Designing & Building My Soffit Mounts

[snailboyawayyy]

As I said, this continuous front wall is not the best approach in your case, I am just pointing it out for the sake of completeness, so that people reading this can understand the principles involved of an ideal infinite baffle design.

Fair!

I wouldn't worry too much about decoupling, it's not going to make a massive audible difference in this design in my opinion unless you have rather flimsy speaker cabinets that vibrate.

Oh, okay! You think I should just make sure everything's very tight and rigid (i.e. no sorbothane)?

What I mean regarding your framing is this...

Yes, I understood what you meant. Does my adjustment not fix that problem?

Or did you mean do mitre joints at all the connection points, not just the one you pointed out? Like so:

ceiling plate w all angled joints.jpg

(Not sure how to go about doing the short ones)

[gullfo]

i would just go simpler - create each plane as a separate flat assembly and just rip posts to fit the join angles. glue & bolt the assemblies with the posts. join to wall. trim baffle plates edges to fit.

i would strongly recommend decoupling the speaker from the speaker box and also the front plate. speakers vibrate. the frame structure and baffle plates become extensions of that if tightly coupled.

[Paulus87]

i would just go simpler - create each plane as a separate flat assembly and just rip posts to fit the join angles. glue & bolt the assemblies with the posts. join to wall. trim baffle plates edges to fit.

i would strongly recommend decoupling the speaker from the speaker box and also the front plate. speakers vibrate. the frame structure and baffle plates become extensions of that if tightly coupled.

That's a cool idea Glen, I like it. Though I don't personally have the tools to rip large lengths of timber with such precision, but if I did then I would probably do it like this.

I am intrigued by what you say about the speaker cabinets vibrating - I have never experienced this with high quality studio monitors, and as I'm sure you're already aware Ethan Winer has tested speaker isolation products and found them to be unnecessary.

https://ethanwiner.com/speaker_isolation.htm

And this video demonstrates it quite clearly:

https://www.youtube.com/watch?v=ttk4y6_afa8

Granted, not all speaker cabinets are created equally.

[gullfo]

the challenge with Ethan's testing it it used a "microphone" to detect changes in "vibration" rather than a "vibration detector" (a simple one would be a piezo attached to the speaker and one on the floor). pretty sure if you touch a speaker in operation, you will feel the vibrations. maybe i'm just sensitive... lol.

while ripping is best done with a table saw, i use my hand power saw upside down on my black&decker workbench to rip 2x4 and 4x4 without an issue. i just find it's easier to get all the parts squared and highly consistent if they're flat (like checking for bowed lumber etc) or even using a jig (think pre-fab). then assembling those is much more precise rather than a "stick build".

[snailboyawayyy]

i would just go simpler - create each plane as a separate flat assembly and just rip posts to fit the join angles. glue & bolt the assemblies with the posts. join to wall. trim baffle plates edges to fit.

Great idea! I was wondering if there was a way to join angles all the way from floor to ceiling

How's this:

new frame w rip posts.jpg

i would strongly recommend decoupling the speaker from the speaker box and also the front plate. speakers vibrate. the frame structure and baffle plates become extensions of that if tightly coupled.

Yeah, I was gonna use sorbothane between the speaker and housing box. Is that what you'd do?

Btw I decided to go for acoustic hangers on both the bottom and top of the soffit. Added a 2nd shelf to the design:

top cavity 60cm height.jpg

top cavity 60cm height side.jpg

As you can see, the bottom cavity is 88.2cm high and the top cavity is 60cm high - is that fine? I just picked a random number smaller than 88.2cm. Could the top cavity be similarly sized to the bottom cavity or would that impede the soffit's effectiveness? Does the size of the module containing the speaker matter or is it really all about the area of the front baffle & the size of the module behind it doesn't matter?

Or maybe it's the bottom cavity that should be smaller? Glen, I noticed in your design that your speaker is raised a bit above the 1st shelf, similar to how Waka does it in his design: https://www.johnlsayers.com/phpBB2/view ... &start=165
But then most others I've seen have the speaker simply sitting on the 1st shelf? Which one is better and why?

