So, finding the spots in the room that have the highest pressure only tells you what mode is the strongest, not where you should specifically place your absorption. Good to know.
Right! It would be the ideal spot to put a pressure-based device, such as a membrane trap for example, but not so ideal for a velocity based device. However, as I mentioned, even though it's not ideal, you can still get usable performance out of insulation placed close to walls / corners, for other reasons. One of those is "angle of incidence". Waves don't just approach the wall head on: after having bounced around the room a bit, waves are approaching at many angles. Ideally, they would be approaching at all angles, evenly, and that is refereed to as "random incidence". Randomly incident sound does not behave the same way as normally incident sound...
1. Is there a reason why a concrete floor (basement studio) and a drywall ceiling would cause the situation described - - where the sound pressure is loudest on the floor/wall intersection of the corner? Or does that difference in densities have no effect on specific mode strengths?
It's possible yes, if the ceiling is not very good, for example. In other words, if the ceiling happens to be partially transparent to that frequency, or even absorptive of that frequency, then you could indeed notice it more at the floor/wall interface tahn the other "end", which is the ceiling/wall interface.
2. Like many musicians/composers, I have only one room to do all my recording, tracking, mixing and mastering, so, you can call this a control room moonlighting as a live room. Are there any nuggets of wisdom in how to approach sound treatment in this type of situation? (I don't feel like this issue is addressed that much in forums, when it's a very common situation) I obviously want a good mixing environment, but would like to do what I can to make instruments (mainly acoustic string instruments, hand percussion) sound decent in the same space.
I have mentioned this a few times before, since a lot of people have the same problem.
So first, the bad news: Tracking / rehearsing has a very, very different set of acoustic needs from mixing / mastering, and it is impossible to have one single set of fixed treatment that works equally well for both. Let's start with the later scenario: mixing / mastering. For that, you need to have totally neutral acoustics, such that the room does not "sound" like anything! It "sounds" like it isn't there. It sounds natural, neutral, transparent. There's a document called "ITU BS.1116-3" (google it) that defines the ideal acoustic specifications for a "critical listening room", which is exactly what you need for a control room (mixing/mastering). BS.1116 defines exactly how the room must behave, acoustically, in order to provide the environment that is needed for critical listening. "Critical Listening" is exactly what you are doing as you sit at your console, putting together a mix, and even more so as you master a mix. You need to give your ears and brain that perfect environment that they need in order to accurately discern what the frequency response, time-domain response, directionality, sound-stage, stereo image, and every other aspect of the DIRECT sound really us, exactly as it comes out of the speakers, and WITHOUT the room modifying that in any way. So the room must not add anything to the direct sound, and it must not take anything away: it must not "color" that sound at all. The acoustic response of a properly treated control room should be totally neutral, flat, and uninteresting. Here's what that acoustic response looks like when the room is done:
http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 and here's what it looks like while the tuning process is in progress (right now! Current situation today of a control room being treated) :
http://www.johnlsayers.com/phpBB2/viewt ... 68&start=0 .
So that's great! Control rooms must be neutral, and have no sound of their own. But LIVE rooms, for tracking / rehearsing / composing are very different! They MUST have a sound of their own! A live room has to be... well.... LIVE! It has to have life, and character, and be interesting, and have "vibe", and be pleasant for musicians to play in, and enhance the sounds of the instruments, providing "warmth" and "air" and "mellowness". It CANNOT be neutral! A neutral room sounds dull, lifeless, not very interesting ... not a good place at all to track.
So there's the problem: The room you need for tracking is very different from the room you need for mixing. Hugely different. Tracking in a neutral room sounds dull. Mixing in a live room is next to impossible. About the only things you can track succesfully in a control room, are vocals and maybe acoustic guitar. Anything else just sounds "off".
Thus, my original statement that you cannot treat a room with fixed treatment to be good for both tracking and also mixing.
"So!", you think: "No problem! I'll just tune my room half way in between! A mixture of both live room and also control room treatment!". However, if you did that then the result would be a room that sucks for both! It would be lousy to track in AND ALSO lousy to mix in! No good for either. Sort of like trying to decide if you want a milkshake or a steak for lunch, then figuring you'll compromise, so you dump all the ingredients for both in a blender for 5 minutes, then pour the result on your grill and cook at 180° for 20 minutes ..... You end up with a disgusting mess that is not at all like a milkshake, and not at all like a steak dinner!
So what can you do? Well, the answer is "variable acoustics". Instead of fixed treatment that produces only one result, you make panels that can be flipped, slid, rotated, opened, close, angled, and otherwise adjusted in any of several ways, to change the acoustic response of the room. Some panels might be absorptive on one side and reflective on the other. Or perhaps broadly diffusive on one side, but narrowly tuned on the other. Etc. The combination of all those would provide the acoustic response needed for a live room in one configuration, and the response needed for a control room in another configuration, plus you also have the benefit of a large range in between those two extremes, so you can cover a multitude of specific cases, and even get creative for tracking unusual things: "What happens if I track Tibetan cow bells with everything set to diffusion? And with everything set to absorption?".
So that's my long, waffling response to your question, for what it's worth.
Of course, designing such treatment is a LOT more difficult than designing either a live room or a control room! And ore expensive too. But it does work, and is a viable solution. Here's variable-acoustic device I designed for one of my customers a few years ago, for a general-purpose small tracking room:
Variable-acoustic-01--panels--construction--half-open-SML.jpg
Variable-acoustic-02--panels--construction--fully-open--SML-ENH.JPG
Variable-acoustic-03--partly-completed--SML-ENH.jpg
Variable-acoustic-04--room--completed--SML-ENH.jpg
And here's the results, showing how the acoustic response changes with the panels in various positions. Not a huge change in this case, but it does what it is supposed to do. The room goes from a bit "dull" with one configuration, to a bit "live" with another. This is a vocal booth / guitar both mainly, so there effect does not need to be dramatic. For your case, it would need to be more drastic.
- Stuart -
variable-acoustic-05--acoustic-rt60-plots-all-positions-t20.jpg