John Sayers' Recording Studio Design Forum Archive

Ok, good to know. I just have a lot of respect for that, because I have never done a drywall ceiling especially with multiple layers, that is quite a lot of mass above my head, you know ...
I will ask someone with more experience for help.

The ceiling rises more questions, though:

1) Can I re-use the framing of the old one? I is shown in a picture in this thread a couple posts earlier.
2) Right now I am looking for the best ceiling thread here on the forum. Is there any recommendation for reading?
3) The actual ceiling (that was not build by myself) is over the the whole room, that i later separated with the wall. I dearly hope, I would not have to tear everything down, to do the ceiling. For the sake of my teaching room I couldn't do that, even if i had to now, as I need it for my monthly income.
4) In case I would find a material to blow into the ceiling that would meet the absorbing qualities needed: Would it be possible to just reinforce the existing ceiling with one or two additional layers of gypsum. Unfortunately, the old one is only 14 mm thick.
5) In case I would really have to tear the old layer down anyways, I thought of using this as an opportunity to tilt the ceiling a little towards the soffit mount. However, when I tried to find out the effect of a 7-10° tilt (and more is obviously impossible with the height of my room - 2.27m plus ca. 10cm for the detached ceiling), I found out it was just moving the point of first reflection back a little - still hitting my sweet spot ... would the tilt have to be way bigger or is there another benefit of that tilt?

because I have never done a drywall ceiling especially with multiple layers, that is quite a lot of mass above my head, you know ...

The easiest way to do it, is to rent a "drywall-lifter", which is a mechanical device that raises up the drywall to the place where you need it, and holds it there, while you nail it into place. Very simple to do it like that.

1) Can I re-use the framing of the old one? I is shown in a picture in this thread a couple posts earlier.

That should be fine, yes. Provided that you use the resilient channel that I mentioned! Since the ceiling framing is not decoupled from the other room, or from the joists, there will not be much isolation and the resonance will continue from the other side of the wall. With resilient channel, you are at lest decoupling the ceiling in the control room.

3) The actual ceiling (that was not build by myself) is over the the whole room, that i later separated with the wall. I dearly hope, I would not have to tear everything down, to do the ceiling. For the sake of my teaching room I couldn't do that, even if i had to now, as I need it for my monthly income.

Like I say, as long as you use resilient channel (RC-1) then you will be OK. If you wanted maximum isolation then you could replace that framing completely, but I don't think that is necessary for the isolation that you want.

4) In case I would find a material to blow into the ceiling that would meet the absorbing qualities needed: Would it be possible to just reinforce the existing ceiling with one or two additional layers of gypsum. Unfortunately, the old one is only 14 mm thick.

I would not do that. There really isn't any acoustically useful "granular" product that I'm aware of, that you could blow in there to do the job that needs to be done. Polystyrene balls are no use at all, for example. Plus the cost of renting the equipment to do it, and hiring the people to do it, would make it more expensive than just taking off the drywall and doing it correctly.

5) In case I would really have to tear the old layer down anyways, I thought of using this as an opportunity to tilt the ceiling a little towards the soffit mount.

You could do that if you want, but it would greatly reduce the available height at the front, where your soffits will be, and since you also want to mount two sets of speaker in that soffit, you might not be able to do that if the ceiling is very low at the front.

I found out it was just moving the point of first reflection back a little - still hitting my sweet spot ... would the tilt have to be way bigger or is there another benefit of that tilt?

The tilt can be for many reasons, but one of those is flutter echo. By tilting the ceiling at least 12° you can eliminate flutter echo between the ceiling and the floor. But there are other ways of dealing with flutter echo. And you are right: to create a reflection free zone from above, you need a much greater tilt angle. 7° is not going to be anywhere near enough.


- Stuart -

I am so sorry! But I already got another list of questions:

You strongly suggested to use a resilient channel. As I understand the RC1 it is there for decoupling the gypsum from the framing and therefore the hard ceiling. However, as isolation is not needed in my case, what are the other benefits? I assume, the resonance of the ceiling could get reduced by the decoupling and that is why even I should not leave it out. Is that the case? If not, what benefits would it have for me, as - with my low ceiling - every inch of lost height counts!
And about the decoupling: If I were just to put the gypsum boards up to the existing walls (drywall or structural wall) and close the edges with compound, wouldn't that undo the decoupling of the resilient channels? If my thoughts are right: How would I deal with the edges (drywall and structural wall)? Do I need to leave a gap and how big? Do I need to seal? Would Silicon do the sealing?
If the purpose would be to decouple the hung ceiling, I suppose I could continue with the soffit mount base structure, as the ceiling would only go up to the point, were it hits the soffit mount (otherwise it would rest on the soffit mount therefore not be decoupled), right? I ask this, as it would be better for me to go ahead with doing the soffit. For the ceiling I would rather wait until the next larger school break, as drywall dust (especially from taking down the old gypsum) is not something I would like to expose my students to (it is only the room next to my control room, but I know it is really impossible to prevent that kind of dust from spreading, even through the tiniest gaps ...

