High Frequency Treatment
@Brien Holcombe @dvdhawk @audiokid @pcrecord @Boswell @Kurt Foster ( et al)
Okay, so, now that I seem to have a better balance of low end in my space ( not perfect by any means but certainly much improved) I had a few questions about upper frequency treatment...
1. The "mirror point" treatment:
I've read about this many times, where you use an actual mirror to find the spot on the walls to the sides of your position that relates to the opposite speaker, so that your left monitor will be hitting a boundary to your right side, and vice versa... the theory being that when you see each opposite monitor in the mirror at a certain place on the wall, that you then treat that spot for reflections.
Truthfully, this has always confused me, in that I was under the impression that sound isn't that "direct" and doesn't travel in a straight line, that when sound leaves the speakers, it emanates in more of a "spherical" pattern, going in all directions - L, R, Up, Down, Angled, to the front, to the rear - So... is this "mirror" method legit? Or just something cooked up by someone on the internet that went viral? I'm not insinuating that it's false. I'm being honest in my query.
2. Too much treatment on the top end?:
Since putting these bass traps behind me, where the wall meets the ceiling, and a 2' x 2' x 3" cloud 3 feet directly above my listening/mixing position, the space sounds far more "even" to me. I'm not claiming to have created the "perfect" space acoustically, but it sounds much more even throughout different points in the room. The thing is, that these traps are rated at a full 100% from 200hz and up... so I'm already getting quite a bit of upper frequency absorption along with the lower frequency treatment.
I have very little horizontal "plane" space between me and the monitors. I'm sure there is some reflection going on there, but it's not as if I have a huge plank table/desk between me and the speakers.
I'm never expecting this room to be that of professional mastering or mixing spaces, but if I can get it closer than what I have now, well, as I've said before, any improvement, even small ones, are still improvements, right?
Is it maybe time for me to step back, and do a week's worth of various mixes to check translation(s), before I do anything else treatment-wise? I have some 2" auralex tiles that I could put on the walls to my left and right, but I don't wanna overdo the treatment, either... possibly resulting in too much top end on my mixes when I check translation on other playback systems.
Kurt mentioned that I might want to consider putting in some diffusion...
Or is it time for me to measure the room as it is now to see what is happening graphically?
Any thoughts, suggestions are welcome. :)
First, lets refresh with why we treat small rooms...so much more than larger rooms. In a larger room the sound comes directly too us and the reflections come milliseconds later that give the listener an indication of size, it can be pleasing to the ear if this is a room that is established for musical settings. Sometimes larger rooms just sound cool because they are big!
In a small room , like a bedroom, we get direct sound almost coupled with first reflection and it can be annoying, it may not sound pleasant and the indication is that you are in a box,,,a small room.
Treatments are an aim at slowing the reflections down not to completely take them away, but to fool the listener into hearing a perceived much larger environment, to mimic a grander room if you will. The first reflection points located with the mirror take those points, from speaker to the listeners ears out of the path of travel so as to extend this perception to the mix position.
As explained by Gik Acoustics "Sit at your listening position as you normally would when listening or mixing. Starting with the left wall, have a friend hold a mirror up against the wall next at your speaker height, then move toward the back of the room. When you can see the reflection of the left speaker in the mirror, mark that spot. That’s your first reflection point. Continue moving down the wall, and when you can see the right speaker, mark that spot. That is your other reflection point. Switch walls and repeat."
In respect to how sound propagates into the environment, it expands as a balloon...like you said, front to rear side to side floor to ceiling and all at the same rate of speed. So essentially everything from the face of the monitor towards the back becomes a potential reflective boundary area. Weird...
I'll take a shot at the 'spherical' nature of sound as it emanates from speakers.
Sound is 3 dimensional. It's easy (and often helpful) to visualize ripples in a pool of water, but that only accounts for one plane.
A flush-mounted soft-dome tweeter will produce a forward facing hemisphere with the high-frequencies it generates. On the other hand, despite the fact that the woofer is also forward facing, the low frequencies are less directional. I think you'll find that the lower the frequency, the more (almost) omni-directional it is. Then you have to factor in how long (in milliseconds) those waves take to develop. The real miracle is, that a relatively little box with an 8" woofer can move enough air to generate a 40Hz wavelength (low E from a standard 4-string bass) that's over 28ft. long - which takes 25ms to go through one full cycle. A wave that long cannot be contained in your entire room, much less constrained to the little speaker box and then aimed in any one direction. The front-facing tuned port is the most directional element of the low-end delivery, as it releases the pressure from inside the box straight toward you, but the lows in general radiate from the box in all directions.
Meanwhile the tweeter is a projecting its highs and mid sound forward. By the time you get up to 13500Hz, for comparison the wavelength is about 1 inch and much more manageable. Of course studio monitors don't really use horns like a PA speaker would, but when manufacturers recess the tweeter, or form any kind of waveguide it's to change the dispersion of the highs. Having hemispherical patterns reflect off the walls, ceiling, console, displays, etc. isn't really ideal either, so some manufacturers recess the tweeter into the box and steer the highs through a carefully flared waveguide.
You can experiment with whatever materials you have on hand. That would be worthwhile, if only for the experimental / educational value.
I'd run the ARC discussed elsewhere, or a REW Analyzer before I spent a lot of money on more treatments.
excellent post Dave!
Direct to what @dvdhawk posted...excellent btw...this could be the whole notion that pushed Thomas Hidley to develop the flush mounted monitor enclosure that eliminated speaker boundary interferance response and encorporated the bass trap area behind the flush mount as well.
God I love this place. ;)