Small Studio in Porta Cabin. Advice please!

Dear all Greeting from sussex in England. I have read this excellent forum for a while & thanks to excellent info & contributions by very knowledgeable members, I am begining to understand some concepts of room acoustics when designing a studio. But so much more to learn! Some advice please! My present venture is designing a studio in the porta-cabin which is in the grounds of our property. The porta-cabin consists of steel frame & outer walls & floors are made of wood I believe. Inside is lined with plywood on the walls, with 3 inch cavity in the walls & ceiling filled with standard insulation. The underlying base appears to be wooden & has a linoleum flooring on it. The inside Length, Width & Height are 24' X 8.5" X 7' (7.3M X 2.59M X 2.14 M) respectively. Please see attached sketchup file which shows two doors & 4 windows as well. I am singer-songwriter & room will be used for recording vocals, tabla (small Indian drums), guitars & hand-held percussion, & then mixing as well. Nearest neighbours are well far away & there is no traffic noise. The only noises I will get will be of birds chirping & occasional neighing of a horse. And I am allowed to be as loud as needed. :-) As per the skp file, the monitors will be facing the long side of the room & listening position will be 0.382 of the length, 2 inches off the midline. The monitors presently sit on my custom made studio desk (almost) as depicted. The present insulation is already there in the wall & ceiling cavity & appears to be the standard stuff of nearly 2" thickness. So effectively, I have a hollow ceiling with insulation in the lower 2" of the hollow. My plan: My budget is upto £1000 (1600 US$). I will be making the stuff my self and am thinking following: 1. Floor-to-Ceiling triangular bass traps 60X43X43 cm in all the four room corners, as the corner door will always be kept closed. 2. Broadband absorbers on side wall reflections (120X60X10 cm) with front half being the fibreglass & back half being void. 3 ?Large broadband absorber or ??diffusor at the back (120X120cm) 4. Other bass traps as dictated by you guys & the room readings as soon as I am set up to take them. 5. Ceiling cloud if it will help in my situation with hollow ceiling. Do these make sense? As I will be recording vocals & acoustic guitar, I am thinking of making two 1.5M tall gobos which will be attached to each other with hinges, and will be on wheels. Could they be used to move appropriately when mixing, hence serving dual-purpose. Which area of the room can I use/develop for vocal recording? The material I am planning to use RS45Rocksilk by Knauf insulation here in UK. It seems to be comparable to OC703. Please chime in with your advice, criticism, directions. All will be gratefully received. Kind regards Hemant

Hi Hemant, and Welcome! Nice first post! :) A couple of comments: 1. That's a very long, narrow room, with an unusual ratio that fails all three BBC criteria for critical listening rooms, and has pretty poor modal spread in the low end. Have you considered splitting it into two rooms, and using the other one as a live room / vocal booth / storage room? I reckon you could improve your ratio somewhat, and get a second room to boot!

listening position will be 0.382 of the length, 2 inches off the midline.

Any particular reason for that? Symmetry is important if you want to get a good tight stereo image with decent sound stage. 2 inches offset isn't much, but enough to destroy symmetry. I also noticed from your SketchUp model that the desk is rotated about 3 degrees to the left. Any reason for that? Same problem: symmetry is important. I'd suggest that you should try to get your head back on the center-line, and also straighten up your desk.

The monitors presently sit on my custom made studio desk (almost) as depicted.

You might want to consider moving them to individual stands. Monitors on desks tend to do too unpleasant things. 1) They transmit vibration to the desk itself, causing the desk and everything on it to vibrate too, thus interfering with the direct sound from speakers to ears. Build massive, heavy stands, and decouple your speakers from them even so. Many people use hollow stands and fill them with sand to get the mass. This might also allow you to improve your speaker geometry. 2) They cause reflections from the desk surface, and also things on the desk, like the console, computer monitors, keyboard, etc. Better to move them back a bit behind the desk, to improve the angles.

Ceiling cloud if it will help in my situation with hollow ceiling.

It probably won't help with that, which might be an issue (resonance), but a you do still want a cloud at your first reflection point on the ceiling. A hard-back cloud at an angle might also help a bit with your major modal issues.

Do these make sense?

The basic plan sounds right, but I'd think about dividing your room to improve the ratio.

Which area of the room can I use/develop for vocal recording?

Build a wall across the rear section, and you get an entire vocal booth or live room! And you improve your ratio, too. :)

The material I am planning to use RS45Rocksilk by Knauf insulation here in UK. It seems to be comparable to OC703.

Looks like it should be OK, but it would be good to see their acoustic specs for it. Can you get those? I didn't see it on that link. - Stuart -

Soundman2020 wrote:

Hi Hemant, and Welcome! Nice first post! :) A couple of comments: That's a very long, narrow room, with an unusual ratio that fails all three BBC criteria for critical listening rooms, and has pretty poor modal spread in the low end. Have you considered splitting it into two rooms?

