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DIY - Subwoofer slabs

Discussion in 'Home Cinema Building DIY' started by iwatkins, Mar 10, 2003.

  1. iwatkins

    iwatkins
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    Hi All,

    I've a suspended wooden floor and a down firing sub. Needless to say the whole setup sounded poor with too much reverberation/vibration.

    So, I 'borrowed' a large concrete paving slab from the garden and that solved the problem no end. Needless to say the slab is ugly and the missus doesn't like it at all (on full view).

    So I had three options 1) buy a nice bit of granite/slate etc. or 2) Modify a concrete slab to the missus liking or 3) Make my own slab from scratch.

    Option1 is fairly expensive, so decided to try options 2 and 3 first. I tired option 2 first and was a right royal disaster. I bought a couple of good clean paving slabs and looked to cut them down to the right size using a diamond disc cutter. This just ended up with another slab with sharp edges that didn't look much better especially as it is difficult to cut a perfect straight line with a 9 inch disc cutter. ;) Both slabs I cut down looked OK if you squinted but even when painted still look like paving slabs.

    Option 3 is what I'm currently on. First attempt was a failure so I'll not go into it. Second attempt is much better:

    Method.

    1. Buy some Exterior Polyfilla or concrete mix (i.e. cement and sand without the gravel). I used Exterior Polyfilla as it is a finer grain, can be sanded easier and I happened to have a large sack of the stuff.

    2. Buy or make a mold. I bought a mold in the form of a plastic square washing up bowl. This has nice rounded edges along the bottom that when used as a mold gives nice rounded top edges and corners to the slab. You can also make up a mold using wood offcuts nailed together in a way that allows them to come apart easily once the slab is set.

    3. If you have some, can get some, get some fine mesh wire mesh for reinforcing. Also, for added weight, see if you have any lead flashing strips.

    4. To make it place you mold on a flat surface.

    5. Make up 1/4 of your mix in another bowl but make it so it is just on the runny side (slury like). Pour into mold and shake mold back and forth to make it settle. This ensures it gets into the corners and removes any trapped air.

    6. Make up 1/2 of your mix and make it just right, i.e. can only be poured with persuassion. Pour half of this in and spread it out over the mold right to the edges.

    7. Cut a sheet of the wire mesh to fit but clear of the edges and place in the mold on mix surface. Put in strips of lead if you have them as well to add weight.

    8. Put in the other half of the mix and again spread over the mold.

    9. Make up the final 1/4 of the mix again back to slurry. Put in another sheet of wire mesh and more lead. Pour rest of the slury mix in and again shake about gently to get it right into the corners.

    10. Leave to set for three or four days.

    11. If you are using a plastic bowl you can simply tip the bowl upside down onto a soft surface and bang out of mold. If using wood, simply take mold apart to remove it.

    12. Allow to dry further for a few days.

    13. Depending on what mold you used you may want to smooth the edges of the slabs by sanding.

    14. Get very clean and you may be able to use the slab directly as is. If not the right colour you can of course paint it.

    15. Finishing touches may be to seal with a gloss/satin/matt laquer/varnish and maybe to add rubber feet.


    I'm actually at 14 at the moment. Waiting for undercoat to dry before painting proper. Will take a few days before I can get photos up.

    However, I've used the slab under my sub for a few days and it works as well as the paving slab and looks a lot better because of the nice rounded edges and smooth surface finish.

    Photos up on this thread when I have them.

    Cheers

    Ian
     
  2. jasonb

    jasonb
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    Hi there I like the sound of this Idea, however wood it be worth making another slab for the top of my sub to stop any vibration whatsoever, or will the thing just collapse. I'm using a Paradigm servo 15 at the moment. Any thoughts
    :smashin:
     
  3. iwatkins

    iwatkins
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    Jason,

    I'm not sure to be honest. I have read threads where it has been suggested by members more knowledgable then me that slabbing the top of a sub can help as well.

    I don't know your sub but I'm guessing that the lighter the sub is in total weight, the more benefit you might get by weighing it down.

    I think the best thing to do is see if it improves things by just putting a cheapo concrete slab (from B&Q etc.) on top first before going the custom route. It it helps, great, if it doesn't you haven't wasted much time or money.

    As for the sub collapsing, well, I doubt it to be honest. Most are built like outhouses ;)

    And that reminds me, must go take some photos....

    Cheers

    Ian
     
  4. iwatkins

    iwatkins
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  5. ReTrO

    ReTrO
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    Looks pretty cool.

