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Air or Insulation in Walls

Discussion in 'Room Acoustics / Studio Design' started by Mark All, Aug 11, 2015.

  1. Mark All

    Mark All Active Member

    We're planning on building a house with a basement, to include a music room. I can’t "build a studio" as such, just hope to optimize construction for better isolation than what a basement would normally have. I won't be building a room within a room or anything that involved. I plan to present the builder with options for them to assess for cost and practicality. The diagram on p. 63 of Rod’s book is helpful, and using RC-1 seems the best option if affordable.

    These are probably newbie questions, but this subject seems overwhelming at times, when we’re already challenged just building a house.

    Exterior walls of studio room: do I want insulation or air between drywall and exterior wall? Insulation seems logical, but I’ve read about the value of air.

    Interior walls: If we can only afford single walls, would using RC-1 on one or both sides still be an improvement? And fill this with insulation?

    Does anyone know of a resource discussing insulation and different materials for sound absorption (as opposed to treatment)? Like Owens Corning 703, 705, Roxul, Audimute’s sound absorption sheets (Cubase), etc? Products like QuietRock or Sheetbok seem way out of my budget.

    Thanks for any illumination.
  2. dvdhawk

    dvdhawk Well-Known Member

    This Noise Control Design Guide pdf from Owens Corning is a great one-stop primer. It has absorption coefficients and NRC ratings of some common building materials. But make sure you study and understand Page 9, which explains NRC, STC, and the limited usefulness of these ratings. They're useful to a point, but much of your concern should be with the uncharted frequencies in the two octaves below 125Hz (bass guitar, kick drum, keyboards). These are the largest, longest waves and the hardest to attenuate, and the most likely to bother the neighbors and anyone upstairs.
    kmetal, audiokid and Mark All like this.
  3. Mark All

    Mark All Active Member

    Thanks, dvdhawk.

    I'm hoping having 2 or 3 walls underground will help with the lows, and thinking about putting the absorption sheets on the other wall(s). The Audimute demo is impressive--even considering they're probably in a well-built studio to begin with. :)
  4. dvdhawk

    dvdhawk Well-Known Member

    I'm sure the Audiomute sheets do pretty well taming down highs and mids above a certain frequency.

    A long time ago we had a cool practice place below an office/apartment building that we used for almost 10 years. A couple of the original band members were related to the family that owned the building, and one of them lived in the apartment upstairs, so we knew we didn't need to worry about annoying the upstairs neighbor. The owners said if we were willing to clean the place out and make it livable, we could use the space for practice. Many truckloads of old construction hardware and trash later, we scrubbed the place up, and framed in a level wooden floor in half of the room, (the existing floor sloped significantly toward the far end of the tunnel). We put in some new receptacles and fluorescent light fixtures, and brought in a small practice PA and back-line we could leave there. [followed by a card table, a fridge, a pinball machine, dart board, etc.] The basement was completely below grade, with about a 40ft concrete-covered tunnel out the back of the building as the only access to the outside world. The walls of the tunnel and the walls of the basement were stacked sandstone and the floors were all concrete. There were no basement window wells anywhere, and the parking area right in front of the building was even paved. So we had a fair amount of dirt for insulation going for us.

    Eventually, my wife and I started renting a ground-floor apartment several hundred feet away, across the 2-lane highway. And since we had made ourselves such a nice (literal) bat-cave, we let some friends practice there once a week with their band too. The tunnel door was several hundred feet away and probably 20 ft. below the elevation of my front door. It pointed directly away for my place into a heavily wooded hillside. When those other guys practiced, all I could hear from my house was bass guitar. Was it vibrating through the earth, water pipes, drain pipes, porting out the tunnel, making the whole building resonate? I don't know, probably some of each.

    Nobody ever called the cops on us, or complained to us or the owners - but it was never a secret to anyone in our little village what day of the week we practiced.
    kmetal and audiokid like this.
  5. Mark All

    Mark All Active Member

    Bass does always seem to be the worst offender. Also, claustrophobia may involved.
  6. Brien Holcombe

    Brien Holcombe Well-Known Member

    Mark All,

    You are at the beginning of a very, very long journey. One filled with new concepts and ideas previously unknown to you and some others that will be reading your posts as you pursue your goal. In respect to that, we can all make better decisions with knowing where you are but also where you have been. I ask that you keep all your posts in one thread if they apply to this topic, The one you started about the "basement incident" would be perfect as a catch all for all posts related to this topic. You might want to consider changing the subject of that thread to something more suitable to long term description that would help others that are surely to come along behind you with the same types/kinds of questions.

    "Exterior walls of studio room: do I want insulation or air between drywall and exterior wall? Insulation seems logical, but I’ve read about the value of air."

