Placement of Absorption

So, two questions in two days, I guess I'm really showing my ignorance. On to the point: 1) If I determine that I need 241.5 sqft of 2" 705 covering the reflective wall surface to produce the desired .5s RT60, does the placement within the room significantly affect the sound, within the sabine equation there is no spatial differintiation between absorption coeffecients. I would prefer to place it all on the ceiling, but I can't predict how that would differ from placing some on the ceiling and some on the vertical walls. Thanks for any direction you guys can give.

OhlsenSoundWorks wrote:

I would prefer to place it all on the ceiling, but I can't predict how that would differ from placing some on the ceiling and some on the vertical walls.

If you treat only the ceiling you'll still have flutter echo between the opposing side walls. And if this is a control room, that does nothing for the reflection points either. So that rules out only treating the ceiling! --Ethan

So, how is the placement determined, if the room's RT60 is in the correct range with the proper square footage of absorbent material? The walls not being parallel should help, correct? I'm including a rough .jpg of the room sorry it's in paint, still trying to get the hang of sketch up. There will be another bass trap in the room in a spot to be determined shortly, again please disregard the horrendous picture. The basic description of the room I've copied from a thread I posted about concrete walls: The room in question is built as such: standard concrete block construction (filled with large aggrigate concrete and rebar) with a timber framed wall on the inside (2x6 on 16" centers with 5/8" plywood onto which the concrete would be sculpted). I guess to reiterate the question, how is the placement of the absorbent material determined, given that the RT60 in the room is right with a given square footage of said material (2" OC 705 in this case, along with some bass traps in the corners).

OhlsenSoundWorks wrote:

how is the placement of the absorbent material determined

The general goal is to spread the absorption evenly around the room. But there are exceptions and preferred places depending on how the room will be used. So far you haven't even told us if this is a control room or a recording room. --Ethan

Sorry, if I have not given enough information. This is the large tracking room at a building I just moved into. The goal is for it to be a relatively live room (from what I understand a RT60 of .5s is a good mark to shoot for) there is a double wall at the bottom of the room, 2x6 framing with 5/8" drywall on the exterior and a 9" air space that is insulated according to one the diagrams in one of my Everest books. I wrongfully assumed that non parallel features of the live rooms walls (the lines in gray) discouraged flutter echos. If anyone can point me to a thread discussing the best placement of absorbant materials I'd be grateful, I guess I haven't done enough homework. Sorry again.

For a tracking room, what I would do is to create a few "sweet spots" for recording in the room that have plenty of absorption on the ceiling and on nearby walls, the idea being that you don't want the microphones to hear any first reflections. Good areas for this in a tracking room are above where the drum kit will be, or above where acoustic instruments are recorded. Once you have these sweet spots taken care of, you will want to continue to add absorption, spaced evenly throughout the room, until you achieve the RT60 you are looking for.