I would like to share with you my Studio Acoustics Build Diary. I have been doing some reading on the subject for a few years now and after reading some DIY threads in addition to Zukan's DIY sticky, i thought i would have a go myself for better or worse.
I would like to give a big thank you to Ethan Winer of www.realtraps.com, Alexander Reynolds of www.gikacoustics.co.uk, and sos forum contributor thefruitfarmer who have answered all my questions thus far on the subject and without whom i would not have felt confident enough to try this project. Thank you also Steven P. Helm from whom i got the idea of using a metal frame.
As a cautionary note to anyone reading this and intending to maybe use some of the ideas mentioned here - This is a DIY work in progress and i do not know if it will be a success or disaster yet !. I may end up doing things completely different.
My room is an odd L shape with a sloping roof (but not in a good way) all around. Internally the room walls are single skin 12.5 mm plasterboard with 100mm isowool behind and between an independent wooden frame (was a very bad idea). The ceiling is 2 layers of 12.5mm plasterboard on 400mm spaced joists with 100mm rockwool inbetween. The floor is 1" boards on 75mm celotex. There are no windows or doors into other rooms.
Here is a basic layout with dimensions :

(I drew the vocal character the wrong way around)
To help understand the odd shape of the room with regards to the ceiling, here is a crude 3 D sketch :

Here is the room looking into the mixing area. You can see the speakers positioned centrally :

Here is another line drawing, this time of proposed broadband absorber panel placement around the mixing area. ( ceiling cloud transparent ) :

Looking away from the mix position :

Looking into small part of the L shape. You can see access door here :

I've used the sos bass staircase to assess the peaks and troughs at my mixing position. I fire the speakers down the longest room length and have tried them at different positions from the wall and from each other but have found there is always a slight trough around ~80hz, a peak at about 125hz and then a very large peak at ~150hz, with almost as strong peaks occurring after this (plus some troughs). There is possibly a very small reduction in the severity of these by offsetting the mixing position by about 6" to the left side wall but its nothing substantial. I then went all around the perimeter of the room whilst listening to the bass staircase test and the worst places (other than the corners) seem to be in the middle of the wall directly behind the speakers at the current mixing position, the side walls here, and also the wall behind the drums (these had the snare wire off, silencing pads on, and a thick pillow in the kick).
I realise the room is a very poor starting point for a recording and mixing room. The goal is to get usable results from the room and work with its limitations once the low end problems are reduced. There is a real lack of symmetry everywhere but it is all i have so i have to make the best of it and i feel very lucky to have a dedicated music space. Having used acoustic panels before in better rooms than this ( which isn't saying much ! ) i know it takes a fair few to make a difference and that mineral wool falls apart when handled unless it is properly supported. Because of the shape and construction of the room i think i will need a lot of broadband absorbers to greatly improve things.
My plan is to make the most effective lightweight (but strong) broadband panels i can make with a budget of less than £500. They need to be the same size as the mineral wool slabs (to avoid cutting and waste) and be able to support the rock mineral wool insulation to stop it from shedding, sagging and deforming over time. It must not be permanently fixed so i can take them down and transport them should i ever move. For these reasons i decided against using the corner super chunk design (despite it being a little more effective).
I have decided to make all the panels the same basic design which uses a steel frame. I hope to make 25 or 26 panels eventually ( including four ceiling cloud panels ) with the following room placements to cover as many room corners (wall-wall and wall-ceiling) as possible to force some symmetry as far as the absorption is concerned.
I have chosen to use Knauf ecowool universal slab (rock) as it does not have voc gases :
www.knaufinsulation.co.uk/en-gb/products/rock-mineral-wool-slabs/universal-slab-(rock).aspx
After speaking to Alexander Reynolds i decided to make most or all of the panels 6" deep instead of 4" and at a density of 60kg/m3 for wall to wall and wall to ceiling placed panels. Discussed here :
www.soundonsound.com/forum/showflat.php ... art=1&vc=1
I would achieve this depth by pairing one 100mm slab with one 50mm slab. For ceiling cloud panels i decided to use a 75mm 100 kg/m3 slab to face into the room ( due to increased structural rigidity ) with one 50mm 60 kg/m3 slab on top. This will give me 12.5 cm deep panels.
As a DIY alternative to using FRK (foil reinforced kraft paper) fiberglass slabs, Ethan Winer suggested bonding parcel wrapping paper/card on the face of the slab/panel which looks into the room instead of FRK. This can greatly improve low end performance of bass traps :
http://www.ethanwiner.com/density.html
Because i don't think there are any useful wall reflections in my room i have decided to make it as dead as possible for recording (with the intension of adding ambience artificially (convolution etc). I asked Ethan if there is any improvement in low end absorption if the paper side is turned around to face the wall instead of into the room, and as long as there is an air gap the answer is yes. I then decided that all panels i make will have paper bonded to the back of them. This will give me the option of keeping the room dead or turning some of panels around so the paper faces into the room for increased bass attenuation and some upper frequency reflections should i decide the room is too oppressive. Panels in the reflection free zone (RFZ) at the mixing area will only have the paper facing the walls.
After reading an article by Ethan, i decided the best air gap size from the walls is the same as the depth of the panels themselves ie 6" in this case (for panels parallel to the wall).
Im not great at DIY but saw this design (by Steven P. Helm) and thought i would have a crack at it :
http://www.radford.edu/~shelm/acoustics/bass-traps.html
I have used the same basic method outlined in this link to construct all my frames. Any extra details, methods and materials needed for the panels will be described on this thread.
Here are the types of tools needed (plus a rough saw). I will again go into specifics here once i explain how i make the panels :

