# THX specs for acoustics



## NBPk402 (Feb 21, 2012)

I just found this, and I find it interesting that THX uses no diffusion and apparently uses absorption on all wall. I would think that the room would be too dead, but it does make sense to me for strictly watching movies. What do you think?


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## NBPk402 (Feb 21, 2012)

Here they suggest using a baffle wall over not using one... I have been going back and forth over this for a while but now it has me wondering again as to which is better. What do you think?


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## bpape (Sep 14, 2006)

You're dealing with a lot larger space, different surround channels, etc. I wouldn't put too much into trying to translate that to a home sized room.


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## NBPk402 (Feb 21, 2012)

bpape said:


> You're dealing with a lot larger space, different surround channels, etc. I wouldn't put too much into trying to translate that to a home sized room.


Wouldn't your sounds be more likely to interact with a smaller room than a larger one though?


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## phazewolf (Feb 5, 2012)

That is part of the issue with advice. A lot of times the person that is giving it is not thinking about a small size room like most of us have but a large theater which in a lot of ways needs different issues dealt with.

It's not that the information is bad it just happens to not apply to us.


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## NBPk402 (Feb 21, 2012)

So how do we know what acoustic treatment is best for our particular room and where to put it? I am assuming we use a mic with REW, but where do we put the mic? Do we put it in the MLP and then turn on only one channel at a time to get our readings to see how it looks, and then also do a reading with all the speakers at once? 

If you do one channel at a time... Do you get the one speaker all dialed in with acoustic treatment before moving on to the next one?


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## phazewolf (Feb 5, 2012)

This is just me but what I tend to do is setup my mic in the master location and do sweeps with REW and try each speaker until I find the best location and then move on to the next speaker.

After I find the best spot for each speaker and play with the mlp and tweak things to get it as smooth at I can.

Then I find the best spot for my subs and place them where they need to go. I start with the other speakers over the subs to work on imaging and sound and then work on the subs for the bass.

Then I tend to try bass traps in any corners I can use and if I can treat the rear wall with bass traps. 

That tends to be where I start and I play with things from there if need be.

Before adding traps I use REW to do sweeps and look at the waterfalls and RT30 sense most home theaters are not really large enough to use a RT60.


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## NBPk402 (Feb 21, 2012)

phazewolf said:


> This is just me but what I tend to do is setup my mic in the master location and do sweeps with REW and try each speaker until I find the best location and then move on to the next speaker.
> 
> After I find the best spot for each speaker and play with the mlp and tweak things to get it as smooth at I can.
> 
> ...


I think I will have to do it a little differently since...
My sub positions are already set for the theater as one in under the rear seating, and the other goes behind the screen although it can be moved left or right. The left and right speakers will have a little range for movement as will my center, but the rest of the speakers are pretty much locked in for their locations.

So I am assuming the way I need to proceed is get all the speakers in their locations, and fine tune the fronts for imaging... Then run REW for each speaker and sub. At this point I would do fine tuning with the minidsps and then after all that is done rerun the sweeps and proceed with acoustic treatments? Do you treat one speaker and then rerun REW on the next speaker before you proceed or does it even matter?

tia,
Ron


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## phazewolf (Feb 5, 2012)

I would run a sweep from say 10hz to 300hz and see what the bass is doing and treat what you need too as in corners are good as well as things like the rear wall sense it tends to cause a peak or null depending the seating location and the frequency in question. Then some like to treat the first reflection points on the side walls.


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## NBPk402 (Feb 21, 2012)

phazewolf said:


> I would run a sweep from say 10hz to 300hz and see what the bass is doing and treat what you need too as in corners are good as well as things like the rear wall sense it tends to cause a peak or null depending the seating location and the frequency in question. Then some like to treat the first reflection points on the side walls.


We are going to be using the mini dsps for active crossovers too... Should we fine tune the crossovers once the room is treated or before?


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## phazewolf (Feb 5, 2012)

I would treat and then tune. But again that's just me. If you tune then treat it may interact with with the treatments. Say there is a large peak and you knock it down, then you treat the rear wall and what caused it is now gone. 

What's left is a dip now and that would be no good so you will end up redoing the mini DSP anyways.


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## NBPk402 (Feb 21, 2012)

phazewolf said:


> I would treat and then tune. But again that's just me. If you tune then treat it may interact with with the treatments. Say there is a large peak and you knock it down, then you treat the rear wall and what caused it is now gone.
> 
> What's left is a dip now and that would be no good so you will end up redoing the mini DSP anyways.


Gotcha. :T


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## phazewolf (Feb 5, 2012)

And I am sure anything I left out or said incorrectly bpape will point out in the morning when he sees what was said.

But over all I think those ideas would be a fairly good start and as we know every room is different and responds differently to things.


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## bpape (Sep 14, 2006)

Set the seats, sub, and speakers for the best response, and that which can be addressed with treatment/EQ if you have a choice between problem sets. 

Then address the known treatment requirements (broadband bass, front wall). Then look at what is happening at your reflection points, how thick the treatments need to be to address phase related issues off the sides, etc. Then look at the overall decay time vs the target for your purpose. In general, it ends up being needing a bit more bass control and with the rear row usually too close to the back wall, that's a prime place for it.


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