Designing My Soffit Mounts

#16

that's a seriously thick baffle.

Yeah that was Stuart's advice from your thread: http://www.johnlsayers.com/phpBB2/viewt ... ck#p142698
"The front baffle of a soffit needs to be very massive, and very rigid. Mine often end up 40 r even 50mm thick, built up from various layers."
But maybe I'll settle for 36mm, I think that's what you did?

Bass radiates from the woofers outwards in all directions. The bottom edge of the baffle is much nearer the centre of each of the woofers than are the sides or top.

Hi Starlight!
So my understanding was that the plywood sheet just below the speaker (that will have insulation on it) was effectively an extension of the baffle, as well as an absorber for reflections from the mixing desk.
In this thread (https://www.johnlsayers.com/phpBB2/view ... &start=195) Stuart recommends that the speaker be placed 3/5 along the width (slight asymmetry on the baffle plate to offset a possible reinforcement of resonances due to modal actions of the plate) and 1/4 of the height of the baffle. I did wonder why the speaker had to be that far off center height-wise, but if you include the plywood + insulation part below the speaker as part of the total baffle, then it ends up being around 1/2 of the total baffle's height (this would be a problem if the total baffle was one solid plate, but because it's made up of two separate, smaller baffles (the thick baffle plate and the plywood + insulation below it), modal resonance isn't an issue).

Will this shortest distance be the defining limit of an infinite baffle? What distance do these woofers need for an infinite baffle?

Well there has to be an opening of around 30cm in height at the bottom of the soffit, so I guess you could say the total baffle starts where that opening ends? And then the distance from this point to the center of the speaker will be around 1/2 of the total baffle's height, so then you figure out the total height from that?
So if the acoustic axis is usually 120cm off the floor, then by this logic a baffle's height (incl the plywood+insulation part) should always be around 180cm?
I sound unsure because I am

someone pls tell me the actual correct answer

The largest possible baffle you could have for the room is one that extends from floor to ceiling, but for rooms that need extensive bass trapping (you could argue all rooms need it, but especially small rooms) it's recommended that you include bass trap cavities at the bottom and top of your soffits which are exposed to the room (which in my case double up as air circulation vents for the speakers)

#17

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.

#18

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!

#19

Greetings,

If you can, go to a timber merchants and inspect the timber yourself before you buy.

Agreed.

We are lucky as our contractor always uses the same lumber yard, and they pick the best boards for him (clearly a win-win for everyone involved). Even if we're doing the bulk of a project ourselves, our contractor will order the lumber on his account and have it delivered (we pay him directly up-front, so he's never out a dime). Always good to have a friend in the business...

All the best,

Paul

#20

snailboyawayyy wrote:Source of the post 1.) CHECK YOUR SPIRIT LEVEL IS ACCURATE

Yes .. and also buy a laser level! So much better ... I use mine for everything, including resetting the measurement mic in the percise same position each time.

#21

ALSO

For the acoustic hangers, how thick should the insulation be on either side of the hanger? In the diagram below it suggests 25mm but I've seen Stuart & others recommend 50mm. Which is better? More panels with thin insulation or fewer panels with thick insulation?

In this thread Stuart says "1" is fine. 2" would be great, if you have the space to do that"
http://www.johnlsayers.com/phpBB2/viewt ... le#p146749
But I don't see how that works - if you're using 2" then you'll simply use less hangers. There's not a minimum number/surface area of hangers that I should use, is there?
What's more confusing is in another thread, Stuart says this:
"That would work, but it doesn't need to be that thick. You can use 2.5cm thick insulation on each side. That allows you to get more hangers into the same space. On the other hand, given the expense of your core material, I can understand you wanting to make your hangers thicker! It will work OK as you are planning, so if the cost would be too high doing a larger number of thinner hangers, then it's fine to do fewer hangers with thicker insulation."
http://www.johnlsayers.com/phpBB2/viewt ... er#p146763
The implication here is that more (thinner) hangers is better, if one can afford it. So now I don't know what to think

The diagram below also says that the hangers should be 150-200mm apart but that seems like quite a lot (for the 25mm hangers at least). Other people have said you can have the hangers a lot closer so long as they're not touching. What do you guys think?

And here's an example of someone using 2" of insulation on their hangers:

http://www.johnlsayers.com/phpBB2/viewt ... &start=180

#22

Hi

These are exactly the questions I’m mulling at the moment and have found the same conflicting information.

I shall continue to research and will share my plans once I’ve formed them.

In the meantime watch out for that builderdepot online shop you shared- they don’t deliver to the whole uk.. you might be lucky.

I’ve found this product which I am hoping to find locally for my hanger cores: https://meyertimber.com/products/commod ... /hardboard

They gave me the details of a timber yard in Stoke on Trent that should stock it but it’s still an hour’s drive away from me.

There is a paper on hangers but the design isn’t the same either, it has more layers!! This is defo a confusing space.

Cheers
Gareth

#23

Just so you know Glenn (gullfo) from John Sayers suggested I go with 50mm on either side of the hangers & position them as close to each other as I can get without them touching.
He also suggested that the insulation lining around the hangers be deeper (100mm ideally)

These are exactly the questions I’m mulling at the moment and have found the same conflicting information.

