Designing & Building My Soffit Mounts

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: (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) 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?

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.

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?

should be ok then.

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 :cen: 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: viewtopic.php?f=10&t=21269&p=154262&hilit=Core%3A+12mm+Ivory+Insulation+Board+Aka.+Softboard+#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! :D

looking good. [list=]the RWA45 should be good all around just fill the center top to bottom with the RWA45 the ivory board should work plywood will work, MDF is a bit denser and somewhat self-damping. decouple the speakers from the box so leave some space in the box to accomplish that. [/list]

Cheers Glenn!

the RWA45 should be good all around

Coolio. How thick do you think the insulation should be for lining the inside of the soffit cavities? In this thread Stuart recommends 2" at least: viewtopic.php?f=2&t=19690&hilit=hangers+apart&start=90#p150872 Also, in the below image John recommends a 12mm core with 25mm insulation on either side, but other people here have said that 50mm is better (i.e. thicker panels)? Notice he also says the hangers should be spaced 150-200mm apart, though other people have said they just need to be close enough without touching. What do you think?

thicker insulation 50mm, and spacing - just enough apart so they're not touching.

thicker insulation 50mm

Just so we're clear - I should use 50mm insulation on both the hangers and the lining around the hangers?

if you can go deeper on the liner - 100mm that would be nicer but the space is at a premium.

if you can go deeper on the liner - 100mm that would be nicer but the space is at a premium.

Ok I'll see if I have space to make the lining deeper Thanks for all the help so far Glenn! It's v much appreciated :yahoo:

How's this for the hanger layout? 12mm core, 50mm RWA45 on either side. 21mm gap between the hangers Angle is 40° (according to Stuart & Gregwor this angle tends to work well, though they're not entirely sure why) And here's the lining: 100mm deep on the 2 walls & ceiling, 50mm deep on the 'floor'

nice but now you have a couple of hangers which are really too small and the rest need to be shortened to accommodate the 100mm on the front... if you haven't built the hangers yet, i'd suggest trying pink insulation in the pocket and see what your response looks like, it's not a huge amount (2 rolls?) and if it's truly not work then perhaps a membrane trap would add the necessary absorption.

nice but now you have a couple of hangers which are really too small

Hmm I figured even very small hangers would be beneficial to the trap. How bout this orientation? (Gap between hangers is now 1.2cm. Small hanger at the end is probably unnecessary but I figured I'd include it so you know what it looks like. I remember Stuart & Gregwor both said having the hangers parallel to the side walls was a suitable alternative to the 40° orientation)

and the rest need to be shortened to accommodate the 100mm on the front

100mm on the front? The front of the upper hanger cavities will only have fabric (and maybe thin plastic) covering it, no? The bottom hanger cavities will have the plywood + insulation part covering it, but I figured it'd still be worth making hangers for them, even if they had to be cut smaller to fit Or did you mean insulation behind the top of the baffle? I was thinking the baffle could end right where the top cavity begins, like so: The speaker is almost in the center of the total baffle (if u include the plywood + insulation part). Wouldn't this be fine? Even if the baffle had to be taller than that, and have 100mm insulation behind it, couldn't the hangers just be cut in an L shape, like so: I'm already doing something like this for the bottom hangers, due to the step:

if you haven't built the hangers yet

Haven't built them yet but I have bought 3 sheets of the 12mm insulation board, so would quite like them not to go to waste (hangers won't fit anywhere else in my room)

i'd suggest trying pink insulation in the pocket and see what your response looks like

So superchunk it? What's the difference between pink insulation and rockwool? I may do something like that for the bottom cavities, as the hangers would have to be smaller and L-shaped if they're going to fit, maybe making them considerably less effective

pink = 24Kg/m3 - semi-rigid typ 48Kg/m3. if the rockwool is closer to the pink stuff - basically ok. on your drawings you have a yellow band on the front edge of the hangers which to me indicates a layer of semi-rigid in front (which is ok by the way) but if that's not what that means and it's just an overlay of other layers (is it legal to say that? :lol: ) that's fine. parallel to the wall is fine because the sound entering will be forced to follow the panels regardless, and the radiation pattern of the LF will ignore the directivity of the panels in most cases. the important aspect is they are of enough size to effect the wave guide function and hang loose enough to be able to be very slightly moved which can improve unit absorption efficiency as the very slight movement is more energy consumption when operating.

pink = 24Kg/m3 - semi-rigid typ 48Kg/m3. if the rockwool is closer to the pink stuff - basically ok.

