Effect of ceiling beams on room modes!

[MattF]

Hi everyone,

So, we’re in the process of building a small studio into an old warehouse in Berlin and I was wondering if anyone could help on the effect of concrete ceiling beams the room modes and other acoustics of the room… We’re on a very tight budget (as little as possible!) and are also keen to be able to re-use as much treatment as possible if we have to move location… Property moves fast in this city so although we have a lease for the space you never know when a building like this will be redeveloped and also once we have got the place up and running and if it is a success we wouldn’t rule out moving to a larger/better location. That said we are dedicated to getting this space to sound as good as possible and see this as a great opportunity to finally have our own recording space for both our own bands and others… Might sound a bit mad but I have read you have to be a little bit of a lunatic to want to get into this game in the first place right?

Below are some drawings of the room and of the beams (in grey). The beam that runs top to bottom and on the left hand side of the drawing is 30cm wide by 50cm deep and the beam that runs across the room (left to right) is 25cm wide by 20cm deep. It is the side-to-side beam that we are most concerned about as the wall below the top-to-bottom beam is basically flush to the edge. (10cm lip or so…) I have been unable to find any information about the effect a structure like this on the ceiling of the room will have on modes and the acoustics, if any??

700control room beam from above copy copy.jpg

700control room beam 3D.jpg

The dimensions of the room are L: 4.54m, W: 4.25m, H: 2.7m. I have used Bob Gold’s room mode calculator and was encouraged to see that the results seemed to be predominantly green… I hope that that is the right interpretation! If only the beam would effectively split the room in two mode-wise it would be closest to a pair of Louden’s 2nd best ratios but I’m fairly sure it doesn’t work like that! The activity seems to be largely between 36 and 196 Hz so LOTS of bass trap building expected – as I have been told to expect from small rooms! My plan, thus far, regarding that is to:

Superchunk all four corners 60cm/2’ wide, floor to ceiling.

Build the back wall into one large absorber – fit wooden batons 20cm/8” deep floor to ceiling 60cm apart. Seal all joints with silicon then fit 10cm/4” Rockwool in front half of “boxes” and cover with breathable fabric. Thus creating a 3m x 2.7m bass trap. Kind of like an “inside out wall” if I have interpreted those corredtly? The back wall is made of brick and all gaps/cracks have already been filled. Although, would the overall effect be reduced if a sofa was placed in front? Otherwise the materials might be better used elsewhere…

Hang a series of clouds in both “halves” of the room, either side of the beam. Two large clouds and 2 small clouds each side. The large clouds would be 120cm X 180cm X 20cm, fronted with 3 panels of 10cm/4” Rockwool, plastic layer and breathable fabric. I am under the impression that these would perform best if they are of the “hard top” variety – a 18mm MDF 5 sided box with all joints sealed with silicon inside and the bottom/face side left open for Rockwool/fabric fronting. These would also be hung angled up towards the middle beam and down to the front and back walls respectively. The smaller clouds would be of the exact same construction but 120cm X 60cm to hold one panel of Rockwool. I thought this arrangement would enable the most absorption while still making them easy enough to handle/hang and the large/small combination would fit between the Superchunks

All of these proposed ideas are shown with the red blocks on the drawing below along with a plan of the mix position.

700Proposed sound treatment 1 copy.jpg

700Plan with mix position copy copy.jpg

It would be a huge help to get some feedback on these initial plans to see if I am headed in the right direction and any ideas for further treatment would be very much appreciated…
I am currently considering whether to continue “inside out” walls around the entire room but wonder whether this would be overkill or whether there is such a thing in such a small room… Would being in excess of 448 Sabins of imperfect absorbtion make up for the imperfections... Hmmm, if only!

As for room build materials, due to the fact that we are surrounded by storage above, below and on all sides isolating people from our noise isn’t such a concern. The control room is entirely surrounded by storage except for the adjacent live room, which is another project! Soon, soon…..

BACK WALL: 1 Brick thick.

