Subwoofer Question

as a data point to the thread for me it was different with different subwoofers.  even with low xo , e.g. 45 hz and steep 28db slope my SVS SB 3000 was directional and pulled the image.  

REL T9i was also directional.  

JL Audio D110 placed in a corner was not directional.  

i believe the issue may be caused by enclosure resonance well above 80 hz.   

@elliottbnewcombjr 

the cone of the driver that makes the fundamental ALSO makes the overtones. They are not generated electronically, they are generated physically, relative to the fundamental

Whatever gave you that idea?  Your first video is no help at all.  Don’t you understand that the harmonics are part of the audio signal which is separated into frequency ranges by crossovers?

Yes, harmonics are not (usually) generated electronically, they are generated by the originating instrument and are what gives each instrument its sound signature.

When a piano, for example, plays a low note, the fundamental may be sent to the sub-woofer but the first harmonic will go to the woofer, the second harmonic maybe to a mid-range driver and some very high harmonics will be handled by the tweeter.

They are absolutely not all handled by the cone of the sub-woofer.

There are special considerations.  If the sub-woofer cone does not follow pistonic motion, but experiences cone breakup, these will show as nasty higher frequencies generated by the sub-woofer cone.

As several others have pointed out, cross-overs are not brick-wall filters so there is some bleed through of higher frequencies.

Some distortion is generated electronically and is sometimes encouraged, for example in valve amplifiers

If you can 'locate' the single sub easily, then of course it affects the imaging.  Even if it does not technically 'pull the image' to one side, the ears  ability to locate the bass affects the image in your brain.  If properly set up, a single sub can often still easily be located.  Just close your eyes and listen.  If you can point right to the sub, it it not nearly as ideal as two subs.  In both of my listening spaces, my pairs of subs are located well off the the sides and are not even easily seen from my listening positions. Placing them here made a huge difference compared to right beside my speakers, but it was for decreasing booming not imaging issues.  Congrats on turning the lowpass filter down to help!