Thanks Stuart for the kind welcome & your comments. Yes, very long room with ratios almost in multiples. I have investigated diving into two rooms. I got the feeling the structure may not be strong enough to take the studs & 2 layers of plasterboard, and a door & maybe a glass window as this end is perched on a sort of elevation. I’ll take some more advice though. It’ll be great if I could, as a vocal booth will be excellent.

listening position will be 0.382 of the length, 2 inches off the midline.

Any particular reason for that?

I remember reading somewhere that exact centre of the room may not be perfect place but I guess I read wrong. So I am back to middle. Thanks.

I also noticed from your SketchUp model that the desk is rotated about 3 degrees

Thats more to do with my sketchup skills. I will try correcting but things got worse when I did last time. :-)

The monitors presently sit on my custom made studio desk (almost) as depicted.

You might want to consider moving them to individual stands. Monitors on desks tend to do too unpleasant things......Build massive, heavy stands, and decouple...... Better to move them back a bit behind the desk, to improve the angles.

I had a feeling about this. Feel a bit silly making that lovely studio desk with my own hands, before I planned it all in detail. I guess I’ll enjoy making the speaker stands too, as I did for for my Audio Note speakers for hifi listening. Sand & lead shot filled stands definitely work.

Ceiling cloud will probably won't help

OK! Ceiling cloud...scrapped. I am making good progress here aren’t I. :-)

Build a wall across the rear section, and you get an entire vocal booth or live room!

If the wall is not mechanically possible, then would that area still be preferred are for vocals or would the area behind the monitors be better? Also, what about the gobos being used as absorbers too? Thanks again. Please see pic for what I think are Knauf insulation absorption coefficients Kind regards Hemant

I got the feeling the structure may not be strong enough to take the studs & 2 layers of plasterboard, and a door & maybe a glass window as this end is perched on a sort of elevation.

So what is the floor made of then? And if that end of the room is a problem, structurally, then how about the other end? Maybe you could flip things around 180°?

I remember reading somewhere that exact centre of the room may not be perfect place but I guess I read wrong. So I am back to middle. Thanks.

Well, the center of the room us not the perfect place, for sure, which is why you want your ears away from the 50% point in all three dimensions, and why the recommendation is for 38% of room depth and to keep your head above or below the center, if possible, but when it comes to "side-to-side" measurement, think about that for a sec: Your ears are not where your nose is, nor are they on the top of your head! :) In fact, they are about 3 inches off to either side of the center line already, assuming that your nose is ON the center line. But doing it the way you had it, with a 2" offset, would place one of your ears about 5" off center and the other one practically right on it! So the best place actually is to keep your head centered left-to-right, which guarantees that your ears are NOT at the center of the room.

OK! Ceiling cloud...scrapped. I am making good progress here aren’t I.

Not really! You missed the rest of what I said there:! :) "but you do still want a cloud at your first reflection point on the ceiling. A hard-back cloud at an angle might also help a bit with your major modal issues." :)

If the wall is not mechanically possible, then would that area still be preferred are for vocals or would the area behind the monitors be better? Also, what about the gobos being used as absorbers too? Thanks again.

Gobos normally are absorbent on one side and reflective on the other (acoustically speaking) which is where one of the many rumored origins of the name comes from: some say they are called "gobos" because they GO BOth ways... But anyway, if you can't do anything wall building, then you probably have no choice and will have to just go with gobos on wheels, and set them up some place in the room that makes sense to you.

Please see pic for what I think are Knauf insulation absorption coefficients

That 76mm 48 kg/m3 stuff looks pretty good to me! I'd go with that. - Stuart -

Soundman2020 wrote:

So what is the floor made of then? And if that end of the room is a problem, structurally, then how about the other end? Maybe you could flip things around 180°?

It appears the floor is wooden (now hidden by linoleum). My present setup is 180° of the sketchup plan, & the reason I changed it was to achieve more symmetry behind the monitors.

your ears are NOT at the center of the room.

Gotcha! Simples, as you said.

OK! Ceiling cloud...scrapped. I am making good progress here aren’t I.

Not really!] You missed the rest of what I said there:! A hard-back cloud at an angle might also help a bit with your major modal issues."[/i] :)

Ok thanks. Clouds are back on. Sun's not gonna shine anymore, I guess. Sorry couldnt resist ;-)

But anyway, if you can't do anything wall building, then you probably have no choice and will have to just go with gobos on wheels

We'll see! I'll get advice from another builder. So, can standard gobos or any other kind of baffles serve a dual purpose for vocal tracking & room treatment?

That 76mm 48 kg/m3 stuff looks pretty good to me! I'd go with that.

