SOUND ON SOUND

[Helmutcrab]

Hi Everyone,

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 . I will also show how i add eye screw supports , show the insulation and paper being fitted and the panels being sealed with rivets.
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

[zenguitar]

As Peter is keeping this as a build diary I've offered to put it up as a sticky thread so it is easy to find for anyone coming back regularly to check progress. The great thing about a build diary is that it shows some of the problems that crop up during a project and how they are solved.

So good luck Peter.

Andy

[thefruitfarmer]

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

I used chicken wire and 4 years on there is no saggage, it is tricky to fit, you have to stretch it and get it taut really with grippers and staple gun it in to a wooden frame.....there must be an easier way of getting some kind of light mesh on the metal frames....

With the placement, build the first batch and then get a few on the walls, move them around a bit to hear what they do. Then you will know whether you really need to make a couple of smaller traps. You can cut Rockwool with a bread knife and if you pick a day that is cold, damp and not windy for the cutting and fitting in the frame then the fibres won't blow about too much.

I would guess that, because of the relatively small size of the room and the L shape, that you would need to go floor to ceiling on both front corners. There may be a way you can fit them in without cutting, any corner is valid in the room. However, I would probably go for making a couple of smaller traps, it will look better when done and will make the fitting slightly easier too.

[Folderol]

I used chicken wire and 4 years on there is no saggage, it is tricky to fit, you have to stretch it and get it taut really with grippers and staple gun it in to a wooden frame.....there must be an easier way of getting some kind of light mesh on the metal frames....

An easy, but tedious way to tension chicken wire is with a pair of broad-nosed pliers. After getting it moderately tight in the first place, just run up the mesh in a straight line giving each wire a little twist. You will be surprised how much this can tighten things up.

P.S.
Learned this helping a bird breeder friend build a flight cage

[Helmutcrab]

Hi thefruitfarmer and Folderol,

Thanks for the advice.

I am really hoping i don't have to use chicken wire as it seems like hard and fiddily work and i don't know how i could fix it to a metal frame without adding wood. I think there are other types of mesh but it would increase cost and cutting this to size and securing it to the metal would significantly increase labour time.

Could anyone tell me if tightly stretched hessian would stop the insulation ( 60 kg/m3 ) sagging in a frame ( like the ones i've made ) without using front/rear face support ?

Thanks,

Peter

[thefruitfarmer]

mesh fencing or maybe something like this place?

I was thinking you could some drill holes in the sides of your metal traps, several pairs, in each corner and some along the long sides too. Then you could use some cable ties to hold a mesh fencing panel under some tension, sitting behind the front lip, so the edge of the mesh fencing panel and cut cable tie ends are not visible.

You should be able to get a roll of mesh fencing the same width as the short side of your traps. I would say the plastic fencing would probably do the job but you would need to tension it. Otherwise you could get a metal grid, which is rigid anyway, and just superglue it in place.

[James Perrett]

The nice thing about using Cara fabric is that it is slightly stretchy which makes it dead easy to get a good looking finish on the panels. I know that it is too late now, but fixing it with staples into wood is fast and easy - not quite sure how you are going to fix the fabric on your frames.

James.

[Helmutcrab]

Thanks thefruitfarmer, i might end up having to do that but im going to have a think about other options first - if there are any !

Hi James,

I would use hot glue with a glue gun to secure fabric tight to rear of frame but i'm now thinking it might have been easier over all to use wood - stapling fabric and fixing eye screws for wall mounting would be a lot easier and quicker. I can still use the metal frames for floor standing corner panels so its not too late just yet. The reason i didn't use wood was price and weight, for 6" deep frames is a lot of wood but i may be able to make a double frame system with corner and side pieces to join the two together into one frame. Problem is i ain't much cop with a saw and don't have the tools.

Can i ask you how you made your traps please - did you compression fit the rock wool into wood frames and then just pull and staple fabric so its tight over the front face ? I'm just wondering if you used any face support - like the chicken wire or wood strips ? Are any of your panels angled forward in corners ( wall - ceiling ) or used as ceiling panels so as to promote sagging ? If so any sag ?

