Asymmetrical Room Treatment

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

John,
Great question you ask. What’s happening at the ear is the sum of direct and indirect reflections which are attenuated and delayed versions of the original direct reflections – in other words reflections of reflections. The reason sound reproduction sounds better in a room than outside is due to the reflections from the room’s surfaces. The surfaces of your room are in their own right sound sources, not of direct sound but of indirect reflected sound. The variables that come into play include reflection strength, direction, and time delays from the direct sound source.
As your mind assimilates direct and reflected sounds, the direction, intensity and time lag from which the reflection is coming helps tell the brain how wide, high, or deep a room is. Think about how music sounds in a large cathedral verses a small residential room – with your eyes closed you can tell if you’re listening in a large or small room. It’s the indirect reflections that provide the mind with the answer.
Reflections from the first reflection points between the speakers and your listening position (side walls, ceiling, floor) tend to pull the perceived sound towards the adjacent surface as your ear hears both the direct sound and reflected but delayed and attenuated versions of itself. Apparent source width, image broadening, impressions of height and depth are the result of reflections occurring at delays of less than 80ms and include the reflections that are included within the recordings.
The sound reflections from the recorded venue which makes up its natural reverb, or electronic reverb introduced into the mix, is what you’re hearing when your kettle drums appear far away.
Hope this helps . . .

Hey everyone, thanks for the responses; they've been very helpful! At the moment I have treated the front wall behind the right speaker pretty heavily, and just with this I can tell that there is a pretty large improvement in imaging detail; instruments seem more defined into specific spatial locations. I will experiment with treating or not treating the rear corners and see what results I get.

On a related note- I currently have two, 4' tall (4" thick) bass traps in the front, right corner (one on top of the other). My ceiling is only about 7'8" tall, so the bottom trap is at a pretty tilted angle, which at the bottom floor/wall/wall corner leaves a substantial airspace, probably about 2' at the furthest point. While I know that having a decent amount of airspace between a trap and wall is beneficial, is there an upper limit on this? My guess would be that about 1 or 2 times the thickness of the trap would be ideal, but I am just guessing here.

Chrisar wrote:
"While I know that having a decent amount of airspace between a trap and wall is beneficial, is there an upper limit on this? My guess would be that about 1 or 2 times the thickness of the trap would be ideal, but I am just guessing here"

If you're using fiberglass filled absorbers (which you are) then you simple change the frequency at which the absorber maximizes its effectiveness at by changing the air space distance. I don't believe there is anything intrincically good or bad about how far you pull the trap out, it's a matter of using that flexibility to your advance to attenuate a problem frequency. Remember that the absorber works best when the particle air speed is fastest which is at the 25% mark of a frequency's wavelength. It's easy enough to calculate what that is as follows using a 440Hz frequency for example:

Speed of sound 1130 / 440Hz *12inches = 30.8" then multiply that by 25% and you get 7.7" which is the airspace needed to max the absorber placement.

I would think other practical issues like asthetics or not having the absorber blocking a walking path through the room etc might factor into it too.

I think Kevin has some very good answers, though I am not sure if the OP can take advantage of all of them due to his restrictions in renting.

My question is regarding a 4" diameter (I am assuming it round) or is it a panel type? If its round, doesn't the 4" diameter preclude it from acting as a bass trap? I was under the impression that for the round tubes, one need really about 16" to get into the bass notes?

FYI - I spent my evening installing some new Real Traps - Corners panels (mondos), a couple of PFZ (?) on the ceiling (suspctd about 4"). On one wall, left, I have four 2 X 2 X 4" thick Real Trap Panel sound panels (tilted, out 6" at the top and flush at the bottom) in a 2 X 2 pattern with 2" between each panel. On the opposite side where my window is, I glued laminate thickness playwood onto the auralux backing. They are 4 feet tall, 2 feet wide and 2" thick. The window is about 3 feet tall by about 5 feet wide. I basically bent the laminate so that panels are wedged between the top and bottom window framing - bowing outwards.

My back wall (behind me) is about 15 feet behind where I sit and am justing letting the physical aspects of what behind me defuse the sound (I have nothing specifically addressing the soundwaves behind me due to the distances involved and it doesn't sound like I need anything).

Finally, I have two of the auralex panels between the speakers (in front of the fireplace opening, positioned at about a 15 degree angle - with a point in the center).

I need to put some decent heavier drapes up over the window and auralex bowed panels, but already the room is sounding much better.

Bass is much tighter and I can play a much high SPLs without the sound breaking up, conjecting and just becoming over energized.

Anybody want to make any additional comments it would be fine. I think I need still some corner (wall/wall/ceiling triangles and possible raise higher my front wall corner traps which are pretty wide frequency ranging).