Here's the scenario. You have a room that you use as a studio. There is carpet on the floor and the walls are wallpapered. The room isn't as bright as a room with wood floor and bare plaster walls would be. But it's still on the reverberant side of desirable.
Unfortunately you spent all your money on equipment. Hands up who would never do that!
A caring friend did though give you a secondhand acoustic tile. It's two meters long and one meter wide, and about 10 centimeters thick. It does therefore provide a good dollop of absorption.
But where should you put it for best effect?
To work out the answer, imagine this…
Imagine the walls and ceiling are all mirrored (steady on… not too much imagination!). Your friend – still helping out – stands in the position of one of the speakers and holds a flashlight.
In which directions can he point the flashlight to get it to shine on you?
OK, he can point it straight at you. But that's OK, we want the sound that travels the direct route. But what other directions…?
Well he can bounce it off the left wall, from the right wall and the ceiling.
He can probably also find more complex paths, particularly if he spends any time playing pool.
But it's those three single-reflection paths that cause the problem where sound is concerned. As well as the direct sound, you will hear strong reflections that will color your judgment.
So clearly you have identified the three main places that could benefit from absorption. One to the left, one to the right, and one above you. Just imagine where light would reflect.
You could place your one absorber on the left. But that would cause an imbalance in the stereo field, as would placing it on the right.
So it's the ceiling then. By placing your absorber here, you have significantly reduced the harm caused by one of the strongest sound reflections in the room.
Clearly your next purchase should be two more sound-absorbing tiles to place on the sides of the room.
You know, this simple treatment will provide so much benefit, compared to what the room was like before. After this, there is no single other treatment that will provide anything like as much gain.