7th floor studio in office building in Melbourne Australia

[princeplanet]

Hi all, I'm looking for advice regarding the building of a 68m2 2 room studio on the top 7th floor in an office building.

The salient points: The space is L shaped, but the structural engineer has decided it's wise to build along the long side of the L which is basically 14m x 4.9m. Ceiling height, once I take out all services and ceiling tiles, will be 3.16M sloping down to 3.04 M. There are structural beams supporting this perimeter, as well as beam support that splits the space in two. So essentially I can build 2 separate rooms (CR and LR) where the lineal load is supported for the walls. The floor has been calculated to hold 500kg/m2 after studying the building plans. I'd like to float the floors with a 75mm slab on isolators (NRD2?) with a 75 mm air gap and insulation.

The walls I'd like to be comprised of 3 layers of 15mm CFC (45mm), although, much of the outer leaf is floor to ceiling window glass (10.38 lam) which will need to be reinforced with either more glass (the views are great!) or CFC. Apart from nearby office and hotel buildings (20m away) there are just 2 neighbours on my floor within spitting distance (them spitting on me if I mess this up!) but my main concern is with neighbours below in several offices beneath the existing 125mm slab on condeck. I conducted some LF tests where it seemed most frequencies between 40 and 200 hz are currently attenuated uniformly by around 40 dB, although listening to a sweep it seemed to peak to my ears b/n 150 and 200z.

I want to record rock bands but am prepared to accept that I may not be able to record drums during business hours, I'm a late owl anyway... However would really love to be able to work all hours to suit client needs. To this end, as part of the live room, it would be great to have a drum booth and a couple of amp booths which might enable me to record during business hours, albeit not ideally. It would be fantastic if I could use movable walls (Hufcor?) to create these booths, and move them back out of the way when I can get away with having more ambience (at the expense of more leakage!).

That's the rough outline. I can't use sketchup (yet) but could provide a mud sketch or 2 along with any other particulars, including the rest of the layout (green room, access to toilets etc). I should say that I have operated 2 different studios over 25 years (both on the first floor), and built my last one in 1998 with a little help from the late Graeme Thirkell.

I'm thinking to complete a design in a few weeks, and am hoping to commence building soon after. Of course there are a lot of details I have left out, but am happy to provide as much as is asked for, should any one care to! I have a ton of questions, as anyone always does in these matters, but I have a feeling, due to the unusually challenging nature of the project, that a couple of you folks may be wanting to ask me some questions first- like "what the hell are you thinking!" ;) .... So, please, shoot me!

[bert stoltenborg]

What is condeck and cfc?

[princeplanet]

Condeck is the thin steel tray the concrete is poured into. Because of its shape it adds strength. CFC is compressed fiber cement, it's density is closer to concrete than it is to drywall.

[bert stoltenborg]

With this floorconstruction (if done right) a drummer generating a conservative 110 dB(A) will be attenuated to about 50 dB(A) on the lower floor. Over here a penalty for music sound is added so it would be 60 dB(A), 15 dB(A) is tolerated.

[bert stoltenborg]

25 is tolerated it should be, sorry.

[princeplanet]

We did some tests and this is what got sent to me upon analysis:

Noise Reduction required:

40Hz = 70dB
63Hz = 75dB
125Hz/250Hz = 80dB

Current NR-

40Hz = 48
63Hz = 48
125/250Hz = 56

Increase in NR required-

40Hz = 22
63Hz = 27
125/250Hz = 24

Proposed floor with 75mm slab + 75mm gap:

40Hz = 60
63Hz = 61
125Hz/250Hz = 76


Upshot - I'd still be short by at least 10 dB where it counts. Anyone disagree with these figures?

