Fix for a vibrating plywood enclosure?

Discussion in 'Archived Threads 2001-2004' started by David Gadd, Aug 26, 2002.

  1. David Gadd

    David Gadd Auditioning

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    Please save me from myself. [​IMG]
    SHORT VERSION
    Large plywood sub enclosure. Vibrates. Sucks.
    RECOMMENDED FIX?
    (1) Build new MDF box? Don't want to. Cutting little holes in inner braces is a pain.
    (2) Glue and screw mdf panels to each side to build MDF box around the ply box? (Flush trim each panel with router. 500 screws per panel. "Soft glue" between ply and MDF whatever that is.)
    Is (2) as good as (1)? Is (2) good enough (ply bracing good)?
    BTW, easy way to remove striped out t-nuts?
    LONG VERSION
    I built a vented EBS Shiva sub with the HS200 amp using Adire's plan. See http://www.adireaudio.com/Files/Vent...plications.PDF . I built the enclosure from "birch plywood" purchased from home depot. I now believe the "birch plywood" to be crap with a pretty birch face. (The ply has 5 layers and screws will self-countersink when driven in with a drill.) The box vibrates to my hand on higher bass notes and on lower notes you can hear the notes through the top of the box when your ear is next to the top. I have it on inch-thick folded over towels so it won't make LOUD buzzing noises on my hardwood floors on upper bass notes.
    POSSIBLE FIXES?
    (1) Build an entire new box out of MDF?
    (2) Build an MDF box around the ply box? (Glue and screw a slightly oversized panel on each side and trim flush with router building a tight MDF outer box.)
    I would prefer (2) as it would be less work (maybe). Will it be as good as (1)? (is the plywood bracing, etc., as good as MDF?)
    Thanks for your help.
    BTW, is there an easy way to remove striped out t-nuts? (Pounded in with a hammer with no glue.) Maybe if I build another 10 subs I'll run out of stupid things to do. Maybe not.
     
  2. Brian Bunge

    Brian Bunge Producer

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    David,

    I think #2 is a good choice. The birch ply is stiffer than MDF so the birch bracing is a good idea. The MDF will add weight (lots of weight) to the enclosure so that will damp some of the panel resonances. As a matter of fact, North Creek Music recommends inner layers of baltic birch, which is different from the standard birch sold at home improvement stores, with a layer of MDF on the outside.

    You might want to simply use Liquid nails to bond the two materials together and then use a few screws or brad nails to hold them in place.

    Let us know how it works out!

    Brian
     
  3. David Gadd

    David Gadd Auditioning

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    Thanks, Brian. I'll give it a try.
     
  4. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Jack is correct. Everyday plywood has LOTS of voids in the inner layers and does resonate. Otherwise, void-free plywood is fine for subwoofers, as it won't resonate at those low frequencies. Opposite is true with higher frequencies/MDF.
    Everyone knows I'm against screws (for speaker enclosures, Brian[​IMG]). Screws add lots of labor and don't make an enclosure stronger than good old yellow carpenters glue. You might try Brian's idea of using Liquid Nails, which would make sort of a "constrained layer" construction, since LN doesn't dry rock-hard. It would be expensive though, since you'd have to apply and even, void-free coating to all sides.
    Good luck and I hope you get rid of the vibes.
     
  5. Or just coat the inside of your enclosure with a 1/2" thick of epoxy resin [​IMG]
    ok, I joke, but not entirely! You never know what some people do for a living, or what their friends do. left over stuff from the job site can be pretty sweet! heck, take construction worker HTFer's who might be able to get all sorts of scrap sonotube for free!
     
  6. ChrisAttebery

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    Or...
    You could buy Corian and cover the box with that. It'd only cost about $1000. [​IMG]
    Chris
     
  7. Brian Bunge

    Brian Bunge Producer

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    Hank,

    Me and a buddy built a 2.75ft^3 enclosure with 1/2" MDF and liquid nails. We used a small trowel and spread liquid nails on a pieces of 1/2" MDF and used several screws to hold the panels together over night. Then the next day we removed the screws and assembled the panels into a box. The baffle was a full 2" thick!

    I still have the cabinets out in the shop out back but I never applied a finish to anything but the baffles since they were mounted in the bottom of my old entertainment center before I bought my RPTV.

    Brian
     
  8. David Gadd

    David Gadd Auditioning

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    It's at least a little bit depressing to resurrect this old thread (have I really been screwing with this for 3 1/2 months?.[​IMG] ).
    Question: what's the best way to protect a polished black lacquer finish?
    Will automotive wax adequately protect the finish?
    Should I brush on the acrylic?
    Should I spray on an acrylic?
    I've finished the box with black lacquer spray paint (Rustoleum brand "Specialty" black lacquer). The paint is very soft in that placing the box on its top on an old couch cushion (to insert the hardware for mounting the Shiva and the port) after the paint dried for 4 days left the impression of couch fabric in the paint. Also, if I lean hard on the box, I leave the pebbled texture of the gloves I wear to wet sand. When it is polished (320, 400, 600, 1000, 1200 wetsand then automotive polishing compound --looks absolutely fabulous)it scratches if you put ANYTHING on it.
    Does the lacquer become substantially harder after a few weeks?
    I can't use a polyurethane as it would react with the paint.
    The water based acrylic (brushed on) that I've tested on a scrap piece left several little "bubbles" and I can scrape it off with a finger nail (admittedly I only put on one coat when the can says "at least 3 coats").
    SO:
    Will automotive wax adequately protect the finish?
    Should I brush on the acrylic?
    Should I spray on an acrylic?
    Update (for those who care): I now have a heavy, 24" x 24" by about 27" box (80 lbs? 100 lbs? Feels ALOT heavier than my 50 lb son who's still young enough to toss around [​IMG] ). I added the 3/4" MDF box around the plywood enclosure. First,I spread a thin layer of liquid nails over face added the MDF panel and then countersunk screws to press it together. I then flush trimmed the excess with a router. I started drinking again with the wood screws, however. (Isn't the first step acknowledging that you have a problem?) I spread the liquid nails as best I could with a 3" putty knife but when I pressed down on the MDF panel on liquid nails and then pulled the MDF off, only part of the board seemed to be coated with adhesive. So I proceeded to put countersunk screws every few inches. Several panels had more than 50 screws (not including the butt joints). I went through more than a 1 pound box of 1 1/4 screws. The panels are solidly together, though. [​IMG] Except for heavy weights on the panels, I couldn't think of any way to make sure the whole panel was pressed into the adhesive.
    I paid for all those screws in the time it took to fill the holes with wood putty. To the extent that the "filled holes" caused me to redo the lacquer finish, I paid with another large block of time and $35 of paint (PITA). BTW, 3 weeks ago, I had it polished, well the "top" 5 sides at least, but I sanded down to primer on one 1/4" spot on one side trying to sand out a dimple in the paint (from the filled friken screw holes). The *&%$ wood putty is softer than the MDF and even with a sanding block, I swear it leaves a dimple MOST of the time (even after fill-sand, fill-sand, fill-sand). I'd have left the 3 small scratches in the top from flipping the box over (unable to sand out without hitting primer) and several small dimples on the back side of the box (got a little lazy on the back panel prep., I guess). Decided to pretty much start over since 3 out of 5 sides had "problems," so 3 coats, sand with 320 'til pretty flat; 3 coats, sand with 320 'til quite flat, and 3 coats are done. Now, to sand with 400 - 1200, and polish with buffing compound. After that, I need your help. [​IMG]
    Thanks a bunch... D
     

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