New Basement Studio Concrete

Greetings! Let me start by saying I hope that I do not break all of the forum rules in a single post.... :P I have a room in my basement that has 3 concrete walls and a fourth wall that is just framed with studs. The ceiling is 26" deep floor joists, awaiting insulation. The room is 11 feet by 14 feet and the ceiling is 8 feet tall. There are no neighbors nearby, as I live in the country on a 2-acre lot. I play acoustic guitar and banjo and have two primary intentions for this space: 1. I want to use part of the room as a mixing area 2. I want to use part of the room as a recording space, primarily acoustic instruments and vocals I am envisioning the following: 1. I will paint the walls white to seal them, and then construct 2x4 broadband absorbtion panels using OC703. The panels will be placed staggered across from each other on facing "side" walls, particularly in the recording end of the room. I am hoping that I can retain some of the crisp live feel that the concrete imparts, while taming using the panels. 2. Leaving the concrete floor concrete and painting that is also something I think will work well. 3. The ceiling will need a "cloud" in the center, and I plan to install about 2 feet of wall board (sheet rock) around the edge of the ceiling, within which I will place lighting. 4. The mixing end of the room will have a small area rug on the concrete floor. At this end I am thinking of building angled walls to reflect the monitor sound back into the live space. 5. From everything I have read, this room is too small to gain much benefit from bass trapping. So these are my thoughts, "cloud" in the ceiling, concrete floor, concrete walls with panels staggered to reduce reflections, but allow the liveness of the concrete to still be present. Am I crazy??? What am I missing???

Hi "simpsongb", and welcome!

The room is 11 feet by 14 feet and the ceiling is 8 feet tall.

That actually works out to a very nice ratio, so your modes should be spread quite evenly.

The ceiling is 26" deep floor joists,

:shock: Wow! Those are deep joists! They must be spanning a very long distance, or supporting something pretty heavy. But that's actually very good for you, since you can fit a LOT of insulation up there! You don't really need 26" of it, but put in as much as you can afford.

1. I want to use part of the room as a mixing area

One thing I noticed with the layout is that your speakers and mix position (head) are not in a good relationship. You should fix that.

1. I will paint the walls white to seal them, and then construct 2x4 broadband absorbtion panels using OC703. The panels will be placed staggered across from each other on facing "side" walls, particularly in the recording end of the room. I am hoping that I can retain some of the crisp live feel that the concrete imparts, while taming using the panels.

That's a good plan. In addition to painting the walls, you should also caulk all around the edges of the drywall wall, where it meats the concrete walls, ceiling and floor, to ensure that you have a good seal. It would also be good to seal the underside of the subfloor above you, to make sure that you have a good seal up there too. I would also make some of the absorption panels bigger than that: Build some 2'x4', some 2'x8', and some 4'x8'.

2. Leaving the concrete floor concrete and painting that is also something I think will work well.

Excellent! Instead of painting it, you could stain it: there are special stains for cement and concrete, and if you are artistic, you can get some very nice effects. Search the forum for "stain concrete floor", and see if you find something interesting... :)

3. The ceiling will need a "cloud" in the center,

Actually, the cloud needs to go over your desk. There is a major first reflection point up there, and it needs to be treated. Build that cloud big, and angle it, so it is lower at the front (over the speakers) and higher at the back (over your head).

and I plan to install about 2 feet of wall board (sheet rock) around the edge of the ceiling, within which I will place lighting.

Before you commit to that plan, put in your first round of treatment, then test the room response using REW, to see what additional treatment you might need up there ...

At this end I am thinking of building angled walls to reflect the monitor sound back into the live space.

That's probably not a good idea. It would be much better to build proper soffits for your speakers, as that would improve things greatly, in may different ways.