Then, for the boards: in all threads here I saw two layers of 16mm drywall to be effective. I had trouble getting 16mm drywall here for the walls, so with the recommendation of my acoustic consultant I went with this:
http://www.knauf.be/batibouw2011/pdf/K7 ... rd_ALL.pdf
It has even more weight per m2 than the fermacell 15mm board and almost as much as the fermacell 20mm board. So, would two layers of this solve my resonance problem? That would be swell, as I would loose a little less height in the room!

And what about the tracking room? RIght now I couldn't replace the ceiling there due to teaching. But for my future plans (maybe over the summer break): How bad would the resonance of of a single 12mm drywall layer without resilient channel on the ceiling affect my recordings? I don't record drums, deepest instrument would be something like a Cello. I guess it will be important! Just hoping, someone will tell me it isn't!


Lastly, I have a very simple problem, but I am afraid Stuart won't be able to answer it ... To all (continental) Europeans:
What the $(=)§" is a resilient channel and where can I buy one. Of course I understand what it is, but I couldn't find a single comparable product to it on german drywall manufacturer (Knauf, Fermacell, etc). Most importantly: I don't even know what it would be called in german ... maybe somebody could tell me!

Another thought on my ceiling:

Since I have no problems with the neighbor above and the currently installed hung ceiling with just one 12mm layer of gypsum without any insulation in between probably didn't much for that anyway, I thought about leaving it out completely and instead install an absorbing ceiling (cloth, wooden frame and mineral wool). This would also solve the height problem I have with my ceiling, as I would gain another 100mm for absorption.
In most studio designs, there is a gypsum ceiling (double layer, decoupled) and an additional ceiling cloud installed. However, isn't that mostly due to isolation? And since that is not what I need to reinforce, wouldn't that be an interesting alternative for me?
Maybe the drywall ceiling serves another purpose, that I am not ware of. In that case, please tell me, why I would need one?

Seems like, it has been done before:
http://www.johnlsayers.com/phpBB2/viewt ... ng#p103120
Unfortunately, no further response on the success of this ...
But the room height in the real traps video attached to this looks kind of similar to mine. Could this be a good solution for me?

And this is the video, where it is explained.
http://www.realtraps.com/video_demo.htm
Meets pretty much my requirements, as I also don't need to isolate and have a pretty low ceiling as well. I might not have quite as much thickness of the fluffy fiber glass, as my ceiling is even a little lower than this, so I would still have some LF-problems left here. But altogether, this seems to be the best idea for my needs! I would really struggle to later put up a ceiling cloud under a suspended drywall ceiling (2 layers) with isolation behind with my 2,37m ceiling (without the existing drywall hung ceiling). I will hardly be able to walk upright through that room (I am 1,85m tall). Do you agree?

Since I have no problems with the neighbor above

Yes, you have already explained that, but you have also said that you DO need isolation between the control room and the tracking room: "The only isolation I need is between the tracking room and the mixing room.". As I already explained, isolation happens in all directions at once, or no directions at all. You cannot only isolate in one single direction: Isolation requires a two-leaf "envelope" around the room, including all six sides (the four walls, plus the ceiling, plus the floor). If you don't isolate one of those sides, then you don't isolate anything. So if you do not isolate your ceiling, then you will not have any isolation at all. Sound will simply use the ceiling to "go around" the walls, and get to the other side, in ALL directions, including the tracking room. Both ways.

So, if your control room does not need ANY isolation at all, and it is ONLY the tracking room that needs isolation, then the solution would be to forget about isolating the control room, and isolate only the tracking room. In that case, you could follow Ethan's suggestion for treating the control room: Take off the drywall and install thick insulation in the joist bays above you. That will not give you any isolation for the control room, but it will greatly improve the room acoustics, provided that you also treat the rest of the room accordingly.

So if you are convinced that the ONLY room that needs isolation is the tracking room, then that would be the way to go: Re-build just the tracking room as a decoupled two-leaf system, and do not try to isolate the control room at all.

BUT! From what you say, I understand that the tracking room is already finished! So you would have to demolish it (perhaps only partially) to be able to fix that.


