Designing & Building My Soffit Mounts

[gullfo]

looking good.

• 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.

[snailboyawayyy]

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: http://www.johnlsayers.com/phpBB2/viewt ... 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)?

HANGERS.jpg

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?

[gullfo]

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

[snailboyawayyy]

thicker insulation 50mm

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

[gullfo]

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

[snailboyawayyy]

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

[snailboyawayyy]

How's this for the hanger layout?

Hangers from Above.jpg

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:

lining.jpg

100mm deep on the 2 walls & ceiling, 50mm deep on the 'floor'

[gullfo]

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.

[snailboyawayyy]

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?

Hangers from above 2.jpg

(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:

Baffle Height.jpg

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:

L hanger (w baffle).jpg

L hanger (no baffle).jpg

I'm already doing something like this for the bottom hangers, due to the step:

step.jpg

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

[gullfo]

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? ) 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.

[snailboyawayyy]

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? ) 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?

[gullfo]

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

[snailboyawayyy]

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.

Housing Box 1.jpg

Housing Box 1 (w speaker).jpg

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?

[gullfo]

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.

[snailboyawayyy]

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?)