Originally Posted by aarons915
This makes sense and is basically what I do but one detail I haven't seen addressed is the frequencies above the summed bass and below your room's schraeder frequency. I believe bass is summed under about 120Hz so it makes sense when correcting up to 120Hz to measure in stereo and use that for your parametric EQ filter, but between 120-200Hz or so, would I still use a stereo measurement or measure individually and apply EQ using the individual measurements?
Aha! You have found the weak spot - above low bass but not above the transition frequency. Incidentally, the Schroeder frequency, according to its creator, Manfred Schroeder, applies to large performance venues, not small rooms - the principle reason has to do with the lack of a genuinely reverberant/difffuse sound field in small dead rooms). The calculated frequency is close, but wrong. I elaborate in Section 6.2 in my book, with examples.
So, back to the topic of interest - measurements - as long as there are active somewhat orderly standing waves in a room it matters greatly whether there are single or multiple sources of sound. This is the topic of Chapter 8 and is well illustrated in Figure 8.13. So, it matters greatly how recordings are made and there are no rules - sometimes bass can be directed to a single channel, sometimes to multiple channels. Because consumer playback systems tend to be lacking in bass, it has become good practice to send bass to both channels, but obviously, this is not always done. If stereo bass is attempted, the recording studio/venue low-frequency modes will add unpredictable differences between stereo mics.
In LPs mono bass prevents vertical stylus movement, which modulates the tracking force, detrimentally affecting tracking capability, and with sufficient bass energy can throw the stylus out of the groove. Not doing this is possible only in recordings with little bass, or by those willing to risk mistracking and distortion.
In the playback situation, to be comprehensive one would need to measure all possible combinations of single and multiple loudspeakers. There would be several answers. The dominant acoustical effects in this frequency range are likely to be associated with boundary effects discussed in Chapter 9. This, of course, is a good argument for bass management and subwoofers but, as you noted, what happens for the next octave? I do not see a single technical answer, but experience tells us that human listeners seem to accommodate these variations as part of adapting to rooms.