I know right? Wish Stuart was still active so he could shed some light on all this

How did you do the hangers for your last studio?

In the meantime watch out for that builderdepot online shop you shared- they don’t deliver to the whole uk.. you might be lucky.

I was! Got 3 sheets arriving tomorrow along with a bunch of RWA45 :yahoo:

I’ve found this product which I am hoping to find locally for my hanger cores: https://meyertimber.com/products/commod ... /hardboard

Density is >250 kg/m3, maybe that's not high enough? I know homasote & sundeala are in the 440-500 range, but then maybe it just needs to not be more dense than that?

#24

I wonder what surface density you are wanting. Around the 500kg/m3 is pine, lighter chipboard and plywood.

#25

I wonder what surface density you are wanting. Around the 500kg/m3 is pine, lighter chipboard and plywood.

I have heard some people make hangers with ply, but it'd need to be fairly low density (conifer, maybe?)
Stuart has said that cork or thick cardboard can work too

#26

It is interesting that Stuart says cork and thick cardboard can work. I just checked my plans and my studio's designer has me down to use 18mm MDF, which means a surface density of a little under 13kg/m2. As hangers are also known as wave guides I guess their purpose is not simply to be a hanger for insulation like a hanger holds a shirt in a wardrobe; I feel sure as an amateur acoustician that their purpose is to help guide the sound waves so that they have a longer path in and out of the trap, making the trap more effective.

In my previous studio I used laminated chipboard on stands to get a 70cm deep rear wall bass trap. It worked really well and music I was familiar with now sounded clearer and with more precise stereo placement of instruments. Here are a few photos. After taking the first photo I realised they were angled the wrong way so turned them all 90 degrees.

Edit: let me add a link to a video of my studio designer, John H. Brandt, where right here he mentions 18mm MDF wave guides. He is talking here about ceiling traps.

#27

Hi

I didn’t really make many hangers for the last studio and I’m not sure how effective they were...

Starlight’s post about using MDF or ply makes me happy as I’d seen that elsewhere and it would be a load easier to just buy some ply and use it rather than go to Stoke on Trent for this sort of not quite homasote stuff...

I have bought many many packs of RW45 and this is what I used in my last studio for superchunk bass traps etc. I know the really loose stuff is recommended but it’s harder to use and the slabs or RW45 will mount into the ceiling bays much easier.

I’m therefore considering slicing some of those 100mm sheets into two 50mm halves for my hangers, or just trying to find some thinner slabs of something. Delivery charges for insulation is expensive so I’d rather use what I’ve already bought....

Framing looks good, by the way. I’m going to do mine in shorter pieces this time to hopefully alleviate some of the issues of warped timber. So I’ll build up to the first ‘shelf’, mount the speaker box, then frame around and up from it..

Cheers
Gareth

#28

As hangers are also known as wave guides I guess their purpose is not simply to be a hanger for insulation like a hanger holds a shirt in a wardrobe; I feel sure as an amateur acoustician that their purpose is to help guide the sound waves so that they have a longer path in and out of the trap, making the trap more effective.

Yes, this was my understanding too. I went with the ivory insulation board because Waka used it for his design (http://www.johnlsayers.com/phpBB2/viewt ... re#p151008) and because it has similar properties to Homasote/Sundeala (which is recommended by John/Stuart/etc) at a fraction of the cost. I wouldn't know if it makes any difference to use ply/MDF instead, though I have heard success stories. Interested to see how yours pan out

In my previous studio I used laminated chipboard on stands to get a 70cm deep rear wall bass trap. It worked really well and music I was familiar with now sounded clearer and with more precise stereo placement of instruments. Here are a few photos.

Interesting that your hangers are touching. I remember Stuart saying in some JS thread that hangers that are too close together can interfere with the panel resonance or bending wave resonance, and that the impedance mismatch at the front would be too high (i.e. it just acts like a bunch of porous absorption), but then like all things hanger there's v little science to back that up. Seems to have worked just fine for you?

I’m therefore considering slicing some of those 100mm sheets into two 50mm halves for my hangers, or just trying to find some thinner slabs of something. Delivery charges for insulation is expensive so I’d rather use what I’ve already bought....

Yeah I was considering doing this to get 25mm layers from my 50mm slabs, but I've decided I'm just going to go with thick hangers.

You might find this useful, epstudio used a homemade jig to split his rockwool:

(Here's his thread: https://www.johnlsayers.com/phpBB2/view ... 0&start=30)

Framing looks good, by the way. I’m going to do mine in shorter pieces this time to hopefully alleviate some of the issues of warped timber. So I’ll build up to the first ‘shelf’, mount the speaker box, then frame around and up from it..

Thanks!
Yeah that seems smart. I only went with long pieces cuz I figured it'd make the whole thing more structurally sound, but I wish I'd done it with shorter pieces now, or just bought better timber. Even some of the really short pieces I have are warping like crazy :cen:

#29

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 how I'm going to line the cavities:

That's 100mm deep on the 2 walls & ceiling and 50mm deep on the 'floor'

#30

Hi
I think your hanger layout looks good. I have seen recommendations for a greater gap between them than 21mm but as you say there’s little science about this. I think the key is that they can each move.

I’m very interested to see the results of these - hopefully you can do some REW measurements before and after. You’re ahead of me with your build!

Cheers
Gareth

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