- Stuart -

Thanks, Stuart, for clearing that up!
I will go with the absorbent ceiling than. If I later find out, the isolation between those rooms is to bad, I can live with it and when possible it would be easier to decouple the the rest of the tracking room. More updates soon!

Since i figured out I will create a soft ceiling, it is time to find out what material to use. I chose a molleton cloth cover (300gr/m2, does not easily burn and I like the look of it), so I tried to figure out which mineral wool to use and how thick. I found this helpful list of materials and absorption of different frequencies:
http://www.bobgolds.com/AbsorptionCoefficients.htm
As I understand this, the goal would be to find a thickness and density of material that does absorb over all frequencies as consistent as possible. Naturally, the LF are not as easily absorbed, as the HF. To my surprise, the 703, plain 6" seems to do a marvelous job at that and I can afford to loose about 15cm due to the ceiling, as I gain about 10cm by taking of the useless gypsum boards off. 5cm deeper ceiling than before (1.27m) will still be way better than having to build an additional cloud over my mixing desk.
As the 700 series is not available in Germany, I tried to find a material as close as possible to this. It is not easy to find a company that lists absorption coeffiecient by frequency. So far, I found only this:
http://www.ursa.de/de-de/produkte/ursa- ... daten.aspx
Would I get about the same absorption by stacking 3 layers of this on top of each other (therefore getting 15cm of porous absorber on the ceiling with about the same acoustical properties as the 703 - even being better at around 150Hz)? The way I understand porous absorbers, there shouldn't be al lot of difference between 3x5cm and 15cm, is there?
Does that material look right to you for this purpose? And what about other applications, like slot resonators and (as Glenn suggested in my speaking-of-speakers thread) soffit face? Especially for the soffit face the absorbing properties look pretty good for 20mm.

EDIT: I found another pretty similar product by knauf:
http://www.knaufinsulation.de/sites/def ... %20440.pdf

To my surprise, the 703, plain 6" seems to do a marvelous job at that

Yep! That's one of the reasons that 703 is so popular with studio builders.

So far, I found only this: ... I found another pretty similar product

Both of those look good. Either will work.

- Stuart -

Hi guys!

It took quite some time, but now I am ready for the next stage of my studio build. I finished most of the front with the exception of the hangars and mineral wool behind it, the front of the bottom center part and the slot resonators (where the gaps on the right and left remain). Next week all the final wiring behind the front will be installed. This is how the front looks like right now: I also covered the ceiling with 10cm of rockwool and cloth cover.
Now, I thought the time was right to make some measuring to plan the rest of the treatment accordingly. For the final tests when all the wiring is finished, I will try to get everything out of the room, but for a little first test to get some perspective what needs to be done, I figured, I could leave some of the building material iside the room. This is how the back of the room looks like: I hope this does not distort the measuring with REW totally! Well, I will only use it to get to learn the program and especially interpret the results. I calibrated the programm with an SPL meter, but the audio inerface is very old and the potis crackl like hell when you turn them! For later measurements I will use my actual studio gear, but at this stage I don't want to put it there quite yet.
Without further ado - her go my results:
Left Speaker WF diagramm: Right Speaker WF diagramm: SPL reading of left, right and stereo: Left speaker RT60 reading: Right speaker RT60 reading: I hope I made a good choice of not too many pics, but the right ones to make a judgement! The Sweep went up to 4kHz, as it will probably be the lower frequencies, that are of inteerst here.
The first thing I did was comparing the results with the room modes in theory (519x365x227cm room dimensions):
1 33.04 Hz C1 1-0-0 ax
2 46.99 Hz F1# 0-1-0 ax
3 57.44 Hz A1# 1-1-0 tan
4 66.09 Hz C2 2-0-0 ax
5 75.55 Hz D2 0-0-1 ax
6 81.09 Hz E2 2-1-0 tan
7 82.46 Hz E2 1-0-1 tan
8 88.97 Hz F2 0-1-1 tan
9 93.97 Hz F2# 0-2-0 ax
10 94.91 Hz F2# 1-1-1 obl
11 99.13 Hz G2 3-0-0 ax
12 99.61 Hz G2 1-2-0 tan
13 100.38 Hz G2 2-0-1 tan
14 109.7 Hz A2 3-1-0 tan
15 110.83 Hz A2 2-1-1 obl
16 114.88 Hz A2# 2-2-0 tan
17 120.58 Hz B2 0-2-1 tan
18 124.64 Hz B2 3-0-1 tan
19 125.02 Hz B2 1-2-1 obl
20 132.18 Hz C3 4-0-0 ax
21 133.2 Hz C3 3-1-1 obl
22 136.59 Hz C3# 3-2-0 tan

The 57.44 Hz (looks more like about 53 in the results ...) mode seems to be the biggest one, although this might become less bad, once I use the EQ on my speakers to compensate for the soffit mounting with a low cut (for a start, I left the speaker at standard settings). The next big thing should be the 81.09 Hz right next to the 82.46 Hz mode. What I know, this should be the one I can (and should) do the most against. Also, there is a bump around 110 Hz followed by a dip.
The main problem I see though is in general the reverberation time of the low frequencies in general. This will probably be less so, once I use the low cut on the monitors Eq, but I supose it will still be there!