Any help appreciated,

Peter

[Folderol]

Disclaimer:
I've never tried what I'm about to suggest!

If you have a stretchy fabric, you can make the equivalent of cushion covers to slide over the frames, with the open edge at the back along one of the long sides, then just blind stitch this.

To hold everything together, and make it look pretty too, get an upholstery needle, some coarse thread, and cloth covered buttons. As well as making classy looking dimples, the thread going right through everything button-to-button will stop things moving and/or sagging.

P.S.
I did do a minimum amount of upholstery repairs very many moons ago

[Helmutcrab]

Thanks for the help so far fellas. This is an update.

As you know i was wondering how to stop the insulation from sagging long term for ceiling and wall-ceiling panels. I found a thread where fiberglass joint mesh tape was used. I used superglue and Duck tape ( apparently superglue only works when oxygen isn't present ). I pulled on the tape once glued to one side to check its hold and it was very strong.



The problem was when i tensioned the mesh it pulled the thin frame in quite a lot and this prevented me from getting the same tension on both mesh strips ( unless i measured exactly the pull in for both - too fiddly ). The other problem is it would bring in the centre of the frame too much, causing compression of the insulation. I then realised the tape strips could be added on the outside of the frame once finished and the side supports would increase rigidity to some extent. However, Ethan Winer mentioned small wood cross braces ( up to one inch ) in the central field of the panels are not a problem even in the RFZ. This is reassuring to know especially for the overhead panels.

My next problem was how to hang the metal frames. I found D-rings with 4 mm holes which i could use with 4 mm pan bolts, nuts and washers from www.ukpictureframingsupplies.co.uk . I got hanging cord from there too.

The pan bolt would go inside the frame ( with the washer ) and would avoid any internal intrusions to the insulation. The next problem was where to put the D-rings, as unlike wood frames the possition of these need to be set before the panels are riveted shut. The only way i could think of was to put one on the outer side ( in the middle ) on each side corner thereby using only two D-rings as support. This would enable the panels to be turned around ( if reflections are required ). However, this only allows the panels to be hung from the ceiling horizontally and not from the walls ( walls here are made wrong and not weight bearing ). It also does not allow them to be used vertically ( either hung from wall or ceiling ). The only way to allow for more hanging options ( should i ever move house and wish to hang from wall ) would be to use 4 D-rings on both sides of the panel ( at 20 % in from the top and bottom in vertical plane ). This method would have to be used on wall - ceiling panels anyway but having to do it on wall only panels is more work and would mean when hanging them from ceiling horizontally they would have cord on an angle which may have to wrap around the wall - ceiling panels above them in order to get to the available joists.

The metal frames take a full working day to structurally complete ( before insulation and final rivets are added ). This, combined with the problems of hanging, the pulling in from tensioning the mesh and having to attach fabric with glue made me try to make a wood panel to see if it was easier and quicker. Once one metal and one wood panel are finished and hung i can decide which type to use. By the way, total costs are very similar for both except for the purchase of rivet gun and tin snips for the metal panels. However, I do already have a power drill and screw driver.

I have to thank my local timber yard www.arbortimber.co.uk who came up with the following design after i explained my needs.



Dressed 2 x 1" timber is used for this. After dressing, dimensions are approx. 20 mm x 45 mm. In order to get a good right angle cut and not take forever, i got the timber yard to cut the wood @: 4 x 1240 mm , 4 x 600 mm, 8 x 60 mm. Due to tolerance whilst cutting the actual lengths were: 1238.5, 58.5 and exactly 60 mm. This last one i was very pleased about as it had to be exact to maintain panel and insulation depth. The other lengths would allow for a small amount of compression to hold the insulation in place.
As you can see four independent frames were made. Each one using only two 70 mm screws either side to attach the 60 mm corner pieces. Plenty of wood glue was used on both adjoining surfaces ( i had 4 failures from only using on one surface initially ).