    If you have read about the value of air it was in respect to interior treatments. When broadband panels are part of a treatment it is often recommended to affix the panels the same distance from the wall as the thickness of the panel. Say a 4 inch panel would be affixed with 4 inchs of air behind it. This increases the ability of the panel to reduce low frequency greater than if it where simply attached directly to the wall face.

    This is not to say that a 2:1 ratio is the final word. 3:1 ratio has been used as well, it just depends on the frequency(s) in question and what it will take to attack it properly.

    That said,
    "Interior walls: If we can only afford single walls, would using RC-1 on one or both sides still be an improvement? And fill this with insulation?"

    I have to submit that you are still on the first part of this journey. As you continue reading Rods book you should come across the term "mass/air/mass". This refers to the typical double boundary assembly used in high isolation ( sound proofed ) environments. A typical "room in a room" uses the mass/air/mass technique also referred to as a fully decoupled isolation assembly.

    In short it is a hard boundary, usually a framed wall with sheetrock on one side, then the air space, then another framed wall with sheetrock on the opposite side of the frame. Ideally you want the largest airspace that can be gained since this will lower the natural frequency of the wall assembly meaning you have to have a lower musical note to excite the wall. This also applies to the ceiling since it is just a wall turned on edge.

    Studies have shown that to get the highest possible transmission loss from a double framed assembly that insulation, regular residential type, should be used in the air space. This helps to stop the resonating that happens when vibration passes thru the wall panels and enters the cavity and reduces the ability to excite the air if it is (and it often is) entrapped.

    Understanding that a double framed assembly is just a hard panel attached to a frame with a decoupling mechanism and another frame with a hard panel let's look at RC-1.

    In a typical use RC is the decoupling mechanism that turns a single frame into a mass/air/mass assembly once panels are installed on one side of the wall assembly and directly to the Rc-1 on the other side.

    The problem is this. When you reduce the air cavity you raise the Natural frequency of the assembly so while you win, you sorta lose. The small air cavity reduces the assemblies ability to contain low frequency, the area in music that each one of us has issues with. Or maybe the neighbors have issue with.

    So taken that you are considering a basement let me recommend a few things after a little more discussion. An Earth damped concrete slab is considered one of the best starting places when trying to develop a high transmission loss recording or critical listening room. So having Earth damped walls should only increase the ability of this room to contain sound...high isolation. The weakest link in a typical basement is windows and door ways and the ceiling since the mass that it took to create the floor (concrete) and the walls (concrete) cannot be matched by light weight sheetrock/plywood and especially single pane glass.

    Like I said earlier, make the basement as tall as possible and as wide as possible and as long as possible and as post free as possible. This is not a sprint...it is a marathon.

    In general it can take 3 to 4 months to get a handle on the simple concepts that you will be working with. In order to convey these concepts to the persons that will be developing your home you should have such a good understanding of these that you can explain to them, should they be the ones to do it, how it is and what it is that you refer to and why.

    Trust me when I tell you this, what it is they know about house building has nothing to do with what we are discussing here. I know because I have done both.

    To represent how fast things can get out of hand...

    The foundation of anything is always the most important so in this case you or someone in your position would have the ability to develop a fully decoupled slab that will have reduced flanking from the existing structure and from the surrounding low frequency that travels at ground level generated by trucks, nearby highways and byways and traffic in general. And may reduce the effects that DVD is talking about to some degree. Just an example.
    kmetal likes this.
  7. Mark All

    Mark All Active Member

    Thanks, Brien, I appreciate your taking the time to reply.
  8. Brien Holcombe

    Brien Holcombe Well-Known Member

    I appreciatte you taking the time to further your education and trying to get this build right.

    I will be around if you run into any thing that needs clarification either by text or graphically or both.
    Mark All likes this.
  9. Brien Holcombe

    Brien Holcombe Well-Known Member

    I would like to address this again:

    "Exterior walls of studio room: do I want insulation or air between drywall and exterior wall? Insulation seems logical, but I’ve read about the value of air.

    Interior walls: If we can only afford single walls, would using RC-1 on one or both sides still be an improvement? And fill this with insulation?"

    The basement wall will become your exterior wall. It will be part of the decoupled wall assembly discussed up topic. In this respect, the RC would not only be redundant, it would gain you nothing and cost more in materials and labor for no added benefit.

    Simply having a framed wall a few inch's from the basement wall (not touching the basement wall or ceilng joists) with sheetrock on the interior side of the framed wall is a typical example of a well isolated wall assembly.