It's all rather confusing

[gullfo]

the hanger cavity on the top could be larger - in fact since you've created the lower barrier, you could just eliminate the top one. you need bracing for the baffle plate. the top hanger supports can be 2x4 (etc) screwed into the ceiling, not necessary to have them part of the frame.
yes, sorbathane is a good choice. i've also seen sylomer, neoprene etc work depending on the market availabilty and your budget.

[snailboyawayyy]

in fact since you've created the lower barrier, you could just eliminate the top one

When you say 'barrier' do you mean the upper shelf, separating the hangers from the speaker module?
How would that work? If you agree that I should have hangers at the top, then surely they need to be separated from the section containing the speaker (which should be filled with loose insulation)?
Literally every design I've seen with hangers at the bottom and top have shelves separating them from the main speaker module.
Example: https://i.ibb.co/Bsd6zmd/IMG-0384.jpg

Or do you mean the plywood panel underneath the speaker (that absorbs reflections from the mixing desk) when you say 'lower barrier'?

you need bracing for the baffle plate

Forgive me Glen, I don't know what you mean...
If you mean the studwork at the front of the central module (gripping the speaker box), I haven't sketched it yet

[gullfo]

the speaker box itself is effectively sealed with only the duct board venting, and of course the front. wires etc enter the box - preferably via a soft rubber grommet or could be caulked. and the box itself is made from mass including plywood, perhaps additional mass of gwb, etc. so there is no real reason to create the internal cavities except to provide structure for the hangers and supporting loose insulation (which could be support by wires etc inside). but - it depends on the size of the units as well - larger assemblies might benefit from separations to adjust air volumes in the space, but for the most part, it's not really necessary unless some testing reveals that altering it is needed.

your framing should have an additional strut spanning about 1/3 from the top of the speaker to the upper strut (bottom of the top opening) so the baffle plate is more rigid and thus raising the resonant frequency and thus most effectively damped.

[snailboyawayyy]

the speaker box itself is effectively sealed with only the duct board venting, and of course the front. wires etc enter the box - preferably via a soft rubber grommet or could be caulked. and the box itself is made from mass including plywood, perhaps additional mass of gwb, etc. so there is no real reason to create the internal cavities except to provide structure for the hangers and supporting loose insulation (which could be support by wires etc inside). but - it depends on the size of the units as well - larger assemblies might benefit from separations to adjust air volumes in the space, but for the most part, it's not really necessary unless some testing reveals that altering it is needed.

So for the housing box I'm following garethmetcalf's design from this thread: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=20895 (he has the same speakers as me)
Here's what it looks like:

Note that there are not just one but 5 quite large slots on all sides of the box, with a lot of space behind the speaker. This is due to the speakers' passive rear radiator, as well as to cool the amps (in that thread Stuart says the slots are "for both cooling and to provide low impedance coupling to the larger cavity around the enclosure box")
So the speaker box is far from sealed. Wouldn't sealing off the central module from the hangers below & above not be more beneficial in my situation?

Also, if you say internal cavities are unnecessary given that the speaker box is well sealed, would I even need the lower barrier? Obv I need some kind of platform for the speaker, but it wouldn't need to be sealed would it?

your framing should have an additional strut spanning about 1/3 from the top of the speaker to the upper strut (bottom of the top opening) so the baffle plate is more rigid and thus raising the resonant frequency and thus most effectively damped.

Ah okay, like this?

Screenshot 2021-02-09 224721.jpg

Thanks again for all your help thus far Glen

[gullfo]

where you are trying to mount rear ported speakers in a baffle, you would need the separations or you could build some "port extensions" from the box and into the baffle to redirect the LF ports out front - of course now you'd be into speaker engineering.

so in this case, keep the separation plates and just try to absorb as much from the ports as feasible. unfortunately in many cases the rear ports are also part of the cooling scheme so it's not likely a way to throttle or block those.

[snailboyawayyy]

so in this case, keep the separation plates and just try to absorb as much from the ports as feasible. unfortunately in many cases the rear ports are also part of the cooling scheme so it's not likely a way to throttle or block those.

Okay, I'll do that!

