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Acoustic Treatment basic FAQ?

post #1 of 80
Thread Starter 
I found the master thread for acoustic treatment. The length of the thread is highly intimidating. And the first post in it doesn't seem to have any kind of faq, like most "master threads" do.

Is there a very basic, beginners guide to DIY acoustic treatment?

Just something that says.... "newbies usually put something here and here, and that is for starters only".

Because I don't want to go crazy. I just want to do the typical DIY treatment, whatever that is.

So what is the very basic DIY treatment for someone who doesn't mind a slight eyesore?
post #2 of 80
I am the exact opposite of an expert in acoustics so I hope that I will get corrected if I am way off base.

The first and most basic acoustic treatment would be to treat your first reflection point(s). Generally this would be two acoustic panels of the appropriate size placed to the left and right of your front speakers. Most people would continue to place acoustic panels every 'x' feet down their sides walls; this is done to treat secondary reflection points and probably because it looks nicer and gives a sense of uniformity.

Next would come bass-trapping but I really don't know much about that except that it's advisable to treat as many corners as possible

I hope this helps and I hope someone who knows more than I do tries to answer your question. I do agree with you though, it would be nice to have a 1-2-3 of Basic Acoustics.
post #3 of 80
Thread Starter 
Thank you, Tom.
Too bad to hear that there is no faq.

Okay so I can put up some of the DIY panels on my side walls. And I can probably gear something up for the top corners as well.

Should I treat the wall behind my speakers or at the opposite end (back) wall also?

Are all the wall treatments supposed to be 2/3 up the wall or 1/2 up the wall?

Thanks!
post #4 of 80
post #5 of 80
Ok, big disclaimers:

I'm NOT an expert. Just a dabbler. I have not even treated a single room (although I'm in the middle of doing mine).

My recommendation: go to the "Acoustical Treatement Master Thread"
http://www.avsforum.com/avs-vb/showthread.php?t=255432

It's a huge thread, but if you take your time and read it, you'll get the general idea of what people are doing. If you really care about sound quality, you'll then likely hire Bryan Pape, Terry Montlick, Dennis Erskine, or another professional to do some online consulting. It doesn't cost as much as you might expect.

If you don't want to do that, then you can muddle through and do some basics. Here is a summary I just put together for a friend:

The basics:

1) get absorption on the first reflection points on the floors and walls. This is the spot on the left/right wall where the sound from various front speakers bounces off the wall and hits the listener. The floor is usually handled by carpet, and the ceiling can be done as well, but most people don't for hassle/aesthetic reasons.

With three front speakers and multiple people in the room, it ends up being a range of dots on the side walls. Put carpet on the floor, and put 1" thick fiberglass or cotton panels on the walls to cover those spots. Lots of advice in the thread above on how to frame/cover the panels so they look ok.

The gain from this is better 'localization'. The soundstage of the front speakers sounds accurate (right sounds from the right, middle from the middle, etc.) and not mushed together.

2) cut down on the echo in the room. This is generally referred to as getting the rt60 under control. (RT60 is ~ the time it takes for the sum of all reflections to decline 60dB once the sound source ceases). This is done by covering a certain amount of the walls (often ~50%) with material that will absorb mid-high frequencies. 1" acoustic material is typical. The first reflection point (FRP) absorption above counts towards this coverage. Often, there isn't any special FRP absorption: people just put absorption on the side walls up to and a bit above ear height along the whole side wall. This takes care of 1 and helps with 2.

3) put absorption on the front wall. Pretty much make the front wall dead (2" fiberglass panels). Same with the back wall. The front wall keeps all the surrounds from bouncing back at you. The back wall absorption (typically close to the back of the seats) counts as a 'first reflection point'. I'm doing 2" fiberglass panels across both front and back. (Some folks prefer to keep the back wall reflecting. "Live-end/Dead-end" was apparently a common desire in music rooms. In my HT, with seats 3' from the back wall, I want the back wall dead)

4) Bass traps. Typical room is going to have resonant frequencies (wall to wall, ceiling to floor, diagonal corners, getting more and more complex). At these frequencies you will get standing waves in the room. Those waves will tend to lead to spots in the room where certain frequencies of bass are much stronger than they should be (peaks) and spots where a certain frequency is completely non-existent (nulls). This is bad. At any given spot in the room, instead of a flattish bass frequency response, you'll get these (potentially big) peaks and nulls. This is typically in the 20Hz to 200Hz range.

The problem with these standing waves is that you can't equalize them out if you have more than one listening spot, and maybe not even then. In your seat, you may have a null at a given frequency, but two seats over the same frequency may be a peak. If you raise it up to fix your null, it makes it even worse for the other spot.

