Before I describe the situation, I'd like to preface my post with a little background on why I'm working on this project. I'm in an engineering design/engineering processes class, and the project we've been given is to convert a given room into a recording space, or to at least propose a design that the client can then choose to integrate. However, because the main purpose of the class is to familiarize ourselves with the process of designing something based on limitations and user requirements, none of us really has any background in recording studio design, so I've been using this forum, and Rod Gervais' book for background information.
Essentially, we're looking to create a recording room for a children's music class at a local children's hospital/school. Many of the students have special needs and are in wheelchairs or stretchers, which is one of our limitations in the project. The room that is to become the recording space has already been built, and the construction is, according to the music teacher, solid concrete that is 8 inches thick, which achieves suitable sound isolation. Therefore, one of our objectives is to make the space into an acoustically-friendly environment for vocal and instrumental (probably guitar) recordings.
Referring to the simple sketchup model (sorry, I'm new to the software), the recording room is in the corner of the music classroom, with the walls with the window and door facing outward into the room. The window is to allow for student/teacher interface, so students will be facing the windowed wall while they sing/record. From what I've researched so far on acoustics, a small, perfectly square room isn't the best environment for recording, and tends to cause reflections that detract from recording quality.
So my question is, what kind of acoustic treatment would be appropriate in such a situation? When looking at sound foam we found it hard to pinpoint where we could spot treat the room without a direct source of sound, but at the same time realized that covering the walls with foam would be inefficient and possibly cost-prohibitive. I apologize for not having more specifics, but because the class is intended to be more process/design oriented instead of technically oriented, I don't have access to a lot of specifications.
Making a 10'x10' room into a recording space
Originally posted at johnlsayers.com, topic 11802.
Hi James, and welcome!
Exactly. A square room is a really bad idea, acoustically, as the modes all line up. A cube is even worse, so I'm hoping that the ceiling height is not also ten feet! I didn't see that on your model. For those dimensions, you will have serious mode issues at 56.5 Hz and 113 Hz, assuming an 8 foot ceiling. If it is a 10 foot ceiling, then you have a total of 29 serious modal issues below 200 Hz! According to acoustic room modes calculation, for a 10 x 10 foot room with an 8 foot ceiling, room mode issues dominate from 56 Hz. to 155 Hz., and from there up to 620 Hz diffraction and diffusion issues dominate. That said, you did mention that this is basically just a vocal booth for childrens vocals, so the low frequency issues should not be too much of a show-stopper for them, since there isn't much acoustic energy in a child's voice down that low. You could probably just set a low cut on the console EQ below 150 Hz while recording, and not lose too much important stuff. It's a kludge, sure, but it would work. I often have to do that kind of thing in live sound. But you also mention guitars: Guitars, however, are a whole different ball game. Plenty of lows in an acoustic guitar. That changes things a bit. But anyway, regarding treatment: Not only do you have a square room, you also have a small room, and you have parallel walls. "Small room" implies a lot of treatment, and "parallel walls" implies flutter echo, which implies a lot of treatment on opposite walls! The good news is that it does not have to be done with manufactured acoustic foam products. It van be done with common construction materials, to save money. 703 semi-rigid insulation is great stuff for acoustic treatment. So is mineral wool, and even pink fluffy fiberglass. You can make simple wooden frames for this, stuff the frames full and stretch acoustic cloth across for aesthetics. Probably the basic plan for treating that room would be to leave the floor as a plain concrete, or maybe put laminate flooring on it, but keep it as a hard reflective surface. Make the ceiling mostly dead, with some kind of acoustic absorption up there on most of the area, several inches thick. Treat the wall area directly opposite the window with acoustic absorption, and treat below the window itself too. On the side walls, maybe you could do something like make several 2-foot square absorption panels, a couple of inches thick, and place panels opposite each other so that you have a kind of "checkerboard" layout: Where there is a square of bare sheetrock on the left wall, opposite that you want an absorption panel on the right wall, and vice-versa. I think I'd shoot for about 50% to 70% coverage of each wall, to get things under control. More than that would probably make the room too dead, and less than that would probably leave too many modal issues. that would be the cheapest way of doing it. If you have more budget, you could take things up a notch, and maybe angle some broadband slot resonators across one wall, tuned to the specific frequencies where your room will exhibit problems. Maybe so something a bit beefier up on the ceiling. Etc. That's my suggestion, for what it's worth, but I'm not an acoustic expert by any means. Maybe one of the real experts can chime in with some other suggestions. You might want to look at this thread here for more ideas: viewtopic.php?f=1&t=11180 Also, use the search feature here, for topics like "vocal booth" and "square room". I guarantee that will turn up much more info on the subject than you ever knew existed! - Stuart -From what I've researched so far on acoustics, a small, perfectly square room isn't the best environment for recording, and tends to cause reflections that detract from recording quality.
