Creating a "sweet spot" in a small room

[timmcallister]

Room
9'10" deep
10-12' wide (2/3 of one wall has a pocket door, other third is a door)
8' high
Ceiling and walls: sheetrock. Floor: carpet

Mix position is on long wall (that is the wall adjacent to garage, I have my computer in garage for sound isolation and run the cables through wall into bedroom) Mix chair is about 40% of the way into room.

Monitors:
Genelec 1029/1091

Acoustical treatment:
(4) 6' x 2' panels, 4" deep Owens Corning 703, one in each corner
(2) 4' x 2' panels, 4" deep Owens Corning 703, hanging on back wall
(1) 4' x 4' foam on front wall
Medium weight drapes over window on left side wall

(still to do) Medium weight drapes over pocket door for symetry.

Test methodology
My ears and a Radio shack analog db meter and test tone generator. Testing from 30-300Hz at 2Hz intervals. I know the RatShack db meter is a little inaccurate, but it should get me in the ballpark.


Problem
Problem frequencies (at mix location) are:
boost (approx 10db) at 55-70 Hz
null (approx -15db) at 105-112 Hz
boost (approx 12 db) at 120-150Hz
The rest of the freqs are "ok"

The center of the room seems to be just simply awful. Freqs smooth out a lot as you move closer to walls. With the room as small as it is, I will sit in about the same location regardless of where I move the desk.

BTW: The problem listed above is with the acoustical panels placed in the room. I tested it with no panels and was shocked to find the panels didn't make a tremendous difference.

Question
What can be done to "create" a sweet (sweeter?) spot in the center of the room?

Thoughts??????



Edit: I have brought in an additional (4) 4x2 foot panels of 4" OC703 and stacked them a few inches off the back wall, making a 4x4 foot, 8 inch deep panel a few inches off the wall. I spot checked a few frequencies and saw no material difference.

[carlsaff]

I don't think you can be in the center of that room. Is it the only choice for listening position? Does standing make a difference in perception of the nulls/peaks?

I've doubled-up 2 2'x4'x4" traps (effectively making an 2'x4'x8" trap) spaced inches off my front wall. That was what it took for me to fight the dips I had at listening position. There's still a slight null, but it's much, much better now.

Small rooms can't really have enough bass trapping.

[timmcallister]

Thanks for your post Carl

I don't think you can be in the center of that room. Is it the only choice for listening position?

The size of the room forces me into about the same place, regardless of where I put the desk.

Does standing make a difference in perception of the nulls/peaks?

Not that I noticed (but I'll double check this), however, moving my head 12-18inches towards the front wall makes a HUGE difference

I've doubled-up 2 2'x4'x4" traps (effectively making an 2'x4'x8" trap) spaced inches off my front wall. That was what it took for me to fight the dips I had at listening position. There's still a slight null, but it's much, much better now.

thanks for the idea, I did this on the back wall with little effect, but I try it!

Small rooms can't really have enough bass trapping.

yes, but at some point, there will be no room left for me

[myfipie]

>BTW: The problem listed above is with the acoustical panels placed in the room. I tested it with no panels and was shocked to find the panels didn't make a tremendous difference. <

I am surprised you did not get better results with treatment.. How did you build them? Maybe you need to straddle more corners.. Like floor to wall and ceiling to wall.. With your room being almost a square it is tough, but you can get it much better.

Glenn

[blunderfonics]

Your problem freqencies roughly correspond to your room modes (do a Google search for Room Mode Calculator) which is hardly surprising. I'm guessing the OC have litte effect because they are not designed to go that low. OC703 is more evffective in the mids. They would need to be a lot deeper in order to be effective around 50Hz

What happens when you turn the sub off? Does the Low Freqency response even out at all? I'm going to guess that you have it placed against one wall in the middle of the wall - because your room is almost square and you have a boost at one frequency and a null at roughly the first harmonic of that freqency. Have you tried moving the sub around in the room? You might see things even out if you place the sub off center and away from the walls.

[jrsgodfrey]

I was forced to work in a little square room about the same size as yours in my house for a while, and I found the formula below on some audiophile site. It's anti-intuitive, as it puts the monitors out in the middle of the room more or less -- but it worked a lot better than the monitors near the front wall the firing into the whole of the room. You have to figure out what to use the space behind the monitors for (I put my organ there) and it might not work for you because of that, but give it a try:

The distance from the center of the woofer face to the side walls is:

Room Width times .276 (RW x .276)

The distance from the center of the woofer face to the wall behind the speaker is:

Room Width times .447 (RW x .447)

For your dimensions, this puts the monitors 3 feet from the side and 5 feet from the front - smack in the middle.

I put my corner traps in back of the speakers and made the wall behind me (which was quite close) dead as possible w/ two layers of 2" 703.

Odd looking, but effective in my case.

Cheers,

Jay