Originally Posted by Ferrari_1996
It's not sub related. When the measurements are done, they are done for each speaker individually. First a frequency sweep is sent to the FL speaker, then the FR speaker and then the sub. So the graphs you see are for each speaker alone. Therefore, the nulls that you see at 150Hz for the FL and FR are without the sub playing. I think you should forget about this as it's a narrow null that is room related and I'm not going to move my speakers. I appreciate you trying to help
Darth was definitely just trying to help, but it seems that the longer this conversation goes on, the more confused some things seem to get.
Perhaps for others reading along, it would be helpful to try to clarify a few things, and then to allow this particular discussion to subside. First, I completely agree that a narrow null at 150Hz would be very unlikely to be audible in any way. For one thing, at that frequency, each note in an 8-note octave would be about 12Hz wide. For another, there would always be harmonics of that note, in any case. For a third, our brains are very good at filling-in any missing information, without us even noticing.
Second, the graphs that you are looking at with the Audyssey app do not represent actual sweeps of the frequency response. Audyssey has no mechanism to self-measure its results, after it sets the filters that attempt to smooth peaks and dips in the frequency response. All 8 microphone positions of XT-32 are used to set the filters. There is no way for Audyssey to measure the results afterwards, which is why some HT owners use REW.
The graphs that you are looking at are simply somewhat crude representations of what Audyssey was trying to accomplish with the control points that it set. They are somewhat crude because the actual control points are far more numerous, and may have much more subtle effects, than what can be shown in those graphs. They give us a general idea of what Audyssey was doing, but our ears and/or our independent measurements are the confirmation of how successful automated room EQ is.
(Incidentally, all systems of automated room EQ work the same way with respect to settings filters. There is no self-measurement mechanism; only independent external measurement, post-calibration, with something such as REW.)
Third, there is often some confusion about the .1 LFE channel. That confusion persists, in part, because we use some terms interchangeably. The LFE channel only exists for 5.1 and higher content. The .1, in 5.1, is the low-frequency effects channel. The LFE channel was specifically created by Dolby/THX to provide louder bass special effects in 5.1 movies. More recently, 5.1 music may also have an LFE channel.
When people speak of 2.1 music, however, they are merely speaking of playing stereo (2-channel) music, with a subwoofer in their audio system. And the term 2.1 is confusing (and technically incorrect) when we use it that way. We aren't adding an LFE channel. We are simply bass-managing the two-channel content to send bass, below a crossover, from our front speakers to our subwoofer(s).
Even if we expand the music to multiple channels, using something like Dolby Pro-logic II (PLII), we are still just playing two-channel music which has been extracted and redirected to a center channel and to surround channels. There is still no LFE channel, in any case. We are still just bass-managing our bass from the various speakers to our subwoofer(s).
I really felt that I needed to clarify some of these issues, for people who might be reading along and getting more, rather than less, confused by the recent discussion. I hope that the clarifications help, and that everyone takes them in the spirit intended.