Thank you very much for the response, the information was definitely helpful in making a preliminary design. The room that we're dealing with does, I believe, have a 10 foot ceiling as well, which looks like it could be bad news acoustically. We're now looking into insulation materials to use, and are debating between using sound foam, such as an Auralex product, or fiberglass, some variation of 703. But just looking through the room treatments section of Gervais' book, there are several charts for absorption coefficients for these materials. If we're looking to do a checkerboard layout, with 50% of the three walls covered, and the ceiling completely covered, what kind of absorption coefficients should we shoot for to get the room under control? Because we will also be dealing with guitars and perhaps a keyboard, would some kind of bass trap be a good idea to even out the absorption at the lower frequencies?
Well, with that shape, absorption is NOT going to help you! If you have a cube, it is basically the worst possible shape you can have (apart from a sphere, maybe!) With a 10x10x10 cube, you will have major modal problems at multiple frequencies between 56.5 Hz and 169.5 Hz. Twenty eight of them, to be precise. The worst offenders are 126.3 Hz and 169.5 Hz. Those are doozies! Closely followed by 56.5 and 113... Then there is the nine-way coincidence at 233 Hz: six tangentials and three obliques, all lined up on exactly the same frequency... In fact, below 250 Hz you have a grand total of 124 modal issues, and they dominate the room up to 144 Hz. If all you want is to control RT60, then theoretically you need 298 Sabins of absorption, arranged as 66% coverage of the walls to get the RT-60 within spec. HOWEVER: even if you did that, the room will still sound like garbage. And you can't make it thick enough, anyway. I doubt that you will ever be able to successfully record drums or bass guitar in there. No way. Guitars wouldn't be possible either, probably (they do put out a fair amount of energy on the low end), and probably even male vocals would be iffy. Anything that puts out significant energy below about 300 Hz is going to be problematic. If all you ever plan to record is the piccolo, then I reckon the room would be good for that! :) Simple absorption will NOT solve your modal problems in a room like that. You'd need to make it so thick that the entire room would be full of it. Literally. To get that 56.5 Hz wave under control, you'd need to make the absorption on your wall exactly five feet thick (a quarter wavelength). Even if you could do that, the room would be so dead as to be useless. The only way to deal with that room, I think, is to move two walls, or one wall and the ceiling. For example, drop your ceiling 2 feet, move one wall in by thirteen inches, and all your problems go away... That would bring you within shouting distance of Sepmeyer's first ratio. Not there, but getting close. (Move the other wall out by thirteen inches, and you nail Sepmeyer #1, pretty much on the head: 8' ceiling, 9'1" wide, 11'1" long. That would give you 1 : 1.13 : 1.38. Sepmeyer #1 is 1 : 1.14 : 1.39- Perfect!) Sorry to be the bearer of bad tidings, but throwing a couple of bits of foam or 703 into a 10 x 10 x 10 cube room is not going to make any appreciable difference. If you put enough treatment in there to make it usable, there won't be any space for you, or your instruments! And it will still sound like junk. Move your walls. It is the only viable solution, as far as I can see, if you want a usable room. IMHO - Stuart -I believe, have a 10 foot ceiling as well, which looks like it could be bad news acoustically. We're now looking into insulation materials to use, and are debating between using sound foam, such as an Auralex product, or fiberglass, some variation of 703.