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Discussion Starter #1
Hello, I am putting together a VERY small 2-channel music room, and will be doing a little bit of acoustic treatment to improve the sound. Currently the room exhibits way too much echo - if you clap your hands, it almost sounds like a high-pitched ringing. The fact that the floor and two walls are concrete just might have something to do with this. :)

I plan to use a combination of absorption to deal with the excessive echo, and diffusion to make the room sound a bit bigger than it is. I've included as much detailed info about the room as I could think of below, as well as they key questions I had.


Room Details:

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The room is 11ft10in wide, 8ft8in long, and 7ft high.

There is a door on the left wall that has to be left open as the ventilation ducts do not feed into this room (was meant as a storage room I guess).

There is a 1ft. by 6in. column at the rear-left of the room. I'm not sure what it's covering.

The front + right walls are drywall + 2x4's over concrete. The rear and left walls are standard drywall + 2x4's.

The floor is concrete with a thick underpad and berber rug. There is also an area rug in the center of the room.

Speakers -

The speakers are floorstanding Mission M74i's placed about a foot out from the wall (the room is only 8ft8in deep), and are rear-ported but I'm using the port plugs.

The frequency response is rated at 44hz-20khz +-3db

Absorber Panels -

I plan to use 6 of the Auralex 4in. Foam Wedges. The dimensions are 2'W x 4'H x 4"D.

One will be mounted behind each speaker, one will be mounted on the side wall by each speaker, and one will be mounted on either side wall by the listening position.

Diffuser Panels -

I plan to use 36 of the Auralex DST Sound Reflectors. The dimensions are 1'W x 1'H x 1" D.

I will arrange these in groups, the first of which will be a 5'W x 3'H section behind the sofa (back wall). The second group will be a 3'x3' section on the front wall between the speakers. The rest will be arranged on the ceiling both above the listening position and above and between the speakers.



The questions I had were as follows:

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1) Are the 4" thick Auralex panels too much absorption for a room this small?

2) Will the room become too "dead" sounding? Auralex seems to recommend the 4" wedges for churches/gymnasiums/drum booths.

3) Is it correct to place diffusion on both the front wall (between the speakers) and the back wall (behind the listener)?

4) If I place diffusion panels on the ceiling, should they be above the listener, above the speakers, or both?

5) Should I "scatter" the diffusers around (like a checkerboard alternating between diffuser/wall/diffuser/wall), or should I have just them all side-by-side? They come 36 to a box (1 sq.ft. each) so I don't think I'll run out.

6) I would have liked to place some diffusers on the left and right walls in between the 2 absorbers, but I can't due to a door that will have to be left open on the left side of the room (only source of ventilation in there). Can the same effect be accomplished by putting some diffusers above the rearleft and right absorbers?


Note that I'm basing my ideas of where to place the absorbers/diffusers based on what I've seen on other setups such as Mike Lavigne's Rives Room ( http://cgi.audioasylum.com/systems/663.html ), as I don't have any personal experience with treating a room yet. :(

As a side note, I know that it's always the poeple with the most knowledge here that get pestered for advice and help, and I know that this can get tiresome after a while. I just wanted to let anyone who replies know that I am really grateful for any advice you can give.

Thank you!


I've included an overhead diagram of the room showing the placement of the speakers and panels. The only ones not showing are the ceiling panels which will be centered above the speakers and above the sofa.

http://members.shaw.ca/erichelin/RoomPlan.JPG
 

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If you're using "Auralex 4in. Foam Wedges", then why not use Auralex's Personalized Room Analysis. http://www.auralex.com/pcf/

Last I heard it was free. Certainly Auralex knows a lot about stereo.
 

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The open door is going to kill your sound stage - why not rotate the room layout 90 degrees for symmetrical walls?


Controlling your reverb is important in a concrete room - and you need a lot more absorption than you have. A pointer to Auralex acoustical coefficient data would help - but then as Bob pointed out they have this data and will do a quicky for you free - you might as well use their services.


The trick you want to accomplish is a pool shot - angle of incidence = angle of reflection. This is easily done on your drawing by mirror imaging your speaker across the walls and drawing a line to your seat. Where it intersects the wall is where you want your panels. absorber/diffusor at that point is up to you and part of tuning your sound stage.


These are things you need to accomplish - enough absorption in the room to kill excess reverb - and enough absorber/diffusor at reflection points to clean up your muddy soundstage, and getting rid of any flutter echo if any. Get the treble fixed - then you can move on to working with the bass. Which will be an issue with deep towers in a tiny concrete room.
 

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Some observations:

You do need to turn the room 90 degrees.

Your speakers are too far apart for good imaging.

If you're going to maintain this layout, you'll have more work to do on the front wall with both absorption and diffusion.

The angled item in the upper left corner of the drawing I guess is copied from some other design ... that mechanism is a bass absorber and needs to be calculated for the specific space rather than "borrowed".

I'm not going to run a model of this space, but my gut is telling me more absorption is needed due to the small room size ... almost any second and third reflection will reach the listening position on very short order and with insufficient decay to be perceived as anything but echo.

If there's a free model you can run, I'd do it.
 

