Originally Posted by popalock
I really want to jump into this conversation without showing my complete and utter igorance, but I doubt that is possible at this point in time. I'll ask a question regardless.
The depth of my current room is right about 14'. Anything above a 14' long wavelength (20Hz and below) is constructive? Or, at least, has a higher probability of being constructive? Is that an overly simplistic view? I'm taking baby steps guys...lol
I'll see your ignorance and raise you more ignorance with a side of rash stupidity, as I take a shot at this.
Here's a 5 hz. wave in a made-up room, with vertical lines indicating what the wave is doing after traveling different distances. Said made-up room has the LP at 10 feet, with first reflection points from walls and ceiling a bit later (all the same so I didn't have to draw a bunch of lines) and another reflection from the back wall another 10 feet behind you. Poor setup choices, I'll admit.
See how the various marks hit the waveform relatively close together? The wave is doing similar things at all these points, reinforcing to some degree and not fighting at all. Lots of gain here, in this ridiculously simple model.
Here's a 10 hz. wave in the same room, same reflections. Now the back wall reflection is approaching 90 degrees (quarter wavelength), and if you do the math (or much simpler and probably smarter, just simply believe what Mark Seaton says) that means the back wall isn't reinforcing much at all any more. It's just sort of there.
At 20 hz things start looking a lot different. See how the back wall is doing almost the opposite of what the first line is doing? It's almost 180 degrees out of phase, which means it's fighting the direct sound and creating a suckout. The side wall reflections are still pretty close to the direct line and reinforcing somewhat, but not as much as they were before.
I could draw a hundred lines in each graph but if you think about it the trend is clear even without all that: the longer the wavelength, the more closely all the reflections in a typical room are going to track each other and reinforce; but as frequency goes up and wavelength shortens, reflections from various parts of the room become more and more randomly distributed on this illusory waveform and it all washes out in a mess of little peaks and nulls that average out to no extra gain at all.
Not much good science here, just my attempt at a way to conceptualize it. I fully expect to be told how wrong I am, but I wanted to give it a shot if only to try and put it straight in my own head, and have an opportunity to be harshly corrected if I have it all totally backwards.
[flame suit on]