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Discussion Starter · #1 ·
I have some Rockwool acoustic panels (4") that I want to use as corner traps. So far I have placed them on the floor at 45deg angle with the top open. Do I need to build a floor to ceilign frame and make sure it's air tight top and bottom? Or maybe there's a specific height the panel should hang? I haven't really found a straight answer to this anywhere. :dunno:
 

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Part of that is because we need more information and need to know what else is going on in the room and how the panels are built.

In general, more is better for broadband bass absorbtion. If that's all the bass control you have in the room, then going floor to ceiling is absolutely a benefit and not too much. No need for them to be air tight.

Bryan
 

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Discussion Starter · #3 ·
The panels are just a slab of 4" thick rockwool acoustic panel, 2' by 4', clothed and leaned tight against the wall. The room is 20' by 13' the fronts 2' from the side wall and 4' from the front wall. My sub is behind the sweetspot, about 5' from the rear wall. I have some nasty dips in my low to mid bass area, from around 40Hz up to about 200Hz. The low end is great, plenty of level there. I'll post a measurement once I get the room to myself. I'll do some measurements with and without the panels in the corners. I have also treated the front's 1st reflections with 1,5" 2'x4' panels. The top-end is all good.
 

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So where specifically is the chair? That's the first thing to deal with. After that, we play with the mains to get that smoothed out and still image right. Lastly, we play with sub position, xover, and phase to get the last bit that we can.

All of that is done without treatment to get the best we can pre treatment. If the treatment is doing it's job, it may mask some potential issues.

Bryan
 

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Discussion Starter · #5 ·
Problem is, the chair is pretty much locked to where it is. I can move the chair a little toward the rear wall, and the sub can go pretty much anywhere in the room, but my screen and projector is mounted in the ceiling and will leave real ugly holes if moved... I'll post a sketch of the room in a minute.
 

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Discussion Starter · #6 ·
Room layout:
The dashed square is a chimney, and the rectangle on the left is the opening to the adjacent room.
1st reflection points are treated on the walls.




I don't have a measured response, so I made a predicted curve from CARA. I know from previous measurements that this gives a general idea of the curve.

 

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Do you have a measurement from your ears to the wall behind you? If the sketch of the layout is relatively accurate, it appears to me you're too far back in the room. Optimal starting point for your ears would be approx 7.5' from the rear wall to about 6.75' from the rear wall.

Also, some of your issues may well be in the width dimension (the null in the 40's). Shifting the speakers and seating about 6" to the left would help with that also.

Bryan
 

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Discussion Starter · #8 ·
Shifting the setup 6" left would mean moving the screen and projector to retain symmetry. My wife would kill me if I made any more holes in the ceiling. Moving closer to the screen would mean a new, smaller screen.... Ach! I am 5' from the rear wall now.

I'll do some predictions in CARA and if they are favourable I'll do a 'dry run' without moving the screen.

Any tips on treatments for the width issue? Shifting left or right would only move the center frequency of the null, wouldn't it?

Edit: Would the shift to the left mess up imaging? I'm psychotic about center image.... :p
 

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Discussion Starter · #9 ·
Ok, I tried your assymetrical setup, and it did look better. So I decided to give CARA more or less free reigns and see what she came up with. First of all, she immediately snapped back to symmetrical, even though I made sure to unhook the symmetry options. Then she followed you advice to move the listener a bit forward. Then there were a lot of unsuccessful trials, until she came up with a slightly altered front speaker position, with them closer to the front wall, and slighty narrower. The predictions looked good, so I'm gonna try them, both yours and CARA. Seems there's not too much that needs to be done to get it as good as it can get under the circumstances.
I also remeasured and made a more accurate sketch.

The room as it stands now:
The dashed areas are where CARA is allowed to try to place the speakers. The area across the front wall is allowed for the sub.



And the predicted response, again.




CARA's suggestion:



 

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Discussion Starter · #10 ·
Ok, measurement after moving the 6" left, and about the same closer to the front wall. The sweetspot moved forward about 2'. Sounds much better for music. The midbass is back, somewhat. I guess some further refinement will cure it. Imaging is good, even with assymetrical speakers. I have a pretty nasty null at just over 70Hz though. I guess you can't win them all... I can tweak the null a bit with my sub's phase control. I can make it shallower but broader, or very deep, but very narrow. Not sure which would be best, I'm gonna have to try it tomorrow when the kids are awake.

This measurement is with the fronts on. Don't worry about the low level, I didn't match levels before measuring.

 

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Discussion Starter · #11 ·
Ok, I am getting some more acoustic panels and I'm gonna make some proper bass traps. The problem is my supplier didn't have as much as I needed for floor-ceiling traps. So I'm thinking I'll do this:

I have enough panels to fill each corner of the room with 180cm of material. My ceiling height is 230cm. So I'll do 90cm from floor and up, then 90cm from ceiling down, and leave the last 50cm with a 3cm thick panel with a cavity behind. So the trap will look like it's from floor to ceiling but the middle 50cm will basically be a cavity with a thin panel to cover it for aestethics. Is this the best way to utilize the panels I have? Should I prioritize some corners instead?
 

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Remeasure with everything the same but move the mic back about 6" and see if the null moves. If it does, then it's likely caused by the rear wall distance to listener. If so, then you can treat that surface and minimize the issues.

Also, you may want to play with sub level/xover/phase and 'cheat' a little to help the null.

Bryan
 

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Discussion Starter · #13 · (Edited)
The problem with my back wall is that it's a double glass door to my office. I've been toying with the idea of removing the actual doors and be left with a 150cm wide opening to my office. I'd just have to switch my computer off for critical listening. That would add approx. another 2,5m to the length of the room.

I can't move the LP any more forward in the room. My screen is as far forward as it will go, and I'm alread at the close limit to my screen. In that case I would have to get a smaller screen. :spend:

I'll do some accurate measurements of my room and adjacent spaces to give you guys a better feel for what I'm up against. And, baby permitting, I'll do some measurements of FR as well.

Also,what would be a good way to treat the rear wall, disregarding the doors? It would have to be pretty supstantial to absorb much down that low, I guess.
 
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