LEFT WALL: 1 Brick thick. Door is new steel door with fire seals.

FRONT WALL: Currently 2 leaf single layer 12.5mm drywall on 75mm metal frame filled with Rockwool. To be bulked up with extra layer of plasterboard on each leaf and acoustic sealant/backing rod all around. Considering green glue between layers of leaves and/or substituting 1 layer of plasterboard for 22mm OSB for added mass….

Window is sealed double glazing with 10mm glass on live room side and 5mm on control room. May not be ideal but was an excellent price – FREE! Fitted into heavy solid wooden frame and sealed meticulously.

RIGHT WALL: Two leaf drywall fitted onto 50mm steel frame and filled with Rockwool. Outer leaf consists of 1 layer 18mm OSB and I layer 15mm plasterboard. Inner leaf is 2 layers 15mm plasterboard. All layers were sealed at each stage with plaster/acoustic sealant/backing rod where necessary

FLOOR: Laminate, underlay and moisture barrier over concrete.

Any of your help and guidance would be great and thanks again to you all for previous posts that have helped us get this far!!

Cheers,

Matt

P.S. Sorry for the poor quality plans. I am still working on getting my head around sketchup!

[MattF]

42 reads and nobody has any ideas?? Can't believe that to be true!

Any thoughts anyone? Please. Pretty Please! Pretty Please with a cherry on top!

[Soundman2020]

Please. Pretty Please! Pretty Please with a cherry on top!

When you ask so nicely, how could anyone refuse?

Hi there Matt, and Welcome to the forum!

Sorry it took so long to get a reply: the forum is really busy right now, but there aren't many people helping out with replies, so it can take a while for me to get around to some threads...

We’re on a very tight budget (as little as possible!)

Right! That's how almost everyone starts out with their studio builds, but most of them end up spending "more than I ever imagined!"

keen to be able to re-use as much treatment as possible if we have to move location…

That can be done too. Making treatment movable is not too hard. Isolation usually can't be moved, but treatment can. Not a problem.

Might sound a bit mad but I have read you have to be a little bit of a lunatic to want to get into this game in the first place right?

Actually, that's a fundamental requirement! If you aren't certifiably nuts, then you probably shouldn't be considering building your own studio anyway. Only we insane folks are able to do that. Mere sane mortals can't handle it...

I have been unable to find any information about the effect a structure like this on the ceiling of the room will have on modes and the acoustics, if any??

To a certain extent, it will partly "break up" modes that are traveling perpendicular to the beams, or at relatively large angles. So for example, you could expect it those beams to affect your axial modes along the front-back axis, as well as the tangential modes that involve the front and back walls and the floor and ceiling, and also the oblique modes, but the beams would have little effect on the other axials, or the tangentials that don't involve the front and rear walls. The effect will most likely be to change the modal frequencies a bit, and reduce the amplitude and decay time for modal ringing. In other words, that would be a good thing, not a bad thing.

If only the beam would effectively split the room in two mode-wise it would be closest to a pair of Louden’s 2nd best ratios but I’m fairly sure it doesn’t work like that!

Nope! Unfortunately, it doesn't work like that...

Superchunk all four corners 60cm/2’ wide, floor to ceiling.

Excellent!

Build the back wall into one large absorber – fit wooden batons 20cm/8” deep floor to ceiling 60cm apart. Seal all joints with silicon then fit 10cm/4” Rockwool in front half of “boxes” and cover with breathable fabric.

The back wall is made of brick and all gaps/cracks have already been filled.

Paint it before you put the treatment up. Paint seals the surface pores of the brick and mortar.

Although, would the overall effect be reduced if a sofa was placed in front? Otherwise the materials might be better used elsewhere…

A sofa would be good to, but "in addition to" not "instead of" the rear wall treatment. It's a small room: it will need all the bass trapping you can get in there, and sofas help a bit as well.

Hang a series of clouds in both “halves” of the room, either side of the beam.

