John Sayers' Recording Studio Design Forum Archive

I am currently building a recording studio.

My concrete slab is vibrating at around 40Hz, I measured it with a lab mic.

I have a 4,4mx6m control room that is 3.3m high which is on the ground floor of my house.

My floor consists of a 20cm concrete foundation, 6cm of Austrotherm EPS 120 hard styrofoam and 3cm of Austrotherm T600 soft styrofoam and a 6cm concrete slab. There is a 1cm Termosilent strip around the edges of the the floor, so the seperation from the rest of the building is excellent, but the problem is the concrete slab is now vibrating around 40Hz upon impact noise by just hitting my feet a little harder on the concrete slab.

The reason i put the styrofoam was to insulate the floor during winter time and to float the floor. But I guess I exagerated a bit, the energy efficiency people wanted me to put 15cm of insulation so I went with 9.

Is this vibration going to be a problem while mixing? Monitors will be Geithain RL 901K so they go pretty low. Should I remove the slab and that ****ty soft 3cm styrofoam T600 since it's so soft and is probably causing the slab to vibratr more, and just pour a thicker concrete slab with construction fittings? Or should I just pour another 6cm on top of the existing slab?

I destroyed the concrete slab in the Live Room and removed all the styrofoam and will put 3cm styrodur instead and a 15cm concrete slab with construction fittings, so it won't vibrate. What do you think?

The studio is located out of town so no big roads, trains or aeroplanes around.

Also the foundings of each studio room are seperated by 5cm.

I know it was a stupid mistake, but can anyone confirm my thoughts?

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

the problem is the concrete slab is now vibrating around 40Hz upon impact noise by just hitting my feet a little harder on the concrete slab.

Clearly, there is insufficient damping under that slab. I very much doubt that "6cm of hard styrofoam ... plus ... 3cm of soft styrofoam" would provide good damping. Do you know what the resilience of that sandwich is? Did you calculate the resonant frequency? You can't just build things that have acoustic purposes using random materials that seem right. It is very important to actually calculate the acoustic properties, to make sure that the results will be as desired.

The reason i put the styrofoam was to insulate the floor during winter time and to float the floor.

Perhaps that stuff will provide good thermal insulation, but it certainly wont float the floor correctly. Instead, it will create a resonant system, and in your case it turns out that the resonance is way up into the low end of the spectrum. 40 Hz resonance implies that the floor won't isolate much at all until about 57 Hz, and will only really provide good isolation above about 80 Hz. Whether or not that is a bog issue for you depends on many other factors that you didn't mention.

Here's a thread on floating floors that you might be interested in:

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

And here's what a correctly floated floor looks like:
And the same floor edge-on:
You can see the springs and polymer pads in there, which are what actually cause the floor to float.

Here's a couple of different type of floor jacks that are used to float floors:
The normal way of doing this is to pour the base concrete slab directly on on the ground (with suitable DPC, of course, and perhaps a layer of sand and/or gravel below), then once that has fully cured, to place plastic sheeting on top of the base slab, along with the floor jacks (placed at the correct locations, as calculated), and reinforcing steel ("rebar"), pour the second slab, then once that has cured, jack it up to the correct height using the floor jacks. If you also needed additional thermal insulation in there, you could lay that below the plastic sheeting. You can tune such a floor to whatever frequency you want, by choosing the correct jacks, air gap size, and concrete thickness, using the equations for MSM resonance. Ideally, you tune it to one octave below the lowest frequency that you need to isolate.

Unfortunately, you cannot do that with your current slab as the base, since it is already a resonant system. If you were to try that, you would end up with a three-leaf system that has two fundamental resonant frequencies, both of which are too high to be usable. In other words, low frequency isolation could potentially be even worse than it is now.

You need to create a two-leaf system, not a three-leaf system.

One other method is to use Sylomar to float the floor.

Is this vibration going to be a problem while mixing?

A problem for whom? What type of music do you mix, and how loud do you mix at (in decibels, DC-weighted, slow response)? How quiet do you need that to be outside of the studio (also in dBC)?

Monitors will be Geithain RL 901K ... they go pretty low

Down to 25 Hz, according to the manufacturer. But the question is, will you actually be putting out significant energy at those low frequencies? If so, then you will have a problem. Not only will the floor not be isolating, you will be on the wrong side of the resonance curve (below MSM), where stiffness governs isolation, but the system itself is resonating and actually amplifying those frequencies: And since you only have a thin slab that is clearly not very stiff, and is laid on a flexible non-damping base, I would suspect that it won't be isolating at all.