5. From everything I have read, this room is too small to gain much benefit from bass trapping.

:shock: :!: :?: You must have been reading in the wrong place then! Small rooms need a LOT of bass trapping. The smaller it is, the more bass trapping it needs!!! Maybe you are getting confused between bass trapping and diffusion? You can't really use some types of diffusion in a small room, but bass trapping is an absolute necessity. For a room like that, at the very least you need large superchunks in the vertical corner, and perhaps in some of the horizontal corners, such as those where you were planning to put the lights... And to prevent those bass traps from "sucking up" too much of the highs, you should cover them with 6mil plastic, or foil, or even thin plywood, as needed. Your REW analysis will help you decide on that.

So these are my thoughts, "cloud" in the ceiling, concrete floor, concrete walls with panels staggered to reduce reflections, but allow the liveness of the concrete to still be present. Am I crazy??? What am I missing???

The basic idea is fine, except for the lack of bass trapping. - Stuart -

SOundman Thanks for the thoughts and suggestions! Actually the mixing desk and speakers are just approximated in the drawing. So in terms of the ceiling, your suggestion is to have it slope downward toward the mixing desk at the bottom of the drawing, angled that is?? You mentioned soffits, but I place my monitors on small speaker stands currently....are you suggesting elevating the speakers and pointing them downward toward the mixing chair?? Lastly, I have read a fair amount of conflicting stuff about small rooms and effective bass treatment, for example: Ethan Winer's statements here: For rooms smaller than 25 by 15 feet you'll do better with broadband bass traps made from thick rigid fiberglass placed in the room corners. Small rooms have peaks and nulls at all frequencies, so broadband absorption straddling corners is better than the tuned traps shown in this article. This is described in my Acoustics FAQ linked above. Once all of the corners are treated, then it makes sense to consider adding bass traps like these flat on the walls. ...seem to suggest that tuning bass traps is very difficult if not impossible in small rooms...one of the flaws of the small room I think. Thoughts???

So in terms of the ceiling, your suggestion is to have it slope downward toward the mixing desk at the bottom of the drawing, angled that is??

Well, you could angle the entire ceiling if you want to, yes, but I was just suggesting a ceiling cloud over the desk.

You mentioned soffits, but I place my monitors on small speaker stands currently....are you suggesting elevating the speakers and pointing them downward toward the mixing chair?

Stands are fine, if that's how you prefer to do it, as long as the stands are massive (very heavy) and the speakers are decoupled from them. But then you will also need acoustic treatment on the front wall, directly between the wall and the speaker, to reduce the artifacts caused by having speakers close to walls, as well as the artifacts caused by small speakers themselves (just due to being small). "Soffits" in the world of acoustics are not like "soffits" in normal construction. In fact, the name is actually not correct, technically, (since it does imply mounting the speakers up high and pointing them down, which is not correct), but that's the name that has stuck! In acoustics, a "speaker soffit" is an infinite baffle, a large flat, rigid, massive surface that surrounds the speaker, basically as an extension of the front panel. It eliminates many of the issues associated with having free-standing speakers in small rooms, such as SBIR, edge diffraction, reflections off the front wall, comb filtering, and other phasing and timing issues. It also corrects the inherent power imbalance that all small speakers suffer from. It's just a good idea, all round. You mentioned "building angled walls to reflect the monitor sound back into the live space", and that sort of is the concept of a soffit: a wall angled at 30° across one side of the front wall, with a hole cut in the middle, and the speaker sitting in the hole, so that it the front of the speaker is flush with the front of the "wall". It's a bit more complicated than that, and very different from just angling a pat of the wall with a speaker in front of it, but the basic concept is sort of similar. The purpose of a soffit is not to reflect the sound towards the room, but rather to fix all the things wrong with small speakers in small rooms. So with a "soffit mount", the speakers are not elevated: they are still located with the acoustic axis at a height of 1.2m above the floor, as normal. The difference is that the front panel is extended outwards on all sides, making it very much bigger, which is why it is referred to technically as an "infinite baffle".