Right! Make them big, as planned, but not so big that they completely fill the area. Leave some type of gap around the edges. Also consider angling the clouds: tilting them.

fronted with 3 panels of 10cm/4” Rockwool, plastic layer and breathable fabric.

4" OC-703 is a very good alternative...

am under the impression that these would perform best if they are of the “hard top” variety – a 18mm MDF 5 sided box with all joints sealed with silicon inside and the bottom/face side left open for Rockwool/fabric fronting.

Hard-backed is good, if you also angle them. But it's not necessary to caulk the joints: they are not tuned devices, so air-tight sealing is no needed. Just nail or screw the "lid" on firmly, and that's all you need.

These would also be hung angled up towards the middle beam and down to the front and back walls respectively.

The rear one needs to be angled the same as the front one. Lower down towards the front of the room, higher up towards the rear.

It would be a huge help to get some feedback on these initial plans to see if I am headed in the right direction and any ideas for further treatment would be very much appreciated…

so far so good!

You will probably also need some treatment on the side walls (first reflections, flutter echo, overall absorption), but I would wait until you have the basic plan in place, then measure the acoustic response using REW, and see what else still needs to be done. Actually, measure the empty room with REW first, so you have a base-line against which you can compare future measurements, to see what has improved and what still needs work.

I am currently considering whether to continue “inside out” walls around the entire room but wonder whether this would be overkill or whether there is such a thing in such a small room…

Inside out is great, but that would likely mean doing something to the existing walls as well if there any 2-leaf walls around: you do not want to get yourself into triple-leaf territory!

And while "overkill" in bass trapping a small room is practically impossible, it IS possible to kill the highs and mids too much. However, an inside-out wall lends it self perfectly to become a slot wall, which can give you the best of all worlds: Mostly reflective and partly diffusive for highs, partly reflective and partly absorptive for mids, and mostly absorptive for lows. It's hard to beat that!

Would being in excess of 448 Sabins of imperfect absorbtion make up for the imperfections... Hmmm, if only!

"If only! ... It's not just the total number of sabins that you need to worry about: the coefficient of absorption of each sabin is important, as well as where you put the, in the room. For example, piling up all your sabins on the right wall, where the coefficient is 0.2 in the lows and 1.0 for the highs, would be a pretty terrible experience...

Door is new steel door with fire seals.

Solid steel (ie. one sheet of steel plate), or hollow-core (two thin sheets with a gap between)?

Currently 2 leaf single layer 12.5mm drywall

MMmmmm.... 12.5 mm is a bit thin. 16mm is much better.

2 leaf single layer 12.5mm drywall on 75mm metal frame filled with Rockwool.

When you say "2-leaf" do you mean "coupled" or "decoupled"? In other words, are both leaves nailed directly to the same studs?

To be bulked up with extra layer of plasterboard on each leaf and acoustic sealant/backing rod all around

Right, but first you need to get one of the leaves fully decoupled, then you can add the additional mass you need .

Considering green glue between layers of leaves and/or substituting 1 layer of plasterboard for 22mm OSB for added mass….

If you go with the 22 mm OSB (which is a great idea), then put that layer on first, on the studs. Then put your 16mm drywall on top, with Green Glue. That's an excellent wall (assuming it is fully decoupled!)

Window is sealed double glazing

How big is the air gap inside? That might not be so good.... Typical commercial double-glazing units are great for isolating mids and highs (typical street noise, office noise, school noise, shop noise), but not so good for lows. As in drums, bass, keyboards, the low end of electric guitars, etc....

May not be ideal but was an excellent price – FREE!

Yeah, free is good, provided it is also useful! My neighbors will give me their garbage for free, but I'm not sure I want it!!!

Fitted into heavy solid wooden frame and sealed meticulously.

Which leaf is the frame-and-window in, and what do you plan to do in the other leaf?

