, it should NOT measure 10dB greater using noise. The best way to set the level is to observe 10dB in-band gain above that of one of the main channels in its operating frequency. In other words, with a 1/3-octave RTSA, if the center channel measures 70dB SPL, then the LFE should read 80dB SPL in its active bands. In a pinch, with your typical Radio Shack analog SPL meter on the C-weighted curve (which rolls off the bass), the LFE with band-limited pink noise should measure approximately 4dB greater than one wideband channel playing pink. The best way is still to use an RTSA though. Holman also mentions this in his book Surorund Sound: Up And Running on page 60. You can read it for yourself on Google Books.