Finally acoustic treating my room. I have a few Q's

[fenderrocker]

Alright, so I've been wanting to sound treat my studio for ages now, but I never had the time or resources to do so. Plus, I just moved into a new apartment, so I'm glad I didn't do it before.

Now I have drawn out the dimensions of my room (LWH=~ 3.35m x 3.55m x 2.43m) and included the furniture. I finally found some Owens Corning 703 locally, and they come in packs of six 2' x 4' pieces. I plan on making panels for the side and back walls, as well as the back corners. I'm also considering building a diffuser for the back wall as well.

Are there any acousticians here that could possibly aid me in this project? If I'm gonna spend the money I want to make sure it's done with the utmost precision and quality.

The insulation place also has IIG Minwool 1200, which has a much higher density than OC 703 (8 lbs. pcf vs 3 lbs. pcf). Should I shell out the extra cash for those, or will the 703's provide sufficient absorption in a room this size?

Here's a link to the drawing of my room: http://imgur.com/uWqsq.jpg

Should I take this thread to another forum? Any suggestions where I should go?

Thanks a million guys.

[Hotcrazyfruit]

There are plenty users here know know lots about acoustics.

I can tell you right off the bat, just 703 wont do justice, as its only good for absortion above about 2 khz (an absorber can only attenuate frequencies that have a quarter wave that is smaller than the thickness of the absorber) A diffuser is a must, back walls and ceilings are good places. I couldn't provide you with accurate numbers, but i'm sure someone will chime in and provide further support.

Nick

[fenderrocker]

Thanks Nick.

Yeah, I figured a diffuser would be essential. These look interesting: http://www.mioculture.com/store/pc/v...=2&idproduct=9

...although, I'm not sure how effective they would be. They're quite small, too.

Perhaps just another DIY project. Anybody have a good link? I'm thinking about trying this one: http://www.ehow.com/way_5606383_diy-...-diffuser.html

703 is the only Owens Corning 700 series insulation the place I found carries. The other mineral board they have is IIG Minwool 1200! This stuff looks like primo acoustic panel material, although I'm not sure on the prices. The specs, however, are great. I think they carry 4" thick, 8 lbs/sq. ft. boards.

Oh, and I spoke with a man from GIK Acoustics (http://www.gikacoustics.com/gik_244.html) who says I should move my workstation to where my dresser is, then put two of those^^ panels to the right an left of my monitors, as well as two centered on the back wall. Here's the link to my room for reference: http://imgur.com/uWqsq.jpg

Thanks again, y'all.

[O.G. Killa]

Hi Jim,

I would suggest you read through a forum like this one for a little bit to start with.

http://recforums.prosoundweb.com/index.php/f/44/0/


One thing about minwool, it tends to sag and fall over time if it doesn't have a frame/support, Which is something to keep in mind. Just like 703, it works best when you stand it up on its edge (to help keep it from sagging or compressing in on itself).

Your room is really small. It is going to be difficult even with bass traps to keep the bottom end in check. One thing I might suggest is to look into building or buying "membrane absorbers" instead of using the standard "frictional absorber" bass trap. But also realize that membrane absorbers reflect high and mid frequencies while absorbing low frequencies. You can also try to do things like slatted helmholtz absorbers, but those are difficult to calculate and build correctly.

First start with putting 703 panels on the walls and ceiling at the first reflection points (anywhere sound will hit the wall or ceiling and bounce directly back at you). These will stop high frequency sound from reflecting back at you and smearing the sound of your speakers.

Next, try tackling the bottom end. You can try to put one membrane absorber across each corner of the room. You might also want to try putting two membrane traps in each corner, one on each wall. Since membrane absorbers flex, you don't HAVE to put them right across the corner. You can put two in the corner, (one on each wall at the corner) in hopes to get even more absorption than one panel alone would do. You can also use the corners where the ceiling meets the wall as well. The purpose of the bass traps is to keep the bottom end from reflecting back into the room and either canceling itself out or amplifying itself. That way you hear the bass from the speakers and that's it.

The mid range is the toughest to deal with. Even though you have panels absorbing high frequency, and panels absorbing bass, it's really tough to find something that will adequately absorb midrange and still keep the room useable. This is why some people use diffusors. But diffusors only start working at a certain distance away, based on how deep the diffusor is. Usually the diffusor will specify this. Shallow ones you should be at least 1 meter away, deep ones you usually need to be at least 2m away.
Instead of absorbing the sound, the diffusor tries to scatter the sound in all directions, so there isn't an "echo" bouncing off the surface back into the room.