    Could do with being bigger though, agree there. It also looks too big to fit nicely on top.

    It'd be worth slabbing the top if the enclosure is not well braced. If the enclosure if heavy and well braced it should not be needed.
     
  6. iwatkins

    iwatkins
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    Retro,

    Yeah, I know, I know. I measured the sub by hanging over the back of the sofa, in the dark, with a tape measure which has worn numbers.

    I of course didn't add on the fact that the rounded corners of the slab means that the actual slab needs to be a couple of inches bigger.

    Oh well, Mark II is in the mold as we speak. The mold is made from wood offcuts this time so that the shape of the slab edges will mirror the shape of the sub edges to give it a more "Was designed for" look.

    The actual Mark I slab performs very well. As well as a bogo standard concrete slab but without the missus moaning that the place looks like a building site. What I didn't show in the picture is that the slab sits on four small nylon slider pads. These are nylon sliders with a foam runner backing then the sticky surface. This should help isolate vibrations to the wood floor even more. Well, in a totally objective test (yeah, right) it certainyl sounds good but honestly does cut down the amount of unwanted vibration throughout the rest of the house.

    The big benefit is that I'm now "allowed" to put the sub where it sounds best as it passes the style police of the household. :eek: Pity that is right in front of the door to the dining room.....

    Cheers

    Ian
     
  7. jasonb

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    It looks great!!!
    As a thought have you tried turning the slab the other way round, your sub might fit better. Once you have the sencond slab are you going to see what it's like putting one above and beneth, purely for research purposes as I'd think we would all be interested in what results you get.
     
  8. RichardH

    RichardH
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    Re isolation between slab and floor...

    I wondered about using a mouse mat between floor and slab. What do you reckon?
     
  9. ReTrO

    ReTrO
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    A sheet of neoprene would do the job, no?
     
  10. RichardH

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    Basically the same stuff, isn't it? I just happen to have a few spare cheapy mouse mats I used to line my HCPC case with. Mind, I also have an old wetsuit somewhere....

    I'm considering trying this with my floorstanders, which are on a very bouncy wooden floor.
     
  11. iwatkins

    iwatkins
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    Jason,
    Yep, did think of turning the slab over, but a) it didn't look right and b) I haven't used that paint effect on the base :)

    When Mark II is dry, I'll certainly try Mark I on top as well and report back.

    Richard,
    I think a neoprene sheet/mouse mat would work well for isolation. I guess the only thing to consider is whether the material you use still have enough to strength to keep some "bounce" in it even after a slab/sub has sat on it for a while. I guess a very thin mouse mat won't work, it'll get too compressed, but some thick wetsuit material would do the job. Try it and see I think is the plan.

    Cheers

    Ian
     
  12. Gary Lightfoot

    Gary Lightfoot
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    Excellent result!

    I'm currently using a 12" slab for my REL, but you've got me thinking now.. :)

    Gary
     
  13. Kristian

    Kristian
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    Just a thought but what about using cement colouring/dye. I know you can get a few different colours and because it's mixed in when you make the cement it would save painting later on. It might make it look more 'natural', if that's the right term for a concrete slab in your living room :D

    Kris.
     
  14. jasonb

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    good idea, sounds like MKIII is coming up..........
     
  15. CopeyJ

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    What sort of quotes did you get for Granite etc?
    The sort of sizes that we require for audio gear is classed as off cuts and normally gets thrown away, I know this because I am fortunate to have a Stone Mason for a father-in-law so getting nice slabs is not a problem, but even so you should not pay over the top for them.
     
  16. hornydragon

    hornydragon
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    Any pics of Mark 11 yet??? Or did you give up on the idea?
     
  17. helenj

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    Just another thought ... what about adding lead shot to the inner mix to weight it evenly rather than add lead flushing?
     
  18. iwatkins

    iwatkins
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    Lead shot would work I guess.

    Mark II went the way of the dodo when it broke in half after falling out of the mold while I was trying to open the mold up. It broke in half over my foot and I couldn't walk properly for three days. I will be having another go when the missus lets me back into my shed. :blush:

    Cheers

    Ian
     
  19. Boink!

    Boink!
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    I shouldn't laugh at your pain, but hey, I can run faster than you at the moment. :D

    [Good luck with Mk III, mate]

    Boink!
     
  20. hornydragon

    hornydragon
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    I like idea but when i eventually get a sub i am going to get quotes for some marble/granite slab from a mason, thinking about the moulded slabs you ar etrying wont they crack crumble around the edge quite easily? Not a critisism just a point of interest!
     

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