RIGHT WALL: Two leaf drywall fitted onto 50mm steel frame and filled with Rockwool. Outer leaf consists of 1 layer 18mm OSB and I layer 15mm plasterboard. Inner leaf is 2 layers 15mm plasterboard. All layers were sealed at each stage with plaster/acoustic sealant/backing rod where necessary

Perfect!

FLOOR: Laminate, underlay and moisture barrier over concrete.

Also prefect!

It seems like overall you are on the right track.

- Stuart -

[MattF]

Hi Stuart,

Thanks for taking the time to reply, especially as you are so busy. You truly are a scholar and a gentleman sir!!

Right! That's how almost everyone starts out with their studio builds, but most of them end up spending "more than I ever imagined!"

Ha ha ha!!! The story of many a musical endeavour!!

To a certain extent, it will partly "break up" modes that are traveling perpendicular to the beams, or at relatively large angles. So for example, you could expect it those beams to affect your axial modes along the front-back axis, as well as the tangential modes that involve the front and back walls and the floor and ceiling, and also the oblique modes, but the beams would have little effect on the other axials, or the tangentials that don't involve the front and rear walls. The effect will most likely be to change the modal frequencies a bit, and reduce the amplitude and decay time for modal ringing. In other words, that would be a good thing, not a bad thing.

Well that's good news!! I was preparing myself for "Oh NO!! That is the greatest modal amplifier know to physics!!! Get out while you can! Run for your life!!!"

Quote:
Superchunk all four corners 60cm/2’ wide, floor to ceiling.
Excellent!

Awesome! Will be starting on those ASAP, and getting that back wall absorber in too... Does the plastic that i cover them with have to be perforated in any way to allow the soundwaves in?

Paint it before you put the treatment up. Paint seals the surface pores of the brick and mortar.

It is painted already but not by us so another coat wont hurt right? Or is it a waste of time and money? Better safe than sorry?

A sofa would be good to, but "in addition to" not "instead of" the rear wall treatment. It's a small room: it will need all the bass trapping you can get in there, and sofas help a bit as well.

Place the sofa in front of the absorber or build the absorber from above the sofa? My guess is the former - not a big difference in materials and great if sofas go out of fashion and we all go for deck chairs instead

Hang a series of clouds in both “halves” of the room, either side of the beam.
Right! Make them big, as planned, but not so big that they completely fill the area. Leave some type of gap around the edges. Also consider angling the clouds: tilting them.

Cool, I will leave some space around. What would you recommend? 20-25cm each side. And tilting wise... You say all down towards the console. Now, should that be in one smooth slope down with them all lined up or can it be in two parallel "tiers" either side of the beam? Might be less space consuming at the front/console...

4" OC-703 is a very good alternative...

As you probably know, over here in Germany we don't have the same products as across the pond in either North or South America apparently. I am planning to use Rockwool Sonoroc which has a density of 45kg/m3 and gas resistance of ≥ 6 kPa.sm2 which from what I have researched is suitable & very close to OC-703. I hope that that is right...?

Hard-backed is good, if you also angle them. But it's not necessary to caulk the joints: they are not tuned devices, so air-tight sealing is no needed. Just nail or screw the "lid" on firmly, and that's all you need.

Well that'll save some time and sticky fingers!

It would be a huge help to get some feedback on these initial plans to see if I am headed in the right direction and any ideas for further treatment would be very much appreciated…
so far so good!

You will probably also need some treatment on the side walls (first reflections, flutter echo, overall absorption), but I would wait until you have the basic plan in place, then measure the acoustic response using REW, and see what else still needs to be done. Actually, measure the empty room with REW first, so you have a base-line against which you can compare future measurements, to see what has improved and what still needs work.

Great. Will do... should i take the trouble of buying a measurement mic or can i use another of my omnidirectional mics? AKG C414 for instance?

Inside out is great, but that would likely mean doing something to the existing walls as well if there any 2-leaf walls around: you do not want to get yourself into triple-leaf territory!

