# Acoustic Panels? Or fiberglass behind drywall?



## jgomez1000 (Feb 3, 2014)

Hello - I am planning out a small home theater, 7 1/2 feet by 15 feet long. The current building has concrete walls. 

To make it the best sounding as possible, I have read that acoustic panels are good. But is there any type of material I can insert in between the drywall that will be installed and the concrete that will have the same effect as the acoustic panels? Fiberglass? If there is something I can put, what should the thickness of it be?

Important note - this is a detached building so I do not need to worry about bothering someone in the next room, etc. so I am guessing that soundproofing is not needed - this would be more to maximize the sound quality (I understand equipment is important, but that is for another thread) - I just want to make sure I maximize the walls and floor first. 

Finally, the floor is concrete and I plan to put carpet on it - of course, any suggestions about any type of padding under the carpet to help the sound would be appreciated as well. 

Thanks!


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## Kal Rubinson (Aug 3, 2006)

If you put any treatment *behind* drywall, its acoustic contribution will be miminized. Alternatively, you could put 6-8" of OC703 between the studs and cover them with cloth that blends well with your painted drywall. Take a look at www.realtraps.com for some information and ideas.


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## eclipse911t (Jan 8, 2013)

Http://realtraps.com


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## jgomez1000 (Feb 3, 2014)

Thank you Kal. 

I'm not sure I understand about the OC703. Would this replace the drywall? Or would this between the drywall and the cement?

I think I understand it as it would replace the drywall, and if that's the case, then how would I hang any lights or speakers?

Also, if I decide to put acoustic panels, is there some type of calculator I can use as to how much I would need? And where they would be placed? It would be a relatively small home theater so I am assuming I would not need many of them? 

Thanks again.


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## bpape (Sep 14, 2006)

The things you will need to address in a home theater are:

Bass control - generally corners and rear wall.

Side wall reflections from the front 3 speakers to each seat

Front wall to stop surround reflections from messing up the front soundstage.


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## Kal Rubinson (Aug 3, 2006)

jgomez1000 said:


> Thank you Kal.
> 
> I'm not sure I understand about the OC703. Would this replace the drywall? Or would this between the drywall and the cement?
> 
> I think I understand it as it would replace the drywall, and if that's the case, then how would I hang any lights or speakers?


Yes. It replaces the drywall. However, you do not have to do the whole wall and can put drywall and acoustic treatment between alternate stud-bays



> Also, if I decide to put acoustic panels, is there some type of calculator I can use as to how much I would need? And where they would be placed? It would be a relatively small home theater so I am assuming I would not need many of them?


Bryan can help you with that.


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## jgomez1000 (Feb 3, 2014)

Thanks Kal.

Question - rather than make it overly complicated for me, I am going to install drywall all over the room walls. The floor will have your regular residential rug (probably a thicker type than standard). If I place some acoustic panels, I should be OK correct? I've seen some diagrams on where they should go.

2nd Question - with the above scenario, would bass traps even fit? Remember I have a narrow room, 7.5 ft by 15 ft so the space is limited. Do bass traps vary in sizes? if so, what sizes should I get and I have read that they need to be placed in the 4 corners?

Thank you.


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## NBPk402 (Feb 21, 2012)

I remember years ago using this method to determine where to put the panels. You have one person walk along the wall holding a mirror and another person sit in the main listening position... When you can see the speaker in the mirror that is where the treatment goes. Now this was over 10 years ago and the methods might have changed but it was a quick way to do it. When Bryan checks in I am sure he will tell you the best way to do it.


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## Kal Rubinson (Aug 3, 2006)

jgomez1000 said:


> Question - rather than make it overly complicated for me, I am going to install drywall all over the room walls. The floor will have your regular residential rug (probably a thicker type than standard). If I place some acoustic panels, I should be OK correct? I've seen some diagrams on where they should go.


Yes. No reason to make it complicated unless necessary.



