John Sayers' Recording Studio Design Forum

I'm currently taking over two bedrooms to turn into a studio of sorts, except I can't do anything too permanent, and I'm not going to worry about isolation at this point. The street is pretty quiet overall anyways, and I won't be recording heavy metal at 2am. So my goal is just to get the best instrument acoustics out of my tracking room, and the best mixing acoustics out of my control room. Diagram attached or link here:
https://dl.dropbox.com/u/3904767/Home%20Studio.png

The bigger room is 10 x 16, and the smaller room is 10 x 13, with that 2ft-deep closet making it even smaller. The ceilings are parallel to the floor, 8.5 ft high.

I currently have it setup as shown, with the bigger room as the control room. I figured the more symmetrical room would be better for mixing, and the room with less parallel walls would be better for tracking. I have a bunch of portable rigid fiberglass things, but after putting it all up in the tracking room I found the room sounded pretty dull. Of course, the bigger room probably has a better natural reverb. SIGH.

I've read a lot of forums and done a lot of portable recording, but this is my first time setting up a somewhat permanent space. My current treatment ideas were...

Control room (bigger room):
- Bass traps floor to ceiling in all corners except where the door is. Some of that corner foam stuff up high in that corner. The bass traps will simply be fiberglass panels placed at an angle across the corner.
- Rigid fiberglass panel on the wall behind the mix position, as well as on the side walls between mix position and monitors.
- Rigid fiberglass panels OR diffuser type piece of plywood at an angle on the roof between mix position and monitors. Would appreciate some input on that decision.

Tracking room (smaller room):
- Again bass traps in the corners except just the corner foam stuff above the door.
- Big diffusers along the long parallel wall (may purchase or make these myself)
- Rigid fiberglass panels on the ceiling in the middle of the room, where the tracking will generally happen.

I record all types of music. Acoustic instruments, drums, vocalists, etc. So far nothing super heavy though.

I have some of the fiberglass panels already, but will need to construct more. Between that and the diffusers, that'll likely max out my budget/free time for treating this. However, if somebody has a really great idea for me, I could probably spend an additional $500 bucks or so.

Any input on my plans?
Improvements?
Thoughts on whether I should switch and use the bigger room for tracking?
I appreciate any comments.

Please try to insert all photo by uploading them into the forum, not linking to off-site photos. I see you did that later in your post, so that's great. The reason is that, if you check come of the old threads on the forum, you'll notice empty spaces and comments about photos that you can¿t see any more, since the places they were linked to no longer exist. So those threads are not much use.

Yep! Absolutely. On the other hand, it is better to have the live room larger than the control room, for other reasons, but I think you called it right here: the other room would not make a good control room either.

That sounds fine, although you don't really need the foam: you can do fiberglass or mineral wool for everything. Acoustic foam is not cheap, and fiberglass / mineral wool are just as effective.

Right: Make it thick, and for the rear of the room, space it away from the wall, if you can.

Are you talking about a poly-cylindrical diffuser? While that is a possibility, I think it would be better to do a traditional absorptive cloud up there. With a poly, you still run the risk of specular reflections at high frequencies, plus in a small room you need lots of absorption anyway.


Sounds fine. Once again, you can save money by swapping the foam for fiberglass or mineral wool.

What type of diffuser? Numeric sequence diffusers can be problematic in small rooms.

About the only thing I would change is to move your speakers right up against the front walls, instead of having them spaced away, as you do now. The room isn't big enough to get them far enough away that SBIR is no longer an issue, so your best bet is up against the front wall. However, you will need to roll off the bass response if you do that: there should be a control on the rear panel for doing just that. Try it at -4 dB and also -6dB, to see which gives you the flattest response.

Apart from that, it looks good.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thanks Stuart, you replied to me in another thread that i posted about the same time as this one, about diffusers, not sure if you realized they're by the same person. Based on that very helpful info I've decided to do away with the idea of diffusers and use absorption and bass traps that are reflective to avoid making the room to dull.

Having said that, in this message you make it sound like maybe there are some diffusers that could work in my situation? I'd really like a nice natural reverb for the tracking room but it is so small it's hard to get.



