# Treatment, where to start?



## Silas (Jul 30, 2011)

I am going to make some DIY panels for my room, the goal being to make it sound as good as possible without Audyssey, then use Audyssey if I feel it's necessary. All panels except the corner bass trap are planned to be 2" right now with a 2" gap between it and the wall. The bass trap is 4". All using Rockboard 60. The thin panels above the screen are angled against the corner. My subwoofer is a JBL 4645C; it's massive and has ridiculous output. It sounds very clean right now and I haven't noticed any boomy sounds.

Here is the room right now, w/o treatment:









Here is my proposed treatment (red = acoustic panel, blue = speaker, yellow = screen):









First: is this a good layout to start? I can't really treat the hobbit closet and can't put a panel in the corner with the gap and the door.

Second: how thick should ceiling tiles be? I'm on a budget and was planning on those only being 2". I'll make them thicker if that would make a big difference in response.

Third: How else can I do some bass trapping? I can move the subwoofer under the speaker in the rear corner and put a big trap (like GIK monster trap) on the wall right there under the projector (projector is on the back wall on a shelf above the sub).


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## ajinfla (May 10, 2009)

Silas said:


> I am going to make some DIY panels for my room, the goal being to make it sound as good as possible without Audyssey, then use Audyssey if I feel it's necessary.


Hi Silas, how is the sound now?



Silas said:


> My subwoofer is a JBL 4645C; it's massive and has ridiculous output. *It sounds very clean right now and I haven't noticed any boomy sounds*.


Yes, I would expect that given your nearfield position to it. I assume you mean in a system context (not just listening to sub alone), that your bass is bass is clean. So...



Silas said:


> The bass trap is 4"
> 
> How else can I do some bass trapping?


For what purpose? Why do you want to convert that sound you've spent money to create, into heat?

Is the purpose of this exercise to make the smallish room smaller, or look better to you, sound better to you, or...??
If the latter, what's wrong with the >bass frequencies sound now?
Just fyi, your hearing system will be immersed in a multi source soundfield, full of "direct" onset sounds from the speakers and then reflections from everywhere, three dimensionally, in the room. The brain is quite adept at adapting and processing it all without effort. As are the eyes. Then it comes down to preferences.

cheers


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## bpape (Sep 14, 2006)

My goal would be to address early reflections and to bring the decay time curve into line instead of being very unbalanced. A simple test or even calculations can determine that the low end has significantly longer decay than the mids and highs. We want to be careful not to overdamp the room in the mids and highs. I would only do full range at side reflections and the front wall. The rest I would use limited range, more bass/lower mids only. A basic damped membrane can accomplish that on a more typical bass absorber. Bass control in the front corners would also be desirable. Just the one single corner in the rear not enough to do what you want by itself - though it is helping to balance the lack of a corner on the other side.


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## Silas (Jul 30, 2011)

It sounds really good right now, except that it clips a bit on loud scenes from where audyssey has placed some boost filters.

My main reason for treating the room is to have some large black panels to kill light reflections back onto the screen. The picture is good but is noticeably washed out from my white walls. I figured I might as well use acoustic panels for that since I can't paint and need something removable, hence the panels right next to the screen (those will kill light the most).

@bpape: Do you have any suggestions on either subwoofer placement or how else to do some bass trapping? I can't put traps in the front wall-wall corners since my screen is fixed. This is a temporary theater until I can buy a house of my own so I'd rather not mess with the screen until that day comes. And do you have an idea of a DIY damped membrane? I'd love to purchase traps from you but it's not really in the cards, budget-wise.

Would putting large traps at the ceiling-front wall corner do much? Its either bass traps there or I cover the front wall and the rest of the walls about 3ft back in black velvet to absorb light before the 1st reflection point panels.


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## blitzer (Mar 5, 2010)

I think the Hobbit closet will function as a huge bass trap for you if you leave the door open. Especially if filled with clothes and hobbitzes. 

I have found that adding absorbing material above ceiling tiles can be beneficial as well for the bass. 

Got thick carpet?


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## Silas (Jul 30, 2011)

blitzer said:


> I think the Hobbit closet will function as a huge bass trap for you if you leave the door open. Especially if filled with clothes and hobbitzes.
> 
> I have found that adding absorbing material above ceiling tiles can be beneficial as well for the bass.
> 
> Got thick carpet?


