# How to Detemine Treatment Needs



## chris0228 (Feb 25, 2014)

I have a 10x18 dedicated theater room that will be in my new home. The ceiling height is 8 feet but tapers on the screen wall and right side due to the pitch of the roof. How do I determine the need for acoustic treatment and/or bass traps in my room? Thanks.


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## NBPk402 (Feb 21, 2012)

Well, the old fashion way to find the first reflections (which would use absorption) is: Have one person sit in the MLP and have another person walk with a mirror along the side walls... When ever the person in the seat can see the speaker treatment needs to go there to stop first reflections. Once you have marked each spot from the MLP, then you do it for another seat.


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## bpape (Sep 14, 2006)

You would need to calculate the average height so you know the cubic footage of the room. Need to know how the room was built, how many seats, how many people, any glass, doors, etc square footage. That will tell you what the room is doing before treatment in terms of decay time. Then you add the items you know you need to do - side reflections, front wall - then we see how far from the target decay time you are across the spectrum. 

In general, rooms are generally already skewed toward being damped enough in the mids and highs with the bass way out of control. Balancing things with thicker panels at reflections and the rear wall helps bring things more into balance along with bass absorption in the front corners generally.

Bryan


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## RH55 (Jan 6, 2014)

bpape said:


> Balancing things with thicker panels at reflections and the rear wall helps bring things more into balance along with bass absorption in the front corners generally.


Brian, does this assume that your subwoofers are in the front of the room, or would you use bass traps in the front corners even if the subs are behind the listening position? As you've no doubt deduced, mine are behind me. I've got a bass trap in the back right corner, but am thinking about doing two more in front.


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## bpape (Sep 14, 2006)

We need to damp front wall reflections anyway so it's a convenient place to put them to good effect. Where the subs are matters more from a frequency response standpoint, not so much for decay time.


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## ajinfla (May 10, 2009)

chris0228 said:


> I have a 10x18 dedicated theater room that will be in my new home. The ceiling height is 8 feet but tapers on the screen wall and right side due to the pitch of the roof.


Hi Chris, pretty narrow, but this is for HT, so the center is (roughly) 5' from the sidewalls...and the prop delays/intensity to your seats corresponding. If you also do a lot of 2ch listening involving acoustic music, I'd lean towards L&R speakers with tight directivity/smooth off axis.



chris0228 said:


> How do I determine the need for acoustic treatment


By putting the horse in front of the cart. Furnish the room with all you needs. Seats. Ottomans. Carpet. Rugs. Media shelfs (preferably towards rear of room).
Do something revolutionary. *Listen with your 2 ears*. *Then* determine if anything needs to be "treated" based on your perceptual preferences.



chris0228 said:


> ....and/or bass traps in my room? Thanks.


See above...and be able to take measurements from say 500hz, on down. Many very inexpensive (<$30) ways to do that.

cheers


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## chris0228 (Feb 25, 2014)

Thanks guys. Yes AJ I agree, I need to finish my room prior to treatment. I am an audio engineer so am fluent with Smaart and other measurement mediums and will utilize those once the room is built to gauge the need. Trying to get a head start on HT treatment as I have never done any of this. Thanks!


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## ajinfla (May 10, 2009)

ellisr63 said:


> When ever the person in the seat can see the speaker treatment needs to go there to stop first reflections.


Yep, that is the old fashion way. Old fashions die hard.

Don't know if Chris in particular will prefer old fashions. It's possible, maybe even probable given expectation, but I suppose we'll see.

cheers


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## ajinfla (May 10, 2009)

bpape said:


> We need to damp front wall reflections anyway so it's a convenient place to put them to good effect.


Hi Brian,

I agree, with the 99.99% probability monopoles Chris is likely to have/acquire, that would be a good place for midbass "traps". Do you guys make one that has a diffusive/reflective skin (>1k or so), that is absorbent from around 100-500hz ish? If yes, what dimensions?

cheers


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## phazewolf (Feb 5, 2012)

You could use a 244 and add a scatter place that should do what you want AJ.


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## bpape (Sep 14, 2006)

I would not cut it off at 1k if trying to stop surround reflections off the front wall messing up the front soundstage. If you just want to deal with boundary interactions, then we can do the range limiter membrane that works up to about 250Hz and stops. Could do a custom membrane that would cut off higher easy enough.


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## ajinfla (May 10, 2009)

bpape said:


> I would not cut it off at 1k if trying to stop surround reflections off the front wall messing up the front soundstage. If you just want to deal with boundary interactions, then we can do the range limiter membrane that works up to about 250Hz and stops. Could do a custom membrane that would cut off higher easy enough.


I wasn't suggesting a 1k cut off, but rather, "diffusive" > the 200-500hz absorption (including >1k).
Not worried about surround reflections of front wall, as those would be decorrelated, delayed and attenuated at the LP. I know of no mechanism for those to mess up the front soundstage.
I would be looking for some "midbass" only spectral absorption immediately behind (monopole) speakers.
The 244 looks like it has good potential.

cheers


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## bpape (Sep 14, 2006)

I would agree that one of the primary goals is to deal with upper bass/lower midrange interactions from the main speakers. I would not agree that reflections from the surround channels cannot be damaging to the imaging aspect.


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## lcaillo (May 2, 2006)

For HT the surround channels are typically relatively low levels and information that is not concurrent with the mains, so affects on imaging from reflections from surround channels are just not something I would be concerned about. Front surround channels maybe, but it depends on the source. Frankly, imaging is not something that I am very worried about with HT.


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## bpape (Sep 14, 2006)

And again, that's a preference. For those who also do multi-channel music, imaging absolutely does matter. Sometimes surround info is lower in level, sometimes not. I would agree that it's later in time than one would normally address IF the room is large enough. In smaller spaces, it can easily be within the generalized 20ms window that we would want to address.

In addition, damping the front wall also tends to help with front to back slap echo in addition to addressing the boundary interactions from the main speakers. I'm just not seeing a negative to doing it and a lot of potential positives if the room is not already overly dead.


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