I have read a fair amount of conflicting stuff about small rooms and effective bass treatment,

Well, it is actually very simple, and there is no conflict here. Small rooms require major bass trapping, simply because they are small, and the laws of physics are fixed and unalterable. Because of the dimensions of the room, there are modal response issues that MUST be treated. This does not happen in large rooms (which need little or no bass trapping) simply because large rooms have multiple modes at all frequencies, across the entire spectrum, even down into the bass area. As rooms get smaller, the dimensions become comparable to the wavelengths of the low frequency sound, and there are fewer and fewer modes in each frequency band. Typically in a home studio, the room is so small that there are no modes at all in the very low end, and just a handful in the first three octaves. So those few modes are spread wide apart, with big gaps. Therefore, each mode is very, very noticeable, and MUST be damped. If you do not damp it, then you will not be hearing the true sound coming out of the speakers, as the room itself will be "coloring" the sound. The room will reinforce some notes, kill some others, and not touching the rest at all. For example, if your room has a mode at 49 Hz. then every time you play a "G" on a bass guitar or keyboard, the room will greatly amplify that note. But if you play the F or A right next to that G, nothing happens: it sounds normal. 49 hz corresponds to a wavelength of about 5' 9", so if any of the dimensions of your room are a multiple of 5' 9", then you will have a mode at that frequency, simply due to the dimensions of the room. Not due to ideas, imagination or opinions, but simply due to the laws of physics and the size of the room. For all rooms with standard ceiling height (8') there will be a mode at 69 Hz, which is C# in the second octave. Modes are a fact of life: there is nothing you can do to prevent them. They are a simple consequence of the laws of physics and the dimensions of your room. They have nothing to do with any opinions, guesses or myths that you might happen to read on the internet. They exist simply because sound travels as compression waves in air, and if a wave happens to fit between two walls, then you have a mode. This is fact, not opinion. So you cannot stop modes from happening. What you CAN do is to damp them. Like I said before, in very large rooms it does not matter, because there are modes for every single note, and multiple modes for most notes, so all notes sound about the same in a large room, as they are all affected in the same way. But in a small room, there just aren't many modes in low frequencies /typically below about 200 Hz or so). So you MUST damp those modes. You MUST have bass traps in your room to damp them. Once again, this is not a matter of opinion, or what somebody thought might happen in small rooms: it is a simple fact of physics. If you do not damp the few low frequency modes in your room, then those notes will sound much louder, and will decay much more slowly, than all other notes. You will not be hearing a true representation of the music, and your mixes will not translate well to other places: songs you mix in that room will just not sound right in all other rooms, since no other room will have the same modes as yours does (unless it is the same size).

Ethan says: "For rooms smaller than 25 by 15 feet you'll do better with broadband bass traps made from thick rigid fiberglass placed in the room corners. Small rooms have peaks and nulls at all frequencies, so broadband absorption straddling corners is better than the tuned traps shown in this article. This is described in my Acoustics FAQ linked above. Once all of the corners are treated, then it makes sense to consider adding bass traps like these flat on the walls."

Exactly. Ethan is saying the exact same thing: Modes are a problem in small rooms, and must be treated. I don't see why you would say that Ethan is disagreeing with me! He's saying the exact same thing: small rooms have modal issues, and need bass trapping.

...seem to suggest that tuning bass traps is very difficult if not impossible in small rooms...one of the flaws of the small room I think.

That's why tuned traps for very low frequencies are not a good idea, and most acousticians do not recommend that. Tuning them is not easy, there's no simple way to accurately predict the exact frequency of the modes in advance, there's no easy way to accurately measure the frequency of the mode in the real room, and there's no way to accurately tune most types of resonant device at low frequencies anyway! That's why most people do not use tuned devices, at low frequencies. Plan old ordinary absorption is far more useful, and effective enough to be a good solution. So once again, I'm not sure why you think that Ethan and I are saying different things: we are both saying exactly the same: In a small room you need lots of broadband bass trapping, such as thick absorption in the corners (where all modes terminate). That's why both Ethan and I are telling you to put absorption in your room corners, starting with the vertical ones, then the horizontal ones, and if that isn't enough, then also against some of the walls. Any acoustician will tell you the same thing: small rooms need bass trapping, LOTS of it. Broadband thick absorption is a simple, effective, inexpensive solution. And the best place to put it is in the corners. If you run out of corners and still need more (quite possible in a small room), then do the ceiling and walls too. So anything you have read to the contrary is simply not correct. Anyone who tells you that small rooms do NOT need bass trapping simply does not understand acoustics. - Stuart -

