Worried about my concrete block/mortar wall

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  • SteveL
    Member
    • Mar 2005
    • 45

    Worried about my concrete block/mortar wall

    I've got a good jump on my dedicated HT construction, but now I'm starting to worry about things... I'm building the HT in my basement, and it will have finished dimensions of 15' W x 21' D x 8.5' H.

    The "front" of the HT will be on the "wall" of my house that is the foundation, which is cement block and mortar. There's one 36"W full-size window on the "outside" wall (the 21' side, which has 2x6 framing). The back wall is a wall that I built, which is 2x6 with double-top plate. The other "side" wall is 2x6 framed, 21' long, and has an unfinished "crawl space" that runs the entire length of my house (95') and is about 15' wide. I plan to use it as my IB.

    Here's where the concerns come in...

    1) I've got 4 18" Avalanches that I'm going to use in an IB line array at the "front" of the room. The magnet assemblies will be exactly 32" from the concrete wall, and the IB will open on the "crawl space" side of the box/riser I'm building.

    I've already got: R4 Dow Styrofoam sheeting glued to the concrete wall, 1/2" "Plytanium" plywood sheeting covering the entire concrete block wall, my 2x6" studded wall, and R30 insulation. So, picture a "sandwich" that goes (from the outside to inside): concrete block, styrofoam insul, plywood, studded wall stuffed w/R30 fiberglass insulation, 32" airspace, woofer magnet.

    Should I be concerned with the subs damaging the concrete? I'd hate to have the mortar (which was a bit crummy in my opinion, so I re-sealed it) rattle loose thanks to the Avalanches... They'll be powered by a Crest Audio CA18, bridged mono, to deliver 3400W. I've got a 30A circuit dedicated for the sub amp, and 2 more 30A circuits for the rest of the audio/video gear. I seriously doubt I'll listen to it 'at maximum volume,' but I'll probably "get after it" a bit every now and then - I'd appreciate your thoughts on what may or may not happen to the concrete block and mortar...



    2) For you guys that have used double layers of drywall, how to you position your gang blocks, junction boxes, and recessed lighting boxes? Any pointers/tips for placing them appropriately and then installing the drywall?
    No, that's not me in my avatar.
  • David Meek
    Moderator Emeritus
    • Aug 2000
    • 8938

    #2
    Hi Steve. Nice avatar. :B

    I don't believe there is any need to worry about the mortar. Shifting of the surface your home rides on happens all the time based on temperature changes, moisture, subsidence, etc. The amount of pressure and vibration you'll be subjecting the wall to won't be more than it already has to cope with. Especially since it won't be continuous, and too powerful. You'll give out before your wall will. :yesnod:

    There should be notches on the gang boxes showing how far out to place its face based on the thickness of the wall board you are using. Just double it for the distance appropriate to the thickness of the 'rock. Junctions are not exposed so that's not an issue.
    .

    David - Trigger-happy HTGuide Admin

    Comment

    • RobP
      Ultra Senior Member
      • Nov 2004
      • 4747

      #3
      Hello Steve, I wouldnt worry about your foundation, the outside pressure of the earth will give it more of a challenge than your subs. As far as the boxes you can purchase extensions for them, they are usually used when tile or stone face is added to a wall. Any hardware store should have them.
      Robert P. 8)

      AKA "Soundgravy"

      Comment

      • SteveL
        Member
        • Mar 2005
        • 45

        #4
        Problem with the wall is that it's exposed... so, I worry about it. I put it up today, and did the insulation + 1/2" plywood. I used liquid nails + screws inbetween each layer...let's see what happens.


        Thanks for the info re: the gang boxes. I'll be installing them tomorrow.

        Thanks again!
        -Steve
        No, that's not me in my avatar.

        Comment

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