Designing & Building My Soffit Mounts

[gullfo]

not sure about the extra weight but maybe reach out to the speaker manufacturer and see what ideas they have...

[snailboyawayyy]

not sure about the extra weight but maybe reach out to the speaker manufacturer and see what ideas they have...

They said I can rest an equally distributed 40lbs on each speaker without concern, so that's good!

Btw, here are some more framing tips for those of you who are inexperienced builders like me and want to avoid wasting time:

1.) ATTACHING TO HOLLOW WALLS
If you need to attach something to a hollow wall you should locate the studs already inside the wall (I knocked the wall & listened for changes in sound but you can also use a stud finder) and screw into them. I didn't bother with this at first because I thought it was very unlikely that my vertical stud would line up exactly with a vertical stud inside the wall. This was a mistake because most walls have horizontal studs that run along the entire length of the wall.
If for some reason you need to attach to the hollow wall alone then I highly recommend using metal hollow wall anchors WITH A FITTING TOOL. If you don't use a fitting tool the T-nut fangs on the anchor will eat into the plasterboard if you try to tighten it (if this happens, you can use a spring toggle fixing in the larger hole so it won't be wasted).
I wouldn't recommend using any other type of wall fixing (e.g. wall plugs, self-driving, plastic spring etc.) if you need your attachment to be very tight. I tried nearly all the different types before settling on the anchors and it was an extremely frustrating ordeal

2.) UNWARPING TIMBER
So it turns out you can unwarp timber but its a bit more of a faff than simply weighing/clamping it down for a few days like I tried to do at first. Follow this here guide: https://www.diydoctor.org.uk/projects/warped-timber.htm (specifically the 'Using Pressure to Fixed Warped Timber' section). You'll need clamps, a large flat table, a bunch of hand towels, cling film & a heat source (I used a heat blanket). It took 7+ days but I can confirm that it does actually work.
I'd only recommend doing this if you're able to keep the timber straight by screwing it to a neighbouring wall/stud at several points, otherwise it might warp back over time (in which case I'd recommend just buying new timber).

3.) CLS vs. PAR TIMBER
I used PAR (planed all round) timber for my framing because I figured it would be better for studs that are attached to each other along their length (more tight & flush, less gaps), however you might want to go with the regular CLS stuff as it's cheaper and is usually stacked horizontally in timber yards (as opposed to PAR which is usually upright). This makes it easier to look at the end grains which will help you find timber that is less likely to warp (here's a good guide on how to do that: https://growitbuildit.com/how-to-buy-lu ... esnt-warp/)

4.) USE A NICE, WHOLE-NUMBERED ANGLE IN YOUR DESIGN
I used 29.4° and I really regret it. Wish I'd gone with 29° or 30°.

5.) DON'T USE GLUE IN YOUR FRAMING, ONLY SCREWS
If you make a mistake you don't want to be chipping away at your fully dried joining for hours trying to separate the timber, trust me. Thankfully I stopped using glue very early on & only used screws for the rest of the framing

[gullfo]

a simpler approach to hollow walls - put a layer of plywood or OSB on it. existing construction depending on the decade and skills of the builder can vary incredibly even with the best of intentions... putting a layer of plywood (3/4") will solve most placement issues as well as add mass. another is running a 1x4 across the studs, about 1/4 ways from top or bottom, so you can fasten into that.

[snailboyawayyy]

A few Qs, for anyone who can answer them:

1.) Can I mount the hangers simply by drilling small eye hooks screws into the ceiling and lower plywood shelves?

I've noticed that most people tend to fasten them to 2x1s, like so:

6D622EB9-B1CC-46AD-BC4E-EF25471C1B4C.jpeg

A big advantage to this is being able to remove the plywood shelves without having to un-mount all the hangers

But surely all those 2x1s will get in the way of the 100mm rockwool lining underneath the shelves? Surely it's preferable to have the entirety of the surface lined with rockwool with little holes for the hooks to poke through?
My main concern is the weight of the hangers bending the plywood shelves downwards, but the hangers can't be THAT heavy can they?


2.) I touched on this earlier in the thread but I need to make a decision soon - which is better: a large baffle that partially obscures the top hanger cavities OR a smaller baffle that ends right as the top hanger cavities start?
Basically, this:

large baffle.jpg

(I've included one example hanger in the top cavity. Note that while the speaker's acoustic axis is exactly halfway on the 'total baffle', the top cavity is partially blocked by the top of the baffle and the hangers need to be cut to accommodate)

OR this?:

small baffle.jpg

(The hangers don't need to be cut, but the speaker is no longer half-way on the baffle)


3.) I plan on filling the entire center section with rockwool (superchunk it) - should I seal the speaker cavities with plywood panels like so:

side panel.jpg

Or is that unnecessary? That is, should I just leave the speaker cavities exposed to the center superchunk?


4.) I've noticed that the insulation people use for their hangers tends to be different from the insulation they line on the walls (see pic above for example). I was planning on using Rockwool RWA45 for both walls & hangers. Would that be fine?


5.) I know that wrapping rockwool in plastic can be acoustically beneficial (reflecting high frequencies) but is it necessary for health reasons? That is, could I expose the rockwool to the room and not worry about breathing in fibers? Or is wrapping rockwool a must?


Thanks y'all! And special thanks to gullfo who's been a huge help throughout

[gullfo]

you can definitely use a plywood layer to attach the hanger hooks.

you can also shift the size (depth) of the hangers to accommodate the angles. you could also as shown - make the hanger partially cut away to accommodate positioning on the structure.

don't wrap the hangers with plastic.

ultimately with the hangers, you're trying to get sufficient wave guide action to redirect the sound to the surrounding insulation (increasing angle of incidence into that insulation causing more absorption) as well as providing some support to shift the modal responses. however, in small spaces, you may be better off facing the entry with semi-rigid insulation (say 4" 100mm) and filling the interior with soft (pink) wall type insulation. to change it up, you can add a layer of MLV behind the semi-rigid insulation to act as a soft membrane.