> 2nd Question - with the above scenario, would bass traps even fit? Remember I have a narrow room, 7.5 ft by 15 ft so the space is limited. Do bass traps vary in sizes? if so, what sizes should I get and I have read that they need to be placed in the 4 corners?


IMHO, bass traps are always needed.
Again, you should follow experts beginning with Bryan Pape here.
Also:
www.gikacoustics.com
www.realtraps.com

Both have lots of info and the operators will respond to inquiries.


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## eclipse911t (Jan 8, 2013)

jgomez1000 said:


> Thanks Kal. Question - rather than make it overly complicated for me, I am going to install drywall all over the room walls. The floor will have your regular residential rug (probably a thicker type than standard). If I place some acoustic panels, I should be OK correct? I've seen some diagrams on where they should go. 2nd Question - with the above scenario, would bass traps even fit? Remember I have a narrow room, 7.5 ft by 15 ft so the space is limited. Do bass traps vary in sizes? if so, what sizes should I get and I have read that they need to be placed in the 4 corners? Thank you.


Yes, bass traps vary in size. The typical rule of thumb is that the large they are the lower their effective frequency.
A rectangle room has 12 corners. Most of the time the front vertical corners are available for bass traps as well as all four wall/ceiling corners. Some are fortunate enough to have space in the two rear vertical corners as well. A quick google image search for "DIY Bass Traps" will give you a typical install. Not everything you see will be right however.

I'd suggest seeking out the GIKAcoustics videos or the stuff Ethan Winer from Real Traps has done and get a crash course.

Finally in regards to insulation and stretch fabric I would advise this method on the rear wall since you are fortunate enough to be in a freestanding building. If you can frame in deeper walls you could use rock wool which is cheaper than OC703. If you can spare 10-12" of space you could use very inexpensive pink fluffy stuff back there and have a very large bass trap.


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## jgomez1000 (Feb 3, 2014)

Ron - thanks for the advice with the mirrors. Will definitely use that when it comes to placing the acoustic panels.

Thank you for the advice regarding the back wall. My back seats (3) will be close to the wall, very close because of limited space. So, could I make the bottom 4 feet as a bass trap along the back wall with the top 4 feet with drywall. That way nothing or nobody will touch the bottom 4 feet of the bass trap (since the last row will be raised). 

If you think this works, all I need is along the whole back wall? Or does it have to include a part of the side walls - like a continuation from the back wall. 

If I do make the back wall 4 feet bass trap and 4 feet drywall, should I do the same on the opposite side where the screen will be? 

I saw that the 703 is a little expensive, but I found this, which I'm willing to do Owens Corning 703 – 2” x 24″ x 48″ – (6 per pack) – $74.99 - this should cover the bottom 4 feet of each end. 

So I would buy 2 of these if it is recommended I do it on both ends of the theater, at the bottom 4 feet, for a bass trap.


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## NBPk402 (Feb 21, 2012)

When I did my first setup years ago... I made some diffusers for the rear wall and bass traps for the corners. I just found this and it might be good for you too. I would make some bass traps for all the corners and go floor to ceiling. Here are some more DIY ones.


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## jgomez1000 (Feb 3, 2014)

View attachment 20140205163818.pdf


Hi - do you mean something like this? The darker corners are where it would be floor to ceiling for the bass traps. Each block represents a foot.


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## bpape (Sep 14, 2006)

That looks good. There is no one single calculator that's going to tell you everything. What you can do is calculate the desired decay time for the room with home theater usage, then figure what the room is doing and see what you have left to do. Bass control is definitely needed as is a dead front wall and addressing side wall reflections. If you have room after that (acoustically) then you do the rear wall with maybe a mix of bass control with scattering/diffusion.


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## jgomez1000 (Feb 3, 2014)

Thank you - so I will plan on doing this the floor to ceiling corners for the bass traps. 
Will also put some acoustic panels on portions of the side walls as well.

What do you mean by a dead front wall? 