Ah good to know! The rockwool is 45kg/m3 - do you generally recommend using lower density insulation for filling superchunks? I was just gonna use the RWA45 for everything

on your drawings you have a yellow band on the front edge of the hangers which to me indicates a layer of semi-rigid in front (which is ok by the way) but if that's not what that means and it's just an overlay of other layers (is it legal to say that? :lol: ) that's fine

Ah right, yeah I should've said earlier but the yellow bands are part of the top plate of the wooden frame, so there's nothing obstructing the hangers at the front of the cavity.

parallel to the wall is fine because the sound entering will be forced to follow the panels regardless, and the radiation pattern of the LF will ignore the directivity of the panels in most cases. the important aspect is they are of enough size to effect the wave guide function and hang loose enough to be able to be very slightly moved which can improve unit absorption efficiency as the very slight movement is more energy consumption when operating.

Grand! I'll go with the 2nd design then (parallel to side walls) as it has a greater total surface area of hanger, unless you think 1.2cm is too close together?

1.2cm should be fine. yes, the RW45 given the small space should be fine. you have it.

So after many a cock-up, I finally finished my soffit framing. Phew! I actually thought I'd finished a few weeks ago but to my horror I noticed that the horizontal studs weren't parallel to the plywood platforms (which are cut at the correct angle), so I knew I'd messed up the angle somehow. I realized that in the process of cutting & fitting the front horizontal studs I was unknowingly bending the whole middle section slightly to one side. So I had to take out all the timber in the front, remove the horizontal studs, buy new timber, cut new studs, fit them again (this time making sure they were parallel with the plywood) and cramming it back in place. Anyways, here's where I'm at: I started working on the housing box design & I'm having some trouble figuring out the Sorbothane, specifically which duro to go for. I've adapted garethmetcalf's design (he has Mackie HR824 speakers as well) to include Sorbothane isolators on the top, bottom & sides of the speaker (i.e. inside the box). As there is no weight pressing on the top & side isolators, the pressure is created by the tightness/dimensions of the box. There will also be a 2nd leaf of isolators underneath the box, which will be pushed down with turnbuckles. So I started with the bottom isolators & input the following into the online Sorbothane calculator: Assumed % Deflection: 20% (apparently the ideal amount of compression for Sorbothane) Load per isolator: 13lbs (5 isolators underneath the 35lb speaker, with 30lbs of added pressure from above) Excitation Frequency: 35Hz (my speaker's cutoff is -3dB at 37Hz so I figured this was fine (most ppl use 35Hz so its easier to compare results)) And here are the results I get for each duro (adjusting the length & width of the isolators by 1/8" increments until the deflection is close to 20%): As you can see, the 2 duros that yield the worst % isolation are 30 and 50 (you'd expect the isolation to increase with each duro upgrade but no, it dips at 50 duro for some reason) Here are the results when I use 6lbs (for the isolators on top of the speaker): Similar results. So why are 30 & 50 duro the most popular choice for people trying to float their speakers? Why not use 70 duro, as it clearly has the best % isolation? Is this because the isolators would be too thin and thus more likely to collapse to one side? Well then surely 60 duro is the next best option? Even 40 yields pretty decent results. What's even more perplexing is that some people here contacted Sorbothane engineers and were recommended 30 duro for floating speakers??? Which one do you guys think I should go for?

the size and shape values are changed significantly you increase the durometer. so instead of larger pads with soft material equaling some number, you have very tiny pads which of course don't transmit much, so small soft materials based on the mass of the speaker unit may need more quantity to reach the desired spring... however since you also don't want the speaker shifting even slightly, the larger soft pads are also less likely to shift compared to tiny pads (degrees of motion etc). so contemplate say 4 pads which are roughly 25x25mm - 50x50mm and 10mm-20mm thick to determine the right spring values with the correct durometer for those. also, you can then use semi-rigid insulation all around to provide damping of the box and some of the speaker itself instead of rubber units all around - to increase the "mass" on the lower units, you can also consider soft top pads with a plate and bolts to apply additional pressure to tune.

the size and shape values are changed significantly you increase the durometer. so instead of larger pads with soft material equaling some number, you have very tiny pads which of course don't transmit much, so small soft materials based on the mass of the speaker unit may need more quantity to reach the desired spring... however since you also don't want the speaker shifting even slightly, the larger soft pads are also less likely to shift compared to tiny pads (degrees of motion etc).

Okay, I think I understand. I'll probably go for 40 duro then as it's a good compromise between % isolation and loaded area. I feel like ~70% isolation is decent for 35Hz

to increase the "mass" on the lower units, you can also consider soft top pads with a plate and bolts to apply additional pressure to tune.

I guess I'm just wondering what's the maximum amount of pressure I can apply to the top of the speaker without damaging it (I was thinking roughly the same weight as the speaker itself would be a safe bet i.e. 33lbs?)

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

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 :cen: 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

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.

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: 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: (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?: (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: 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 :thu:

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.