Nothing above me and no basement.
Great! So single story, slab-on-grade floor. Excellent.
Modal response? Links to a good read? Where could I find some set dimensions?
Modal response: That refers to the way a sound wave can "fit in" perfectly between walls, bouncing back on itself, and reinforcing itself, building up, getting louder, and "ringing". That happens for every tone where the wavelength happens to match the distance between two walls. Like this:
When that happens, the wave bounces back and forth between those walls, setting up a pattern of peaks and troughs in the room at fixed locations. Like this:
How-Standing-Waves-Form--sound-wave-reflect-animated.gif
That is called a "standing wave" for obvious reasons. The wave does not actually stand still, though! It keeps on moving. It just creates pressure peaks and nulls in the room, so it SOUNDS like it is standing still, but in reality it isn't. Here's another way of looking at it, showing the pressure peaks and dips:
room-mode-animated.gif
The top image is in 1 dimension, so you get a mental picture of how it works, and this one is in 2D, so you can see how the patterns form in the room, and how some places will have a different sound intensity from others for any given mode. In reality, it all happens in 3D, not 1D or 2D, and since there it can happen in all three directions at once, things get complicated:
mode320.gif
On each trip around the room, the wave adds a bit more energy to itself, so it gets loud, fast. And after the tone stops, the mode carries on. So after you stop playing the note that caused that resonance, the resonance continues for a while, slowly dying away. In other words, the room carries on playing that note after you stopped! But for low frequencies, usually the very next note up the scale, or down the scale, does not have a mode associated with it, so it does not "ring". Meaning that some notes ring, while others don't. Not a happy situation.
It would be fine if every note on the scale had a mode or two associated with it, since the room would then sound the same for all notes, and that is indeed what happens for mid and high frequencies, where there are many dozens, or even hundreds, of modes for any given note. But as you go down the scale, they get fewer and further between, until at some point (referred to as the Schroeder frequency), there aren't enough modes to go around any more. You start finding notes that have no modes. And the lower down you go, the worse it gets, until at the very bottom end, there are no modes at all.
The problem occurs in small rooms, not so much in large rooms, simply because large rooms have large dimensions, and therefore many ways that a wave can bounce around. But small rooms don't. There's a limited number of modes. So one of your goals in designing a room is to find a set of dimensions that forces the modes to be spread out evenly, rather than concentrated in one or two points.
Here's an illustration that I just happened to have prepared earlier today, to show another member why his small room will not be able to sound like a large room (he refuses to believe me, but that's his problem, not mine!
).
Here's the predicted modal spread for his room, which measures 10 feet long by seven feet wide by seven feet high:
modal-prediction-10-x-7-x-7-room-2.jpg
As you can see, there are no modes at all below about 50 Hz, and only 3 modes below 100 Hz. So as you play your bass guitar in there, each time you happen to hit one of those three notes, the room will sing along with you, loudly, and carry on singing after you stop playing that note, but for all the other notes it won't do that. Imagine how disconcerting it would be to play bass in there! Or electric guitar. Or keyboards. In fact, in that particular room, there is no real modal field below about 400 Hz, which is well up into the voice range, so even vocals and acoustic guitars would be affected.
On the other hand, here's the predicted modal response for a beautiful live room, which I'll call "studio B":
modal-prediction-45-x-35-x-23-room-2.jpg
That room measures 45 feet long by 35 wide by 23 high, and you can see that it has hundreds of possible modes, all across the low end of the spectrum, smoothly spread out. It has full modal support down to 45 Hz, and pretty decent response even below that, down to about 23 Hz (the first note that has no mode at all). So bass, drums, keyboards, guitars, vocals, and everything else will sound just fine in there, because there are plenty of modes, and they are smoothly spread out. That room is said to be among the best in the world for drums, and the modal spread data shows one o the reasons why.
So, when you design your rooms, you need to take into account the modal spread. To get good modal spread, the rooms need to be as large as possible, with ceilings as high as possible, and a good relationship between the dimensions, such that no two dimensions are mathematically related (such as being 7 feet wide and 7 feet high, for example, nor 7 and 14), and also not within 5% of being related. There are other rules as well, but you can play around on your own to find a good modal spread. Use one of these Room Ratio calculators to figure out the best dimensions for your room:
http://www.bobgolds.com/Mode/RoomModes.htm
http://amroc.andymel.eu/
Both of those are very good, and will help you to decide how best to build your room.
Is it possible to have the face of it at a angle like that? Is it even a good idea to have it at an angle like that?
The control room MUST be symmetrical. If not, your left ear won't hear the same acoustic response as your right ear, and you will subconsciously attempt to "fix" that in the mix... You might get it sounding perfectly balanced in your room, but it would sound lousy when played elsewhere, since no other place on earth would have the same imbalance as your room.
So you need to draw an imaginary line down the length of your room, splitting it in half, and the left half should be a mirror image of the right half. At least for the front part of the room (from your ears to the front wall), that's an absolute necessity. You can relax that rule a bit for hte part of the room behind your head, but for the front, symmetry is critical.
- Stuart -