Also, there's the issue of how those speakers will be mounted and positioned: Those are REALLY big monsters! Huge, in fact. Possibly too big for that room, and I'd be very interested in seeing the geometry of how they will be positioned in the room, and even more important, how they will be mounted physically.

... and just pour a thicker concrete slab with construction fittings ...

I'm not sure what you mean by "construction fittings", Please could you explain that, or provide links, photos, etc.

I know it was a stupid mistake, but can anyone confirm my thoughts?

I guess the big question here is: "What effect will this 40 Hz slab resonance have on the studio acoustics?". That's a tough one to answer. It might be "no problem at all", or it might be "major resonance making the room unusable". For example, if your speakers happen to put out enough energy to get the floor resonating, that could indeed cause you major headaches when mixing, as it would change the frequency domain response and time domain response of the room considerably, "coloring" the sound so that you are not actually hearing the same sounds that the speakers are producing. Also, if there is something in or around the building that happens to produce a 40Hz vibration, your floor would likely pick that up and start resonating sympathetically, so your entire room would be "humming".

Are you going to build your inner-leaf walls on top of the floor? Or will they be built on separate foundations? That's a major question: if you are going to have your inner-leaf walls and ceiling resting on that slab, the the additional mass will obviously change the resonant frequency, pushing it down lower. If there is enough mass, it might push the resonant frequency down low enough that it is no longer a problem.

There are so many factors in play here that it's practically impossible to predict if that 40 Hz resonance is important or not. On the one hand, it's possible that there might not be any problem at all after you build your control room on that slab, but on the other hand, it is more likely that there will be some type of problem, either with isolation, or with acoustics, or both. But you won't know until the room is done....

So I guess the most important question is: "Are you prepared to risk it?"


- Stuart -

Soundman2020 wrote:Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

Sorry about that!

I'm not sure what you mean by "construction fittings", Please could you explain that, or provide links, photos, etc.

The stuff they use to keep concrete together, here's a picture:

Soundman2020 wrote:Clearly, there is insufficient damping under that slab. I very much doubt that "6cm of hard styrofoam ... plus ... 3cm of soft styrofoam" would provide good damping. Do you know what the resilience of that sandwich is? Did you calculate the resonant frequency? You can't just build things that have acoustic purposes using random materials that seem right. It is very important to actually calculate the acoustic properties, to make sure that the results will be as desired.

Perhaps that stuff will provide good thermal insulation, but it certainly wont float the floor correctly. Instead, it will create a resonant system, and in your case it turns out that the resonance is way up into the low end of the spectrum. 40 Hz resonance implies that the floor won't isolate much at all until about 57 Hz, and will only really provide good isolation above about 80 Hz. Whether or not that is a bog issue for you depends on many other factors that you didn't mention.

The control room is located on the ground floor, so there won't be problems from underneath it, but above it there probably will since the Living Room is directly on top of it and has the same styrofoam and slab. The floor upstairs is 15cm slab with construction fittings, 6cm+3cm styrofoam and 6cm slab.

Soundman2020 wrote:The normal way of doing this is to pour the base concrete slab directly on on the ground (with suitable DPC, of course, and perhaps a layer of sand and/or gravel below), then once that has fully cured, to place plastic sheeting on top of the base slab, along with the floor jacks (placed at the correct locations, as calculated), and reinforcing steel ("rebar"), pour the second slab, then once that has cured, jack it up to the correct height using the floor jacks. If you also needed additional thermal insulation in there, you could lay that below the plastic sheeting. You can tune such a floor to whatever frequency you want, by choosing the correct jacks, air gap size, and concrete thickness, using the equations for MSM resonance. Ideally, you tune it to one octave below the lowest frequency that you need to isolate.

Unfortunately, you cannot do that with your current slab as the base, since it is already a resonant system. If you were to try that, you would end up with a three-leaf system that has two fundamental resonant frequencies, both of which are too high to be usable. In other words, low frequency isolation could potentially be even worse than it is now.

You need to create a two-leaf system, not a three-leaf system.

So adding more concrete slab could create even more problems? (6cm+3cm styrofoam + 6cm slab + 6cm slab).

A problem for whom? What type of music do you mix, and how loud do you mix at (in decibels, DC-weighted, slow response)? How quiet do you need that to be outside of the studio (also in dBC)?

