Need Advice on how to Stop Walls from Resonating

Discussion in 'Archived Threads 2001-2004' started by Jason Bell, Jun 29, 2002.

  1. Jason Bell

    Jason Bell Stunt Coordinator

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    My walls are made of metal studs with standard drywall then covered in plaster. The problem is that I can literally hear them resonating. Not exactly sure what frequency its at. But I believe it would be considered as midbass. It is really annoying and now that I notice it more it is turning my system into a low volume experience in order to avoid it. This added layer of noise or harmonics not sure what you would call it is causing me listener fatigue. My speakers are only about a foot from my front wall but I dont have much more room to pull them out. So what type of room treatment can fix this? I'm about ready to hire a contractor to come out and redo the front wall with different materials. Not sure this would be very cost effective though.[​IMG]. Any advice would be appreciated I would like to get a couple more DBs out of my system.
    Forgot to mention my floors are concrete covered with carpet so the resonations are not starting in the floor and moving into the walls.
     
  2. Joseph_W

    Joseph_W Stunt Coordinator

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  3. Cees Alons

    Cees Alons Moderator
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    Redoing a whole wall could turn out to be very drastic and costly - especially if you find out later it is something else that's resonating.
    You have to investigate a bit further to be more certain about the real cause.

    It cannot be through the floor, but what about the ceiling? Is it a lowered one? How are the walls fixed to it (or vice versa)? The frequencies you hear resonating may be harmonic overtones (because of the distortion) of the frequencies that cause the resonations. If you switch off your sub, is it gone? Is it possible to feel the resonations if you put your fingertips superficially to parts of the walls?
    If it appears to be something inside the wall - yes then you may have to redo it, but that isn't highly probable in the first place. If you can feel the surface resonating, try to see if you can stop it by pushing tightly. If you can, perhaps the drywall could be fixed better than it is now by a set of bolts all through it (pulling both sides firmly together, so to say).

    Bottom line is: before anything else, find out more facts. It's difficult to locate a resonance by ear alone. It may even originate from another place (i.e. the ceiling). But it's the (wrongly) moving parts that have to be fixed in the first place!

    Cees
     
  4. Joseph_W

    Joseph_W Stunt Coordinator

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  5. MarkPayton

    MarkPayton Stunt Coordinator

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    I am also interested in finding a solution to a similar problem. My HT is set up in a downstairs (concrete floor covered with carpet), L-shaped room, with the HT backed up against a load-bearing exterior wall. The front speakers and sub are facing, open space (the L) on the left, a large window on the right, and a hollow (drywall) interior wall directly ahead. An SVS 20-39CS is corner-loaded in the front along the window/load-bearing walls. The couch is a large L-shaped couch along the window and reflective wall (facing HT of course). (Will try to post a diagram of the room and of the room response graph as soon as I figure out how :b)


    Anyway, I have used an RS meter to plot the room response, and it seems I have a lot of resonance between 20 and 50hz, ranging between 19 and 23.5db above the calibration level. I have a BFD on order, but I'm wondering what room treatments might also to reduce the reflectivity of the window and interior wall, which I suspect are creating the resonances. At this stage, the resonance isn't so bad except on certain movies, but for example Jurassic Park seems to have most of its bass in exactly the peak resonance frequencies for my room, making it sound unbearably boomy in my room.

    How hard is it to fill a wall with insulation? Would hanging a tapestry and installing drapes along the window help?
     
  6. Cees Alons

    Cees Alons Moderator
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    Mark,

    If you can determine which frequency is especially "resonating" as you call it - more probably this is a standing wave! - you could probably find out which two parallel surfaces are the culprit, having a distance equal to the wavelength.

    Cees
     
  7. Chu Gai

    Chu Gai Lead Actor

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    Certainly you'll have to determine if it is a standing wave or the resonance of the wall. I have the following to add, should the issue be a wall and one opts to fill the wall with insulation.

    To begin with, even after one has filled a wall with insulation, there is still likely to be a low frequency resonance that will require some sort of treatment. To fill a wall with insulation one first needs to ensure that the process does not pose an environmental hazard such as formaldehyde. Once you've confirmed that, then you'll find there are two typical ways to get the insulation in: spray and pour. Sprayed in insulation is no where near as dense and stif as poured-in material. It is usually applied before you've put the wall in. Excess foam is shaved down to the studs. Poured-in foam is done by drilling holes in the wallboard and there'll be holes drilled in between the studs. Depending upon the contractor, for some also specialize in acoustic treatments apart from the insulating properties of foam, there are likely to be grades of material varying in their density. If that is an option that you'll be seriously considering then please ask for product data, foam samples, and several customers that you can call to check on their satisfaction. I also would check my local Better Business Bureau to see if there have been any complaints. This will result in a significant deadening, although as I said, I'd expect there to be some low frequency components that'll have to be tamed in other ways.
    Hanging carpets, etc., draperies, cellular blinds, will have only a neglible effect on the low frequency components.
     
  8. Jason Bell

    Jason Bell Stunt Coordinator

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    I'm almost positive it is the wall resonating. The way my wall is there is an indent into the wall 8x6x2 HxWxD. They call it a media center it just lets you push your TV or entertainment center inside it so its not sitting out in your room. Seemed like a great idea when I was looking at models.[​IMG] I have my two speakers on either side of this indent. I was back behind my Entertainment center messing with wires when I noticed it. Almost sounds like a really fast humm sound. I then took my SPL meter back there and it was like 15db louder back there and real real boomy. When I placed my hand on the wall in the back you can feel pretty large vibrations. This is only at 80db at the my listening position about 8 ft away. Is this a Standing Wave causing this? I really noticed it in the opening bass line in Darkside Of the Moon right after the hearbeat. I also can hear some high frequency echoes back in there to. I think if I just treat all the area inside this with acoustic treatments it would be a big help. I dont really have any room though to place those Cylinder Bass traps but I saw a product that looks kinda of like crown molding but its still foam and I have no idea how ugly this stuff would look installed in my living room even though it would be inside this indent. What disc would you recommend for finding out what exact frequency its at. Right now I just have S&V Home Theater Tune Up and I dont think it has a signal sweep. How do these work do they just play a tone and show on the screen what frequency its playing? Thanks for taking the time to help me.
     
  9. Cees Alons

    Cees Alons Moderator
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    Jason,

    From your description that certainly looks like resonations. I think you should concentrate on fixing, in the sense of dampening those moving (trembling) parts better.
    BTW in principle there's nothing wrong with an "entertainment center" like that!

    Cees
     
  10. Joseph_W

    Joseph_W Stunt Coordinator

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  11. Jason Bell

    Jason Bell Stunt Coordinator

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    I dont know Cees you should hear what it sounds like when your back there it really is messing with the sound. There are good things about this design. It keeps there from being anything between my speakers and it looks nice. Today I pulled the speakers out about three foot from the front wall and I could not believe what a difference it made. This puts the speakers almost in the middle of the room.[​IMG] I'm just gonna go without spikes so I can pull the speakers out when I want to listen to music and I'll just settle with reduced quality for movies, for now. I didnt notice a difference with or without spikes anyways. My father is really good at construction so I'm gonna ask him what we could do to stiffen that wall. But I dont think this will fix the bass hump I'm getting and definitely not the High frequency echoes. Does anyone have experience with these different foams? I found a local dealer of Auralex so I might see if theyll give me a few sample pieces to see how well it works. After I try it I'll post back. Thanks again everyone.
     

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