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Massive mistake...flanking nightmare

Discussion in 'Room Acoustics / Isolation / Treatment' started by Noah Shain, Apr 18, 2015.

  1. Noah Shain

    Noah Shain Active Member

    Well...I built a studio on the 6th floor of a concrete building. I was dying for natural light and fresh air. I knew it was risky but I did it.
    You can all pause for a laugh here...
    Okay so, I basically built partition walls floor to ceiling. It's a two leaf system with about a foot between leafs. I left 1/4 inch gaps and caulked as described in many threads here. I did two door openings, also decoupled.
    The walls are 2 layers of 5/8 drywall with green glue between. The reduction of airborn sound is OUTSTANDING. I was meticulous in the construction and sealing and it worked great.
    Like a fool, though, I anchored the wall framing, floor and ceiling to the concrete building.
    Guitar amps, bass amps...barely a whisper outside my room. Drums, however, are easily heard resonating in the walls, ceiling and floor of the building. They are sitting on 2 layers of 1/2" plywood fastened together to make a 1" deck which sits on 2 layers of 703. This I got from the gervais book. So there is no impact noise from the drums themselves.
    It seems to me that what is happening is that the drums are vibrating my wall system which is passing directly in to the concrete structure. Does that sound right? Flanking 101?
    Okay. I am WELL aware of my error. My question is this:
    Will adding mass to my wall decrease the flanking noise at all? It's not very loud...just above acceptable. If I could decrease it even a small amount it would be worth the effort and expense. It's hard to work knowing I'm disturbing my neighbors.
    Like i said it's not TERRIBLE but it's there.
    Is there any hope for me besides starting over? Because I can't afford the time or $$ to do it all again.
    Can I expect ANY reduction in flanking volume or maybe lower the frequency which is transferring through the flanking path by making the wall heavier? Adding more drywall? And will additional green glue between layers help me or hurt me in this scenario? It seems I need a heavier, stiffer wall. Will green glue work against me since I'm not concerned with sound traveling through the wall to the air but in to the concrete.
    Again, I humbly own my terrible mistake but I'm hoping I might make an improvement, even if only a small one.

    Thanks gang
  2. DonnyThompson

    DonnyThompson Distinguished Member

    I can't answer your question(s) - because I'm not an acoustics expert... but as a person who runs his own business, I can present you with something to think about...

    Are you legally zoned to do what you do? If you are, and there are no restrictions that stipulate that you have to keep sound leakage to within a certain db - and as long as noise pollution coming in from outside your studio isn't a problem, then do you really need to be worried about it?

    Would the cost of the fix really be worth it - or, more accurately phrased, how much is it going to cost you to make improvements that might not even make a noticeable difference? So maybe you can end up attenuating by a couple db... ( I'm sure there's a way, there's always a way) but how much is it going to cost you to improve by that small amount? If you are looking for complete and total isolation, you might very well be facing an entire rebuild.. and again, I'm no expert, but that doesn't sound like it would be cheap. You need to determine how much it's going to cost you to reduce your leakage by what you refer to as "any reduction".

    Any reduction kinda implies that you'd be happy with even a half db of improvement - but how much is it going to cost you to get that? And, will it really be worth it?

    I understand that you'd rather get along with your neighbors than not, I think most people feel that way, but ... if you are legally zoned to do what you are doing, and you've already done more than what your local regulations may require, then there's not much your neighbors can do, other than complain to deaf ears.

    That being said, if you aren't zoned legally, or if there are laws which dictate noise levels, or you are hearing noises from outside that are getting in to your studio and it's negatively effecting your recordings, then that's a different subject altogether, and one of our resident experts will need to chime in.

    I was just attempting to get you to look at it from the POV of being a business owner, where revenue vs. cost and profit vs loss is your bottom line. ;)
  3. Noah Shain

    Noah Shain Active Member

    Thanks Donny. I appreciate the perspective.
    I suppose I'll see if I can make a reasonable improvement. If I can't I suppose I'll consider your perspective more closely.
  4. DonnyThompson

    DonnyThompson Distinguished Member

    I think that this is kind of the operative word here... "reasonable"... and finding out if the cost of making the improvements is worth making them, in terms of how effective those treatments may end up being.

    I guess what I'm getting at is, if it's gong to cost you 2 grand to improve your leakage by only 1 db or so... well, I'm sure you get where I'm going with the rest of that train of thought.

    OTOH, if you can improve your situation by maybe, say, 5 db or better, and for only a couple hundred, then yes, that makes sense and I think you should.

