Putting slab under sub?

Discussion in 'Archived Threads 2001-2004' started by Jeremy Anderson, Jul 24, 2001.

  1. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    I remember seeing a thread here a while back about people putting concrete slab pieces under their sub to tighten up the bass, but I can't find it by searching. Lately, I find myself pretty satisfied with the major components of my home theater, so I'm now doing minor tweaks to eke out the last bit of performance possible. Last week, it was backlighting my TV (which worked out quite well), and this week that slab thing popped to mind.
    So does anyone have any suggestions on whether I should bother doing this, or any personal experience with this? My sub is a Polk PSW-350, which is forward-firing, so I wasn't sure if the slab would help much. The only reason I thought of this was that the floor in my HT is carpet over slab (no basement, ground level), and I wasn't sure how much I have to worry about coupling the sub to the floor.
    Of course, this could all just be masturbatory, but I'm always looking for ways to make cheap equipment sound expensive. [​IMG] I would appreciate any suggestions, comments, tales of personal woe, etc.
     
  2. Saurav

    Saurav Cinematographer

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    I tried it with a Sony SA-WM40 sub, and I think I can hear an improvement. I have a very springy wooden floor, so that might have been a factor, I don't know.
     
  3. Andrew W

    Andrew W Supporting Actor

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    I have a springy laminate floor and realized my sub was vibrating the laminate and making undesirable sound.
    I cut up one of those old thick rubbery mouse pads into little round disks to put under each leg. It isolated the sub very nicely and no more rattling floor.
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    Andrew in Austin
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    Sony DVP-S530D DVD Player
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    Sony KP-57XBR10W Rear Projection TV (16:9)
    Infintiy SM 120 (L & R)
    Infinity SM Video (center)
    Infinity SM 165 (surround)
    Infinity BU-120 (subwoofer)
     
  4. Phil A

    Phil A Producer

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    You can try it but with a forward firing sub I don't think it would do much. I have a ceramic tile under the 2 ".1" channel subs in the main system and the one in the bedroom system but they are downward firing. I have a forward firing sub on my rears but it is set-up more of a woofer than a subwoofer and I put DH cones under it and it seemed to make a small improvement. You may wish to consider that or Vibrapods or look at stuff at www.brightstaraudio.com.
     
  5. Rob Gillespie

    Rob Gillespie Producer

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    Yes, it helps and costs very little (if anything). I put one under my Boston VR2000 (front-firing).
    Total tweak cost = £1
     
  6. Saurav

    Saurav Cinematographer

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  7. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    So is there any particular type of slab I should look for, or is it just a regular piece like they sell at Home Depot's garden department?
     
  8. Paul Gere

    Paul Gere Second Unit

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    Home Depot it is. If you really feel crazy, go for two layers of block. That'll set you back at least a buck or two. Hey, I thought it made a small difference in my system.
     
  9. Ron-P

    Ron-P Producer

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    Jeremy,
    I put a 2" thick piece of slate rock under my Velodyne and notice quite a difference. HD sells small thin pieces which I have under my mains, but for the large piece under my sub I went to a landscape supply shop. The piece was 2'x3'x2" and was $20.00.
    Peace Out~ [​IMG]
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    The Green Room | Rons DVDs
     
  10. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    Okay, I made my Home Depot run yesterday. I picked up an 18"x18"x2" smooth white concrete patio stone and a 12"x12"x2" one. Before I moved anything, I set my receiver to reference level and tested the sub's SPL reading with Avia. After putting the 18 underneath the sub, I tested and found a 1db increase on the SPL meter. Then I placed the 12 on top of the sub and checked with Avia and my SPL meter just to see if there was a difference. Oddly enough, at my reference level the subwoofer was now 2db higher than without the patio stones.
    So I backed my receiver's sub level down 2db and took another measurement to make sure it was back to reference. Then I ran a bass sweep to compare to a reading I'd taken last week (using the correction chart for the Radio Shack SPL meter). Normally, my sub has a really ugly peak at the frequency of the port (50hz), but with the stones in place I didn't notice much change at this frequency (which is great!). What I DID notice, however, is that the SPL reading at 25hz was about 3db higher than last week's reading.
    Now, I'm not going to pretend to understand WHY the concrete would make this much of a difference with my forward-firing sub, but I will say that it was worth every bit of $5. I spent two hours last night popping in various CD's with fast bass (stuff with dual kicks, Rush's YYZ, etc.) and there was a very noticable difference. Then I popped in several of the DVDs that normally cause audible port noise from my sub (Toy Story 2, Independence Day, Fantasia 2000, etc.), and found that I no longer heard the port chuffing. I imagine this has to do with me not having to push the sub as hard.
    Final analysis:
    12"x12"x2" patio stone -- $1.09
    18"x18"x2" patio stone -- $3.48
    Feeling the couch shake at the end of Fight Club -- PRICELESS!
     
  11. Todd Hochard

    Todd Hochard Cinematographer

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  12. Saurav

    Saurav Cinematographer

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    Not only that, placing a slab on the sub stiffens the cabinet, which makes it vibrate less, and this can potentially clean up the sound of the sub. This will make a more noticable difference in a cheaper sub, where the cabinet wouldn't be as well braced and/or damped as a better built sub. I tried this with my Sony SA-WM40, and there was a definite improvement in the sound.
     
  13. Nate Thompson

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    Would this also help keep the lower frequencies from transferring through the floor into rooms below? I live in an apartment and don't want to annoy the neighbors below me with a sub. Anyone know anything else that I could do to minimize noise/vibrations?
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    Nate Thompson
     
  14. Rob Gillespie

    Rob Gillespie Producer

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  15. JerryHatchett

    JerryHatchett Stunt Coordinator

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    One could really go nuts, figure out a way to bolt the sub to the floor, and have a sub and tactile transducer all in one. [​IMG]
    I wonder if I can figure out how to sneak THAT mod past the wife. Hmmmm. She freaked when the SVS came in to replace the Sunfire. "Oh no! You are not putting that thing in our sunroom are you?????" Hehehe. Of course, the sub no longer looked so large once the 65H80 moved in alongside it.
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  16. Saurav

    Saurav Cinematographer

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  17. Eric Bass

    Eric Bass Second Unit

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    A 12x12 slab of marble from Home Depot is currently sitting betweem my Sony and the floor, seems to help and it's damn cheap.
     
  18. Sam R. Aucoin

    Sam R. Aucoin Stunt Coordinator

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    I, too, placed one concrete slab underneath and one concret slab on top of my M&K THX sub (mine included the stones, as they were heavier and I assumed would absorb more vibration than just plain concrete). Immediately, I noticed a difference (for the better).
    Of course, I did not put slabs against the sub itself - I "insulated" the slabs by wrapping them with one layer of a large bathroom towel. This was to protect the finish of the speakers.
    Regards,
    Sam
    [Edited last by Sam R. Aucoin on July 26, 2001 at 06:32 PM]
     

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