Let me clarify some things. Room modes are LOW FREQUENCY. They reflect out of corners. Place a resistance absorber ACROSS the diagonal of ANY corner, and it in essence becomes a "bass trap". IF this corner happens to be a WALL/CEILING intersection, then YES, the panel is hanging at a VERTICAL angle.
Since wavelengths approaching the dimensions of a room are long, it stands to reason, they are LOW FREQUENCIES(BASS) If you hang a resistance absorber at an angle off a wall, it still will not absorb longer wavelengths BECAUSE of this limitation. So where does that leave for it to work as a bass trap? CORNERS! The VERTICAL angle has nothing to do with it. It is placing it at a diagonal across ANY corner or filling the corner that gives it more depth at a place WHERE the reflection of low frequencies OCCURS. It also stands to reason, the depth from a corner to a face of a panel placed across it is what lowers its absorption bandwidth as you are increasing the depth from the face of the panel to a boundary. However, it STILL requires THICKNESS of the panel to REALLY lower the absorption bandwidth of panels on a wall. Remember, a 100hz wavelength is about 11.3 feet LONG! 1/4 wavelength is about 34 inchs!! That means for straight panels to REALLY be effective as bass traps, they would have to be at a thickness approaching this depth.
Furthermore, you need to understand the concept of SABINES and absorption coefficients. Since an open window is a PERFECT absorber, one square foot of OPEN WINDOW, is equal to ONE SABINE of absorption. The absorption coefficients of resistance materials are based on this principle, and is FREQUENCY related. A coefficient of 1 at a given frequency means that ONE SQUARE FOOT of it will absorb ONE SABINE at that frequency(I believe-see disclaimer
) However, it is more complex and is beyond the scope of my little explanation and knowlege to expand on. You might want to do a search on the net for a thorough explanation, as this is an ONGOING research issue. In fact, there are
MANY issues in this regard that are subject to expert opinion and analysis. Lab testing around the world is an interesting starting point for further investigation. Acoustics is a DEEP rabit hole from which I barely escaped, and have no desire to re enter. So please understand, my little explanations are barely scratching the surface of known data on the subjects, and I stick my neck out every time I try to help guys here with understanding the basic concepts.
Now for my disclaimer. I am NOT an expert and my .02 is subject to correction by those that ARE.
fitZ