First off, I am not an expert (as many know) but generally act like I am
A "bass trap" should be designed to do one thing:
That is to trap or ineffectuate reflected bass energy from retruning to the direct bass path and negatively affecting any direct energy with its return energy.
I have many times stated that the job of room treatment is to make room boundaries "acoustically transparent". Like they weren't there.
That said, bass moves out from the speaker in large circular waves and travels to the listener.
But the bad news is that some of this energy will travel along boundaries (floors/ceilings/walls) until they intersect in what we call "corners" (two surfaces intersecting) and "tri-corners" (three surfaces intersecting).
The energies that travel along these surfaces will ultimatley be "directed" into each other. Depending on their individual strenghs they will then join/sum and rebound or fire back into the room, to go back through the direct energy wave and apply their remaining energies against the ones we need to hear.
This anti or opposing energy can either "add" energy (Modes) to the direct wave if it is traveling in the same path and direction, or it can subtract energy (Nodes) if it is traveling against incoming direct energy.
Bass can also "rebound" straight off the rear wall, but its energy, depending on frequency, is also deflected along the wall much like how waves/ripples move in a swimming pool.
So the goal again is to keep any and all "non-direct" waves from coming back and attacking the direct waves and degrading their sonic properties.
The most concentrated "return" waves are usually those which have "collected" in the corners and tricorners and are thrown back at the original.
The second most damaging are those which reflect exactly off the back wall and straight back at the oncoming direct waves
Corner and tricorner bass traps are generally the first line of defense.
These traps don't have to be "store bought", or DIY, but they seem to work the best since it is in their design to do the job.
That said, some well placed furnture can also "assist" in the job.
Placing large couches and chairs on the rear wall or in room cornes will certainly help to the extent of the "specific" area they cover and absorb or block.
Anything in its path will either absorb, deflect, or reflect energy depending of several factors including size, shape, density and texture.
But seldon do they run the full length of the corners from floor to ceiling, or all along the front or rear wall.
Now I might stick my neck out and say that bass devices used anywhere but along the wall will have "little" overall effect (or maybe I should suggest "less") compared to those in the corners which can effectively "trap" the bass from "firing/rebounding" back into the room. Or those along a "highly traveled" wall, where they can perform smaller trapping/absorbing/diffusing duties.
Bass devices that are placed "into" the room (off the walls) merely offer an obstacle (unless it is HUGE) for the bass wave to encounter, be slightly absorbed by, and then "move around" and continue traveling to a room boundary.
So effectiveness is actually greatest in the corners and tricorners. It is (IMHO) secondarily effective simply along walls of travel, and then least effective in "open space" unless they are employed in large numbers or mass.
Just take that swimming pool example and stick a few upright logs for the ripples to encounter. They will blow right by them, unless you plant a forest of them.
Just my meanderings on the simple physics and simple observation of how it works.
I welcome criticism,
agreement
and other comments or clarifications.