And while "overkill" in bass trapping a small room is practically impossible, it IS possible to kill the highs and mids too much. However, an inside-out wall lends it self perfectly to become a slot wall, which can give you the best of all worlds: Mostly reflective and partly diffusive for highs, partly reflective and partly absorptive for mids, and mostly absorptive for lows. It's hard to beat that!

My thought about the use of "inside out" walls was to build more of the type of absorber I described for he rear wall but shallower. Basically mounting 4" batons on the wall with rockwool between and covered in breathable fabric as opposed to making any adjustments to the existing walls. Or does that still take me into 3 leaf territory somehow?? I have always loved the look of slot walls in studios that i have worked on bit never really understood them. Getting into the research now though... What is the difference between a helmholz resonator and slot wall for instance? can I attach random sized pieces of any wood over an absorber and expect things to sound better?? Surely not, but are slot walls tuned in any way? Does it make any difference if I use pine, MDF or solid walnut?

And just out of curiosity, would old wood, say reclaimed timber from an old 19 century building have some kind of interesting resonant effect due to the aging/breakdown of the cellulose? Similar to the sustain on a vintage solid body guitar? I don't happen to have any old wood but was just interested to know!

If only! ... It's not just the total number of sabins that you need to worry about: the coefficient of absorption of each sabin is important, as well as where you put the, in the room. For example, piling up all your sabins on the right wall, where the coefficient is 0.2 in the lows and 1.0 for the highs, would be a pretty terrible experience...

Close to spontaneous combustion?

Solid steel (ie. one sheet of steel plate), or hollow-core (two thin sheets with a gap between)?

It is a hollow core security door with what I believe to be a sheet of 20mm plasterboard inside... Hellishly heavy! Good? Bad? It is actually fitted into a shallow alcove in the room that I was thinking about building somekind of inner "plug" door/hinged absorber, perhaps even slot absorber after what you said, which could be mirrored onto the opposite wall too... I'd be sure to track down a good cantilevered freezer handle to ensure a good seal too!

MMmmmm.... 12.5 mm is a bit thin. 16mm is much better.

Is two layers 12.5 better still? As I have the material already... Sealed of course!

When you say "2-leaf" do you mean "coupled" or "decoupled"? In other words, are both leaves nailed directly to the same studs?

That would be coupled at the present moment. Or not so much anything as much as a work in progress... To rework the arrangement isn't an issue other than time which we would be investing anyway and we want to get this right. right?)

As for decoupling, would an additional off-set frame be best or would resilient channel work? Say a wall, consisting from one side to the other - 12.5mm plasterboard, 22mm OSB, steel frame & rockwool, resilient channel 16mm plasterboard, green glue, 12.5mm plasterboard. All plastered/backing rodded and sealed?

I mention the 12.5mm plasterboard as I already have 2 layers worth from dismantling another wall... Maybe 12.5mm, 12.5mm, 22mm OSB as one leaf??

How big is the air gap inside? That might not be so good.... Typical commercial double-glazing units are great for isolating mids and highs (typical street noise, office noise, school noise, shop noise), but not so good for lows. As in drums, bass, keyboards, the low end of electric guitars, etc....

The air gap is 15mm... How does that do??? Can't say I'm not feeling a little apprehensive... It is currently mounted in a wooden stud frame within the steel stud frame of the current half built wall (coupled to the steel frame...)

Yeah, free is good, provided it is also useful! My neighbors will give me their garbage for free, but I'm not sure I want it!!!

HA HA HA HA HA HA HA!!! Very true!!!

Which leaf is the frame-and-window in, and what do you plan to do in the other leaf?

Within the wall construction as mentioned above I would intend to mount the window onto the frame pnto which the plasterboard OSB leaf is mounted and take it on from there. Sealing around the decoupled leaf and windowframe with acoustic sealant abe being awfully certain of no shorting!

Perfect!

AWESOME!

Also prefect!

It seems like overall you are on the right track.