For tracking rooms diffusors are great because you can balance the sound without making the room dead. For control rooms, because they are smaller, diffusors are limited in use. Mainly people put them on the back wall because that is the only spot they can go and still maintain the correct distance from the diffusor. Some studios that are wider than they are long, will have them on the sides. But in any event, for a room that small the diffusor should be the last step.

with acoustics, its very easy to do too much and kill the sound of the room. Start sparingly and add to it and or tweak what you have. You might not need mid range diffusion. You might need lots of bass traps. You might find floating the 703 panels off the wall by an 1" or 2" helps deal with the midrange enough...and so on.

in a room, sound hits a boundary and then reflects off. As sound gets closer to the wall, it switches from air movement to air pressure. The air can't move and so it gets squished up against the wall and then pushes back out from the wall.

Because of this, a panel on a wall can only absorb based on it's thickness and/or distance from the wall, even though the panel itself is rated at absorbing from 20KHz down to 50Hz.

I posted this in another thread but it's worth repeating...

The maximum absorption happens at 1/4 and 3/4 of a soundwave's length because that is where the most motion is happening (90 and 270 degrees on a sine wave). At 0, 180 and 360 degrees the air is standing still.

So if a panel is 2" thick and it is placed flush up against a wall, it can absorb sound down to a frequency where 1/4 of the frequency's wavelength is 2". 2" x 4 = 6". So whatever frequency has a wavelength of 6", that is what the panel against the wall will absorb down to.

Frequency = Speed of Sound / Wavelength

Frequency = 13,560in/sec / 6in

Frequency = 2,260Hz (or 2.26KHz)

So a panel flush with the wall that is 2" thick will absorb down to 2.26KHz, below that it really won't do much, if anything at all. Above that, it will follow the rated absorption specs per frequency band listed on the manufacturer's website. Granted, this isn't exact, because sound coming at the panel at an angle will see the panel as being thicker since the sound wave is traveling through the panel at an angle... but that might make it 2K instead of 2.26K...it really depends on the angle the sound source is to the speakers... but for all intensive purposes we'll just look at direct sound for this example.

Now what happens if you hang that 2" panel off the wall by 2"? So the face is 4" from the wall, and it has a 2" airgap behind it.

Since the panel is farther out into the room, it can effectively stop a frequency of... If we do the calculations again...

4" x 4 = 16"

Frequency = 13,560in/sec / 16in

Frequency = 847.5Hz

So by suspending the panel out off the wall by 2" you've dropped it's effective absorption down to 847.5Hz from 2,260Hz. If you stacked two 2" panels and put it flush up against the wall, this would also absorb down to 847.5Hz, but the amount of absorption above 847.5Hz would be more per frequency band than with the 2" panel.

And so I guess this brings me to another point I should make. Just because a panel is absorptive, doesn't mean it absorbs 100% of all sound across the whole frequency spectrum.

Here are the specs for 703, 1" and 2" panels in an anechoic chamber...

Freq= 1"Rating, 2"Rating
125 = 11%, 17%
250 = 28%, 86%
500 = 68%, 114%
1000 = 90%, 107%
2000 = 90%, 102%
4000 = 96%, 98%

So now, looking at the above numbers we see that 1" absorbs 90% of sound at 1KHz and 2" absorbs 107% of sound at 1KHz... but with the 2" panel flush up against the wall, it won't absorb anything below 2.26KHz. The the specs below 2KHz are meaningless to you at that point.

Make sense? And while Owens-Corning doesn't list the ratings for more than 2" thick 703, you can see how it dramatically increases absorption over the midrange and upper bottom end just going from 1" to 2".

This is also why you need to make your bass corner traps REALLY THICK if you are going to use 703 as a frictional absorber instead of using a membrane absorber. The thicker it gets the higher the percentage absorption down at the bottom end is (and the higher it gets in top end too, but not by as much).