Currently waiting on the timber to arrive, but here's the finished(?) design for the framing:

Soffits Finished Framing.jpg

Above.jpg

(the triangular rip posts are proving a lot harder to obtain than I thought. I don't have (or know anyone who has) a table saw so I'm trying to find a joiner that will cut them for me, but for some reason I'm not having much luck)

left soffit.jpg

right soffit (just framing).jpg

framing around box.jpg

Is there anything that anyone here would do differently w/ the wood framing?

Gonna use screws & glue to connect most of the timber together (brackets for certain joints) and also for connecting to the walls, ceiling & floor.
I guess I should also use caulk for filling the gaps right?

For air circulation, is it fine to have the air go in through the bottom hangers, up through speaker port, through a hole in the upper shelf to the top hangers, then out the opening at the ceiling, like in my design?
Or is there a particular reason why some people go for the 'hole in the baffle' route?
Here's an example of someone doing it my way:



Also, as you can see in the pics, I've sealed off the speaker sections from the tall middle section with a sheet of plywood - should I do this with the upper/lower hanger sections as well or is it fine to have them exposed to the middle part?

WhatsApp Image 2021-02-12 at 12.26.33.jpeg

[gullfo]

your approach as shown in the drawing should be fine. one thought on the angle of the speakers - do you need to flatten that bit or are you going to be listening in that close? it seems like a tight angle for a narrow space.

[snailboyawayyy]

one thought on the angle of the speakers - do you need to flatten that bit or are you going to be listening in that close? it seems like a tight angle for a narrow space.

Angle is 29.4°, listening position is at 35%, speakers are 55% of the room width apart and aimed at ~13" behind the head. Is that not okay?

[gullfo]

should be ok then.

[snailboyawayyy]

Hey y'all, here's a belated update on the soffit mounts








As you can see I haven't gotten very far, considering how long its been since my last post. If you want to avoid wasting as much time as I did on the framing, heed the following :
(These are probably pretty obvious to most of you guys but whatever, someone out there might be as stupid as I am)

1.) CHECK YOUR SPIRIT LEVEL IS ACCURATE
This is so important and so easy to do. Good God, the time I wasted correcting all my uneven studs After realizing the level I was using for all my framing was slightly off I borrowed 4 more spirit levels from friends/family and checked them all - they were all innacurate. In the end I bought some new Stabila levels (apparently this is the brand to go for).
Also, get yourself a range of lengths (Stabila do sets - I bought a 4-piece set with lengths from 25cm to 1.8m)

2.) INSPECT YOUR TIMBER BEFORE YOU BUY
Another huge waste of my time that could've been easily avoided. You'll notice in my photos that I've yet to put in the front 4 king studs - I realized yesterday as I was putting them in place that 3 of them were warped (2 were crooked, 1 was twisted). If you can, go to a timber merchants and inspect the timber yourself before you buy. Check it's not warped (bowed, twisted, crooked or cupped) and check the dampness & end grains to ensure it won't warp later (look up how to do this). This does mean you'll have to figure out how to transport the timber yourself
I decided to try pressing my warped timber into shape with a bunch of concrete blocks, but if this doesn't work I'll have to go buy some new timber


I have some questions for the stages ahead, if any of you guys are able to help me out:

- For the insulation I'm told the UK equivalents for OC 703 and 705 are Rockwool RWA45 and RW3 respectively. What should I use for what? Can I just use RWA45 for everything (hangers, loose insulation, panels etc) or do I need to use RW3 for certain things?

- For the acoustic hangers, would this be okay to use for the core?
https://www.builderdepot.co.uk/12mm-ivo ... -8ft-x-4ft
(The UK equivalent for Homasote is Sundeala which is v expensive. Waka used the above for his hangers: http://www.johnlsayers.com/phpBB2/viewt ... d+#p154262)

- Would plywood be fine for the box housing the speakers? Or would MDF be better?

- I'm not sure what to put in the middle section. Should I make some really long, thin acoustic hangers, like in the design below? Or should I just fill it with insulation? A lot of soffit designs I've seen don't have anything at all in the middle section, so maybe I shouldn't worry too much about it?


Thanks!