Better midbass, how?

[atledreier]

Hello!

I have a room I'm pretty pleased with, both sonically and aestethically. The last nagging concern is the midbass. I have a rough area between 100Hz and 200Hz that make many instruments lose drama and presence, and I'd like to try to make it better.

This is mainly for stereo, although it is in my theater.
I use Dali MS4 fronts (2,5 way floorstanders, two 6,5"woofers, rear firing ports, one for each.
Due to my screen size and room layout, the speakers are 65cm from the side wall and 1m from the front wall (to center of tweeter ribbon). The listening position is 140cm from the back wall. The room is 520cm long by 395cm wide, and 230cm ceiling.

I have two LLT sonotubes in the back of the room. I use Audyssey to integrate mains and subs and general room EQ.

I have treated all four corners with Rockwool triangles up to about 110cm height, then a 10cm rockwool sheet straddling the corner on top of that, so I treat floor to ceiling. The front wall istreated with stacks of rockwool triangles directly behind the speakers up to about 80cm height. I also have one 10cm rockwool sheet behind my center speaker against the front wall, and one 3cm sheet at either side of the center sheet. The rear wall has four 3cm sheets of Rockwool. The 1st reflection points on the side walls each have one 10cm sheet of Rockwool.

I can move the listening position forward slightly, but not too much, as I'd get too close to the screen. The main speakers can go forward slightly, but not away from the side walls, they are right against the screen already. They can go back slightly if I make some arrangements for my curtains (to hide the acoustic treatments and create a nice acoustically transparent wall.

Attached some measurements. The red graph is with Audyssey, the green is without. The 50Hz in the waterfall is obvious mains noise from somewhere. The predicted frequency response is pretty similar to the real one in the problematic region.

[bpape]

Being that close to boundaries is going to cause some issues no matter what you do. Any chance of getting a panel directly beside each of the front speakers to deal with the closeness and resulting SBIR?

You MIGHT be able to tweak the position and depth of a couple of the issues by working with front speaker position.

Also, you appear to have some 50hz noise (most likely a grounding issue)

Bryan

[atledreier]

That 50Hz noise is generated by my laptop for some reason. I don't get it when I use my wife's laptop.

I can easily do a panel beside the front speakers. How thick would it need to be?

That would basically mean I have damped all the corner from roght behind the speaker, the cornerchunks, beside the speaker and then 1st reflection. That would make almost a continuous damping. Maybe that would even help with aestethics... I'll try that.

So my front rigth corner would look something like this, seen from above. The filled rectangles are absorbers. The wavy bit is my attempt at drawing a curtain, or false wall.

[bpape]

I'd try to make the panel probably 75-100mm thick.

One other thing to consider. The following distances should not be the same or multiples:

Front speaker baffle to wall behind.
Center of speaker to wall beside
Ears to front wall
Ears to side wall
Ears to wall behind

Bryan

[atledreier]

But the rule of thirds would put both the listener and speakers at multiples from both front and back wall, wouldn't it?

If your room is 6 meters long, the rule of thirds dictate front baffle at 2m from front wall, and listener 2m from back wall... Or am I misunderstanding something?

I think I have some 10cm panels I can put up beside the speakers. I'll test this weekend.

Anything else I can try?

Edit:
I just had a little look into this... 100Hz has a 1/4 wavelength of about 80cm, 200Hz is 40ish... how can I hope to do any good that low with a 10cm panel? I'm trying to think of a way to get damping material further from the wall while still having it look good... Ideally I'd lean a 10cm sheet right against the speaker. That'd kill the 1st reflections too.

[bpape]

From my personal experience, the 'rule of thirds' rarely works well from the perspective of smoothing bass response. It does help get you away from a wall and also give some space to the speakers though.

Try moving yourself to 62% of the room length if you can.

While 10cm isn't going to be a fix-all for the problems, it will certainly help some to minimize the constructive and destructive interference from the wall reinforcement to the direct waves.

As for getting the panels away from the wall, that can help some certainly. However, once you get the space behind the panel more than the thickness of the absorbant, you can actually start filtering as it will create a hump in absorption based on the quarter wave of the distance from the front of the absorbant to the boundary.

Bryan

[atledreier]

So I'd be better off going two or three panels deep to get the surface of the panels out from the wall? I guess that would make the absorbtion more linear as frequency rose.

Edit: Also, it looks like moving my speakers 10cm forward will improve things alot. I'll try that once the kids are in bed.

[bpape]

Just remember that quarter wave is 'optimal'. Doesn't mean it doesn't do anything below that. If you want to go deep, you just need thickness. Again, 6" with a 4" gap will go pretty low.

Bryan