Sleeping pod design

[HermanDio]

From very early in the morning, fork lifts with trailers:


are moving all kinds of stuff in front of my window. When they go over bumps, whatever they're carrying bounces around on the trailer and creates a loud sound. I have yet to record it with a good mic and plot the spectrum of it but to my ear it sounds mostly like mid/high-frequency. Despite wearing earplugs it wakes me up early and I'm planning on doing something about it.

What I'm building to solve this problem for me is not technically a studio, but I'm looking for sound isolation and this seemed to be the best subforum on this site. I'm looking to build a sleeping pod: it will have a wooden frame, isolated from the ground on neoprene isolation pads for the right weight, and screwed on the wooden frame is a drywall/green glue/drywall assembly.

I've started the design, viewable here: link to onshape document

I have yet to add a door (solid wood with a quiet ventilation system (Aeropac) to the design but the basics are there: 12.5mm drywall, green glue in between, and 5mm spacing between drywall and the legs of the thing, so I can seal everything with acoustical sealer (which is more dense than drywall).

From my understanding, this will isolate sound waves according to the 'mass law': https://www.engineeringtoolbox.com/soun ... _1409.html
One panel is 9.5kg/m2, two is ~20kg/m2, so a value of 30dB isolation (at 500 Hz). At 63 Hz this is 30 - 13 = 17 dB isolation which is already quite good, and of course it gets even better at high frequencies. Cost should be < €1000.

Does anyone have feedback for the design? Can I make it better without a 15cm air gap or is this already at the sweet spot?

[Gregwor]

Unfortunately the onshape document just continually spins saying "Loading Workspace". This is a major reason we use SketchUp here. We can easily post SKP files onto the site that will be here forever (so long as people use the Donate button!!).

It seems like you have a good understanding of mass law. The only concern I have is your ventilation. I can't see how the Aeropac system is going to introduce much insertion loss at bothersome frequencies. I tried opening a few of the tech documents and 404 pages loaded instead.

I think I would research the Aeropac systems a bit before buying one. If they don't look like they will do the job you can always build silencer boxes like we do in the studio world!

Greg

[HermanDio]

Oops, onshape must be having an issue then. I already used Aeropac ventilation units in my previous apartment, which was next to a busy street but on the 9th floor. They were not very good for my heating bill because they don't have heat recovery. I slept a lot better though, with some fresh air at night instead of having everything hermetically closed and the CO2 levels off the charts!

I could find a datasheet for the new Aeropac ventilators (I actually bought 4 of the older model, for €25 a piece) but not a complete graph of the isolation. The 'sound absorption' according to the specs is 50-57dB, depending on how many sliders you have open. This is measured according to DIN EN ISO 20140-10, which I couldn't find the specifications of without paying money. The 'internal noise' is specced as : EN ISO 3741 at 60 m3/h (with A0 = 10 m2): LPA = 24 dB(A). From my experience they're quiet, the fan is suspended in foam and all you hear is the sound of the air moving. They're around €450 which IMO is unreasonable considering what they are, but the competing Sonairs are just as expensive.

Attached some screenshots of the plans in onshape, this week I've planned to finish them.

[HermanDio]

I've finalized the design! See the Onshape link in my first post. I'm planning to order materials tomorrow! Planning to get C24 lumber, higher quality than C16.

Not quite sure if the the wood construction is engineered properly - maybe it's too flimsy or too heavy. I guess I'll build the frame first and then strengthen it if it's too flimsy.

I know I'm supposed to have big drywall panels so the resonance frequency stays low so I've tried to incorporate that into the design. I'm planning on not getting the cheapest drywall, but 'gyproc db soundbloc', which has a higher mass and I assume is more flexible for a lower resonance frequency. Is it worth it or just marketing? Additionally, steel beams (ikea skorva) are used to support the mattress frame because I didn't want to place strain on the beams 2 by 4's supporting the drywall panels.

Any thoughts before I start building?

[Gregwor]

Planning to get C24 lumber, higher quality than C16.

This is a little room, I'm not sure if more expensive framing material is worth the extra cost.

Not quite sure if the the wood construction is engineered properly - maybe it's too flimsy or too heavy.

You should have two sistered top plates for your framing. Also, you should have your ceiling joists on edge. If height is an issue, i would at least run your joists across the short span of the ceiling, not the long one like you have drawn.

I'm planning on not getting the cheapest drywall, but 'gyproc db soundbloc', which has a higher mass and I assume is more flexible for a lower resonance frequency. Is it worth it or just marketing

I'm not sure what the price difference is between that and regular old heavy fire rated drywall. 15mm Regular fire rated drywall has a surface density of 11.8 kg/m². Soundbloc at 15mm has a surface density of 12.6 kg/m². Now, that is an improvement, but figure out if the cost increase is worth it. Put Green Glue Compound between the layers of drywall for a nice transmission loss improvement.

Greg

[HermanDio]

Thanks for your response. I'm not sure what you mean by sistered top plates, should I not use 2x4's but plates? And why?

Also you say my ceiling joists should be on edge. What does that mean? And I can run them across the short span, but why would that make it better? I calculated the deflection of the long beams to be less than 5mm.

There is going to be GG between the drywall of course. The density improvement is negligible but isn't the lower resonance frequency worth anything?

[Gregwor]

I'm not sure what you mean by sistered top plates

I just meant putting two layers of top plates.

should I not use 2x4's but plates? And why?

Yes, but since the walls are load bearing you should have two top plates.

Also you say my ceiling joists should be on edge. What does that mean?

The strength of joists comes from depth, not width. What I meant by having them edge is to rotate them 90 degrees so that the vertical dimension would be larger giving you the strength needed to hold up the weight of your ceiling sheathing.

And I can run them across the short span, but why would that make it better? I calculated the deflection of the long beams to be less than 5mm.

Less deflection is always better. Shorter spans = less deflection.

There is going to be GG between the drywall of course. The density improvement is negligible but isn't the lower resonance frequency worth anything?

GG is a cheap easy way to get great isolation improvements.

Greg

[HermanDio]

The design already has two layers of drywall on top so I still don't quite grasp what you mean.
Thanks for the idea to put the joists vertical/on edge! I was at the building supplies store today and played around with a 2x4, I put my whole weight on a 2x4 beam and the difference in deflection was quite extreme between vertical/horizontal orientation. I think I'll put all my beams/joists vertical, the design gets 10cm taller this way but that's fine.

[Gregwor]

The design already has two layers of drywall on top so I still don't quite grasp what you mean.

Google "double top plate" and I think the pictures will clear up any confusion.

I'm excited to see your build pictures!

Greg