Updated sketch. I am showing 4" traps in the four corners of the room. Should these be 8' high? Or can they be 4' high and placed at the 2'-6' height?? Then the remainder of the panels are 2" 2x4' panels. The rounded rectangle is a cloud above the mixing and the recording positions... Does this make sense?? Is this too much on the walls?? Too little in the corners?? What say those of you as this to start with, or am I over-engineering????

Updated sketch.

That's an improvement. Much better.

I am showing 4" traps in the four corners of the room. Should these be 8' high?

They should be as big as possible, and they are most effective in the "tri-corners" of the room, where three surfaces meet, so they do need to run from floor to ceiling for best effect.

The rounded rectangle is a cloud above the mixing and the recording positions...

It is still in the wrong place. It needs to be moved forward, over the mix position. Part of the purpose of that cloud is to treat the first reflections from the ceiling, and yours is not doing that.

Does this make sense?? Is this too much on the walls?? Too little in the corners??

It's a good start, but you might want to consider building "superchunk" traps for your corners. Those are the most effective of all. I would do what you are showing there, then measure the acoustic response of the room, to see what still needs doing. - Stuart -

Thanks Stuart Lastly, is this too much absorption?? Will it kill the live sound of the room I want for tracking acoustic guitar, banjo, etc????? I suppose if it gets too dead I can always pull some of the panels out and rearrange....

The total amount is about right for meeting EBU specifications, but the balance of which frequencies are being treated might not be correct. If you find that you are missing too much of the high end, then you can cover the front of the bass traps with thick plastic (6mil) or even thin plywood panels. That will still allow the low frequencies to get through and be absorbed, while reflecting the highs back into the room. The best thing to do is to actually test the room with acoustic analysis software, such as REW. That will tell you what the frequency balance is looking like, and provide the information needed to decide on the next step. The main point here is that it is a small room and therefore needs a large amount of low frequency, broad-band absorption. The highs can be kept in the room easily as needed, but the lows need a LOT of treatment. - Stuart -

So in my garage I have 3 cases of Rockboard 60 (Thank you ATS). I plan to build 4 4" 2x4 panels and 8 2" 2x4 panels. Then I plan to place the 4" panels in the four corners of the room and use the remaining 8 for refflection points, as shown roughly in my drawing. A couple of questions: 1. I am concerned that the 4" traps may suck too much mid and high out of the room, since I want to do recording in the top end of the room. So I am thinking that for the bass traps in that end of the room I will face them with pastic to reflect the mids and highs back, while helping with the bass.???? 2. WHile I know that the preferred approach is to treat the corner floor to ceiling, I really do not have enough $$$ for enough panels to do so. I am wondering if the 2x4 trap will be more effective on the floor, or at the 2'-6' level??? 3. The 2" panels will go against walls, to help with reflectiuon and flutter echoes. Can they be flat against the wall for this purpose, or should they still be 2" away??? 4. Does anyone have any good ideas for attaching/hanging in a concrete room....I do think I may just make some sort of "hangers" that suspend all the way from the floor joists overhead. Has anyone ever built stands for the panels???? 5. For the cloud, I plan to fill the 26" floor joists with insulation, and then cover that with some sort of fabric. I have seen some suggestions that this may deaden the room too much, but with 3 concrete walls and a cocrete floor, do you think so???? I supposse I could always build it this way, and if it feels too dead, then add some refrelction around the edges of the ceiling.... All in all, getting pretty excited here. I am planning on framing the Rockboard, and wrappiig in burlap. My wife is a quilter/sewer and knows fabric stuff really well, so I expect these will end up looking quite nice. Now to research paniting and staining concrete....... And to get pricing on insulation for the 26" floor joists overhead - should be a nice soft cloud..... THANKS!

