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[Sonovo]

I'm in the process of building 'superchunks' in the front corners of my room.

The hypotenuse across the corner is approx 2m. Length from apex (inner corner) to outer points of the triangle is approx 1.4m at the floor.

I'm using Glava mineral wool A37, 15cm thick, 2x60cm wide (I've left the two adjoining rolls loosely connected, allowing me to almost span the corner with one width). This product was chosen on the advice of an acoustician.

I've built a wooden frame of 2x2" beams around each corner, which I plan to cover with fabric when the insulation is in place.

My problem is that as the stack grows in height, everything gets unstable and risks toppling over. So I'm wondering what methods others have used to stabilize things.

Two solutions spring to mind, but I don't know if either is recommended:

1. Find some longish wooden dowels or metal rods, stick them through the stack at several points to provide some support and fasten the stack better together. Add more as the stack grows in height. Will these resonate or otherwise cause problems?

2. Get some long wooden slats (like 1x2" or so) and fasten them to the frame between the floor and ceiling to retain the insulation, it leans out and the slats stop it. I'll allow enough room so that they don't get in the way of the fabric covering. 2 or 3 should do it, I don't suppose this would in any way affect the audio absorbtion of the mineral wool?

Anyone else using loose mineral wool (i.e. the fluffy stuff, not the compressed mats) for corner treatment? How are you keeping things stable?

Oh, one other detail that makes this a bit extra complicated is that my walls are slanted, they slant in towards the ceiling from the floor, at about 10 degrees or so.

Picture enclosed. It isn't as obvious there, but after adding a few more layers the whole things starts leaning ominously...

Cheers,
Thor

[J.F.Oros]

Hi Thor,

This is I think the simplest way of building SuperChunks : two vertical wood studs (triangle section) and wire stapled between them to keep the wool triangles in place, and then you can easily cover it with the cloth of your choice.

[franman]

Thor,

The stability and even more the settling over time, is why we usually hang our batts that are used in deep traps. We use unfaced R11 or R19 fiberglass typically behind a 4" layer of rigid fiberglass friction fit into the framing.. The batts are hung from the ceiling by using a nailer or some sorts to staple them into the ceiling. They don't have to be so densely packed and some space between them is okay. This way, you can be assured that over time, the entire cavity will remain damped as opposed to the insulation settling over time and leaving the top third (or more) un damped... Just another approach to think about....

[Tom C]

Thor,
I predicted the same problem and divided the corner traps in
3 segments, each about 32" high.
Each segment has it's own (wooden) casing and fabric.

The advantages I see:

- no need to build these things inside your room (dust!) because
 they are easy to transport.

- they are movable, that's great if you ever have to change your
 room or if there's a problem with the wall/electrics/whatever
 in the wall behind the traps.

- when all 3 are stapled one single light removable frame with the
 fabric you'll finally see comes in front of them, so it looks
 the same.

If you're not in a hurry I can post a picture of one of this
(empty) segments next week.

Tom

[zmix]

my 2

[Sonovo]

Thanks guys for many good suggestions.

J.F., I think your idea is a good one, but isn't practical for my application because of the slanted side and back walls, and also because the fibreglass is quite loose and doesn't stack well. If I was using compressed mats I think it would be an excellent suggestion. The wire back and forth was definately a good tip that I will look into.

Fran, you're the man. I hadn't even thought about hanging them, but it strikes me as being obvious and probably pretty simple. I won't get as much material in the corner that way however, will that affect the efficiency of the absorber? We're shooting for sub-100Hz frequencies (distance of a line from inner corner out to bisect the hypotenuse is approx 1m!). I'll also be building a Helmholz resonator to target one specific frequency in a rear corner of the room, in addition to the other treatments (superchunks, added absorbtion in the existing suspended ceiling, additional absorbtion to first reflection points). Could I leave what I have (stabilized in some way first) and then just add hanging lengths for the upper half of the space? Would that work ok?

Could you give me a bit more info as to how I can hang these? I have a sheetrock ceiling, I don't know if staples will hold a 2.5m length. And won't the weight of each length tend to tear it away from the fastener?

Tom - that's something I also was considering, not really with a casing, but some sort of shelf (like zmix suggested). I think one shelf for each insulation layer would be overkill (and maybe have some acoustic side effect), but dividing the corner into sections with a shelf or even just a few thin braces to relieve some of the weight of the insulation would seem a good thing to try.

Any other ideas, tips or suggestions? I think I'll have a look at the local builders mart and see what materials are most readily available and will allow me to get this finished as quickly (and professionally) as possible.

Cheers,
Thor

[franman]

Thor,

First, to make sure you do have some material at the boundaries, you can apply 2-4" directly to the corner walls.. Glue or mount however you see fit.

TO hang longer batts, I would put up something on the ceiling to use as a nailer and then use small peices of wood lattice (thin strips used in light weight fences and trellices) to 'pinch' the top of the insulation against the nailer and nail this strip with the end of the insulation behind it, to the ceiling nailer. Does this make sense??

[Sonovo]

Fran,

indeed it does.