I tried some hand clamps to hold the pieces in place but they were not strong enough so i used my dad's hands instead who was helping me for the day !

Next i had to glue and screw one short and one long frame together in a right angle. I bought a corner clamp for £2.99 but when i checked it was indeed a right angle with my metal square i found it was off.



And then it broke !



I also bought different metal drill bits ( both normal and titanium ) from the same manufacturer which made this cheap clamp. Unlike the clamp here, the drill bits were not much less than good brand competitors and every single one snapped within a few goes. This is very dangerous and non of these products are fit for purpose. I won't name and shame but suffice to say if you stick to Dewalt and Bosch you won't go wrong with drill bits.

I then had to come up with another way of getting a right angle. I do not have a work bench so am using the dining room table with another old table top on top of it. My dad was a carpenter many moons ago and had the idea of screwing a long thin mdf panel to the table top at both ends - checking it had a true right angle first :







I then screwed a small piece of wood at exactly 60 mm down from and at a right angle to the top of the mdf :



I then made sure the two frames joined at a right angle :



Marked the wood to indicate the width i have available to screw into :



Then i marked the position the screws ( 50 mm ) would go into. Six screws are used to secure each corner. From the markings you can see that each piece of wood will have 2 screws in it. One on the outer side and one on the inner side. This is very important as these 50 mm screws have to go past the sides of the 70 mm screws ( making the individual frames ) that are perpendicular to them, otherwise they would run into the 70 mm screws and not bed fully. This makes the frame corners strong and negates the use of supports thereby allowing the insulation to fit properly without needing to be cut or compressed. Remember to number the frames ( 2 and 2 on the top in this case ) in case you don't get time to screw them together.



Next apply plenty of wood glue to BOTH adjoining frames.

Then counter sink and drill using a 3 mm drill bit and power drill through the first piece of wood and slightly into the second so the 50 mm screws can get a hold and without splitting the wood.



Next screw in the screws :



Once i had joined two corners together i had two L shaped frames. I positioned these together :



In order to get the full frame length level on the table i had to use wood and wedge supports at the other end :



This time however i stopped once i had drilled holes as the intention was to put the two L shaped frames around the insulation, then glue and screw to finish it. This would allow me to not disturb the insulation by pushing it down into a finished frame. However i may just do that as it will be difficult to work outside without a solid bench/table and i want to maximise my time outside when i do eventually get a good day.
It is still snowing and is now very windy but as soon as i can get outside i will pva spry the insulation, glue the paper to it and fit it in both metal and wood frames.

Here's hoping for a good day soon !

[James Perrett]

Can i ask you how you made your traps please - did you compression fit the rock wool into wood frames and then just pull and staple fabric so its tight over the front face ? I'm just wondering if you used any face support - like the chicken wire or wood strips ? Are any of your panels angled forward in corners ( wall - ceiling ) or used as ceiling panels so as to promote sagging ? If so any sag ?

Sorry, I missed this first time round...

I just used a simple frame made of 2x1 with triangles of plywood in the corners to keep them square. However, I was using thinner rockwool than you. I've not noticed any sagging from the panels at 45 degrees between the wall and ceiling.

Hopefully you can see more by looking at my studio build on Facebook at

http://www.facebook.com/media/set/?set=a.1580972001141.77410.1140919619&type=3

James.

[Helmutcrab]

Hi James,

That looks like a great studio. You don't seem to have used any face support for the panels - even the ones on the ceiling ? Thats reassuring.
What density rockwool were you using please ?

Fruitfarmer and co. ,

Ive finished my first wood panel and added insulation - it was so windy the insulation blew away - thats the North East of England for you. You can't have it sunny without the wind. I gave up on waiting for a good day - it may never come !.

I added the insulation after i had made the frame. This was the worst way to do it as it got compressed and damaged at the sides where i had to use a scraper to get it in and was impossible to get the 50 mm slab to sit just right . Still its a usable frame.