Can you elaborate on this? I figured going away from the walls will at least diminish the effect of SBIR. What gains do I get from moving them up against the wall? I do have that window right in the middle of the speakers, how does that play into my acoustics?

I must admit, I hadn't noticed! That's one of the reasons why it is best to keep all of the posts about your build in one thread, where possible.

Anyway:
The "bad guys" in small rooms are the various types of diffusers based on numeric sequences, with wells of various depths. They cause lobing issues close up. Other types, such as polycylindricals, are more useful, and John's famous "slot wall" also has some good diffusion properties, so you might want to consider that as a possibility.

Yup! That is indeed the issue in small rooms. And the problem is the very term "small". An acoustically small room actually does not have a statistical reverberant filed, and cannot possibly ever have one, due to the laws of physics. In order to have a true reverberant field in a room, it needs to be several times larger than the longest wavelength of interest. There needs to be enough space for the waves to get around several times, back and forth, in order to have a reverberant filed. Small rooms just do not have that. For example, if all you want is a reverberant field for spoken word (voice-overs, for example), then the lowest frequency you need to worry about is maybe 150 Hz. A full wave for 200 Hz, is about 5 and a half feet, so you need a room at least 11 feet long for that to sound reasonably natural, and preferably 35 feet long (theoretically). But if you want your drum kit to sound good, and your kick is tuned with a lowest fundamental of 80 Hz, then then room should be at least 30 feet long, and more like 90 feet, to get a true natural reverberant field! Clearly, that just ain't possible in the vast majority of him studios.

That doesn't mean that you can't make a small room sound reasonable: it means that you cannot get a true reverberant field. But what you can do is to make the room as large as possible, and keep your possible paths as long as possible by keeping the room reasonably "live", reflective, and allowing for longer paths between bounces. Angled surfaces on the walls are good for that... such as slot walls, for example...

But in very small rooms, even that doesn't help, and the only real alternative is to make it dead, then add reverb electronically. But "dead" doesn't sound nice. It is unpleasant to work in a truly dead acoustical environment. So you have to trade off, and strike some type of balance, keeping the room live enough that it isn't annoying, but not so live that it sounds annoying!

The other issue in very small rooms, is modal behavior: You'll often see people talking about the RT-60 times of their small rooms, and showing graphs and waterfall plots of the "reverb times". But in reality, they aren't really measuring RT-60 at all! "RT-60" is a technical term that refers to how long it takes the reverberant field in a room to decay by 60 decibels: "Reverberant Time - 60 dB". But since there is no reverberant field in a small room at low frequencies, what they are actually measuring is flutter echo, reflections, and room modes: Not sure if you already know about modes, but basically a room mode is a specific type of resonance that occurs when the wave of a specific tone happens to fit in perfectly between two (or more) walls. So there is a path around the room that allows the wave to bounce of the walls and get back to where it started, in phase with itself, and going the same way. So the wave reinforces itself at every point: the peaks become huge, the dips become very deep, and you have a "standing wave" in the room: even after the note that caused it stops, it will carry on bouncing around the room for a while (several hundred milliseconds, or maybe even several seconds in extreme cases), since it "has stored" energy, and an easy reinforced path, so it take a long time to die down. And that is a big problem: some specific note will make the room itself "ring" and resonate, while others will not. And depending on where you are in the room, your ears might be in either the peak of that standing wave, or the null. so you hear it way too loud, or way too soft.

So for a small room, what you see on an RT-60 graph is not really the reverberant field of the room, but rather the modal behavior: All rooms have modes, and there is nothing you can do to make them go away, since they are a direct consequence of the dimensions of the room: Change a dimension, and all you succeed in doing is to move the mode to a different frequency, but it is still there. In a large room, it doesn't matter, since there are modes for every single possible frequency in the spectrum, so all notes sound the same. But in a small room, there just aren't many modes at all, and there are large gaps in the spectrum between modes at low frequencies. So as you run up or down, playing scales on the piano for example, every now and then you'll hit a mode, and that note will sound either very loud or very quite (depending on if you are in a null or a peak). The smaller the room is, the fewer modes there are in the low end, and the more predominant they are. For very small rooms, there are only a handful of modes under 300 Hz., and they are VERY noticeable.