[bert stoltenborg]

The floor you are proposing does about:

63 Hz - 35 dB
125 - 40 dB
250 - 43 dB
500 - 50 dB
1000 - 58 dB
2000 - 64 dB

When you sum these values according to a music spectrum weighting you get the numbers I told you.
The values you mention are totally unrealistic, or you live in a warped universe

[princeplanet]

Haha- well, maybe my "expert" does... Hmmm, upon further examination, I think those figures he gave me are ridiculous. Thanks for pointing it out Bert! So, given that you seem to know about these things, what would you say is the "threshold of annoyance" for the people below me at 40, 63 and 125hz ?

[bert stoltenborg]

I have no idea how your laws are, but over here:
At 63 Hz the music correction is 27 dB, at 125 Hz it's 14 dB, at 250 it's 9 dB.
So that is what you get for free because your hearing is insensitive at these frequencies.
The background noise in an office is around 55-65 dB(A), you want to be 20 dB under that, so a drumset at 110 dB(A)@63 Hz is 83 dB(A) and has to be reduced to 35 dB with a 10 dB penalty, so you need 58 dB reduction.
A drumset at 110 dB(A)@125 Hz is 96 dB(A) and has to be reduced to 35 dB with a 10 dB penalty, so you need 71 dB reduction.
\
In other words: in a normal building it is impossible to have a studio or practice room where you can play drums, when you are able to have a discrete foundation or a very heavy floating floor it is possible, but not on the 7th floor with the restrictions you mention.
I'm sorry.

[princeplanet]

Are you an Acoustician, or a Studio Designer? Have you constructed floating floors on upper levels? You seem to write with a high degree of assuredness, but before I choose to believe you, I thought I might ask what you're credentials are. Oh, and please don't be offended, I'm finding Studio Designers have more ego than most musicians!

[bert stoltenborg]

I'm into acoustics and music, meaning I earn money doing acoustics and spending it being a musician .

The data mentioned are measurements from official labs and you can find a lot of 'm on this site.
In a dedicated building and having enough money you can do anything you want, in an existing building not everything you like is possible.

[princeplanet]

Cool, OK, because I have a serious question for you. If i were to only build a small 8 m2 drum booth within a rooms and needed to get, say, 70dB TL at 125hz along with the expected TL at other frequencies below and above 125hz, then what would this booth need be made of? How heavy would it need to be? What sort of cavity? What sort of isolators (springs or rubber)?

Further, If I wanted a 34m2 live room to be floating on only 50mm of concrete with a 100 mm insulated gap, but I wished to have the "drum booth from hell" (as described in the previous paragraph) in the LR corner, then would the drum booth floor and ceiling (which would need to be much denser) simply be thicker than the rest of the floor and ceiling? Would the walls, floor and ceiling need to be decoupled from the rest of the room (e.g.- separated by a layer of dense rubber)? Would the drum booth walls create a triple layer effect because the rest of the room is "room within a room"? Is there an ideal way to configure an extreme iso drum booth within a moderately isolated larger room?

[bert stoltenborg]

I would need to have very precise information to answer this because you already have a room that is interacting with your new room.
But 2 concrete 100 mm slabs with a 50 mm woolfilled gap gets you 56 dB of TL@125 Hz.
You expect another 14 dB, so an increase of, depending on several variable parameters, in the worst case more than 20 times. So you have to think in making the construction 20 times heavier. Doubling mass give you 3 - 5 dB extra, doubling the gap gives 3 dB.

"Further, If I wanted a 34m2 live room to be floating on only 50mm of concrete with a 100 mm insulated gap, but I wished to have the "drum booth from hell" (as described in the previous paragraph) in the LR corner, then would the drum booth floor and ceiling (which would need to be much denser) simply be thicker than the rest of the floor and ceiling?"

The whole booth would have to be ridiculously heavy, not to mention the problems with the door and ventilation.

"Would the walls, floor and ceiling need to be decoupled from the rest of the room (e.g.- separated by a layer of dense rubber)?"

Decoupling is not just putting stuff on rubber

"Would the drum booth walls create a triple layer effect because the rest of the room is "room within a room"? Is there an ideal way to configure an extreme iso drum booth within a moderately isolated larger room?"

You get a triple leaf for sure and have to worry about the second question.