1. I am concerned that the 4" traps may suck too much mid and high out of the room, since I want to do recording in the top end of the room. So I am thinking that for the bass traps in that end of the room I will face them with pastic to reflect the mids and highs back, while helping with the bass.????

Exactly. 6 mil polyethylene plastic is the normal recommendation. That's the type that is often used for vapor barriers.

2. WHile I know that the preferred approach is to treat the corner floor to ceiling, I really do not have enough $$$ for enough panels to do so. I am wondering if the 2x4 trap will be more effective on the floor, or at the 2'-6' level???

Tri-corners are the most effective points. That's the triple corner where the floor meets two walls, or the ceiling meets two walls. So put one of your traps down at the bottom, and another up top. The middle section is still important, but the tri-corners are your best bet.

3. The 2" panels will go against walls, to help with reflectiuon and flutter echoes. Can they be flat against the wall for this purpose, or should they still be 2" away???

The more you space them away from the wall, the more effective they are at lower frequencies.

4. Does anyone have any good ideas for attaching/hanging in a concrete room....I do think I may just make some sort of "hangers" that suspend all the way from the floor joists overhead. Has anyone ever built stands for the panels????

There are many types of anchor you can use in concrete walls. Take a look around your local Home Depot or equivalent store.

5. For the cloud, I plan to fill the 26" floor joists with insulation, and then cover that with some sort of fabric. I have seen some suggestions that this may deaden the room too much, but with 3 concrete walls and a cocrete floor, do you think so???? I supposse I could always build it this way, and if it feels too dead, then add some refrelction around the edges of the ceiling....

Bob Golds calculator will tell you how much total absorption you need in your room to meet ITU specs. You should be fine, and if you do discover that you are losing too much in the highs after testing with REW, then just cover some of that ceiling insulation with plastic too.

And to get pricing on insulation for the 26" floor joists overhead - should be a nice soft cloud.....

You might not need to fill the entire cavity, although it sure wouldn't hurt! For example, you could put 4" up against the ceiling, then leave a gap, then put another 6" or 8" at the bottom of the joists. That would still be very effective, but with much less cost. - Stuart -

Corneers. I am only able to build 4 4" 2x4 traps........so floor to ceiling will not happen......should I make them 2x2 instead of 2x4 and put one high and one low.....????? To get the tri-corners????

should I make them 2x2 instead of 2x4 and put one high and one low.....?????

That will work, yes. But if you can make then bigger, it would be better. Also make them thicker, if you can: more insulation. - Stuart -

So, a crazy idea. The wall at the top of the picture is a stud wall next to stairs. I could fill between the studs with insulation, but instead of sheetrock , I could face the wall with fabric. This would make the wall one large trap...would this kill the room sound, or help with bass trapping??????

So, a crazy idea. The wall at the top of the picture is a stud wall next to stairs. I could fill between the studs with insulation, but instead of sheetrock , I could face the wall with fabric. This would make the wall one large trap...would this kill the room sound, or help with bass trapping??????

That would help a lot! Good idea. - Stuart -

Fini!! or almost.....I do have a closet door to add and put the corner trap back in the corner, and a main door to add also. The corner traps are 4" Rockboard 60...2x4 feet.....the remaining panels are also 2x4, but only 2" thick....the mix end of the room sounds very tight to me. The panning is easily heard, the instruments separate nicely, vox also. Meanwhile the "live" end of the room has less paneling, and has a "brighter" sound...I know, it is all subjective....but I have no omni mic to run testing with REW....ceiling is 26" joists with faced insulation, facing dow to protote brightness in the live end, and then covered with fabric......... Wanted to send pics ..............THANKS to all for the advice......