Room Treatment...help!!!

[1tribeca]

I'm having some trouble figuring out how I should attack my den for some sort of sound treatment. I've attached a quick diagram of the room dimensions. There's a wicked "ring" in the room as it stands now (makes sense with the small size & parallel walls)

I'd like to try to minimize the standing waves, and if possible, compensate for any bass problems vis-a-vis bass traps.

I don't want to just waste money throwing up sound panels indiscriminately on the walls if there's no acoustic point to their placement.

A couple things if you look at the sketch...Firstly, the TV and components will be going on the end where the doorway leads out...plus, the wall where the sliding glass door is, there's a 9"X9" bulkhead running along the entire length of the room at ceiling level which you obviously can't see cuz this is a "top view" of the layout. The ceiling is spray stucco with 6 potlights running the length of.

I'm planning to use either on-wall or in-walls for the front 3 speaks, and on-wall for the rears (can't go in-wall cuz it's a common wall with my neighbor...only 1"X2" on cinder block! There'll be a couple theatre seats midway into the room, and a 50" Pio Elite for the TV. The room is carpeted already.

Any suggestions from the pros 'round here would be most excellent!

 

[Frugal]

room resonance

I'm not an expert but I've had some experience. It's best to get the basic room shape corrected first and then look at room treatments.
I notice by your diagram the room width divides exactly into the room length. That means the 2nd harmonic of the room length is the same as the fundamental resonance of the room width. If the height is close to 8.5 feet you have a real problem, it'll ring like a bell. The best thing to do is frame one end of the room to shorten it by a couple of feet. How tall is the ceiling? How tall at the bulkhead and what percentage of the ceiling does the bulkhead cover? What material covers the ceiling?

 

[1tribeca]

Well, I'm planning to bring the far wall out about 16"...so it's even with the left side corner box (this is mainly to make it easier to install all the speaks/panel too) It will have the affect of shortening the room by a bit...as you suggested.

The room height is a standard 8'...the bulkhead is 9" X 9" and runs the length of the left side of the ceiling...percentage? Don't know...I guess the width of the room minus 9".

The ceiling is spray stucco...standard builder stuff...with 6 potlights relatively evenly spaced running the length.

 

[Frugal]

room resonance

I calculated the fundamental (f1) resonant frequency and second (f2) and third (f3) harmonics for the length, width and height of your room. You can see how close the length f2 and the width/height f1s are. Even after shortening the room, length f2, is very close. This room will have a huge peak around 145hz with big troughs on either side. It will also have a peak around 280hz and more troughs. I don't no how to fix this without moving walls. Maybe some the Audioholics out there have some ideas.

Length f1-69.00 f2-138.00 f3-207.00
Width f1-136.63 f2-273.27 f3-409.90
Height f1-143.75 f2-287.50 f3-431.25

Length after shortening room 16" f1-75.00 f2-150.00 f3-225.00

To calculate resonance: 1150/distance in feet. X2 and X3 for 2nd and 3rd harmonics.

 

[1tribeca]

Much appreciated. One thing I'm thinking of doing is building out the far wall to 20" now (in light of the room needed for components & wiring) Not sure if this will make any significant difference to the acoustics.

Should I just throw up some panels throughout the walls, add a diffuser on the rear wall and hope for the best?

 

[Frugal]

cheap bass traps

You could buy half a dozen or more bundles of fiberglass insulation and keep them sealed. They make excellent bass traps down below 40hz. Move them around and experiment. You can cover them with fabric later or return them as unused building material.

 

[ParadigmDawg]

huh......?

You could buy half a dozen or more bundles of fiberglass insulation and keep them sealed. They make excellent bass traps down below 40hz. Move them around and experiment. You can cover them with fabric later or return them as unused building material.

 

[Frugal]

huh

huh...what?

 

[1tribeca]

Yeah..I was thinking of using a portion of the empty space between the real wall and the 20" gap I create with the second wall for bass trap treatment. The lower portion would probably work best...since I'll most likely be doing in-walls. I should have ample space below the speaks, and to each side of whatever cabinet I instll for components...just brainstorming.

BTW Greg, nice system pics!!!

 

[Frugal]

typo

You could buy half a dozen or more bundles of fiberglass insulation and keep them sealed. They make excellent bass traps down below 40hz. Move them around and experiment. You can cover them with fabric later or return them as unused building material.

typo: "bass traps down below 40hz." should have been "bass traps to down below 40hz." ie: all the way down to 40hz and deeper. my bad

 

[Frugal]

Yeah..I was thinking of using a portion of the empty space between the real wall and the 20" gap I create with the second wall for bass trap treatment.

That will lower the resonant frequency for the length of the room and that should help. That still leaves the problem of the equal height and width. I wonder if it's possible to make traps that absorb bass only down to 90hz. They should be fairly thin and you could place 3 or 4 of them along the left wall. Come to think of it you could tune the length to 55hz the same way. I've read that the ideal room dimension ratio is 1:1.62:2.62. For an 8' ceiling that would be 8' high by 13'wide by 21' long. That's how I chose 90hz and 55hz.
Does anyone out there know if it's possible to tune traps to absorb bass to a certain frequency and no lower?

 

[1tribeca]

Ok, couple questions...

Why only along the left wall?

How "thin" a trap do you figure?

I have a feeling I might just say screw it, and toss up as much absorption product as space alllows and make do. This is getting frustrating and it's not a George Lucas theatre we're talkin' here...it's a simple den! I just thought there would be a relatively simple fix...doesn't appear that way huh?

 

[Frugal]

just go for it

They could be on either side and I'm guessing 9" of high density Roxul or equal. I think you should build the end wall and leave access for later. Set up your system and tweak it over time. A massive couch might help too.