Typical thing to do here is to build bass traps in the corners (corners because all standing waves have at least some connection to corners, so you can be most effective there. It's also often the easiest place to get a deep bass trap. A very easy and well reputed DIY trap is the studiotips superchunk (http://forum.studiotips.com/viewtopic.php?t=535). Triangles of fiberglass panels stacked in the corners. There are also panel bass traps you can buy. In general, more bass traps is better.

-----------------------------

So: it's much more complicated than that, but it seems safe to say that if you have:
- carpet of some kind between speakers and front seats.
- front wall dead.
- 1" absorption up to ear level on the side walls.
- Bass traps in the corners

That you will have a better sounding room than if you do nothing at all. Will it sound better (or can you get away with less/different) if you hire a pro? Probably.

Good luck, and remember, this is simply my (imperfect) learnings from reading the master thread. It's worth what you paid for it...
post #6 of 80
Quote:
Originally Posted by CZ Eddie View Post

Is there a very basic, beginners guide to DIY acoustic treatment?

Here ya go:

Acoustics FAQ

--Ethan
post #7 of 80
Quote:
Originally Posted by tomdahlberg View Post

I am the exact opposite of an expert in acoustics so I hope that I will get corrected if I am way off base.

The first and most basic acoustic treatment would be to treat your first reflection point(s). Generally this would be two acoustic panels of the appropriate size placed to the left and right of your front speakers. Most people would continue to place acoustic panels every 'x' feet down their sides walls; this is done to treat secondary reflection points and probably because it looks nicer and gives a sense of uniformity.

Next would come bass-trapping but I really don't know much about that except that it's advisable to treat as many corners as possible

I hope this helps and I hope someone who knows more than I do tries to answer your question. I do agree with you though, it would be nice to have a 1-2-3 of Basic Acoustics.

Just one small correction...I'd start with bass trapping first, then move to the first reflection points in most cases.

Frank
post #8 of 80
Quote:
Originally Posted by Ethan Winer View Post

Here ya go:

Acoustics FAQ

--Ethan

Nice Ethan...

Quick question...
I am trying to correct a center speaker that unfortunately is to close to my ceiling and making it sound bright. I have no other choice but to have it there. I have it directed down towards the listening area.
I have some left over 1" knauf from my build a few years ago. Would doubling the thickness and making a ceiling panel help my issue, or would 1" be adequate?
post #9 of 80
Disclaimer: I'm not an expert, and am in the midst of my first HT. Also, every room is different.

My room configuration: 12x15 with 8 foot soffits, ceiling is 9 feet. Back wall is open, but will have double-doors. Visit signature for pics.

Wanted to share my plan, which I think is "sound" :-)

Steps/Approach:

1) Install furring strips for fabric on all four walls
2) Ensure that front wall has furring strips to hang screen
3) Cover entire front wall with 1" linacoustic
4) Cover sides and back wall with 1" linacoustic up to ear level
5) Cover remaining sides and back wall with 1" mineral wool or cotton batting
6) Complete two bass trap frames for front corners up to the soffits (8 feet)
7) Install OC-703 cut triangles into the bass trap frames
8) Install black, light absorbant fabric for front wall and bass traps, and up to the intended location for the chair rail on sides and back
9) Install patterned fabric on remaining sides and back up to soffits
10) Install solid double door in back of room
11) No treatments for soffits, under the soffits, or ceiling

Only concerns I have are:
1) For a 12x15 room is this overkill - NOTE: I did do double drywall and GG only, no risc clips. Am also caulking all possible leak points for sound.
2) How in the hell do I build the furring strips to hold the bass traps (need to research bit more).

Figured maybe my approach may be a guide or possible suggestion. Treat it with skepticism.
post #10 of 80
Quote:
Originally Posted by huntrm View Post

Disclaimer: I'm not an expert, and am in the midst of my first HT. Also, every room is different.

My room configuration: 12x15 with 8 foot soffits, ceiling is 9 feet. Back wall is open, but will have double-doors. Visit signature for pics.

Wanted to share my plan, which I think is "sound" :-)

Steps/Approach:

1) Install furring strips for fabric on all four walls
2) Ensure that front wall has furring strips to hang screen
3) Cover entire front wall with 1" linacoustic
4) Cover sides and back wall with 1" linacoustic up to ear level
5) Cover remaining sides and back wall with 1" mineral wool or cotton batting
6) Complete two bass trap frames for front corners up to the soffits (8 feet)
7) Install OC-703 cut triangles into the bass trap frames
8) Install black, light absorbant fabric for front wall and bass traps, and up to the intended location for the chair rail on sides and back
9) Install patterned fabric on remaining sides and back up to soffits
10) Install solid double door in back of room

Only concerns I have are:
1) For a 12x15 room is this overkill - NOTE: I did do double drywall and GG only, no risc clips. Am also caulking all possible leak points for sound.
2) How in the hell do I build the furring strips to hold the bass traps (need to research bit more).

