Attic Shaped Studio

#331

Thanks Glenn. Before adding this second layer, the wall had standard 12.5mm plasterboard + skim coat on either side. I estimate 9 kg/m2 per side, for a total of 18 kg/m2.

This second layer has a surface density of 13.5 kg/m2, meaning the mass on one side has more than doubled, and total mass of both sides has increased by about 70%. By mass law alone this should hopefully give a few dBs of improvement, with the green glue pushing it higher still.

Cheers,
Jennifer

#332

I left a several millimeter gap between all the plasterboard joins and perimeter, then filled those with backer rod and caulk. Now onto plastering over the screws and joins.

From a few casual listening tests I'd say there is a noticeable reduction in low frequencies coming out of the room, as predicted by the graphs in an earlier post. Black line was "before", red line is now. Quite encouraging.

#333

very nice! the lowest stuff will be due to structure transfer - one test put your speaker on one of your isolation pads and see what you get.

#334

That's a good plan Glenn, I'll do an extensive test like that once the room is back together.

I should point out that graph was derived from similar wall & door structures from IR761 and the Green Glue website, it's not an actual measurement of the room. My ear definitely confirms it though, with the aforementioned reduction in low frequencies. And also a not noticeable reduction around 240Hz e.g. low end of snare drum sounds pretty much as it did. To improve that I'll need to add mass to the door.

Cheers,
Jennifer

#335

are you thinking of replacing the door with something like a sand filled door :-)

or simply adding some MDF to the existing one? the sand filled door would likely weigh quite a bit more and thus potential stressing on the frame and hinges. whereas an MDF sheet + GG might do the trick.

#336

No worries, I've already beefed up the door frame, surrounding studs and connections in anticipation of a heavier door

Bought stronger hinges too. The current door is a solid core fire door and weighs about 45kg so the existing frame was pretty sturdy. I've been thinking about adding 18mm MDF or plywood and perhaps some code 3 lead. If I did this it would approximately double the mass of the door.

Do you reckon Green Glue would be effective on a single leaf?

Cheers,
Jennifer

#337

if using lead, then i'd skip the gg as the lead will provide a decent damping factor. otherwise gg can be effective with the door + mdf addition in terms of damping. less costly - 5mm MLV could also be used to provide that as well as increasing mass.

#338

The MLV is a good call Glenn thanks. Two layers of 10kg/m2 MLV and a layer of 18mm plywood would double the door mass.

Cheers,
Jennifer

#339

I've plastered over the joins and screw heads, and repainted the wall. It now looks the same as it did before, just 15mm thicker :lol:

I also had to extend the door frame by 15mm to match the thicker walls, otherwise the architrave wouldn't go back on properly. The lighter strip of oak is the added 15mm part. And it's great to finally have these light switches in a proper surface box.

#340

very very nice! ready to test...

#341

Cheers Glenn. No formal tests yet, but we had an electric violin tracking session in the room last week. Going by the volume control of my calibrated monitor controller, the volume got up to about 94 dB. My wife didn't hear anything in the living room, so top marks there!

#342

I'm gathering materials to add mass to the room 1 door. The door is an FD30 rated fire door with a solid ceramic core. It has a gasket round the perimeter, and I've already installed a drop down seal at the bottom. I estimate the weight is about 40kg, to be verified on scales next time I remove it.

Since the wall has already been improved, the current attenuation is represented by the red line on the following graph. The door is currently a weak link in sound transmission chain, offering less attenuation than the wall, particularly between 100Hz and 2000Hz By improving the door, my goal is to move the theoretical attenuation of the combined wall and door from the red line to the green one.

So far I've acquired the following;

- 18mm plywood @ 11.5 kg/m2
- 5 kg/m2 MLV, enough for several layers
- Overhead door closer rated at 100kg with "fully adjustable variable power with latching action, backcheck & delayed action"
- Heavy duty ball bearing hinges rated up to 120kg

I have ordered some better weatherstripping to evaluate. As detailed earlier in this thread, I've already strengthened the stud work around the door frame.

In an ideal world I'd build the door like Rod Gervais super door, with sufficient MLV sandwiched between the door and the 18mm ply. This is applied to the push side of the door. Unfortunately this option is not available to me as the door has this lovely paneled finish I'd like to retain on the push side. It's the side that opens into our landing area, so has to look matched and proper with the other doors in the house.

The door pull side faces into the studio, and will be almost 100% covered with absorption anyway, so it's not essential to retain the door panels there. So that's the side I'll add the mass to. Fortunately the door frame & architrave will permit a "bank vault" style seal to be applied by making the added plywood a little larger than the door. This will work on the top and latch side of the door, but not on the hinge side as the overhang would foul on the hinges. I figure this isn't such a big deal though, as the compression on the gaskets along that side of the door will give an excellent seal anyway.

The door is thinner where the face panels are recessed, so I'll fill those in with thin strips of MLV and insulation padding to make the mass even across the door.

So, it will go from the current door profile that looks like this;

: current door profile.png (25.04 KiB) Viewed 10885 times

: current door profile.png (25.04 KiB) Viewed 10885 times

to this. This has two layers of MLV with a depth of 4mm between the door and 18mm plywood.

I'll install appropriate gaskets wherever possible, and perhaps another drop seal on the push side face. Two layers of MLV should bring the door to about 80kg total mass, around 49 kg/m2.
.
Does this plan seem sane?

There are currently three fire door hinges, one near the top, one near the bottom, and another in the middle. I'll replace these with the 120kg rated ones I've bought. Will it be necessary to fit another one between the top and middle as I've seen on some other heavy doors?

Cheers!
Jennifer

#343

i think the approach is good - i would consider a magnetic seal on the extended edge to the jamb in case the pressure seal has any give. with the door closer you might be able to properly guarantee the pressure.

#344

Thanks Glenn, much appreciated. And thank you again for your recommendation to use MLV instead of lead sheet for this door, that was an excellent call.

Cheers,
Jennifer

#345

I've started work on the door.

First job is to upgrade the door hinges to heavy duty ball bearing types. The new hinges are slightly larger & thicker so I'll have to lengthen and deepen their mortises to ensure they fit flush, so the gap between door and door frame doesn't increase. To speed things up I made a router template jig, much faster than chiseling them by hand. It worked on a test piece of wood, fingers crossed it will work on the real door!

There are currently three hinges, one each at top, bottom and middle. I've noticed that most of the heavy exterior doors in my house, and also heavy interior doors elsewhere have two hinges close together near the top, so I plan to add a fourth hinge for this. In truth though I'm just copying what I've seen, I've no idea what the physics are behind this. Any tips welcome!

Edited to add, I've just remembered the following post by Stuart describing a mega door that has the necessary answers. His door has six hinges (!) but is a little bit heavier than the one I am planning.

viewtopic.php?f=12&t=23

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