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Dear Forum, I have a home studio that I use for doing sound design for theatre, mixing acoustic theatre (theatrical installations and radio drama) and composing electro-acoustic music. I'm gradually diminishing the reverb in the room and I'd like some advice please on further steps I can take on a low budget (we renovated this house recently so I'm doing things slowly!).

The room has the dimensions: 480 x 350 x 250cm (15.74 x 11.48 x 8.2 feet). My monitors are Tannoy System 12 DMT IIs, a mid-field system. The dual concentric cones of these are placed 2m apart at ear-height with more than a metre away from the rear wall (the 350cm length) and slightly less from the side walls - I used a golden mean ratio - and they sound good where they are now, after having tries various positions in the room.

Behind the speakers is a large double doorway of glass (which can be folded away) and wooden shutters (Venetian style) which are generally exposed when I work. There's another glass/shutter window, a recessed doorway, hardwood floor, flat plaster ceiling and parallel plaster walls

Carpet is a bit of luxury item here in Brazil and I've managed to cover probably about 70% with rugs. I have 3 fairly lightweight foam mattresses placed on the walls to the sides and behind the listening position as a temporary measure.

At present, if clap my hands, I estimate the reverb time to be one second. I'd like to reduce this and I wonder what an ideal reverb time would be?

Right now I have the opportunity to buy acoustic wall panels left over from the refurbishment of a cinema. I don't their specifications yet nor the price, but wonder what sort of of wall coverage forum members would recommend? ie. what percentage - and where.

I'm not trying to isolate the sound, just improve the internal acoustics. I don't have a acoustic testing mic, but I can afford a Behringer if necessary. I have a sound meter though and software to play pink-noise, sine-sweeps etc.

Thanks!

Comments

Profile picture for user paulears

paulears Sat, 01/24/2015 - 03:55

I'd seriously suggest Rod Gervais' book - Home recording studio, which will show you quite clearly how to make the gizmos you need, but a few things come to mind. However, a couple of things come to mind straight away. You have 1 second reverb time, when you clap. Many churches don't have that much! So what is probably happening is the unpleasant reflections that come from multiple parallel surfaces. One thing is clear - you've got a less than developed idea of what sound treatment is and does. Carpet is pretty rubbish, and blankets and mattresses just soak up the very top end, leaving the medium and low frequencies to go straight through and reflect back. In Rod's book he explains how to identify and fix lots of room problems. Absorbers and traps are devices that will 'soak up' particular frequencies and diffusers are different devices to reflect sound in multiple directions. Some are wide band devices, others are tuned to soak up specific problem frequencies. Some big and chunky things, others foam of various depths. They all do different things and help cure different problems. All the carpet, blankets egg boxes and other stuff won't cure a rotten sound outside of their capabilities. Simple stuff like acoustic foam comes in various depths to do different things. In my studio, there's just one little area where reflections from the glass created a strange 'tinniness' if you stick a mic half way between the window and the wall - which ironically is exactly the best physical place for the mic! Just a couple of 50mm foam tiles cure this one, but in my edit suite, to do any recording, as a spill over space I have to be careful because it's boomy at the bottom end - and at some point I will get round this and put some treatment in. At the moment, audio recorded in there is bass light, unless I compensate.

Have a Google for some of these gizmos, but if you can work with wood, get the book, and build some of the designs in it.

Surdo Sat, 01/24/2015 - 04:28

"One thing is clear - you've got a less than developed idea of what sound treatment is and does"

Thank you for pointing that out, that's why I'm here, but I have to say that for want of anything better the carpet and mattresses help significantly. I'll have a look for the book, thanks for the suggestion. Yes, the walls are parallel and do give a nasty echo especially without any furnishings. I mentioned the acoustic panels from the cinema that are available, do you have any recommendations on where I can place these and how many square metres I might need?

Profile picture for user pcrecord

pcrecord Sat, 01/24/2015 - 05:36

+ 1 on Rod's book

Surdo, post: 424154, member: 47791 wrote: Carpet is a bit of luxury item here in Brazil and I've managed to cover probably about 70% with rugs. I have 3 fairly lightweight foam mattresses placed on the walls to the sides and behind the listening position as a temporary measure.

As Paulears said, every material affect the sound differently, the worst thing you could do is improvise and create problems.
Foam mattresses are not the same as acoustic foam. Acoustic foams have regular cell structure and accurate control of the cell size, higher air flow resistance, and therefore better acoustical absorption.

Other than absorbtion, you can go a long way with diffusion. Having a bookshelf in the room with uneven stuff on it will break a good part of room echo without taming random requencies.

Anyway read some theory before you invest. You will save some deceptions.

Surdo Sat, 01/24/2015 - 05:56

I did say "temporary measure" - but I'm sorry I mentioned the mattresses... a red rag to a bull it seems. The shutters at the front and on the window act as good diffusers and a diffuser on the two side parallel walls is probably a good idea. But again, any opinion on on the acoustic panels and where I can put 'em.