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Agree totally with what has been said so far. I'd lean toward more absorbtion and less diffusion. Also, I'd lean toward almost exclusively thicker absorbtion. In that small a space, you don't have the luxury of spot treatments for different parts of the spectrum. Pretty much everything needs to deal with the whole thing.


Also, seriously consider rigid fiberglass or acoustical cotton and DIY your absorbers. They'll be less expensive and more effective than the auralex foam.
 

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Quote:
Originally Posted by CaptainKellog
The only ones not showing are the ceiling panels which will be centered above the speakers and above the sofa.
But that's not where the ceiling reflections will be. Same with the wall panels: you have them right beside the speakers and right beside the seating area, when that's not where the wall reflections will occur.


You can use the mirror trick. Sit in the sweet spot and have a friend drag a mirror along the wall. Make a mark where ever you see the reflection of either speaker. Those are the first reflection points. Repeat for ceiling first reflections.


Good Luck,

Sanjay
 

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Discussion Starter #7
WOW! I actually got a response from all three audio gurus. Thank you guys! :)


Dennis - the angled piece on the top left of the diagram is actually the door to the room - it doesn't open completely flat. :)


I would never have thought of rotating the setup 90 degrees (putting the speakers on the "short" wall. I always thought this would be worse for imaging. I wil certainly give that a try.


I also never thought that more absorption would be better either. I didn't even realize that the concrete + the small size were what was causing the echo. I just assumed it was the bare walls. However, when I tried the "hand-clap test" in another larger room in the basement that is also empty, it definitely doesn't "ring" as much as the small room. You guys are right on the money once again.


A few more questions -

Should I limit my absorbers to the walls and stick with diffusers for the ceiling, or should I look at some absorbers for the ceiling reflections as well (ceiling is wood frame with a floor above it)?

Should I put absorbers in between the two front speakers, or diffusers?

Would it be bad to treat the entire room (as in virtually every surface covered on all walls + ceiling), or is this overkill?


It definitely pays to get advice from people who do this for a living. Thank you again so much for the tips. I will revise and post a new diagram once I get a chance!


Also, thank you BasementBob for the Auralex link, and thank you Sanjay for the mirror tip.
 

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Cap'n,


You already got the right advice, and I'll just add this: An even bigger benefit from rotating your setup 90 degrees is that will improve the low frequency response substantially. The LF peaks and nulls get worse and worse as you get closer to the wall behind you. Once you get to a few feet away the comb filtering affects mid and high frequencies too. Then, once you rotate your setup, place your seat 4'6" from the front wall to get the most uniform LF response.


--Ethan
 

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Discussion Starter #9
Wow, I can't believe how many pro's are replying to my thread! Thanks again guys!

I almost feel guilty getting this level of advice for free. :)


Well, I'm now done with the new layout diagram - I'm looking forward to everyone's feedback/advice regarding it.


The only major drawback I see is the sofa I'm using. The sofa is 5ft.6in. wide, and the room is 8ft.8in. wide - making for a tight squeeze. If necessary I can always switch to 2 single seaters and position them side by side.


The other change I've made is to move the equipment rack to the rear so it won't interfere with stereo imaging (it was previously in between the speakers).


The only thing you can't see on the diagram is the ceiling treatments, I'm thinking absorption on the front first reflection point, and some diffusion in the rear. Is this correct?


Here is the new layout:
http://members.shaw.ca/erichelin/RoomPlan2.JPG
 

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Every room is different. What you have now is much better. The things that are non-symmetric are now in both the length dimension and behind you. If you have to have it, that's where it should be.


The choice of diffusion or absorbtion in front is a contentious issue. There are good reasons for both. You'll just have to play with it and see what you like better.


IMO, for pure 2 channel listening, I'd ditch the absorbtion on the rear wall potentially - at least at first. If this were for multi-channel, I'd say leave it there.


Also, where is your bass absorbtion?


Lastly, either DIY or have someone else run a basic analysis of the space and see what it will support in terms of absorbtion without killing the decay times too much and how much is needed where in the frequency spectrum.


With that hard a room, I don't think you'll have a lot of issues with too much absorbtion, however, you could easily (as you have it drawn now) do too much in some places (mids/highs) and not enough in others (bass).
 

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Discussion Starter #12
Hi bpape,


For my absorption, I was planning on the 4" Auralex Wedges. They are 2 feet wide by 4 feet long, and the literature on Auralex seems to suggest they will absorb a lot of bass as well. As my speakers are only rated to go down to 44hz +-3db, I had hoped the 4-inchers would be able to handle this.


I think in my second diagram I may have gone a little too crazy with the number of panels. Maybe 3 on each side wall and two on the front wall, then just diffusers at the rear?


I will try the mirror method tonight to at least find my first reflection points on the side walls and ceiling. Is there an easy way to find second reflection points? Two mirrors maybe? :)


Also, thanks for the pointer about the ceiling - I will try it with both diffusers and absorbers. What about the front wall in between the speakers? Should this be absorbed or diffused?


As a last note, I checked out the site in your link and noticed your panel prices are quite reasonable. Do you build them with any sort of integrated method of hanging them on the wall, or is it strictly caulk/glue based?
 