    But... past that, Noah, I'm not an expert in the field, so I can't give you actual acoustical / isolation advice.
  5. Noah Shain

    Noah Shain Active Member

    Thanks Donny
    I knew before asking that nobody could give me an accurate answer and I am certainly not looking for any promise or commitment.
    I was hoping one of the pro builders might simply chime in with an instinctive response.
    The simple question I COULD have asked is:
    Will increasing the mass of a wall system that is directly coupled to the floor and ceiling reduce the flanking noise?
    I was prepared for the answer to be "it might".
    I suppose I'm gonna give it a shot. Even a couple DB will make a difference in my scenario.
    If anyone has any helpful tips or tricks they'd be appreciated.
  6. Brien Holcombe

    Brien Holcombe Well-Known Member

    "Will increasing the mass of a wall system that is directly coupled to the floor and ceiling reduce the flanking noise?"

    No, it will not. If anything it will make it worse due to a solid partition that refuses to move and acts as a conduit for whatever transmissions enter the membrane
  7. Noah Shain

    Noah Shain Active Member

    Thanks Brian. Curious if you are speaking from experience? Mr Gervais advised me that it MIGHT do me some good, that it MIGHT lower the frequency of the flanking sound. I did not ask him for a commited definitive answer and he did not offer one. He only suggested that it might.
    Your answer seems very confident. I wouldn't presume to ask any professionals to commit to any solid answer here, being that I botched this project so thoroughly. Just want to compile as much solid info as I can before I take my next step.
    Thanks for taking the time.
  8. Brien Holcombe

    Brien Holcombe Well-Known Member

    The shorter the wall the more rigid it becomes, it will transmit sound to and from the acoustical environment. It will amplify or allow sound to travel like it was in a conduit. The taller the wall it MIGHT achieve a reduction as more mass is added. This in no way goes against what my friend Rod has said, it should be in line with his thinking.

    As you said, you botched it up...I wish you would have asked or displayed a design first, but it is what it is. I recognize that money is not always a driving force and the end result is the sought for goal.

    To correct something of the magnitude of this incorrect structure, you have to ask yourself how bad do I want it? Because you can throw good money after bad and still never achieve your intended results.

    I would submit that this interior acoustical wall needs to be modified, cut down, and an interior framed ceiling be placed on it in order to achieve the highest possible sound proofing or isolation.

    But even in order to do that we have to know is the interior framed sound proofed wall able to support the load? Is there a shear wall design that can support it?

    Too many questions after the fact, and as I understand it, these keywords may not help.
    kmetal likes this.
  9. DonnyThompson

    DonnyThompson Distinguished Member

    Brien is an expert, so you can trust what he says to be accurate, factual.

    I'm sorry to hear that there is no quick and easy fix for this, but at least you've gotten your answer, and you have also gained some valuable wisdom for any possible future projects you might undertake. ;)
  10. Noah Shain

    Noah Shain Active Member

    Thank you both for your thoughtful replys.
    I wish I had done a bit more research. I new just enough to hang myself here. Truly I wish I had hired a pro. If I had the resources I would not have hesitated to do so.
    Unfortunately I am forced by financial concerns to move forward with the existing structure. I make my living in these wonderful sounding rooms and my family does not currently have the resources to afford another option.
    Man... Concrete is one hell of a blocker of airborn sound! But one hell of a transmitter of flanking sound.
    Lesson humbly learned.
    I have 1 question that I hope you might venture to answer:
    Because my commitment is so total here I am going to move forward and add some more mass to the walls. Like I said, even a small improvement will make a big difference in my ability to work. The question is this: In my case do you think that MLV will help dampen the vibration of my walls and thus decrease flanking noise? Do you think Green Glue will help? Do you think more drywall alone is my best bet?
    Can you envision a "best" option for me?
    Thanks again for your time and thoughtful replys.
  11. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Why not just take a sawz all to the walls? It could probably be done carefully and neatly. maybe there is a way to secure your walls but maintaining a higher level of isolation. If your gonna break out the tools and drywall, I'd aim towards the solution. Or just live with it. Adding mass is a lot of work, and money, to diminish the return to a 'maybe' from knowledgable people sounds like a bad buisness move to me. I'm not an expert, but I am a professional audio engineer, and I observe how sucessful and un sucessful studios and buisnesses in general operate. just my humble 2cents.
  12. Noah Shain

    Noah Shain Active Member

    You're right, adding mass is a lot of work but demolishing and rebuilding is 10 times the work AND expense. Like I said above I'm not looking for a gigantic improvement.
    If i had unlimited time and money I would do what you're saying for sure.

    Thanks for your response.
  13. Brien Holcombe

    Brien Holcombe Well-Known Member

    The best thing, no harm intended, would have been to learn what it is you were wanting to do first. After the fact is always a pain. To build anything, you must approach it like it is your home and you detail everything and you understand every cost.

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