My plan to continue looks like this:
1) Do the wiring and put hangars and mineral wool behind the front.
2) Do a nother test to see, what the insulation has helped and what is left to be done.
3) Build the slot resonators' depth and slot sizes according to the tests.
4) Design the back wall: I tend towards mineral wool in the corners, some short hangars at floor level and above a shelf for putting microphones in.
5) Build some more Slot resonators (I gues absorbers would kill too much high frequnecies at this point) on the sides.

Still some way to go! My questions to you guys:
Does my measuring look ok or do you see any mistakes there? How about the interpretation? What did I miss in the analysis? How bad/good is the status quo considering the point I am at? Do you have any remarks on the further steps I have planned? What would you suggest for further treatment?

I know, I probably did many mistakes in planing this, but, hey: This is my first studio build! I learned a lot, but at some point I also had to learn, my first build will not be perfect. So please, be kind with me!

A little addition:
for the back of the mixing room I plan to make the entire backwall a shelf with about 60cm of depth. This way I hope it will become easier to get the aesthetics to work in an easier build. Depending of further meauring and comparing with different amounts an kinds of minral and glass wool, my rough plan of this stucture is currently:
- corners filled with rockwool (like a suberchunk, but square shaped instead of triangular, to close with the rest of the shelve) and covered with cloth stretched over a frame
- same thing for the portion of the wall close to the ceiling above door height
- small bass hangar comparment from the floor up to about height of the hips
- some sort of resonator in the center tuned to specific frequency needed (either slat resonator or some other membrane resonator, whatever I will hopefully see fits)
- remaining space filled with storage (shelf) compartments with the option of closing these with doors covered with HF diffusor (for LF diffusion those doors would become to thick and heavy)

Basically, the plan is that the entire wall will come about 60cm out, except for the area of the door frame. Due to the door, I am aware, that the distribution of soft and hard parts of that new "wall" would not be one hundred percent symetrical. Do you think, this is generally a good or a bad idea? I like it asthetically, but I am not sure how much the assymetry will weigh.
Also, is a small hangar compartment like this (about 2m wide, 1m high and 50-70 cms deep) worth it for further control of the LF problems? Many people here keep telling, that bass hangars DO work very well, but since there is no theoretical background available, I have no way of knowing at what size they are working for what frequency.

What do you think of this shelf idea in general? Worth to give it more thought, or should I rather go with the usual super-chunks in corners and a big resonator in the middle to keep the symmetry? I don't have much space in the other room, so some place for storage in the mixing room would really help a lot! And if the general idea is not bad in your opinion, would the shelf doors with diffusion help at all or would you rather leave them open (they could also have a 20cm of rockwool in the back for more absorption as an alternative)?

Based on the REW graphs, you have some major modal problems, which is not surprising since you don't have any bass trapping at all in there yet! Also to be expected is that your largest single problem is the first-order tangential length-width mode, at around 54 Hz, and since your first-order axial width mode is also rather prominent, and it seems that the second-order length mode too, then it is clear that your width and length dimensions are an issue, so you should plan for lots of bass trapping associated with those. In other words, your rear wall should should have major bass trapping in the two vertical corners, so your idea of square superchunks is excellent, but you also need a lot more trapping back there: I would do the entire rear wall with thick absorption.

I also covered the ceiling with 10cm of rockwool and cloth cover.

Excellent! That's why your REW data is showing that there are not many problems in the vertical plan....

I hope this does not distort the measuring with REW totally!

That's fine. It won't be making a huge difference, and this is just a rough test, to see approximately what the room is doing.

The Sweep went up to 4kHz, as it will probably be the lower frequencies, that are of inteerst here.

Do full sweeps, from 15 Hz to 20 kHz, always.

mode seems to be the biggest one, although this might become less bad, once I use the EQ on my speakers to compensate for the soffit mounting with a low cut

That won't make much difference, actually, since it is a mode that is being excited. EQ does not change modal response, and cannot fix modal response.

