diffusors

[sm272a07]

[I realize I posted this at the wrong place, so not having access to move a thread, I reposted here]

Hi,

I know this is an old classic in forums, especially this one and I feel somewhat guilty for posting this, once more..

But I did my homeworks! (I think )

I read Ethan Winer's document on accoustics (Acoustic Treatment and Design for Recording Studios and Listening Rooms), and I read many, many posts about DIY acoustics (thanks to Ethan for his contribution, which teached me a LOT, and to other posters also)

Now I have this room, which is faily small 10'x13', and I am trying to get the optimal sound for my home studio.

I have bought some Auralex 3' wedge foam, which I used in my older appartment, but it just doesn't seem to do it (It is good, but not enough obviously). I have read and also watched videos from realtraps about bass traps, and I have to think of a solution on building my own (I don't have money to invest in material for now, but I have lots of time).

Now the main question is: In a room as small as this, I was thinking of building some diffusors to help the acoustics. I am not sure though of the difference of each of them. I am thinking of whether QRD diffusors or Skyline. Skyline seems to be a pain to build, but hey, if it helps the sound then there's no cost for that . Foam seems out of option, too fragile, and I am thinking of doing it in wood.

Whew, long post for a newcomer..

Now what do you guys think/recommend?

Thanks for reading/helping.

[Glenn Kuras]

You could use QRD's on the back wall and the back side walls but not in the front of the room. With the diffusion in the back of the room I still would recommend thick panels on the back wall around the diffusors. There are strong nulls and peaks from that area.
For the foam you have, use that in the early reflection points of the room.
What Are Early Reflection Points. SPOTLIGHT:Bob Ebeling - Revolution Studio

[SaSi_SiDi]

For a small room, absorbtion is needed more than diffusion. Since a diffusor needs a couple of wavelengths distance from the listener to form a coherent field, for a small room diffusors tuned for higher frequencies are more suitable.

I would start with some measurements, establish the current RT60 and view the "ugly" frequecy response caused by peaks and nulls.

Then add thick absorbers to the front corners and each corner that is free, while at the same time repeating the measurements.

The room will have "enough" absorbtion when the RT60 reaches 0.5 sec or lower. But don't expect to achieve this using just a couple of panels.

[Glenn Kuras]

Originally Posted by SaSi_SiDi

For a small room, absorbtion is needed more than diffusion. Since a diffusor needs a couple of wavelengths distance from the listener to form a coherent field, for a small room diffusors tuned for higher frequencies are more suitable.

I would start with some measurements, establish the current RT60 and view the "ugly" frequecy response caused by peaks and nulls.

Then add thick absorbers to the front corners and each corner that is free, while at the same time repeating the measurements.

The room will have "enough" absorbtion when the RT60 reaches 0.5 sec or lower. But don't expect to achieve this using just a couple of panels.

totally agree. Think of diffusion as icing on the cake in a room that size.

[sm272a07]

Wow, quick reply Glenn and Sasi_Sidi!

I will read that document hopefully I will understand a bit more about it,
thanks for sharing the link.

[Nordenstam]

There are pros and cons of each type of design. The skylines without well dividers should have a smaller nearfield zone, making it possible to use it closer to the listener. The 2D spread of energy may also be more suitable for a small room, as the larger spread means that less energy is going straight towards the sweet spot.

The 1D diffusers are typically quadratic residue diffusers (QRD). There's also the option of using primitive root diffusers (PRD). The QRD's are typically used for 1D and PRD's for 2D. The PRD's have the added benefit of suppressing the specular reflection (the angle in=angle out reflection). The suppresion is 20(log(N-1)) in deciBel, where N is the prime number being used for the primitive root sequence. This means that the archetypical PRD based on prime 157 will dampen the specular reflection by 20(log(156))=43dB. It could make the difference between a bothersome rear wall reflection from the diffuser vs useful room ambience. Though it's bound to be a limited success, as the specular reflection suppresion only works at multiplies of the design frequency. All diffusers do that. They're frequency selective devices. At some frequencies, they're perfectly spreading the energy, at other frequencies, it's just a lump of mass giving some incidental diffusion and at some frequencies again it'll act as a perfectly flat wall.. There's tradeoffs in everything! Choose the placement for the diffuser carefully and measure the results if you can.

I tried (2D) diffusers straight behind me but prefered to have the first reflection points on the rear wall absorptive. Moved the diffusers to other parts of the rear wall instead. In a small room, that may be hard to do without taking up much space that could be better used for absorption. Which brings on perhaps the main point of this post: The main concern I have with diffusers in any small room is that they eat up space that could be used for absorption.


Check the stickies on top of the forum page and if you want to dig deep, the "2 channel listening room" thread have silly amounts of info on quadratic residue diffusers.


Cheers,

Andreas Nordenstam

[Glenn Kuras]

Originally Posted by sm272a07

Wow, quick reply Glenn and Sasi_Sidi!

I will read that document hopefully I will understand a bit more about it,
thanks for sharing the link.

As your at it read the following to understand how diffusion will work in your room.
Diffusion is a Wonderful Tool by Jeff Hedback
How Diffusion Really Works. Spotlight on MASSIVE Mastering.

[sm272a07]

Good afternoon everyone,

So I have read your documents Glenn, and they are pretty useful. And as SaSi_SiDi said, I might think of going with absorbtion before thinking of diffusors for now. I think the foam will do a part of the job, but I think I will spend more time reading on bass traps. Plus they seem to be fairly easier to build compared to the diffusors, which should give me more time to get into the correct mathematics for the diffusors (More homeworks needed I guess).

I might choose to go with 6" panels made with rockwood. I will read more docs on how to build them. Do you guys think it's better to go with tricorner bass traps, or just panels set in the corner would do? (Considering the space between the wall and the panel might be useful)

Thank you guys,

[Glenn Kuras]

You could go either way. Filling the corner will help more below 60hz so if you can do it, but if not then panels work just fine and if 6" they will work even BETTER.

[sm272a07]

Okay so here's my final decision,

I think it will be necessary to go with many bass trap before going with diffusers for now.

I will buy a few Roxul Safe'n'sound insulation (I know they are soft and harder to work with, but I am being restrained by my budget), 3,5" and will double them to make myself 12 panels of 6 inches deep, 2'x4' and cover the corners, and a few walls. I will have to document myself more to find the crucial points of the room where it is more necessary. I think I will also have to move my workstation for the monitors to face the back wall and eventually put 4 panels of skyline diffusers 2'x4'. (Not sure yet if it's a good idea to have a straight wall in my back from what I have read so far though, but with the diffusers it might solve the issue ).

I haven't think of the ceiling yet, but considering it's a rented appartment, I will have to find of a non-permanent solution for this one.. Good advantage of making the panels though is I will be able to move them along with me when I proceed to buying a house sooner or later.

So going further in my reading, do you guys have any documentation on finding those "crucial spots"?

I will try to build a small plan on google sketchup to show it to you guys as well as pics of the current setting.

Again, thanks a lot Glenn, SaSi_SiDi and Lupo for those valuable comments and suggestions thumbsup

Frank

[SaSi_SiDi]

Originally Posted by Glenn Kuras

totally agree. Think of diffusion as icing on the cake in a room that size.

You know, with some cakes I just enjoy the icing...

[Glenn Kuras]

So going further in my reading, do you guys have any documentation on finding those "crucial spots"?

Well you can use the following as a guide.
GIK Acoustics: Room Setup