Figured maybe my approach may be a guide or possible suggestion. Treat it with skepticism.

Rear corners? Back wall? Those are both critical areas; some of your highest peaks and deepest nulls will come off the back wall...low end will build up in the back corners like it will in the front.

Frank
post #11 of 80
Frank,

Yup, this is something I fear. However, based on the build of the theater, there's only one of the back corners that could support a trap. The other back corner has a small panel that accesses the equipment.

Not ideal, but best that I can do based on room layout. Here's picture of the back wall, and you can see my dilemma.



Back corner with rack:
post #12 of 80
Hmmmm...yes, I see the problem.

Frank
post #13 of 80
Thread Starter 
There is some truly excellent information in this thread. Thanks, everyone!!!!!

I'll be purchasing the rigid fiberglass from Lowe's. It's not 703, but it's similar material. 16 sheets of 24x48x5/8" for $70. I'll start with one container and double up to give myself slightly less than 2".
I'll treat the front, sides & rear walls, as well as my ceiling. I'm going to hit the 50% distance for my side walls & ceiling.

Then I need to find a carpet to place on the floor between my listening position and front speakers. It's bare floor right now.
post #14 of 80
any advice on an ht room that will also be used for 2 channel? it seems that every time i've tried to work on treatments within my room, 2 channel sounds way too dead and unlively. i like the sense of sound around you and treatments negate that. what would be a good compromise in this situation?
post #15 of 80
Quote:
Originally Posted by CZ Eddie View Post

I'll be purchasing the rigid fiberglass from Lowe's. It's not 703, but it's similar material. 16 sheets of 24x48x5/8" for $70. I'll start with one container and double up to give myself slightly less thI'll treat the front, sides & rear walls, as well as my ceiling. I'm going to hit the 50% distance for my side walls & ceiling.

Do you know what the stuff is called? How about the density number? Just trying to make sure you end up with the right thing.

Frank
post #16 of 80
Quote:
Originally Posted by Weasel9992 View Post

Do you know what the stuff is called? How about the density number? Just trying to make sure you end up with the right thing.

Frank

You can get the coefficient numbers here:

http://www.bobgolds.com/AbsorptionCoefficients.htm

Basement Bob doesn't post in the builder forum as much as he used to, but his website is chock full of good stuff.
post #17 of 80
Thread Starter 
Quote:
Originally Posted by Weasel9992 View Post

Do you know what the stuff is called? How about the density number? Just trying to make sure you end up with the right thing.

Frank

It is Armstrong 420. I was wrong about the price though. It's actually $79 and you get 128 sqft (16 sheets 4x2 @ 5/8").

Here is Ethan's comments from another forum, regarding the 420.

Quote:
Originally Posted by Ethan Winer View Post

Wilkins,

A couple of comments:

> I saw some at Lowe's today <<br />
Yes, that stuff will work okay. You need to peel off all the plastic layers, and place them adjacent to be at least 2 inches thick for mid/high frequency control, or 4 inches thick for bass trapping.

> The NRC is 0.55 <<br />
NRC is a useless spec for audio work because it's an average of the absorption at speech frequencies only. What really matters is how well the material absorbs in each band over the entire audible range. But assuming the stuff is real rigid fiberglass, it will work.

--Ethan


Quote:
Originally Posted by dc_pilgrim View Post

You can get the coefficient numbers here:

http://www.bobgolds.com/AbsorptionCoefficients.htm

Basement Bob doesn't post in the builder forum as much as he used to, but his website is chock full of good stuff.

Great link!
post #18 of 80
Quote:
Originally Posted by suffolk112000 View Post

I am trying to correct a center speaker that unfortunately is to close to my ceiling and making it sound bright.

Yeah, that's a terrible place for a loudspeaker. Much better would be too close to the floor. At least that would be closer to ear height.

Quote:


I have some left over 1" knauf from my build a few years ago. Would doubling the thickness and making a ceiling panel help my issue, or would 1" be adequate?

The thicker the better. Always.

--Ethan
post #19 of 80
$79 for 16 sheets of 2x4 5/8" is not that good a price. 5/8" is too thin and if you were to double them up, now you only have 8 sheets of 1 1/4" fibreglass. I paid $45 for 6 sheets of 2" material (same quantity as 12 sheets of 1").
post #20 of 80
Thread Starter 
Quote:
Originally Posted by Jesse S View Post

I paid $45 for 6 sheets of 2" material (same quantity as 12 sheets of 1").