The main problem I see though is in general the reverberation time of the low frequencies in general. This will probably be less so, once I use the low cut on the monitors Eq, but I supose it will still be there!

same as above: EQ does not change modal response much. All small rooms require huge amounts of bass trapping, and that is what will damp the modal issues. Not EQ. Your room is showing roughly what can be expected for any small room.

My plan to continue looks like this:

Looks about right, except for the rear wall...

for the back of the mixing room I plan to ...

You cannot have hard reflective surfaces on the back wall. The basic concept of an RFZ room (which is the design philosophy you seem to be following) is to direct all first reflections to the back of the room, where they are absorbed greatly. The back wall needs to be mostly absorption.

- Stuart -

Thanks so much, Stuart! I don't know what this place would be without you ...
It really helps to see, that it is after all no magic involved, just analyzing the measurements correctly and act accordingly.
So, I will follow your advice and see that the almost the whole back wall becomes an absorber. You already stated, fat square super chunks (about 50x50 cm) will do good in the corners. For this I could use the same higher density Rockwool (Termarock 50 with 50 kg per cubic meter). But I have read that with deeper absorbers for LF absorption a less dense material could be appropriate. So, would a lighter Rockwool be better here? I also got a hint from somebody, I could experiment with different layers of different density, like e.g. 10cm of Termarock 50 followed by 50 cm of a lighter material or vice versa. Does this have any promise?
Also, what do you think about the hangar compartment with a height of about 1m? The back wall has the audio able port outlet to the tracking room, so a hangar compartment would combine further bass absorption with easy acces to the cables. I am just not sure at which size of hangars and which volume of the compartment hangars are with it.
Further, I am not sure at which amount of pure porous absorption (mineral wool) the high frequencies become too weak and the room gets dull. That is why I thought of a big slat resonator in the center (behind the listening position), maybe with a V-shape to defeat the possible flutter echoe with the parallel front section. This would give me the opportunity to defeat some low/mid fq broadband and tune to a specific problematic fq as well, while it would leave some of the HFq intact.
The same goes for the left and right wall, where I consider putting one or two slat walls, which might be tilted to deflect the HFq towards the absorbing back of the room.
And lastly: would two small shelf compartments in this constructions really hurt, if they where only about 30-40 cm deep and followed by clothing and 20 - 30cm of Termarock? Wouldn't this kind of thickness of mineral wool be sufficient to have more LF absorption in the back?

And one more thing regarding the back wall becoming a porous absorber (as insulation covered by textile can only be a porous absorber): to be effective for a specific fq a porous absorber has to have a quarter of its wavelength distance to the hard surface behind it. If I would want to decrease the most problematic area of modal resonance of about 50Hz, the distance to the wall would therefore have to be around 170cm!!! I surely would not want to do that! The only meaningful way of achieving that would be some kind of free standing absorber, so that the space behind that could be used somehow, but even that would IMO not be very pretty ...
So, if you suggest making the back wall all porous absorber, I guess you imply that the low frequencies around 50Hz will not be affected by that and that I will probably never loose any of these? What would be the way to get rid of them? Helmholtz resonator? I got quite a lot of people telling me not to go into building these, as they are very difficult to tune ...

I also found another resonator type, which is not to difficult to built, but is very effective in the 60-500 Hz area with only 10cm thickness. It is a membrane absorber of a built I couldn't find there, the so called VPR (Verbundplattenresonator). It is the result of a study by the German Fraunhofer Institut.
You can find details about it here, but in German, so I will explain a little bit:
http://www.casakustik.de/forum/index.ph ... ,29.0.html

You get a steal panel of 1m x 1,5m with a thickness of 1mm and stick it with elastic glue on 10cm of foam with the same dimensions (basotect is recommended). The foam can be glued on a wooden surface, which again can be mounted on the wall. The nice thing about it is that it has a high degree of efficiency within 60-500 Hz and you may also stick another layer of foam on top of the steel plate, which can add high frequency absorption if needed.
As I understand it, it works, because the steal panel gets excited in multiple low frequencies dampened by the foam. The technique is patented and researched by Fraunhofer and two German companies are offering it as a commercial product:
http://www.renz-akustik.de/page/index.php?id=46
For the frequencies most problematic in my room, the efficiency is unfortunately low in the 50 Hz area, but it Semester to be perfectly suitable for the other room modes in the 60-100Hz area and could also be used for broadband reverb reduction with more porous absorption layer on top. And all that with loosing only 10-20 cm of space in the back. Looks promising to me and I will investigate including this one or the other way in the back of the room and possibly also on the side walls. Has anyone heared of or tried building a similar resonator?