So what to do? You can't make them go away, but you can damp them: Reduce the intensity so much that they don't get triggered, and don't have much effect on the room. There are several ways of damping them, but the most effective is ordinary thick absorption. And since all modes must terminate in the corners of the room, that's the best place to put the treatment: That's why you always see "bass traps" in corners: they catch the largest number of modes there. Some people also try to deal with modes using tuned devices, such as Helmholtz resonators, membrane traps, perforated panels, etc., that are designed to deal with a specific mode. That is possible, but not as easy as it sounds. Broadband absorption is the simplest.

The above is normally though of as applying to control rooms, but live rooms are the same: the principles of acoustics apply in exactly the same way to live rooms, so the same approach can be used to treat a live room. The only difference is the "live" part. A control room should be neutral, with the RT-60 times for each frequency band strictly adhering to EBU guidelines. But a live room is not normally meant to be neutral! It is supposed to have some "life", some "character", to "color" the sound in pleasing ways. So it becomes more a matter of personal taste, and what YOU consider "pleasing": Some drummers like their drum room to sound like a concrete cave, with massively bright reflections, others prefer that it sound like death. Most prefer something in between. So maybe one idea you could consider, is to make the acoustics of your room variable! Have sliding or folding panels on the walls that can uncover vast oceans of absorption when you want the room to sound dead, and cover them up when you want it more lively. Or have large diffusers that can be covered or uncovered, as well. Moveable gobos on wheels are another option. Yet another is to make one area "live", and another area "dead", but that's hard to do in a small room: more applicable to large rooms.

So rather than trying to do the impossible an make a small room sound perfect, maybe just making it variable is a better choice, so it can be different shades of "not too bad", in different ways, as needed for each session.

Just a thought...

Well, yes, if you move them far enough away form the wall then you can move the SBIR artifacts down to low enough frequencies where they are no longer an issue. The problem is "far enough". You need at least 1.5, (about 4.5 feet) before that happens. Above that, SBIR and the other artifacts are right there, smack in the middle of the lows and mids, where they do the most damage. so the nest best thing is to move the speakers in so close to the wall that they move up even higher, into the upper end of the spectrum, where they are not so objectionable.

This is all about wavelengths and frequencies. If the speaker is exactly a quarter wavelength from a wall, then when the wave comes back, it cancels itself out at. Gone. If it is a full wavelength away, then it reinforces itself on the way back. So you have alternating patterns of cancellation and reinforcement, for different tones, based purely on the distance between speaker and wall. Between about 8" and 4.5 feet, that occurs at frequencies in the low to mid range. Not nice.

So the 4 best positions for speakers are:

1. Soffit mounted: No SBIR at all. Also corrects a bunch of other issues.
2. Far away from all walls. At least 4.5 feet.
3. Right up against the front wall.
4. Anywhere else.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Yeah, sorry about that, I linked this post in that one, and felt like it should be a separate thread because it was exclusively about a certain type of diffuser, but of course that right away came back to what kind of room I'd be using it in. We left it off there that I'd do some analyzing of the control room to figure out what I need, I'm still trying to find time to do that.

Anyways, this is great info. I have noticed so far that my bass response is very unclear with my monitors where they are. Of course I don't have bass traps set up yet, so I thought that was the problem. I'll try them against the wall/window, that gives me more room too. In other situations I've tried to put up at least one absorption panel on the wall behind the monitors to help my RFZ but I need access to that window so I guess I'll just have to live with some reflections off the window. Hopefully the lower ones will go right through and end up outside?

I'll also look into the slot wall or cylindrical diffuser, as I feel like a diffuser could be helpful to help with my boxy tracking room problem without totally killing the sound in there. With a room that small I think I'll focus on just getting it sounding a nice medium, not too dead, not too live, but most importantly getting rid of the flutter echo and modes without making it a vacuum for sound.

Thanks for all your help, I'm learning tons