So ideally, placing ONE 2" 703 panel across the corners of your room won't do much, because one panel only absorbs 17% of the energy at 125Hz. If you fill in the space behind the panel with fiberglass (it doesn't have to be 703, you can use R11 batt rolls to fill in behind, staple them to the ceiling and let them hang down to the floor) you then increase the percentage of absorption down at 125 and below... and again, stopping at 1/4 wavelength from the distance of the front panel to the corner.

So if you put a panel across your corner, and the panel came out from the corner by 3' (1 meter), you would be absorbing down to 70Hz (give or take). If you then fill in behind it, you increase the AMOUNT of bass that gets absorbed down to 94.167 Hz.

Is this making sense? Am I explaining it well enough for you to understand it?

[fenderrocker]

Originally Posted by O.G. Killa

Is this making sense? Am I explaining it well enough for you to understand it?

Certainly. Although, 2" x 4 = 8", making the absorbance of a 2" 703 panel 1.695+ kHz.

Nonetheless, great explanation. Bass is most definitely the biggest issue I have when I move my music to another system, so I probably will want to go with the IIG Minwool 1200. Either that, or I'll find a way to make membrane traps with the 2" 703 boards.

My plan for the panels is to put them in a 2" x 4" frame, so there will be a gap of 2" between the panel and the wall, meaning it will absorb frequencies down to 848 Hz, as you said. But this isn't even in the bass range, so I will need bass traps.

What will be the best solution for a room this size? Keep in mind I'm moving my dresser into my closet, and putting my workstation where the dresser is currently. I will probably also center my bed on the back wall.

1.) Should I go for the IIG Minwool 1200 and make thicker panels? I think they come in 4" panels, and they have a density of 8 lbs./sq. ft.

2.) Or, should I make a few mid range absorbers and a few membrane bass traps for the back corners?

[albee1952]

O.G. dropped some great info there. I would get both and use the minwool in the corners. You almost can't have too much there. My corners are 12 inches of a similar material, and maybe would benefit from more. I have about a 4' frame across the corner with 4" in the frame, plus pegboard hung behind that, with 4" on each side. With a room as small as you(and I) have, there will still be some low frequency issues to deal with. My solution was to dial up a sub-woofer on a digital crossover so I could filter and time-align it and set it to counter the cancellations at my mix position(I used SMAART Live as a tuning&alignment aid here as its tough to do by ear).

[fenderrocker]

Originally Posted by albee1952

O.G. dropped some great info there. I would get both and use the minwool in the corners. You almost can't have too much there. My corners are 12 inches of a similar material, and maybe would benefit from more. I have about a 4' frame across the corner with 4" in the frame, plus pegboard hung behind that, with 4" on each side. With a room as small as you(and I) have, there will still be some low frequency issues to deal with. My solution was to dial up a sub-woofer on a digital crossover so I could filter and time-align it and set it to counter the cancellations at my mix position(I used SMAART Live as a tuning&alignment aid here as its tough to do by ear).

If I get both I'll probably have left over, which is fine because I need panels for a vocal "booth" in my closet.

I don't have the money right now for a subwoofer. I'm selling my current speakers (AV30's) and getting some KRK Rockit 5 G2's. I think they have a response down to around 60 Hz.

I'm also trying to sell my PODxt Live with a POD Farm license. I haven't gotten any bites yet though

Looks like I'll be spending more than I thought on this, though. No problem. I'm really excited to get a great sounding room and great monitors. I've been making music for years now, but I've never had the right equipment to make a great mix. Hopefully this will give me that edge I need to take my music to the next level.

[albee1952]

If you can squeeze the extra cash, the Rokit 6's would be a bit stronger in the low end, and have a bit more power(so they should stay clean to a louder level).

[fenderrocker]

Originally Posted by albee1952

If you can squeeze the extra cash, the Rokit 6's would be a bit stronger in the low end, and have a bit more power(so they should stay clean to a louder level).

While tempting, I don't think I can squeeze the cash. I don't even think I'll have enough money to buy the RoKit 5's after I sound treat my room. That's why I have to sell my pedalboard!

[O.G. Killa]

Originally Posted by fenderrocker

Certainly. Although, 2" x 4 = 8", making the absorbance of a 2" 703 panel 1.695+ kHz.

Oh no! It took me like an hour to write that post. I kept doing a couple minutes then working on other stuff then coming back again. Sorry for the mess up. I don't know how I came up with 6"!?!?! it's been one of those days!