    This (what it is you seem to be asking) is a typical 3 leaf assembly also known to cost more and be less effective at low frequency isolation.
    Mark All likes this.
  10. Mark All

    Mark All Active Member

    In trying to be brief, I probably didn't describe clearly what I have in mind. Keeping in mind, I'm mostly planning on a standard basement with a few improvements, to keep expenses manageable and maintain resale value. I'm aware this is NOT the ideal, I'm just trying to make it a little better than a normal basement would be.

    By exterior wall, I meant the side of the studio along the exterior wall of the basement, which would be: cinder block, or whatever the basement wall is; the wood frame would be against it (not separated from it, though that would be better); 703 or 705 or whatever insulation between the studs; resilient channel on the inside/studio side of the frame; and drywall attached to that.

    By interior wall, I meant the wall of the studio with another room on the other side of it. These will not be the ideal wall shown on p. 63 of Rod's book, but the 2nd one from the left, a wood frame with drywall on either side of it, and insulation in the middle. This is where I was wondering if there is any advantage to using resilient channel on either side of the frame to attach the drywall to, either for decouplng or to provide more space for insulation between the drywall.

    Yes, it would be wonderful to do the version with the STC 63 rating, but we're already at the high end of what we planned to spend on the house, so I can't spend a lot on isolating the studio. I'll just have to do the best I can to make it better than it would be if they just built normal basement room walls.
  11. Brien Holcombe

    Brien Holcombe Well-Known Member

  12. Brien Holcombe

    Brien Holcombe Well-Known Member

    "By exterior wall, I meant the side of the studio along the exterior wall of the basement, which would be: cinder block, or whatever the basement wall is; "

    Basements back in the day, the ones you have read horror stories on, had several things in common. One is that they were made out of cinder block. Why is cinder block not a good material for this you ask? Because it is porous, like a sponge and each block can soak up water. And the joints become the weak part of the structure against the Earth moving. And when the joints begin to loose the lateral battle, and they will, the joints crack. Direct moisture path at your service.

    The inclusion of a sump pump anticipates that water will be present. I wouldn't have one since the water proofing preparation starts from the outside of the structure. Like shingles on a roof only different.
    kmetal likes this.
  13. Mark All

    Mark All Active Member

    Right, so I'm thinking now that the basement walls will be poured concrete. Like I said, this is all new to me. We're meeting with the builder soon to draw up plan options, including my suggestions for improving the acoustic isolation of the basement studio room. I'll ask about a sump pump, but he hasn't mentioned one, and from what he told me about the water table and the area's history, it sounds like we'll be okay.
  14. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Since you have to put up walls anyway, spacing them off the foundation only costs sqf. But it forms the start of an ISO system.

    With high ceilings you can save some money by putting in an independent ceiling. This is the best way from a cost vs benefit perspective.

    High ceilings will genrally be more comfortable to perform in, especially in a basement, and acoustically easier, much easier. With typical 7' ceilings the average person is only a foot and half away from a hard reflective boundary, which by the time you add basic soft acoustic absorbsion, becomes very very close to head height.

    Observing things from a cost benefit perspective, might make it more expensive upfront, but it can pay dividends end.

    The channel is a great alternative if the ceiling height is low, but is typically more expensive than a wood framed ceiling, and has a more limited ability to hold drywall.

    There's a couple of pics of a project I'm involved with. The wall frame was built on the floor, then put in place (temporarily in this case) but sit spaced off the foundation. The RSIC 1 clips were used due to low ceiling height, and selected based on our ISO needs.

    Attached Files:

    Mark All likes this.
  15. Mark All

    Mark All Active Member

    Thanks, kmetal. I'll ask the builder about putting the frames a few inches away from the wall as you and Brien mentioned. The ceiling height will have to be whatever it is, we're at the top of our price range getting the house even before these modifications. But I'm sure all these options will help.

    I'm putting together a list for the builder, plus options for me to do post construction treatment (acoustic door sweep, possibly Audimute absorption sheets, etc.). I may post it for comment and for a possible starting place for anyone else who knew nothing coming into this like I did. With the caveat that it's compromise, not ideal best practices. We're probably not the typical membership of a sophisticated forum like this, but I expect there are a lot of musicians out there who have these needs, know nothing, and waste a lot of time, effort, and money doing useless/wrong things out of ignorance.
    kmetal likes this.
  16. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    The most important thing to keep in mind, is the chain is string as its weakest link. So you want everything proportional. an over spec d window, on a typical wall for instance, would have little added benefit, and a lot of added cost.

    RO is a great forum, and I discovered it through acoustics. Certainly a more candid forum than most.
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  17. Brien Holcombe

    Brien Holcombe Well-Known Member

    Make certain it is one of those underground windows.....
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