Also, what do I do with the ceiling for acoustics? I plan on installing ceiling tiles, or maybe nothing at all - depends on the cost. Just a regular plywood/drywall ceiling since it already has a ceiling that is around 10 feet tall. 

Is it OK if I don't put anything on the roof and just deal with the acoustic portion with the corners as we have mentioned and the side wall panels?


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## NBPk402 (Feb 21, 2012)

jgomez1000 said:


> Thank you - so I will plan on doing this the floor to ceiling corners for the bass traps.
> Will also put some acoustic panels on portions of the side walls as well.
> 
> What do you mean by a dead front wall?
> ...


A dead wall would be one where sounds are absorbed and a live wall would be where sounds are reflected. The link I posted shows DIY Diffusers which would be a live treatment and some type of foam panel would be an absorption (like the bass traps).


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## bpape (Sep 14, 2006)

The idea on the front wall is to stop reflections from the surrounds coming off the front wall and messing up the imaging/screen lock. Absorption is generally used unless you have a dipole/bipole type speaker for your mains.


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## jgomez1000 (Feb 3, 2014)

Thank you - I really would not want to have the whole front wall also with the soft material even though it will just be the part of the room where the screen will be. 

If do not make it a soft wall, then I need a dipole/bipole speaker.

I guess my question, is what is better price wise. 
1 - The dead wall with regular speakers or
2 - Non-dead wall with dipole/bipole speaker.

Please remember I only have a 7.5 foot wide wall.


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## bpape (Sep 14, 2006)

Well, a dipole in the front simply limits the ability to treat the front wall, it's not a solution for not wanting one. If you do not treat it, then you'll have reflections from the surrounds and the imaging will not be as good as it could be. Treating the wall also has another benefit. When you do it, you recess the screen so it's a very slick looking setup. Plus if you use dark fabric (black is best), you get an increase in perceived video contrast and create a more imersive experience.


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## jgomez1000 (Feb 3, 2014)

Thanks - makes sense on the screen and the look. OK - so I have attached what would be the layout. 

I will treat the front wall as well. 

Every line is 1 ft. As you will see, I will put the speakers behind the screen and the subwoofers on the ground. I also have put 5.1 speakers since I am guessing the 7.1 would be overkill in such a small room.

Let me know if this would work and if you think this is a good idea. 

Any suggestions would be greatly appreciated.


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## bpape (Sep 14, 2006)

That looks good. Just need to address the side wall reflections then. You'll have an area of reflection from each of the front 3 speakers to each seat - so 3 speakers, 5 seats, 15 reflection points to cover. Likely at least 3 panels per side will be needed.


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## jgomez1000 (Feb 3, 2014)

Thanks!! I will add to the side walls too.

Final question - what about the roof - I am going to put ceiling tiles that are not acoustic (they are cheaper and price is a consideration with me).


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## bpape (Sep 14, 2006)

If you're doing drop tile, insulate above it to allow it to function in a broader manner.


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## jgomez1000 (Feb 3, 2014)

Thanks - will do. Considering i have flexibility for the ceiling, should I make it drywall with insulation on top of it? Would that help? 

So if you are in the room looking up - it will be in order - ceiling tile / drywall / regular home insulation. Like that?


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## bpape (Sep 14, 2006)

Confused. Why drop tile below drywall???


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## jgomez1000 (Feb 3, 2014)

Sorry - I am not explaining it right. 

The tile will be glued onto the drywall facing down, obviously towards the home theater - then on the opposite side of the drywall - where it would be facing up towards the roof - that's where I put the fiberglass insulation (so the insulation will be between the drywall and the attic). 

I hope I explained it better there.


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## bpape (Sep 14, 2006)

Then the fiberglass simply damps the cavity and provides very little help for the interior room acoustics.


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## jgomez1000 (Feb 3, 2014)

OK - so how do I do it then? Consider it will be a drywall ceiling and I would install the glue ceiling tiles. So where would the insulation go?


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## bpape (Sep 14, 2006)

Insulate above still. I just don't know why you're gluing ceiling tiles to the drywall.


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