GREAT NEWS!! Even if the track is very winding and fraught with pitfalls!! Well, if it was easy then where would the fun be?

Thanks so much for your help Stuart. It really is massively appreciated! I hope that you might find the time to make your way through this vast post before too long!!

All the best,

Matt

[Soundman2020]

It is painted already but not by us so another coat wont hurt right? Or is it a waste of time and money? Better safe than sorry?

A can of paint isn't that expensive: I'd give it another coat, just to be sure.

Place the sofa in front of the absorber or build the absorber from above the sofa? My guess is the former -

Right.

You say all down towards the console. Now, should that be in one smooth slope down with them all lined up or can it be in two parallel "tiers" either side of the beam? Might be less space consuming at the front/console...

It can be in sections if you prefer. No problem.

I am planning to use Rockwool Sonoroc which has a density of 45kg/m3 and gas resistance of ≥ 6 kPa.sm2 which from what I have researched is suitable & very close to OC-703. I hope that that is right...?

That will work just fine.

Will do... should i take the trouble of buying a measurement mic or can i use another of my omnidirectional mics? AKG C414 for instance?

You can use any good omni, but a proper measurement mic isn't that expensive: a good one will cost you under US$ 100, new, and you can sometimes find them used on e-bay for even less.

I have always loved the look of slot walls in studios that i have worked on bit never really understood them.

They aren't that complicated: just a series of tuned resonators. One thing to be aware o: if the ratio of open gaps ("slots") to wood is higher than about 10%, then the wall acts more like a broadband device. If the open area is less than that, then it acts more like a series of individual resonators, each tuned to it's own frequency.

What is the difference between a helmholz resonator and slot wall for instance?

Nothing! A slot resonator IS a Helmholtz device. You have a "slug" of air that vibrates back and forth in the "neck" of the slot (the gap between two adjacent slats", and you have a sealed resonant cavity behind that, with absorption in it. That's an Helmholtz resonator. A slot wall is just a series of Helmholtz resonators, next to each other.

can I attach random sized pieces of any wood over an absorber and expect things to sound better??

Probably not. You could expect it to sound different , but not necessarily better. That can sometimes help over bass traps for example, provided that the gaps are very large.

Surely not, but are slot walls tuned in any way?

Tuned just like any other Helmholtz resonator: by changing the cavity volume, the neck size, and the neck depth. There are equations for that...

Does it make any difference if I use pine, MDF or solid walnut?

Nope. As long as the wood is fairly rigid, that's all that really matters. The wood does not take part in the resonating process: that is all done by the gaps between the wood, and by the sealed cavity behind.

And just out of curiosity, would old wood, say reclaimed timber from an old 19 century building have some kind of interesting resonant effect due to the aging/breakdown of the cellulose?

Nope. No difference at all: the only purpose of the wood, from the acoustic point of view, is to create the walls of the resonant "container". The wood itself does not vibrate or resonate. Or rather, it shouldn't vibrate: that's not part of the Helmholtz process. That's why you want it to be as rigid (stiff) as possible.

I mention the 12.5mm plasterboard as I already have 2 layers worth from dismantling another wall... Maybe 12.5mm, 12.5mm, 22mm OSB as one leaf??

Each layer acts independently in some senses, and the all act together in other senses. For the part of the spectrum where layers act independently, thinner drywall is not as good as thick drywall.

The air gap is 15mm... How does that do???

Not so well.... thin air gaps mean high resonant frequency, which implies poor isolation in the low frequency part of the spectrum...

Sorry about the long delay in replying! Lots going on right now...

- Stuart -

[julian.david]

Hi Matt,

I've just joined the forum as I'm about to build my own mixing room in Cologne, Germany (post on the forum to follow soon). Small budget, down to earth kind of design, so probably something like what you are doing. I might have some questions regarding sources for building materials (green glue, OC703/Sonoroc) since some of it seems to be difficult to get in Germany.
What kind of plastic foil did you decide to use for the clouds?

Thanks,
Julian