Attic Shaped Studio

#496

I phoned the electrician this morning, he said he'd arrive just after lunch so I had a busy morning ripping out the rest of the superfluous wood and building a new light cable nailer that runs above the inside out modules. I only just got it finished before he arrived! It's dark so can't get a decent photo, so will post some tomorrow.

Cheers!
Jennifer

#497

New mains lighting cable arrangement. The cables run along the top of a nailer that goes above the inside out modules, dropping down at the correct points for the lighting rails.

A partially built OSB part of the inside out module. The sloped ends and the cutouts round the beams will be properly covered for the final fit.

Test fit worked well.

Cheers!
Jennifer

#498

I've built the OSB layer of one module with all surfaces attached.

Took it upstairs for another test fit. The riser it is sitting on is 6 feet long, should give an idea of the size of the module.

I spent the rest of the day cutting OSB for other modules. Now I've figured out the dimensions and assembly sequence, the other modules should be quicker to build.

Cheers!
Jennifer

#499

very cool!

#500

Thanks Glenn.

I've built and sealed the OSB parts of all four modules.

This module has an extra triangle profile cutout to accommodate the "diagonal beam that probably should not be removed" discussed earlier.

Now it is time to pray to the gods of acoustics that my measurement were accurate!

Cheers,
Jennifer

#501

it would be interesting to compare the room response to your previous measurements - esp if you did empty room ones. see what the additional air volume does. in theory you should see a some change in your axial modes length and width, perhaps slight vertical.

#502

That would indeed be interesting to see Glenn. I'm sure something like that happened when I added the 60cm deep recesses at the rear of the room.

Cheers,
Jennifer

#503

A friend helped me lift the first three modules into place between the rafters in the ceiling. Fortunately they fitted!

Sloped ceiling at the front of the room. There was already a noggin nailed into the rafters for the existing plasterboard. Once I've sealed the gap between the module and the noggin it'll provide a nice base for a butt joint to the module plasterboard

Sloped ceiling at the back of the room. There wasn't a convenient noggin nailed to the rafters here so I built the module with an overlapping lip that goes under the existing plasterboard by an inch or so, giving a good joining point for the new plasterboard.

There's a small beam running through the part of the rafters occupied by the last module. This is the module next to it; I had to cut a small square hole to fit round the end of the beam! Sealed round it to preserve soundproofing.

Cheers!
Jennifer

#504

awesome!

#505

I am so impressed with your work, Jennifer. Well done!

#506

Thank you Glenn and Lester, much appreciated. How's your place coming along Lester? I was reading your thread again the other day, the hexagon space couplers are amazing!

The entire OSB part of the ceiling leaf is now in place, and I've moved the lights further forward into the room to allow space for ceiling mounted microphone booms below two of the joists towards the rear.

A quick ear test of sound transmission to the room across from this with reference tracks played at reference level revealed a slightly lower level of sound attenuation since replacing the flat plasterboard ceiling with the OSB modules. It's probably only a few decibels but worth investigating before adding the plasterboard layer to the modules.

I can think of several possibilities that may be causing this:

(1) The volume of the roof / ceiling cavity above the modules has been reduced.
(2) Because of (1) there is less insulation in the roof / ceiling cavity above the modules.
(3) The OSB board has a surface density of 10.4 kg/m2, slightly lower than the previous plasterboard + skim coat of about 11.25 kg/m2.
(4) The OSB board is less rigid than the plasterboard, and/or resonates at a different frequencies.

I always planned to add a plasterboard layer on top of the OSB which will double the mass of the leaf, giving perhaps ~5dB increase in attenuation which should compensate for the observed loss. Does this seem like a reasonable expectation? I have some Green Glue and feel inclined to apply it between them just in case. I did this for the rear wall modules in the room and the sound transmission reduction of those was good.

(5) The span of the leaf between fixings to the rafters has increased from about 600mm to about 1200mm, allowing the leaf to flex and resonate more, or at different frequencies. This is shown in the following cross section:

I can add more screws securing the modules higher up on the ceiling beams, and perhaps even the purlin cross beams. The would reduce the span between fixings by coupling the modules more securely to the rafters, perhaps meaning the modules behave less like drum skins. I suppose it could potentially make matters worse by the modules structurally transmitting more of their vibrations to the rafters, but this seems intuitively unlikely given the huge difference in mass between the roof / rafter assembly and the modules. I'm out of my theoretical depth here, but adding the screws is easy and relatively quick. It's also easy to undo and fill the holes if it makes things worse.

(6) Big conjecture but worth considering: I've removed four 2x4' ceiling absorbers and several other large broadband absorbers from the room, and music at reference levels in the room now sounds louder to my ears than it did before. Perhaps this is slightly contributing to the sound being pushed through the new ceiling leaf, and perhaps it's also more "concentrated" in the ceiling "corner" which is shorter and more pointy than before?

Adding 200mm low density glasswool insulation inside the módules as planned would help this, and it might also help point (2) above.

I've just had another listen after applying a second layer of perimeter sealant around the OSB to old plasterboard joins. Adjusting monitor volume relative to the reference level to get the transmitted sound level "back to normal" in the adjacent room shows an increase in sound leakage of about 3dB. It's definitely coming through the ceiling / roof cavity which is shared between the two rooms.

Theory and intuition tells me that it'll all work out fine once I've added the plasterboard, fingers crossed, and other any thoughts welcome :-)

Cheers!
Jennifer

#507

the single layer of OSB may be a contributing factor. adding the drywall to those surfaces will increase TL. without the absorption in the room, it will sound louder - less energy is converted and scattering of energy on the other surfaces will support keeping the level higher.

adding the drywall to improve isolation - check
adding insulation abd absorbers back - check
future addition of slats to improve scattering :-)

cheers!

#508

Thanks Glenn, that's reassuring, much appreciated. I've added some more screws from the sides of the modules to the rafters, a good idea in any case for heavy objects at height. Also done another round of sealing along along the joins between modules and the existing drywall. I've done this with backer rod followed by three thin layers with one day drying time in between rather than one thick layer all at once, which is more prone to crack when curing. Should be ready for drywall application tomorrow

Cheers!
Jennifer

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