3" black shag rug. Very thick...and sucks in food remnants like no other.

Unfortunately I'm not housing any hobbitzes but it is filled with clothes and boxes of stuff. My htpc and the amps are also back there to keep the noise down in the seating area.

One option I could do if trapping the front corners is crucial is I could bring the screen out from the wall, a la this: http://www.avsforum.com/t/1406360/floating-fixed-projector-screen-mount

My only issue with that is I'd have to bring it out about a foot and that will create some ridiculous pincushion from my anamorphic lens. I suppose it may be a necessary sacrifice


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## bpape (Sep 14, 2006)

you can absolutely do the wall/ceiling junctions. Anywhere in the room can help with the time domain.


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## Silas (Jul 30, 2011)

bpape said:


> you can absolutely do the wall/ceiling junctions. Anywhere in the room can help with the time domain.


Are there specific corners in the room that provide more "bang for the buck" when deciding where to place treatment?

Also, having the subwoofer in the rear of the room vs. the front: does that make a difference in which corners I should focus on trapping? I can't place it in the front due to its size. I can move the sub to the corner and put a super thick trap on the back wall if you think that would be better than the front wall/ceiling junction.


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## bpape (Sep 14, 2006)

As I said, in terms of decay time control, not really. If trying to address a specific frequency response issue that can be dealt with via corners, then it can make a difference. That said, with your restrictions, the wall/ceiling is about it. If you have some trapping in the rear, then I would do wall/ceiling in the front to spread it out more and make it more efficient.


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## Silas (Jul 30, 2011)

bpape said:


> As I said, in terms of decay time control, not really. If trying to address a specific frequency response issue that can be dealt with via corners, then it can make a difference. That said, with your restrictions, the wall/ceiling is about it. If you have some trapping in the rear, then I would do wall/ceiling in the front to spread it out more and make it more efficient.


Ok. So, from what it sounds like, my room may just be best served (in terms of cost-benefit) by addressing the first reflection points on the sides and ceiling. Perhaps I'll start there and then go into bass trapping if I feel the need. Since I haven't noticed any crazy booming bass it's possible that bass trapping won't provide me enough of a change to justify the cost and time to set it up. Does that sound like a good start, in your opinion?

If I just have two panels in the ceiling and on the sides, I can have 2" side panels and 4" ceiling panels. It sounds like this may be my best bet to get started and will only cost me about $125.


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## bpape (Sep 14, 2006)

I would do thicker on the side walls also to better deal with SBIR and get a bit more broadband control in the room overall.


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## Silas (Jul 30, 2011)

bpape said:


> I would do thicker on the side walls also to better deal with SBIR and get a bit more broadband control in the room overall.


Ok. I'm going to buy two packs of Rockboard 60 for a total of 12 2'x4' sheets. Here is my plan:

Sides: 1 4" thick panel with a 3" gap on each side. I'll try to do a 4" gap but I don't think I'll have room for it.
Ceiling: 2 4" think panels with 4"+ gap.
Rear (behind couch where sub currently is): 1 6" thick panel with 6" gap. Should this be 8" with an 8" gap? I'm trying to replicate the GIK monster trap here.

How big should the air gap be? This setup leaves me with one spare panel that I could stick in my bedroom or something.


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## bpape (Sep 14, 2006)

1 panel in the back isn't enough to bother with. Do at least 2. Same for the side walls. Just 1 isn't going to come close to catching reflections from 3 speakers to multiple seats. Map your points and see what you need. You can live with less gap on the sides. 1-2" is fine.

Skip the ceiling for now if needed to get sufficient panels in the other positions.


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## Silas (Jul 30, 2011)

bpape said:


> 1 panel in the back isn't enough to bother with. Do at least 2. Same for the side walls. Just 1 isn't going to come close to catching reflections from 3 speakers to multiple seats. Map your points and see what you need. You can live with less gap on the sides. 1-2" is fine.
> 
> Skip the ceiling for now if needed to get sufficient panels in the other positions.


Ok. 2 each on the sides, 4" thick with a 2" gap. On the back wall is it more important to have broadband panels all behind the listening positions or am I doing 1 bass trap in the corner and 1 on the back wall like you have in the GIK Room Kit #2?

