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room treatment to reduce reverb/echo

Discussion in 'Room Acoustics / Isolation / Treatment' started by Surdo, Jan 24, 2015.

  1. Surdo

    Surdo Active Member

    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.

  2. paulears

    paulears Well-Known Member

    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.
  3. Surdo

    Surdo Active Member

    "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?
  4. pcrecord

    pcrecord Don't you want the best recording like I do ? Well-Known Member

    + 1 on Rod's book

    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.
  5. Surdo

    Surdo Active Member

    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.
  6. Space

    Space Well-Known Member

  7. Surdo

    Surdo Active Member

    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)
  8. paulears

    paulears Well-Known Member

    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?
  9. Kurt Foster

    Kurt Foster Distinguished Member

    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 superchunks. what' is on the back wall?

    here's what you need. oh, and get Rod's book. Everest's too.

    Space likes this.
  10. Surdo

    Surdo Active Member

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

    Side left (with camera and window):


    Side right:

    Rear wall showing recessed door:

    (mod edit, removed dead links)
  11. pcrecord

    pcrecord Don't you want the best recording like I do ? Well-Known Member

    Some ideas from Sweetwater rep :
    View: https://www.youtube.com/watch?v=FuRiqoNRDmc&list=RDFuRiqoNRDmc#t=2183

    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)

    View: https://www.youtube.com/watch?v=pf_7sC9wV8Q
    bigtree likes this.
  12. pcrecord

    pcrecord Don't you want the best recording like I do ? Well-Known Member

    View: https://www.youtube.com/watch?v=RqZPhfxSaTk
    Kurt Foster likes this.
  13. audiokid

    audiokid Staff

    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?
  14. Kurt Foster

    Kurt Foster Distinguished Member

    real traps are tuned membrane bass traps. the things that guy built in the video were absorbers. not the same thing.
  15. audiokid

    audiokid Staff

    Hmm, I thought they are similar. Whats the big difference, Kurt? I guess I should know. I just know I like them.
  16. Kurt Foster

    Kurt Foster Distinguished Member

    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.
  17. audiokid

    audiokid Staff

    I'm going to ask Ethan. Stand by...

  18. Kurt Foster

    Kurt Foster Distinguished Member

    ohh goodie!
    bigtree likes this.
  19. Reverend Lucas

    Reverend Lucas Active Member

    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.
    bigtree likes this.
  20. audiokid

    audiokid Staff

    And this is why, me liky RealTraps! :D :love:

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