I recently finished my theater (https://www.avsforum.com/forum/19-ded...ent-build.html
). I'm still in the process of dialing everything in but I have a serious room null that's driving me crazy. I've spent close to 10 hours moving subs and measuring and I just can't seem to get a handle on it. I've also spent multiple hours on the forums and have read through the Harmon white paper on sub placement. No matter what, I seem to have a 2-3 foot null for basically 80hz and below that spans the entire length of the room right down the middle (impacting both front and rear center seats).
My room is 18' x 12.5" with low ceilings (80"). The room fairly air tight and was built with DD+GG. I've got a media cabinet and equipment rack in the rear two corners (floor to ceiling drywall) connected by an 8" x 8" soffit. All of the empty areas were stuffed with insulation. Currently the subs sit on a sand/insulation filled stage (6" tall). I've also got a 4'10" x 7'6" x 16" riser which doubles as a bass trap (filled with insulation and lots of 3" holes). The front corners have floor to ceiling "super chunks" which span 24" across and fill the entire corner. The room also has 6 - 2'x4'x2" acoustic panels. My current setup includes two Def Tech ProSub 1000's connected to a Yamaha A2050 AVR.
Here's a couple shots of the room:
I also put together a quick drawing with dimensions and locations I've tried so far. The wavy lines in the middle represent the null.
I've not done a detailed analysis, so far I've just been testing using 31, 40, 50, 63, and 80hz test tones. However, I can say the difference is dramatic across all of those bands. In most cases, especially 50 and lower, I'm seeing a 15-25db difference in the left and right seats vs. the middle. The left and right seats for both rows remain within 2-3db in the majority of placements.
Current setup is in position 1 which is basically me giving up for the moment. Corner loading them makes no difference in the null, moving them from the side walls a bit seems to provide a little smoother response outside the null so that's where I've landed for now. I've also tried basically every position possible across the stage (including placing them higher, pointing them in every direction possible, etc.). Basically no placement in the front seems to make much of a difference for null or otherwise. Position 8 (front and rear center placement) provided the best results in terms of leveling out the null. However, this position is less than ideal as my second row is against the back wall and it still didn't eliminate the null. The "crawl" method with single sub in front center chair yielded the most db in position 7. While it did increase the db in the null, there was still a huge difference seat to seat (not to mention the left and right seats were too boomy). Position 9 (opposite corners) also helped with the null but created much larger dips and peaks between seats. Oddly enough, the null is actually reduced when I unplug one sub, normally a 3-6db increase at the null. However, this may be normal due to some sound waves cancelling each other out. I perform more detailed measurements if it would help (i.e. write down db's for each seat with different placements). I haven't done that as of now because I don't need to see the numbers to tell how big of a difference there is. Essentially, you can stand 2 feet left or right of center and bass is overwhelming, step to center and you can't even tell they are on.
Anyways, hoping some of you experts may have some additional thoughts. I'm looking at upgrading my speakers/subs but don't want to invest in bigger & better subs with this nasty null. I'd also like to avoid adding two more subs due to space (not to mention my wife would likely kill me and I'm not convinced it would help). Moving the seating also makes no difference as the null is the same from front wall to back wall. I've also played around with moving the couch just to see if it impacts anything, it does not. I'm at a loss...