I mix both loud and acoustical music, I have experience in both and will be doing both, from Metal Music, to Pop Electronic, to Indie to Jazz.
I don't tend to mix very loudly but it's always good to check how metal or pop music sounds when you turn it up, and it always impresses the clients more haha.

Also, there's the issue of how those speakers will be mounted and positioned: Those are REALLY big monsters! Huge, in fact. Possibly too big for that room, and I'd be very interested in seeing the geometry of how they will be positioned in the room, and even more important, how they will be mounted physically.

Thank you very much for your interest! Here are some ideas for a RFZ control room, the idea is to have the front wall made out of glass and to soffit mount the speakers into it. I have friends in a glass factory and a technician friend that can remove the amps from the speakers so we can put them in a place where they can cool down.

Here are some pictures showing the shell, we used Odeon to simulate how sound is dispersed in the room. There has been some tweaking with the ceiling geometry in the meanwhile but I don't have the pictures right now.

Are you going to build your inner-leaf walls on top of the floor? Or will they be built on separate foundations? That's a major question: if you are going to have your inner-leaf walls and ceiling resting on that slab, the the additional mass will obviously change the resonant frequency, pushing it down lower. If there is enough mass, it might push the resonant frequency down low enough that it is no longer a problem.

There are so many factors in play here that it's practically impossible to predict if that 40 Hz resonance is important or not. On the one hand, it's possible that there might not be any problem at all after you build your control room on that slab, but on the other hand, it is more likely that there will be some type of problem, either with isolation, or with acoustics, or both. But you won't know until the room is done....

So I guess the most important question is: "Are you prepared to risk it?"

The plan was to build the inner-leaf walls on top of the floor, not on separate foundations.

Don't think I'm prepared to risk it, removing that styrofoam and pouring a 15cm concrete slab with fittings instead should resolve the problem in the studio as a whole, but the problem of the living room on top of the control room might remain to be a serious problem.

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

Sorry about that!

But clearly you still have not read the rules, because you have not fixed the glaring problem...

The stuff they use to keep concrete together,

That's steel mesh, not "construction fittings".

The control room is located on the ground floor, so there won't be problems from underneath it

Sorry, but you DO have a problem underneath it, as I already explained. You have 6cm of hard Styrofoam plus 3cm of soft Styrofoam, but you did not do the calculations to determine what the resilience of that is, so you do not know what the resonant frequency is, and you do not know how much damping you are getting. So you SO have a problem underneath your slab, because you used materials that you don't understand, in ways that you don't understand. Which is why you have a 40 Hz resonance problem.

You need to create a two-leaf system, not a three-leaf system.

So adding more concrete slab could create even more problems? (6cm+3cm styrofoam + 6cm slab + 6cm slab).

No, because that would still be a 2-leaf system, not a 3-leaf system. Because that's NOT what I was suggesting that you do! Please go back and read over my post again, so you understand it.

I showed you how a floated slab should be done, correctly, to make a 2-leaf system. And then I commented that you cannot do that because you already have a 2-leaf system (that is not correctly done), so if you add a floating slab above that, you would end up with a 3-leaf system. That is not at all the same as adding mass to the existing 2-leaf system, which is an entirely different thing from what I was saying.

You should probably read this, to understand how floated floors work:

http://archive.nrc-cnrc.gc.ca/obj/irc/d ... /ir802.pdf

and

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

You need to learn that math as well, so that you can calculate the resonant frequency that you would get from any give method and set of materials. Just guessing every time is not a good idea.

Adding more mass will, indeed, bring down the resonant frequency. But since you don't know the parameters of the Styrofoam that you used, it is impossible to calculate what the result would be.

I don't tend to mix very loudly but it's always good to check how metal or pop music sounds when you turn it up, and it always impresses the clients more..

That is no use. That is subjective. As I said, you need to say how loud you are AS MEASURED IN DECIBELS, USING "C" WEIGHTING.

Thank you very much for your interest! Here are some ideas for a RFZ control room,

Please check the forum rules about posting images.

Also, that is not an RFZ design. There are clearly going to be first-order reflections arriving at the mix position very much inside the Haas time. Also, the mix position appears to be very close to the geometric center of the room, which is the worst possible location. There is also no bass trapping evident in that room, of if there is some, it is grossly insufficient.

the idea is to have the front wall made out of glass and to soffit mount the speakers into it. I have friends in a glass factory

That can work, yes. But it will be very expensive to have those glass panels manufactured correctly. You do understand that you will need very thick laminated glass for that? Are you certain that the factory where your friend works is able to manufacture laminated glass panels that have a hole in the middle? The hole has to be very accurate: the exact size of the front bezel of the speaker, plus 1mm.