Okay thats good. Is it better to make multiple absorbers in the room with 75mm insulation & 25mm gap behind or 50mm gap behind 50mm insulation? Apologies about the noob questions. I appreciate you taking the time. Kind regards Hemant

"Ok thanks. Clouds are back on. Sun's not gonna shine anymore, I guess. Sorry couldnt resist " 8)

Had a builder in advising on the build. He thinks there isn't enough support around the perimeter of my (planned) wall, to divide the room. Thats a bummer, as I had got into the idea of vocal booth again after Stuart's post. Anyway, in future I'll have an opportunity to move the studio to another part of the property with enough space; for now, i m here. Could anybody advise if rest of my treatments look OKish? I am planning baffles at first reflection points with 2" fibreglass in front of 2" empty space, also confirmed by a post by Ethan recently. I plan to use any good looking cloth, thru which I can blow air, for the front covering. I understand I don't need acoustically transparent cloth as a bit of HF absorption will not be a problem anyway. Also, my idea of making gobos which will also function as broadband absorbers when mixing - is that possible? Getting excited about this project now :). Will post some readings & pics in the future. Regards Hemant

Hi Guys & Gals I am almost ready to apply the acoustic treatments. The rockwool (RWA45 75 & 50mm) has arrived, the timber has been cut to size & frames are being made. The cloth, the varnish - its all a go! Plan is for chunky triangular traps in all four corners (60X43X43cm), 100mm 120X90 cm broadband absorbers at first side reflections, hopefully a light foam cloud to compensate for my rather flimsy ceiling, three more 120X60 and one 60X60 trap. Also, I am making two folding gobos based on John Sayers design (thanks John) - each gobo will have two sections of 120X40cm connected by piano hinges. When fully opened, these will do double duty in the room as absorbers when mixing. Any hoo, here is a reading from the mix position. I have reversed the position after a comment by Stuart so now I am facing north in the skp file. As this is my first time with REW, I am hoping I am taking the readings correctly before I go ahead any further. Please have a look & tell me what you think. The mic is ECM8000 & I had to use line in of my MBP as REW would talk to my Focusrite Liquid Saffire. Kind regards Hemant

you will definitely want to add a hard backed cloud to your list of treatments to temper the floor-ceiling response. for a test you could hang a 4'x8' 3/4" MDF panel sideways over your mix position angled about 15 degrees low in front high in back to see the result. assuming you see the deep responses shift toward flatter, then you'll add a 5/8" plywood layer to ensure it stays flat, then the cloth covered absorption on the front - 4" thick, and add a 4" absorber on the ceiling above the panel. you might need to trim the panel to make it fit so you have at least 12" or so around the edges. if you hang it on chains and hooks you can readily adjust the height and angle to find the right combination. you might make one flatter to the ceiling so you're creating a wave guide effect across the ceiling and adding some additional trapping in the "live space".

gullfo wrote:

you will definitely want to add a hard backed cloud to your list of treatments to temper the floor-ceiling response. for a test you could hang a 4'x8' 3/4" MDF panel sideways over your mix position angled about 15 degrees low in front high in back to see the result. assuming you see the deep responses shift toward flatter, then you'll add a 5/8" plywood layer to ensure it stays flat, then the cloth covered absorption on the front - 4" thick, and add a 4" absorber on the ceiling above the panel. you might need to trim the panel to make it fit so you have at least 12" or so around the edges. if you hang it on chains and hooks you can readily adjust the height and angle to find the right combination. you might make one flatter to the ceiling so you're creating a wave guide effect across the ceiling and adding some additional trapping in the "live space".

Thank you Glen. Appreciate your comments. Does this absorption have to be rockwool etc or could I use the profoam as linked below? I still need to work out the strength of the ceiling so I can push it accordingly. One design I have seen is where the rpg foam has been glued directly to a perforated mdf board & then hung with chains. http://www.rpg-europe.co.uk/products/Profoam/index.html. One more thing. Is there an advantage in putting a plastic film on the front of absorbers to stop HF absorption (except the ones at first reflections)?. Thanks Kind regards Hemant

do you have the foam or plan on buying? depending on what you are trying to treat with the foam it has its uses. yes, adding the plastic under the cloth is a good means of keeping HF alive but its not a good idea on your key reflection points...

gullfo wrote:

do you have the foam or plan on buying? depending on what you are trying to treat with the foam it has its uses

I haven't bought the foam yet. My only use of the foam, if recommended, would be as the cloud due to not too strong a ceiling. I have seen it being glued directly to say a perforated mdf board & hung as a cloud. Regards Hemant

you could use multiple smaller clouds hung on angles - thus still use the rigid back/rigid insulation approach which is likely to be more effective although if your ceiling will have a decent amount of transmission through the ceiling (low isolation) then a light cloud meant to only cut first reflections could be effective.