sub measurement, now what

[Matteo]

Hey all,
I have an modified IB setup in my riser using 4 15" Avalanche drivers by Ascendant. So, I can't move the subs to equalize. Here is my graph. Wondering if the big dip around 40hz is something I can help. I tried adding another sub to the front of the room, which helped the dip a little, but added more distortion elsewhere.
So, I am wondering if I should just EQ with my Behringer, or try some room treatments first. How would I go about helping this dip? Is it a trial and error thing, or is there some way to narrow down my options? Thanks for any advice.
Roly

[bpape]

Hi Roly

Is the dip there at all seating locations?

What are the room dimensions?

Bryan

[Matteo]

I should have thought to measure all seating areas first. My room is about 17ft wide, 21 feet long. However, I have a 20 inch high riser that starts at 12 feet from the front and extends to the back wall. So it takes up a lot of volume. I have my sub built into the face of it. I also have an HVAC system that runs from front to back on the right ceiling and is 4 feet x 1 foot. Also, my foundation extends into the room on the left and is 2 x 5 x 2. My 4 corners are at 45 angles, not 90. Here is the graph of my 6 seating positions. I can post some pics if it will help. It looks like the dip goes away on the front row, but is throughout the back row. The back row sits 20" higher and sits on the sub riser, while the front couch has its back directly in front of the subs. So the subs face the back of the couch on the front row. Thanks.
roly

[bpape]

Hmmm. Tough situation. You lost all your room corners to treat and the sub position is fixed.

To prove whether the issue is related to height or length, try measuring back a couple of feet at the same ear level as the rear row - or - measure at the rear row but up say 18" or so.

Bryan

[Matteo]

Dang. I thought I was doing my room a favor by eliminating those 90 degree corners. Could I pack them with something besides insulation to help out? Here are my measurements at rear center 18" higher, and rear center 18" forward of position and then rear center 18" back and then a graph with all of them combined. Thanks.

[Matteo]

Or, I could make the front row the main position, which may work out better anyway. Here is the graph for it. Would this be an easier fix. If I knocked down the peak from about 30-60, it wouldn't be so bad, would it?

[bpape]

Well, the corners are technically gone so unless you knock them out and re-drywall so we can treat, not much you can do.

Looks like any of the 3 options got rid of the big offending null. Looks like the first option is the best so that would mean treating the ceiling with something thick enough to deal with the lower frequencies and doing so directly over the seating position.

Bryan

[Matteo]

Are you saying you like the green graph the best, the one that is 18" higher than listening position? If so, I would have to put something thick enough right behind my projector. What kinds of materials could I use? Am I trying to reflect some of the bass back into the room, or absorb a frequency? Also, I suppose it would have to go full width of the room.
Next question. If I did decide to go with the front row as main position, where there is a peak from 40-70hz, would this treatment in the rear possibly make the front row worse? Thanks again Bryan.

[bpape]

What I'm saying is that you won't be sitting there but changing heights did help so we need to kill that dimension. Doesn't need to go full width but covering seating positions would be necessary.

I have no idea on the front row without doing some experiments to see what's causing the issue.

Also, remember that for right now, you're only looking at the frequency response. You haven't looked at the time domain (decay time muddiness and cancellations)

Bryan

[Matteo]

so what kind of treatment would you suggest above the back rows to kill that dimension? I will try to read up more on the time domain and figure out how to measure that. thanks.