You did not say how much your budget is, but it will have to be big. That glass is going to cost you many thousands of dollars to have custom built for your speakers.

Here are some pictures showing the shell, we used Odeon to simulate how sound is dispersed in the room.

Then it seems that you did not set up the initial conditions correctly, because that room will not work well acoustically, using the current design. Also, if you are using Odeon, then that means you already have a qualified acoustic engineer operating it... so how come he did not notice the problems with the room?

The plan was to build the inner-leaf walls on top of the floor, not on separate foundations.

Then the slab you have is totally inadequate, since a 6cm flat slab would not be able to support that. Didn't your structural engineer warn you about that? You will need a hybrid slab to do that.

removing that styrofoam and pouring a 15cm concrete slab with fittings instead should resolve the problem in the studio as a whole,

Actually, not it wont solve the problem: it will just change it to a different problem. It seems that you don't actually know what you are doing, and are just guessing. That's a bad idea.

One other thing I noticed: there is no indication of HVAC in your current plans, and no place to put it. HVAC takes up a lot of space in studios, and absolutely must be designed properly...

I would suggest that, before you do anything else, you should stop and learn about vibration, resonance, 2-leaf systems, 3-leaf systems, structures, and how to calculate all of that. It would be a big mistake to pour a new slab before the studio design is completed, because you will not know the total mass of the studio until then, but you need to know that in order to do the calculations for the slab! You also need to know how the mass will be distributed on the slab, and many other factors.


- Stuart -

Soundman2020 wrote:But clearly you still have not read the rules, because you have not fixed the glaring problem...

The budget is not more than 15000€ for the acoustics only (not counting HVAC, electricity and etc). The studio is located in Belgrade, Serbia.

All the studio walls are heavy 25cm wide concrete blocks filled with sand. The CR is also surrounded by a 5cm air gap and another 20cm wide clay blocks. You will see this in the ventilacion plans below.

Is there anything else I should point out?

You should probably read this, to understand how floated floors work:

http://archive.nrc-cnrc.gc.ca/obj/irc/d ... /ir802.pdf

and

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

So if I understood well what is written there, I don't need a floating floor because I don't have a basement, I can just use the ground underneath the house as the damper right?

One other thing I noticed: there is no indication of HVAC in your current plans, and no place to put it. HVAC takes up a lot of space in studios, and absolutely must be designed properly...

The company that is doing the ventilation project wants to place the machinery in the attic which is two floors above the Control Room, then enter the control room and live room from the ceiling, here are some pictures:

This is the machinery location in the attic (left third of the pictures) I'm guessing the places where the air is coming in and out should be changed once the geometry of the room is finished?

That's steel mesh, not "construction fittings".

Ok thanks, my bad.

That is no use. That is subjective. As I said, you need to say how loud you are AS MEASURED IN DECIBELS, USING "C" WEIGHTING.

Ok I will have to get me a level meter to be able to tell you objectively, hopefully soon.

Also, that is not an RFZ design. There are clearly going to be first-order reflections arriving at the mix position very much inside the Haas time. Also, the mix position appears to be very close to the geometric center of the room, which is the worst possible location. There is also no bass trapping evident in that room, of if there is some, it is grossly insufficient.

I have a friend that studies Acoustics that's how I used Odeon. The readings said the impulse response was outside of Haas time, and the room modes looked pretty good. I will get some of those readings and post them for you if you could check them please.

Then it seems that you did not set up the initial conditions correctly, because that room will not work well acoustically, using the current design.

What are the most evident mistakes you see?

That can work, yes. But it will be very expensive to have those glass panels manufactured correctly. You do understand that you will need very thick laminated glass for that? Are you certain that the factory where your friend works is able to manufacture laminated glass panels that have a hole in the middle? The hole has to be very accurate: the exact size of the front bezel of the speaker, plus 1mm.

My friend is the owner of the factory and they do all kinds of requirements, so the price will be much lower, also in my country construction seams to be a lot cheaper in general. How thick do you propose the frontal glass to be and how would you mount the monitors? Speakers' weight with the amps is 48Kg and they measure 550mmx500mmx430mm (HxWxD).