# Absorption- Quality vs Quantity?



## Keet (Mar 16, 2011)

or maybe it's NRC vs SQFT of coverage?

I'm looking to adventure into treating my movie room and like many have a budget, with so many options out there I guess I was looking for some guidance.
I know... it always "depends on the situation".
But is there any kind of general rule with setting up absorption?

Doing some research and reading all these marketing materials I think I've lost my way...:dontknow:

Situation is I have a room about 13.5' x 17' and 8' ceiling.
So just the wall surface is almost 500sqft.
To start with I know I have a pretty evident slap echo and the room is boomy with LFE.

Do I want to simply cover as many sqft of walls/corners/ceiling as I can? is the effect additive?
Or, do I aim for specific primary reflection points and just buy the best I can?

ie. Should I get 100-150 sqft of foam panels and bass traps?
Or do I get a pair of tri-traps and a set of 3 acoustic panels?
Pros/Cons?

Thanks!


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## SAC (Dec 3, 2009)

Keet said:


> Do I want to simply cover as many sqft of walls/corners/ceiling as I can? is the effect additive?
> Or, do I aim for specific primary reflection points and just buy the best I can?
> 
> ie. Should I get 100-150 sqft of foam panels and bass traps?
> Or do I get a pair of tri-traps and a set of 3 acoustic panels?


Far too many DO simply install absorption following the oft quoted "You can't have too much absorption" following the absolutely absurd notion that "reflections are evil".

Absorption is a tool best applied surgically. Using only as much as is absolutely necessary and then only to mitigate specific destructive stimuli - primarily high gain indirect specular signals that destructively combine (superpose) to degrade imaging, localization, timber, and intelligibility.

Ideally you make waterfall measurements and map the actual behavior and distribution of modal peaks and nulls.

And following addressing modal behavior (you can minimize peaks and locate the listening position in a region 'between' peaks and nulls, but you CANNOT eliminate modal behavior in general and nulls in particular). The most common, though not the most efficient/effective, method is via the use of large corner traps.

Specular reflections are analyzed using the ETC response variant of the Impulse response. Absorption , redirection, diffusion is applied at critical points of incidence in order to effect the specific response desired in order to effect the specific acoustical modification appropriate for a given 'part' of the total acoustical response of the room.

...Intentionally vague in order to simply address how treatment is used rather than to specify criterion for any particular response model. This is NOT intended to tell you what and how much to buy and where to put it. But that said, I would definitely be looking at using non-formaldehyde binder versions of Fiberglass or Rockwool porous absorption for bass traps and broadband absorbent panels (products such as Knauf's Ecose) rather than foam.

So, unless you simply want to treat a room based upon pattern recognition and 'napkin analysis' - quick simplistic assumptions based on generalization and supposition rather than actual measurements that identify actual behavior, the way to proceed is with a free analysis tool such as RoomEQWizard. And from the information provided, specifically target the real behaviors with appropriate treatment.

Admittedly a bit of "and then a miracle happens", but the actual process is a bit beyond the scope of this post and the question of whether you serendipitously apply beau coup treatment or target it towards specific Actual behavior.


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## Owen Bartley (Oct 18, 2006)

Keet, if your room is already built and up and running, see if you can run REW to figure out what's going on. I think if you can manage to get some measurements, you will find some help reading into those measurements here on the forum, and you will be able to treat more specifically as SAC said above. That will undoubtedly give you the best results. 

If not, and I'm going out on a limb here, I would think that the first place to start might be with corner bass traps (and experiment with the location of the sub if possible) to fix your boom, and then maybe a few of the usual DIY panels that you can move around the room to test before permanently mounting might help with your echo.

Unfortunately, as I learned much to my dismay, properly treating a room can be very complicated. :dizzy:


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