Surdo Sat, 01/24/2015 - 08:53

Thanks Space. My room is similar to the model in the link you sent. If I place bass traps, they would have to be at the front-right and at the left-rear due to a window and the main doorway (not the double doors). I'm not sure if diagonal bass traps will cause any problems. An overhead cloud is possible as are two lateral broadband absorbers. Here is a photo of the room:

(Mod edit: dead links removed)

Profile picture for user paulears

paulears Sat, 01/24/2015 - 11:03

The snag with using cinema size products is that they were probably built to tame the problems that space had, so if they are designed to 'suck out' certain resonant frequencies the room enhances, then the chances that you want the same are slim. On the other had they could be broadband products - but unless you can pull them apart and work out what they are designed to do, the best you can do is flood some pink noise into the room and measure the before and after response to see what they do - they could be good for you, or the reverse.

I had a pair of the Tannoys, the 15" ones, and I really loved them - BUT - they do have a rather specific sound, but if you like it, as I did, they're rather nice because the sound doesn't change very much as you stand up, which most conventional ones do. You're probably getting quite a lot of reflection back to those doors from the monitor - it's rather close to the speakers. what is on the wall where the camera is?

Profile picture for user Kurt Foster

Kurt Foster Sat, 01/24/2015 - 11:12

wow! that's a crazy hard room and an awful lot of speaker for it. the shutters aren't going to diffuse as much as you think. you need mass and depth for a true diffuser. get some sheets of ridgid fiberglass and put them on the walls in the corners. look up [="http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0CEcQFjAJ&url=http%3A%2F%2Fforum.studiotips.com%2Fviewtopic.php%3Ft%3D535&ei=L-7DVPfDH4mzoQSSlIK4DA&usg=AFQjCNGF1fDEww_-R6vFsgI47f0xii_JHg&bvm=bv.84349003,d.cGU"]superchunks[/]="http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja…"]superchunks[/]. what' is on the back wall?

here's what you need. oh, and get Rod's book. [[url=http://="http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&…"]Everest's[/]="http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&…"]Everest's[/] too.

Surdo Sat, 01/24/2015 - 11:53

Thanks. Yes, I like the Tannoys a lot. Here are the other walls:

Side left (with camera and window):

Front

Side right:

Rear wall showing recessed door:

(mod edit, removed dead links)

Profile picture for user pcrecord

pcrecord Sat, 01/24/2015 - 14:01

Some ideas from Sweetwater rep :

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And this guy which not everything he says is accurate but it's a starter ( he didn't threat the back wall which you should)

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bigtree Sat, 01/24/2015 - 14:57

Excellent video Marco. This guy is right on.

Okay, I have Real Traps and there are some differences. Lets find out if they matter?

Mine are 4 inches thick and have open slots all the way around the traps. They are excellent and look great and I do hang them off the wall so the waves get behind them. Real Traps are made of thin, well designed metal which may be lighter than wood.
They are costly compared but who cares if these work. Or, I don't mind paying more for and improved product.
I am an excellent builder, and plan on adding another 20 for my next room.

Here are the things I do wonder about.

Poplar from this area twists pretty extremely so just saying... But, its strong and will hold up if it doesn't start going wonky.

Maybe Ethan or Space knows how important RealTraps perforated sides are? Real Traps have slots cut all the way around them so Im assuming, the sound disperses?

Profile picture for user Kurt Foster

Kurt Foster Sat, 01/24/2015 - 15:46

i have a limited knowledge on this so i stand to be corrected.

the absorbers he built are broadband. but they are not bass traps. they are absorbers.

tuned membrane bass traps are designed to resonoate at specific frequencies and absorb them.

Profile picture for user Reverend Lucas

Reverend Lucas Sat, 01/24/2015 - 19:24

Until the expert gets here... absorptive bass traps are basically the same as broad band traps, but made thicker to extend to lower frequencies. Tuned traps are tuned by their geometry to operate at a specific frequency, and drop off in effectiveness as frequencies get further from the tuned frequency.

Surdo Sun, 01/25/2015 - 01:55

Thanks for the links. I'll watch the videos now. Posting here some info on locally available materials:

Still waiting on information on the cinema material and I'm also trying to find a local equivalent to the "Owens Corning 703" fibreglass wads (importing is not usually a viable option due to high taxes - usually 100% - and delays), but here are some options that are available for acoustic foam:

1. This one is typical of the acoustic foam available here. 26Kg/m3 at R$25 per square metre. 35mm thick when "open" and 45mm when "closed", which I assume means 2 panels back-to-back.

http://produto.mercadolivre.com.br/MLB-618976479-espuma-acustica-antichama-100x100mx35mm-laudio-fabricante-_JM

2. A made-to-order cloth-covered material with a choice of colours and easily mountable from top. R$32 per square metre. I was interested in this, but looking further, the foam, "D33", seems to be used for mattress construction:

http://produto.mercadolivre.com.br/MLB-617984126-espuma-isolamento-acustico-_JM

3. Bass traps made of "Lã de Rocha" - which I believe translates to "rockwool". Cloth covered wedges, 144Kg/m3, with the dimensions (faces of the wedge) of 80cm X 43cm X 32cm. Pricey at R$240 per unit.

http://produto.mercadolivre.com.br/MLB-621321342-bass-trap-em-l-de-rocha-144kg-m-tratamento-acustico-rtr-_JM

4. I found this rockwool manufacturer in São Paulo that has a site in English. See the products link. I don't know if they sell direct to the public but perhaps this might be a cheap option for bass traps or broadband absorbers?

http://www.rockfibras.com.br/en/index.html