Innerspace (NMF part 5)

With the interior skeleton largely in place it is time to turn my attention to putting some skin on these bones–the inside bones anyway.

So to begin, first we have to ensure that there is a layer of dampening material between each layer of the structure.  In this case I’m using an underlayment foam.  It is relatively inexpensive, easy to come by (the flooring isle), and effective in covering a large surface area.  This is partly to dampen the wall surface and partly to help create another layer to seal one side from the other.  It isn’t much of a barrier to sound, but it does help.

Beginning with the roll foam:

This is a simple process, albeit a pain in the butt until you figure out that a couple quick staples to hold it in place can easily be pulled out to line it up and tension it.  Once in place, a few staples along the side of the stud lock it down.  Rinse and repeat for the next level up, and then cut to fit when you get to the top.

Stretched and tensioned.  Overlap each layer slightly to minimize waste and ensure there isn’t a gap.

With all the walls done:  (note the gap between the wall sections…we’ll get to that in a bit)

The other side:

Now that all of the walls are covered we need to do something about the gaps between the walls.  To that end we make good use of the blue roll of foam above.  Remember we used that on the joists holding up the floor.  It is a bit thicker than the underlayment, and it easily fits the gap with staples along each side.

Gaps filled with the blue foam:

Now onto the interior wall surfaces. ..

The skin I’m after should be as inert as practicable, have every crevice sealed, and hopefully not have any deleterious health effects.  We have a wide range of choices, but since I’ll be covering most of the finish later with acoustic panels it doesn’t have to be particularly pretty.

Sheetrock, MDF, plywood (especially the special quiet type), and chip-board are all commonly available materials at your local hardware or lumber merchant.  For this project I chose MDF.  Other materials would suit, but I wasn’t interested in taping, mudding and sanding seams, plywood was more expensive at the same thickness, and MDF is generally more inert (less resonant) than the other materials.  In fact, MDF is essentially several different materials all pressed together with glue to make a new material, so in terms of resonances it does better than most.  It isn’t the prettiest, it isn’t the lightest, and it doesn’t suffer moisture very well, so be sure you consider those aspects before making your own choice.

*As a side note if you use sheetrock use two layers of different thicknesses with either an elastomeric coating in between or a layer of foam (underlayment that comes in the roll works well enough).  There are also specialized low-noise sheetrock options although they are very expensive compared to regular sheetrock.  For a project of this size it might be a legitimate option because it works well and you won’t need much.  Look for Quietrock or something similar if you want to go that route.

The bottom layer is pretty straight forward.  We only need to cut one end to fit on the bottom layer.  Everything else on this layer is square (or nearly so).  I used some shims along the bottom to ensure there was a small gap.  Behind the gap is the baseplate of the wall, so it isn’t open to sound.  We caulk the gap anyway, but this is to keep from stressing the wall surface when the booth flexes when it is moved around.  (Note I don’t know if it matters or not, but I figured it was easy enough to do and way easier than fixing stress cracked walls later.)

The first layer:

The bottom layer finished: (note the shims are just small cuts of scrap 1/4″ ply)

The second layer up: (Note since I was doing this by myself I used the first layer as a ledge for the second layer to sit on while I positioned and fastened it)

Next up, the ceiling.  Because of the odd shape, a single sheet of MDF would not span in a single piece.  For that reason I opted to piece it together like a puzzle.  First off I cut some triangular pieces for each side corner.  This let me piece the middle together from a standard sheet.   (This is much easier said than done because the angles are all very odd.  Just measuring each side and cutting a triangle to match got me close, but not close enough.  I had to trim these pieces several times until I got the hang of it.)

The triangle corner: (note there is foam behind it)

You can see the foam in between the joists and the corner panel:

I remembered to take a picture of the foam before I covered it for this part:

All the sections are up: (looking through the door towards the nose)

All together:

The floor got caulked and fully screwed down at this point too using screws long enough to reach the first floating layer but not penetrate it to the base platform:

Now all that is left before I can start the outside walls is to insulate the space between the walls.  It just so happened that I had insulation left over from the new roof  and wall insulation I had installed in our shop.  This is fortunate because it is exactly the material I want to use.  It is cheap per square foot, it is in a wide (6′) roll, and it has a PSK (Poly Scrim Kraft) facing that works well for absorbing low frequency energy.  You may recall that low frequency energy is specifically the energy we were trying extra hard to eliminate, so this combination is pretty awesome.  Plus it is leftover material from another project, so for the purposes of this project it was essentially free.  (Note loads of this stuff is tossed as scrap when putting up a new roof or metal building.  It is worth asking if you can keep the scrap.  You probably will be able to grab it.  Just be sure to get it before it rains.)

Since it is a roll, I simply attached it at the top with staples, rolled it down the side of the wall, and then cut it to length at the bottom.  Since the top of the walls aren’t  square I left a little overlap at the top and trimed it back when I was done.  Once it is hung it is just a matter of putting a ton of staples in along the length of each stud.  It naturally pillows which enhances it’s diaphragmatic behavior.  Remember that the diaphragmatic behavior is what makes it so well suited to affecting low frequency energy.

The first roll out: (note the eerie similarity between the insulation on the wall of the booth with the insulation on the wall and ceiling in the background…spooky.)

All walls up and taped together at the corners:

The ceiling essentially just lays on top.  I tacked it down with some staples, but that is as much to keep from moving it by accident later:

And just like that we’re ready to start on the exterior walls.   The good thing is it is starting to take shape, and all we’re able to show something for all the work so far.