Originally Posted by LTD02
"I believe Ricci had the same problem but even lower in freq., and it was either his floor or one of his walls resonating and acting as an absorber."
this is probably what is happening.
Yup, have the same thing in my front row, room is too small to have a mode that low, but the ceiling above moves about 1/8" at 17Hz at around 100dB at the main listening row. You can only do so much sometimes. But let's face it, just 7 years ago getting a 'flat' freq response on a sub was simply a matter of luck, and there were very little EQ or measurement options for either subs or mains/center/surrounds. Things like REW, Audyssey, YPAO and MCACC have made the home listening experience MUCH better. How did we EVER think we got good sound with simply an SPL meter and tape measure to set delays and levels on a receiver that had only one crossover freq selectable (Large or Small)?? By chance.
We live in a golden era of HT, where we can get more ULF extension than in any theater, at the expense of getting the midbass right due to room size. Systems being made by DIYers now are capable of running 6-10dB BELOW power and excursion limitations, for a truly clean sound. How many times have you been to a cinema and heard the mains being pushed too hard?
I have a very cheap and compromised system, but I have enough resolution and detail to uncover poor mic'ing jobs in films (lots of the voices in TF:ROTF are clipped). Would have never picked that up before on the old system....
OK, way too OT now....but seriously, if your only serious null is at 20Hz, you have done well. It would suck to have that null at 50Hz and take away the visceral 'punch' effect....