The rockboard is fairly cheap and I may be able to order quantities from Home Depot not in multiples of 6. Is having some large panels on the ceiling worth as well or should I then focus on putting traps in wall/ceiling junctions (since I can't put traps in wall/wall corners other than the back right) if I decide to do more treatment than the above?


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## ajinfla (May 10, 2009)

Silas said:


> It sounds really good right now, except that it clips a bit on loud scenes from where audyssey has placed some boost filters.


That's a problem with Audyssey (being "dumb" and trying to fill energy storage issues at the pressure mic position). Perhaps some manual trimming if allowed, would be pertinent.
If it *sounds* really good to your ears, I'm puzzled why you would plot a course that could make it *sound* markedly worse to your ears. There is no guarantee that "treatments" will _improve_ sound. They are not an elixir, despite widespread beliefs in elixirs, even in 2014! They can and often do make sound worse to human ears/perception, especially when eyes and belief systems are removed from the equation, which they never are with anecdotal "testimonials" about efficacy.
Read this to better understand the scientific reality (vs opinion, intuition, technobabble, etc) I speak of: http://www.madronadigital.com/Library/RoomReflections.html.



Silas said:


> The picture is good but is noticeably washed out from my white walls. I figured I might as well use acoustic panels for that since I can't paint and need something removable, hence the panels right next to the screen (those will kill light the most).


Why not black paint or black fabric cover a sheet of drywall, plywood, etc, (on the sidewalls) instead, if you wish to kill only light? Much cheaper and pyschoacoustically superior to absorbers, especially when your sound is already "really good". I don't know how that would rate on a fashion scale vs something thicker/projecting further into room, to be honest with you.
Or perhaps you could try a bit a both (absorber vs solid surface) interchangeably, to see what _your_ sighted preferences are for your ears, before doing anything more permanent?

cheers


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## Silas (Jul 30, 2011)

I should probably change my wording. It sounds really good, but there is a noticeable echo, even when just talking. When listening to music this becomes annoying. It's less noticeable with movies, but still there.


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## ajinfla (May 10, 2009)

A really good sounding echo?:scratch:
Is the floor carpeted? Perhaps you could also start by add some diffusion to the rear/sides. Unless your LR speakers lateral response is rather poor (which is quite possible), sidewall absorption will detract, especially with music. It will kill spaciousness/realism. But you may actually prefer that overall, so slowly adding absorption may indeed be your ticket.

cheers


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## Silas (Jul 30, 2011)

ajinfla said:


> A really good sounding echo?:scratch:
> Is the floor carpeted? Perhaps you could also start by add some diffusion to the rear/sides. Unless your LR speakers lateral response is rather poor (which is quite possible), sidewall absorption will detract, especially with music. It will kill spaciousness/realism. But you may actually prefer that overall, so slowly adding absorption may indeed be your ticket.
> 
> cheers


Shoot...I'm not being very helpful, am I? I haven't ever heard a properly treated room so my version of good is simply based on how clear and dynamic the speakers are, not how good the room sounds as a whole. My speakers are all JBL pro cinema speakers, so my version of "good" is probably better described as "epic."


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## ajinfla (May 10, 2009)

Silas said:


> Shoot...I'm not being very helpful, am I?


You're doing just fine. Seemed contradictory to have both great sound and echo...but you've further explained.



Silas said:


> I haven't ever heard a properly treated room so my version of good is simply based on how clear and dynamic the speakers are, not how good the room sounds as a whole.


And therein lies the rub. There is no such thing as "a properly" treated room, just various standards, general recommendations of limits (for RT60 as an example), etc., often based on preferences.
I prefer a more "lively" (2ch) sound much like one would hear at a concert hall/jazz club. Others prefer a deader more studio environment like construct. No right or wrong, just preference. The only one that matters is yours. Hearing someone else "properly" treated room may not tell you how yours will sound even if you follow the same script. You may very well prefer it, or not. Best to try things non-permanently in stages, based on your particular tastes in reproduction.



Silas said:


> My speakers are all JBL pro cinema speakers, so my version of "good" is probably better described as "epic."


I most certainly wouldn't use side absorption with those! Direct descendants of all that Harman research. Definitely fall into the well controlled lateral off axis, precisely the type of speakers that sound better without, worse with (in ears only tests). The opposite of non-smooth/uncontrolled, speaker designs, where making less-worse (with absorption), is often "better".

cheers


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## bpape (Sep 14, 2006)

I would agree that much of it is indeed preference.