Unfortunately, the very light weight angle beads Steven used are no longer available and i could not find anything suitable despite an extensive search. I did try to make a panel out of 25mm flange metal angle beads but there was not enough metal surface left at the corners to rivet corner posts :

I then tried Richter metal channels (3M length by 25mm flange, 0.7mm thickness) :


The main problem with these channels is that they are angled at about 110 degrees instead of 90, which made the insulation fit poorly and sag in the frame.
The other problem is 0.7mm metal is difficult to drill and results in a frame too heavy for my needs.
I wanted to use GA1 www.british-gypsum.com/products/gypframe_metal_products/gypframe_steel_angles.aspx
Unfortunately, these have been replaced by FA1 :
Here is a frame made from FA1 (240 cm x 2.3 cm x 0.55mm thickness ) :

And here's more :

One side of the Frames don't have rivets added to the corner posts or side supports yet to allow insulation to be added.
British Gypsum GFS1 fixing strap (240 cm x 7 cm x 0.55 mm thickness) was used for the side supports.
In my next few posts i hope to show you how i made these panels in detail by making more of them, as i forgot to take photos of the process so far

However, the frames were made indoors and the insulation has to be added outside. Unfortunately, its the dead of winter at the moment and snowing so i am unable to see how the insulation fits into the frames i have made. Having already built 5 frames without knowing if the insulation fits properly ( i just couldn't get outside ), i can't make anymore until i know the insulation fits right and final rivets can be secured.
I am aware that mineral wool sags over time and i am now concerned that the front face of these panels does not provide enough support for the 60 kg m/3 insulation i have chosen ( particularly when fitted at the wall - ceiling corners ). The flange on FA1 is only 2.1 cm internally which is not much support at all around the periphery of the slabs. I think i also read Max mentioning that even denser insulation will sag over time. This will be a problem for the ceiling placed panels also. I am now wondering how to avoid this sagging using these metal frames. I know chicken wire was used on bass traps in Zukan's build but that is probably not an option here. My initial idea was to wrap the front and sides of the panels in 4 oz polyester wadding to attenuate high frequencies ( to counteract the effect of pva ) and assist in fitting the final covering ( like Steven P. Helm did ) and then use heavy duty hessian (potato sack material) pulled tight and glued to rear of frame to avoid sagging. The rear side slab of panels (50 mm slabs ) will be spray glued and have paper stuck to this which may increase rigidity a little ?.
In the long term, I am not convinced this will prevent sagging and putting metal bars or wood supports across the face of the panels will upset the acoustic properties especially for the RFZ.
I have a few questions :
1. Can anyone give me advice or experiences with regards to the issue of sagging ? Would some small thin wooden cross members work or be necessary ? ( stuck to inner side of frame ).
2. Do the ceiling cloud panels need to be 100mm + deep with regards to the ceiling being sloped to some degree. ie does the slope reduce bass modes ?
3. What do people think of my proposed panel placement around the mixing area ?
Im not sure about angling the vertical upper corner panels. My thinking was to avoid having to make a 3 ft panel for the smaller corner as two 4 ft panels don't fit and also to cover as much of that corner (wall - wall and wall - ceiling area ) as possible. Im also not sure it would fit in with the other panels in such close proximity. Its certainly close.
Also, any advice or experiences regarding anything else mentioned here is welcome.
Thanks,
Peter