Ive now learned you need to finish the panel with screws but then take the screws out of the last two corners and put the two L shaped frames around the pva sprayed insulation then glue and re-screw the last corners.
Im very happy with how the wood works so i will be using only wood panels.

After making the wood frame i realised the metal frames just don't have enough support to prevent the insulation from being handled whist moving them around. There is a 1" lip all around the sides of the wood panels that can be handled and protects the insulation.

So, ive scrapped the metal panel idea - they would work but just not as well as the wood. They take a couple of hours longer to build and changing hanging options are not available once sealed. Getting the final rivets in would have disturbed the insulation too much also. This became obvious after handling the insulation - i forgot just how fragile it was.

Also, i think i will be spraying a 1 : 20 PVA glue solution twice (before and after panel completion ) for the rest of the panels instead of 1: 10. 1 :10 just seemed to release too many thick patches.
Im bulk ordering the wood today for the rest of the 24 panels and will report back once ive got some finished.

Cheers

Peter

[thefruitfarmer]

Also, i think i will be spraying a 1 : 20 PVA glue solution twice (before and after panel completion ) for the rest of the panels instead of 1: 10. 1 :10 just seemed to release too many thick patches.
Im bulk ordering the wood today for the rest of the 24 panels and will report back once ive got some finished.

You can add a drop of washing up liquid to the PVA solution, it makes it work better ( I forget exactly why but if you search the stickys the reason will be there )...

I should not worry too much about thick patches on the mineral wool slabs, it is all going to be covered anyway and it will serve the purpose of keeping the fibres contained...however, if you DO find one coating of 1:20 and a second coating of 1:20 PVA works easily to get an even covering then you might have found a good trick....

Pity about your corner clamp. I paid about £15 for a pair of them and they made the job so much easier.


Will you soon be in a position to mount the completed traps and have a listen before building the remainder?

[Helmutcrab]

Cheers thefruitfarmer,

I added a few drops of washing up liquid but still seemed a bit thick.

I think i will be fitting the panels straight into their place once made. I need to get some material covering now.

Can i ask you exactly what dimensions you used for the wood to compression fit around the insulation ?

I used 2 mm off the 1240 x 600 mm ( 1238 x 598 ) because thats what the wood measured after it was cut, but it was a little warped on one side so it ended up being 4 mm down in the centre. It all seemed a bit tight but i think that was because i pushed the insulation into the double frame instead of finishing the panel around it.

Much Obliged,

Peter

[thefruitfarmer]

I added a few drops of washing up liquid but still seemed a bit thick.

I think i will be fitting the panels straight into their place once made. I need to get some material covering now.

Can i ask you exactly what dimensions you used for the wood to compression fit around the insulation ?

I used 2 mm off the 1240 x 600 mm ( 1238 x 598 ) because thats what the wood measured after it was cut, but it was a little warped on one side so it ended up being 4 mm down in the centre. It all seemed a bit tight but i think that was because i pushed the insulation into the double frame instead of finishing the panel around it.

How are you applying the PVA/washing up liquid? I used a cheap plant sprayer and the 1:10 solution was as thick as milk. So long as it goes through the spray nozzle and dries to a crust it will be fine.

I would get the finished panels up ASAP. Then you will be able to assess the effect they have, move them about a bit and then work out how many more you will need.

I did not actually compression fit around the insulation. I just built the frame to have internal dimensions of the Rockwool slab, fitted chicken wire to the front face and then dropped the slab in place. It was at this point I sprayed the slab with the PVA solution, let it dry and then covered it with fabric.

The slab was a snug fit, but with the 60kg per m3 rockwool there is enough give for it to not be a problem.

The compression fitting is not essential. So long as the air can vibrate the fibres in the mineral wool, thus converting the sound energy in to (a small amount of) heat then the trap is doing its job. However, the compression fitting would probably give you a better finish.