Where did you get this price, and on what? That definately is a better deal. Unless you're paying huge shipping costs on top of that?
The lowes bundle is about $75 after tax & 10% off coupon.
post #21 of 80
Quote:
Originally Posted by Ethan Winer View Post

Yeah, that's a terrible place for a loudspeaker. Much better would be too close to the floor. At least that would be closer to ear height.



The thicker the better. Always.

--Ethan

Thanks Ethan...
You are an asset to the forum.
post #22 of 80
Quote:
Originally Posted by CZ Eddie View Post

Where did you get this price, and on what? That definately is a better deal. Unless you're paying huge shipping costs on top of that?
The lowes bundle is about $75 after tax & 10% off coupon.

Local insulation supplier in Toronto. I bought 24 for myself and another 12 for a friend so the price was important.

The product is known as OFI-48, which is 3lb/cu' density. Identical to OC703 but less than 1/3rd the cost.

This thread in Ethan's forum can help you find a local place-

http://forums.musicplayer.com/ubbthr...fa#Post1653963
post #23 of 80
Quote:
Originally Posted by pmeyer View Post

2) cut down on the echo in the room. This is generally referred to as getting the rt60 under control. (RT60 is ~ the time it takes for the sum of all reflections to decline 60dB once the sound source ceases). This is done by covering a certain amount of the walls (often ~50%) with material that will absorb mid-high frequencies. 1" acoustic material is typical. The first reflection point (FRP) absorption above counts towards this coverage.

Would superchunk bass traps in the corners also count towards this coverage?

Thanks.
post #24 of 80
If the center is too close to any boundary, high or low, you'll have issues. My suggestion would be to use a minimum of 1" and potentially 2" thick reflection panel on the ceiling directly in front of the center channel to minimize any filtering and boundary effects.

Bryan
post #25 of 80
Quote:
Originally Posted by elee532 View Post

Would superchunk bass traps in the corners also count towards this coverage?

Thanks.

Yep. If the bass traps were deadening too much, you could add a reflective facing like cardboard to them. They still absorb the low end but then reflect mid and high frequencies.

Over-absorption from too many bass traps isn't an issue until you have 20-30+ like Ethan. Also it's good to absorb mids/highs going into a corner because of how they reflect back out at the same angle as the entry angle.
post #26 of 80
Some great info in this thread, thanks!
post #27 of 80
It is not necessarily the best idea (and sometimes a bad idea) to simply place absorption at the early reflection points. Doing so can collapse the sound stage. Diffusive treatments or "absorbers" are a better choice depending on the speakers being used. When the speakers have a good off axis response, lean in the direction of diffusion. Also recognize you have a bunch of early relection points ... each row will have a different set of points for the L, the C, and the R speakers.
post #28 of 80
Quote:
Originally Posted by Dennis Erskine View Post

It is not necessarily the best idea (and sometimes a bad idea) to simply place absorption at the early reflection points. Doing so can collapse the sound stage. Diffusive treatments or "absorbers" are a better choice depending on the speakers being used. When the speakers have a good off axis response, lean in the direction of diffusion. Also recognize you have a bunch of early relection points ... each row will have a different set of points for the L, the C, and the R speakers.

Dennis, I'll be using Triad Gold In-Rooms for my L and R to match Gold Center. I was planning on just treating the first reflection point with linacoustic from floor to ceiling (behind column). Based on your comment above, is this potentially a bad idea?
post #29 of 80
For those, you might consider using an RPG BAD panel or similar.
post #30 of 80
Quote:
Originally Posted by Dennis Erskine View Post

It is not necessarily the best idea (and sometimes a bad idea) to simply place absorption at the early reflection points. Doing so can collapse the sound stage. Diffusive treatments or "absorbers" are a better choice depending on the speakers being used. When the speakers have a good off axis response, lean in the direction of diffusion. Also recognize you have a bunch of early relection points ... each row will have a different set of points for the L, the C, and the R speakers.

Dennis, now you have me second guessing my plan to put absorbers at the first reflection point in my music/home theater room. I honestly barely understand off axis response. However, I know that my Salk Song Towers are said to have above average off axis response.

If it means anything, I have tested my speakers in both corner placement and traditional straigt-on placement into the long end of the room. Imaging seems much more precise in the corner placement (unfortunately, this layout isn't really practical for my room). Anyway, it's my understanding that some absorption at first reflection points can get me this same soundstage imaging in the straight-on layout.

Any insight you can offer much apprciated!
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