Asymmetrical Room Treatment

Hi Chris.
Putting some 4 inch absorbers in fromt of the window will definatly be a good choise.

They will act as bass traps and controle the mid and high reflections.

I found when you treat the rear corners of a room (behind the listening chair) it seems to kill the sound stage.
You must keep the rear corners lively and work on the first reflection points.

The foam you are useing is not doing much to absorb lower highs and lower.

The compressed fiberglass in the two inch size does a much better job.

Go to my system and read how to get the room treatment really cheap.

It's a do DIY set and you can do a room very well with minimum yen.

Hope this helps.
John

Hi Chris,

Thanks for your additional info. I have a different perspective and/or interpretation than one of the other replies so let me explain.

Back Wall Treatments: (1) A window on your back wall will act as the perfect bass trap – the long frequencies won’t even ‘see’ the window and will escape the room easily. So, I would redeploy your back wall bass traps elsewhere, not because it will damage the soundstage because that is more of a side wall reflections phenonmenum. (2) Drape absorbency is dependent upon the type and weight of material, degree of fold, and distance out from the wall. The heavier the fabric is the greater the absorption. From F. Alton Everest’s book, the absorption effect for velour drapes is concentrated in the 500-1KHz region using 18oz/yd2 material, but for 10-14oz/yd2 fabric is more within the 2kHz-4kHz range where the absorption coefficient tops out at 0.4 (40%). The deeper the folds within the drapes the greater the surface area for absorption – taking a drape pulled straight and then introducing folds deep enough that the drape is now only 50% as wide as it was when pulled straight increased the absorption coefficient from about 0.2 to 0.8 for 1kHz. A 1kHz wavelength is 13.6” long so placing the drapes at the 25% point of 13.6” means placing them out from the wall 3.4” to maximize the absorption effectiveness. I would suggest keeping your drapes or upgrading their density/thickness and creating deeper ‘folds’ in the material as you likely can’t move them farther away from the window/wall. (3) Making a diffuser for the back wall should be easy enough, but making it easily movable won’t be, so I’d stick with the thicker drapes for now. You can still place bass traps in the back wall corners from ceiling to floor should you decide to make or buy more.

Side Wall Treatments: (1) Your open-cell foam WILL absorb mid to higher frequencies depending on its thickness. A 2” Sonex foam with the anechoic-type wedges has an absorption coefficient of about 0.6 at 500Hz and the same coefficient at 250Hz when the thickness is doubled to 4”. The wedges look cool but actually reduce the absorption abilities due to the missing material in creating the wedges, and the surface isn’t hard enough to effectively diffuse frequencies. Your better off using OC701 or 703 material for increased absorption capabilities. (2) Soundstage width is a more a function of side wall reflections than back wall corner reflections. Back wall reflections create “listener envelopment” as per Toole in helping the trick the mind into thinking the room is larger than it is. Absorbing or diffusing/reflecting the side wall reflections, especially at the 1st reflection points, is a matter of taste, and the former will make the soundstage narrower with instruments as pinpoints in space whereas the latter will broaden the soundstage/apparent source width and size of instruments to being more life-like. In my latest incarnation of room treatments I’ve used planks of ¾” thick oak angled upwards to preserve the mid/high frequency energy so as to prevent over dampening the room and redirecting the reflections upwards to the RPG Skylines on my ceiling where they are diffused. It is also very effective at eliminating slap echoes between the two side walls.

Front Wall Treatment: If you were to put up a temporary hard surface in the doorway behind your left speaker, then that should keep some mid/high frequency energy in the room – the low frequencies will escape as it’s neither air tight nor thick enough. I think I’d be inclined to keep the opening as is and add broadband absorption to the middle and right side of the front wall to emulate the open doorway situation by the left speaker.

h
Having said all this, have you a SPL meter and test tones where you can get some rudimentary Freq VS SPL measurements to see how flat the frequency response is?

Good luck

Kevin.
The bass wave doesn't go right through the glass because it's see through.
It reflects back into the room because of solidity of the window.
Now, if the window was open then it would escape into the outdoors.
It's obviouse you have spoken above my comprehention, but I know for a fact, not just assuming, that if you dampen the rear corners it will kill the soundstage if the first reflections are treated.

Been there done that.

I guess if the glass window was several inches thick then maybe the bass waves will reflect off it . . . The size of a low freq wave is huge in comparison to a thin pane of glass so as I said before it will easily pass right through it. You need only to listen to the boom-boom of car subwoofers a block away despite their windows being rolled up. Smaller freq wavelenghts will "see" the glass as a hard reflective surface and but bass won't - it's physics.

You have a nice small listening room so I might imagine that with your seat so close to the back wall and hence close to your back wall corners that absorption in the back corners - on top of all the other absorption you have in place - will reduce the reflections further and prevent any kind of envelopment which is not soundstage. Soundstage width is side wall dependant, depth is front wall dependant and height is well ceiling dependnat. Make sense? Maybe we're defining 'soundstage' differently . . .

Kevin.

I've often wondered about soundstage depth and width.
Since it all happens at the ear, how does the width of a room and depth of a room affect what happens at your ear ?

I can hear or perhaps preceive that a kettle drum is thirty feet behind my speakers when in fact, the wall is only three feet behind my speakers.

Is it the illusion of depth from reverberation in the mixing of the music ?

I have some Mapleshade CD's that doesn't go through the mixer, but goes from the mike strait to two track and the depth goes well beyond my wall.

If you can explain this to me it would help me understand the three dim. soundstage much better.

John