I can't speak to those speakers as I'm not finding specs for off axis response. I would love to see them. And if they are good off axis and very well controlled dispersion, then you may be able to deal without mid/high absorption at the reflection points. Still likely will have SBIR issues but those can be addressed somewhat with limited range treatments. I'm just unable to make that call based on who the parent company is and go blindly on without seeing test results.

None of what has been addressed though can address peaks/cancellations/excessive decay times. Again, more of a problem in the bass that can be addressed with placement to a certain extent (not time domain) and limited range control. THX specs require 'tight reverberation control' for a theater.


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## Silas (Jul 30, 2011)

Here are the specs sheets for the speakers I'm using:

LCR mains: Pi Speakers 4Pi using upgraded JBL and B&C drivers
Surrounds: JBL 8340
Subwoofer: JBL 4645C

@bpape: Will treating the first reflection points help to eliminate the echo? That is the only thing which really bugs me about the room.


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## bpape (Sep 14, 2006)

They're falling off a bit off axis farfield as most do but not too bad. Looks like they're designed to be corner mounted which is not normal in a residential space but they can still work fine.

The reflections are not generally where I would treat if purely for 'echo'. Much of that happens high on the walls where there is nothing to absorb or break up sound like there is down lower (furniture, people, curtains, etc.) Just remember that your ear is sensitive to echo in the mids and highs much moreso than it is able to identify 'echo' in the lower frequencies. Does not mean it does not exist and can't be damaging via constructive and destructive interference, just that your ear doesn't identify that as ''echo" per se.

Reflections are more to deal with longer path out of time/phase information interacting with the direct sound and smearing the image and possibly causing peaks and dips in response form the difference in phase between direct and reflected sound - not to mention cross channel information (right speaker reflecting off left wall and the other way around, etc.)


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## ajinfla (May 10, 2009)

Well, those fronts aren't quite JBL Cinema , which have large horns....but the off axis is still pretty smooth and controlled >2k. Any pics? A smaller horn I imagine?
Perhaps some diffusion/absorption combo on your rear/rear-side walls will bring down your RT60 a bit without reducing too much spaciousness. I prefer not to treat the front/front side walls with CD speakers, but YMMV.
Oh and you still didn't say whether carpeted...

cheers


Edit: Is this them?


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## Silas (Jul 30, 2011)

Here's the front of the theater. Those 4Pi's are correct. They're using a JBL 2226H driver which is why I included them. They have very similar response to the 3722 mains.










Regarding bass echo, it sounds totally fine to me. It's only the mid-highs that bother me, as I get this ringing sound whenever I'm watching a movie, typically during big scenes with lots of glass breaking.


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## ajinfla (May 10, 2009)

Silas said:


> Here's the front of the theater. Those 4Pi's are correct. They're using a JBL 2226H driver which is why I included them.


Understood...but not quite "all JBL pro cinema". I've heard those set up by Wayne P himself. Very nice sound. Definitely from the smooth/controlled off axis school.



Silas said:


> They have very similar response to the 3722 mains.


No . The 3722s massive 30" horn renders that a physical impossibility. But that should not be your concern, as your off axis is "smooth enough". The issue is perhaps the room, sparsely furnished, being a bit too lively.



Silas said:


> Regarding bass echo, it sounds totally fine to me.


Yep, that falls in line with psycho-acoustics. I've posted the link before where Genelec found where 3 seconds(!) of "ringing" at 50hz...was inaudible to human ears. Visually it may cause much drama for those who don't/can't correlate measurements to perception, but audibly, benign. Far more important, is addressing peaks in amplitude via EQ.



Silas said:


> It's only the mid-highs that bother me, as I get this ringing sound whenever I'm watching a movie, typically during big scenes with lots of glass breaking.


Again, I suggest diffusion first, rear, rear/side walls aft of seats. Then, if necessary, some absorption added in combination. Brian can help you in both areas there.
I would also suggest a heavier toe-in for the L&R speakers, i.e. point them to form an equilateral triangle with the center/sweet spot LP, the tip of the triangle about 6" in front of your nose.

My 2c

cheers


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