It’s not my fault…. (Part 3)

Laying the Foundation

For the backstory see:

https://www.theburningplatform.com/2017/02/12/its-not-my-fault-part-1/

https://www.theburningplatform.com/2017/02/17/its-not-my-fault-part-2/

As with nearly any building project, big or small, you build the base and work up from there.  This project is no different; however, we want our base to have a few interesting and unusual properties.  In this case we want our base to provide access for ducting, we want it to be as isolated as we can make it, and we want it to be easily portable.  Easily portable?  That is absolutely essential.

This recording booth will live in my warehouse when it is complete, and my warehouse is largely built around the concept of rolling shelves.  Since we do a significant amount of custom work, we need a flexible space.  Even though this booth will be fairly small and fit inside a 7′ x 7′ footprint, it will almost certainly at some point be in the way.  I want to be able to move it around and put it outside if my needs require it.  That means I have to have an easy way to move it around.

“But it’s a friggin’ building!” you say.  No worries it is a small building and only a couple thousand pounds when it is all said and done.  It is way too heavy to scoot around, but no problem for a pallet jack or a fork lift.  Even so, we’ll have to plan that feature into the base since it would be nearly impossible to add it later.

We start by laying out the outline of the base platform.  Since this has to be portable we can’t just build it onto the existing floor.  Moreover, since we want to use the floor as additional isolation we want it to float above the building slab.   Far more sound transmits up through a concrete slab than you may realize, and we want to kill as much sound as we can.  In this respect our desire to move it about and our desire for isolation go hand in hand.

Since we’re aiming for a non-parallel space I opted for a pentagonal footprint.   You can see the basic footprint along with the first accommodations for the pallet jack.  I also roped my daughter into a lesson on how to use a impact driver.  I don’t make my kids do nearly enough, but I try to teach them something useful where I can.

Below is the finished platform structure.  The center of gravity was barely over the forks, but hey it works, so no worries.  I braced the lifting area with 2×8’s with 4 long decking screws through each end.  I wasn’t sure I made it strong enough, but it has done well so far.

Before we get too far along we want to be sure that we’ve provided adequate accommodations for future duct work.  This will be *very* difficult to access later, so we want to be sure we create a way in for air and make it difficult for sound.  The plan here is to provide access into the base of the platform and turn 90° up into the recording space.  We want to be sure this turn is lined with absorptive material, so I built small enclosures to fit into the base and lined each with absorptive material I had left over from a previous project.  I had saved numerous angled cuts and otherwise useless remnants for this type of DIY project where it would be OK to piece it together.  This white board is called “Recore” and it is made of recycled plastic bottles.  It is not the cheapest option, but it was left over so that made it a cheap option for me.

The basic box:

The box in the base with absorption installed (staple gun)

The vent:

Side note: I took a bunch of pictures like this one with a tape measure.  I wanted to be sure that I could easily find the studs and such once it was all covered up.  It turned out to be very useful.  I highly recommend you do that. (note the sharpied ID that let me know easily which side I was looking at in the picture.  Hand written notes, measurements, and such are all useful info for reference pictures that tend to look the same later.  Just sayin’)

Next up we have to make sure all layers have some sort of dampening layer to help minimize the natural tendency to vibrate (and hence pass sound).  To that end I used 1/4″ thick roll foam between the decking and the support timbers.  This will do more to prevent squeaking and similar noised than it will influence transmitted noises, but since all noise is bad I made sure each seam had foam.

Now that the frame is ready it is time to put on the decking.  There may be an easier way, but I just screwed down the ply in a couple places and then used a sharpie to mark the outline of the deck where it overlapped.  Then I cut the outline about 1/2″ smaller than my outline.  It worked great and my decking was an exact fit for the frame.

The first layer finished: (Note the sharpied area marks where the door framing will go.  It can’t touch the inside framing since it is attached to the outside framing, so the inside has to cut around it.  The base decking, the base, the future door, and the future exterior walls are all one unit.  The interior walls, ceiling, and floor are a second unit that doesn’t attach to the outside unit.  It was the process of keeping that separation that took a lot of time and effort especially when it came to thinking through each step.)

Before the next layer could go down I needed to have some way to keep the interior structure from sliding around inside the exterior shell.  To that end I drilled several holes and filled them with caulk.  Then when I put the first layer of interior ply I used construction anchors counter sunk into the ply to act as pegs that would, at worst, barely touch the base deck and keep the interior from sliding around.  My main fear was that since this is a portable structure I could accidentally run it into something like the door frame of the roll up door, a conex outside or one of our vehicles.  If that happened the interior could slip until it came into contact with the outside structure as they are only separated by fractions of an inch.  Once in contact it would significantly defeat all of the effort I put into keeping them separately.

The holes prepped in the base layer:

The anchors acting as pegs:

The foam for the interior floor: (Note the white dots under the foam are the caulked holes for the future anchor-pegs)

The first layer of interior ply:

The Second Layer: (Note the first layer was ply, the second layer was chip board, and the third layer was MDF.  Using dissimilar materials helps prevent the inherent resonances in the materials from being the same and thus allowing the resonant frequency easy entry into our hopefully silent space.  Also the seams are rotated 90 degrees to minimize any overlap, and the first layer seam doesn’t line up with the third layer seam.  The seams are also caulked.)

A close up showing the layers and the foam in between each: (Note not shown here the top layer was screwed into the second layer carefully to ensure the screws didn’t penetrate through to the base layer and negate the whole effect)

And so the base is ready for me to erect the interior walls…

Reposted from: http://thesonicsingularity.com/laying-the-foundation/