I thought about it and asked a few builders what they would do in a similar situation, ending up with a long length of thin nylon cord and screw-eyelets screwed into the wall just behind the fabric cover frame. This afternoon I tried it one one of the corners, and in fact it actually works really well.

So I've done up the other corner similarly and will have the insulation finished by tomorrow, the next thing on the list is getting the side framing members shaped to fit and finding a big enough piece of fabric to use to hide the whole thing.

Then it's on to the back wall, at which point I should be 'done'. For this time. Oh wait, I forgot the Helmholz resonator as well.

Any tips/URL for building the box itself? MDF? Plywood? Thin/thick? Glue or screws? Airtight box, or gaps ok? The actual port and length will be calculated after I build the box (to fit into a niche in a rear corner), which I'll be aiming for about 60 litre capacity.

Cheers,
Thor

[Sonovo]

Well, the stacks are stabilized.

Thanks for the suggestions. J.F.'s idea turned out to be the most practical for my situation, I used small eyelets screwed into the walls with nylon cord stretched between them like shoelaces.

Now to get the rest of the frame built and find a suitable fabric covering.

I do notice that the room sounds different. Not a night and day difference, but things in the lower mids and deep bass seem to have cleared up a bit as compared to previously. I'll need to measure again when it's all done.

Cheers,
Thor

[franman]

I'm sure Lars would agree (and SET).. build a Helmholtz Resonator like a ported reflex speaker enclosure... Use 19mm MDF and make the joints tight... glued and screwed is fine.... Fill it with loose batt insulation and tune up the port. Make sure they get installed at areas of pressure max (or at least high pressure)..

[Tom C]

franman wrote on Wed, 21 February 2007 07:49

I'm sure Lars would agree (and SET).. build a Helmholtz Resonator like a ported reflex speaker enclosure... Use 19mm MDF and make the joints tight... glued and screwed is fine.... Fill it with loose batt insulation and tune up the port. Make sure they get installed at areas of pressure max (or at least high pressure)..

Hehe, that's where I'm right now: one nasty 127.5 Hz peak
and all good (Helmholtz-) places are already occupied by
broadband absorbers.

I need one more room corner...

Tom

[Sonovo]

Hi Fran,

yes, that's pretty much what I thought, just wanted to make sure.

Stig Erik said I should aim for a minimum of 50 litres, I got a free aquarium brochure (with dimensions and capacities) and plan on making one approximately 60-70 litres. Well, without the fish, obviously .

With the Superchunks in the front corners, the rear corners are available for other tweaks. I have a weird 'niche' rear corner where we found the highest level of low bass when measuring the room. The frequency we spotted as being a problem (66Hz) was most pronounced there, and the corner niche is perfect for the Helmholz box, I'll build it to fit exactly in the available space.

Stig Erik will calculate the size and length of the reflex port when I'm finished building. I was unsure as to what materials and construction were appropriate, thanks for the info. Does it make any difference where the port opening points? I.e. can I cut the hole in the bottom (like some subs) and put it on spikes, so it just looks like a wooden box? Or should the port face forward, like a normal speaker would.

Looking at Tom C's response, I wonder if 66Hz is an uncommonly low frequency to find in a smallish listening room. The response in general was pretty good, at least as compared to some of the 'worst case' examples you see on many websites.

Cheers,
Thor

franman wrote on Wed, 21 February 2007 03:49

I'm sure Lars would agree (and SET).. build a Helmholtz Resonator like a ported reflex speaker enclosure... Use 19mm MDF and make the joints tight... glued and screwed is fine.... Fill it with loose batt insulation and tune up the port. Make sure they get installed at areas of pressure max (or at least high pressure)..

[Tom C]

Thor Legvold wrote on Wed, 21 February 2007 20:57

Looking at Tom C's response, I wonder if 66Hz is an uncommonly low frequency to find in a smallish listening room. The response in general was pretty good, at least as compared to some of the 'worst case' examples you see on many websites.

Is one room dimension about 5.15 m (202 inch)?

My room is 2.49m high, but acoustically (measured) it's 2.66m.
It's a nice way to find out what's between the visible wall and
the concrete/brick wall itself.

Tom

[Sonovo]

Approximately 5.5m between side walls. Since they're both angled and splayed, an exact measurement is pretty impossible. That's the nice thing with acoustic measuring .

My room is also about 2.5m high, but my monitors are line sources so I don't see a lot of reflections (or nodes) between ceiling and floor. The building itself is wood and drywall for the most part.

Cheers,
Thor

Tom C wrote on Wed, 21 February 2007 17:40

Thor Legvold wrote on Wed, 21 February 2007 20:57 Looking at Tom C's response, I wonder if 66Hz is an uncommonly low frequency to find in a smallish listening room. The response in general was pretty good, at least as compared to some of the 'worst case' examples you see on many websites. Is one room dimension about 5.15 m (202 inch)? My room is 2.49m high, but acoustically (measured) it's 2.66m. It's a nice way to find out what's between the visible wall and the concrete/brick wall itself. Tom