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Mid/High Absorb/Diffus at 1st points
Old 5th June 2006
  #1
Mid/High Absorb/Diffus at 1st points

What are folks using for 1st reflection points behind, in front of, and above the mixer? I know the bass traps go for the corners. What about the rest? Pyramid foam? Expensive random tower diffusers? Looking for ideas here. The room is otherwise sounding very good and shaped well for the task. We are definately at the buy and build stage of things, quite quickly actually---sigh.


Thanks

KT
Old 5th June 2006
  #2
Gear Guru
 
Glenn Kuras's Avatar
Quote:
Originally Posted by natpub
What are folks using for 1st reflection points behind, in front of, and above the mixer? I know the bass traps go for the corners. What about the rest? Pyramid foam? Expensive random tower diffusers? Looking for ideas here. The room is otherwise sounding very good and shaped well for the task. We are definately at the buy and build stage of things, quite quickly actually---sigh.


Thanks

KT

I would recommend 2" rigid fiberglass spaced off the wall 2". Not only with the spacing help pick up more of the low end, but high end comes in from the sides, hits the wall then the back of the panel.

Glenn
Old 5th June 2006
  #3


Ridgid fiberglass is popular.

I've had good luck with cotton insulation too (Ultra-touch is the brand I found locally, but there are others)



-tINY

Old 5th June 2006
  #4
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cramseur's Avatar
4 inches of Roxul brand rockwool (it was 1/2 the density of OC703) in homemade, hand-built panels. Plus 2 inches across the ceiling (I removed the drop ceiling panels and placed the rockwool in their place. Also I use some old Auralex 2" across the ceiling under the rockwool.
Old 6th June 2006
  #5
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Ethan Winer's Avatar
 

> What are folks using for 1st reflection points behind, in front of, and above the mixer? <

It depends on the size of the room and how far away those points are from your ears. Absorption is usually better than diffusion unless the distances are large. Also, just to be clear, the front wall that you face is not a first reflection point and so is less important to treat. Unless the room is so short front to back that the round trip from the speakers, to the back wall, to the front wall, to your ears, is less than about 20 feet. Even then, after that many bounces it's not usually a problem.

--Ethan
Old 6th June 2006
  #6
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tvanveen's Avatar
 

Quote:
Originally Posted by Ethan Winer
Also, just to be clear, the front wall that you face is not a first reflection point and so is less important to treat.
But it's still pretty important if you have rear loading speakers, right?

tv
Old 6th June 2006
  #7
Here for the gear
 

I've used front wall treatment to combat boundary interference with success, though in that case you're really just treating one notch, not a whole range of frequencies. If it's audible, you shudl take care of it; if not, no point.
Old 6th June 2006
  #8
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Glenn Kuras's Avatar
Quote:
Originally Posted by tvanveen
But it's still pretty important if you have rear loading speakers, right?

tv
Everything in important, but I seem to like to treat the front wall. Maybe not my first line of attack..

Glenn
Old 6th June 2006
  #9
Quote:
Originally Posted by natpub
What are folks using for 1st reflection points behind, in front of, and above the mixer? I know the bass traps go for the corners. What about the rest?
The point about bass traps in the corners is often overstated. It's a good place to start for the inexperienced DIY-er in a non-purpose built room, but don't get too hung up on it. The corners are where the greatest pressure builds up as there are the most boundaries coming together, but your listening position is not in the corner. You need traps elswhere, and sometimes the corners aren't the most effective location for traps. You want the most effective treatment placement to improve your primary listening position. Still, for the DIY crowd, the corner is a good place to start.

There are other issues with corners besides bass buildup. Reflections essentially bounce back in the direction from which they came when they encounter a corner. Depending on your listening position, monitor position, and room geometry, these reflections can be another issue.

For killing first reflections, a couple inches of 703 in a frame covered with 701 fabric is the classic. Spaced a couple inches off the wall will make it effective a little lower, but still not in deep bass territory. However, you are trying to control things other than bass with this particular treatment, so you can treat that as a different issue.

You don't want to just keep adding absorption as an overly dead room is going to be of no help. You could do a quick Sabine calculation to get a rough idea if your room is likely to be too dead or too live based on your planned treatment. Remember that you can use reflection to your advantage. Some reflections you can aim away from the listening position into absorbers or diffusors in the back of the room. This stops them from interfering in your listening position without making an overly dead room.

The right balance of absorption (bass, mid, and high), reflection, and diffusion is what to strive for. I'm not saying that you shouldn't absorb at first reflection points, just that there are other options depending on the whole-room plan. It should be a system that works together as a whole.
Old 6th June 2006
  #10
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Quote:
Originally Posted by jayfrigo
I'm not saying that you shouldn't absorb at first reflection points, just that there are other options depending on the whole-room plan. It should be a system that works together as a whole.
I agree, a friend of mine is using diffusers in the first reflection zones. When I saw it first I thought "huh that's a bit odd", I was not sure if this could work. But then when I listened for the first time... WOW what an open and balanced sound! Of course, also in this case it was a well meant combination of different elements working together.

Andreas
Old 7th June 2006
  #11
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Ethan Winer's Avatar
 

> But it's still pretty important if you have rear loading speakers, right? <

Only if the absorption is effective down to bass frequencies. I often see people put thin rigid fiberglass on the front wall, but most loudspeakers don't send sound that way. Speakers do become more or less omnidirectional below around 300 Hz, but 1 inch thick material is useless that low. If you'd like to see a more technical analysis of this issue, track down the article Front wall absorption on the Articles page of my company's web site.

--Ethan
Old 7th June 2006
  #12
Gear Guru
 
Ethan Winer's Avatar
 

Jay,

Those are all good points. I do believe that corners are the best place to start in the smaller rooms folks mix in these days. Especially when they're just dipping their toes in the water, so to speak, and starting with only 4 or 8 bass traps. But you are correct that this is not the final word, and a true "total solution" will have a lot more bass trapping than just one in each corner. I have 39 traps in my living room home theater, including most of the rear wall. The rear wall in particular is a good place to treat because that's the direction the main "wave front" travels in the room, from front to rear.

--Ethan
Old 8th June 2006
  #13
Great comments from Jay and Ethan. Thank you mucho! Jay, you really got me thinking more clearly, appreciate it. BTW, what's a "sabine" calculation?
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