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CaptainKellog

Quote:
For my absorption, I was planning on the 4" Auralex Wedges. They are 2 feet wide by 4 feet long, and the literature on Auralex seems to suggest they will absorb a lot of bass as well.
from: http://www.auralex.com/testdata/


4" Studiofoam Wedges

125hz 0.31

250hz 0.85

500hz 1.25

1000hz 1.14

2000hz 1.06

4000hz 1.09


It starts to drop off around 250hz. I doubt it would be doing much at 44hz.
 

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CaptainKellog:

Quote:
They are 2 feet wide by 4 feet long .. I think in my second diagram I may have gone a little too crazy with the number of panels. Maybe 3 on each side wall and two on the front wall
That's 8 panels of 8 ft^2 each, or about 64 ft^2. That's still a fairly live for a room that size.


Room Dimensions: Length=11.92 ft, Width=8.67 ft, Height=7 ft

Room Ratio: 1 : 1.23 : 1.7

R. Walker BBC 1996:

- 1.1w / h
- l
- no integer multiple within 5%: Pass

Volume: 723 ft^3

Surface Area Total: 492 ft^2

Surface Area Floor: 103 ft^2

Surface Area Ceiling+Floor: 206 ft^2

Surface Area Front Wall: 60 ft^2

Surface Area Front and Rear Wall: 120 ft^2

Surface Area Left Wall: 83 ft^2

Surface Area Left and Right Wall: 166 ft^2

Surface Area 4 Walls: 286 ft^2

Surface Area 4 Walls + floor: 389 ft^2

Schroeder Fc: 160hz

Frequency Regions:

- No modal boost: 1hz to 47hz

- Room Modes dominate: 47hz to 160hz

- Diffraction and Diffusion dominate: 160hz to 640hz

- Specular reflections and ray accoustics prevail: 640hz to 20000hz

Count (47.3-285hz) : Axials=13, Tangentials=54, Obliques=72


47.4 hz 23'10", 11'11", 5'12" (1,0,0 Axial)

65.2 hz 17'4", 8'8", 4'4" (0,1,0 Axial)
80.6 hz 14'0", 7'0", 3'6" (1,1,0 Tangential)

80.7 hz 14'0", 7'0", 3'6" (0,0,1 Axial)


93.6 hz 12'1", 6'0", 3'0" (1,0,1 Tangential)

94.8 hz 11'11", 5'12", 2'12" (2,0,0 Axial)

103.7 hz 10'11", 5'5", 2'9" (0,1,1 Tangential)

114.1 hz 9'11", 4'11", 2'6" (1,1,1 Oblique)

115.0 hz 9'10", 4'11", 2'5" (2,1,0 Tangential)

124.5 hz 9'1", 4'6", 2'3" (2,0,1 Tangential)

130.3 hz 8'8", 4'4", 2'2" (0,2,0 Axial)

138.7 hz 8'2", 4'1", 2'0" (1,2,0 Tangential)

140.5 hz 8'1", 4'0", 2'0" (2,1,1 Oblique)

142.2 hz 7'11", 3'12", 1'12" (3,0,0 Axial)
 

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Discussion Starter #15
BasementBob - thank you for the test data link! I was wondering where to find Auralex test data. I also found this one, but you may already have it:
http://www.bobgolds.com/AbsorptionCoefficients.htm

(Edit: MAN I feel like an idiot! ....I just posted a link to BasementBob's own website thinking "Hey I'll bet Bob will really like this site". Doh!) :(


Sorry if this this is a dumb question, but how do you read these stats?

Is an absorbtion coefficient below 1.0 a bad thing?
 

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Discussion Starter #16
Thank you again BasementBob!


(From Bob's post: )

- Room Modes dominate: 47hz to 160hz

- Diffraction and Diffusion dominate: 160hz to 640hz

- Specular reflections and ray accoustics prevail: 640hz to 20000hz


The edited stats you posted look much more readable to me. Let me know if I'm interpreting this correctly:


For a room of my dimensions, I should be concerned with treating the frequencies from 47hz-160hz to deal with room modes, and treat for reflectionsfrom 640hz-20khz?
 

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They can be ordered with mounting hardward or plain so you can use impaling clips.


If you can do a little DIY, you can do the bass absorbers cheaper and get better performance with fiberglass, acoustical cotton, or rockwool. I redid a room not too long ago where I replaced the Auralex LENRDs (much better in bass than 4" wedge) with 4" of acoustical cotton on the front and 4" of rigid fiberglass on the rear (corners). No comparison. They reached MUCH deeper than the LENRDs had previously. With room modes starting at 47Hz, you'll want to get down as far as possible.
 

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Discussion Starter #18
bpape - you answered my next question before I even asked it.


I was sifting through your site and the 4" acoustic wool Bass Buster caught my eye. It seems to reach a lot deeper than the 2" Owens Corning rigid fiberglass panels. Do you offer the option to do the frame/GOM fabric and sell it finished? If so, what would the cost be per finished 2'x4'x4" panel?


Thanks!
 

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This should really be taken offline.
 
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