Open back against wall = closed back??

Discussion in 'Amps and Cabs' started by Benlevy, Oct 16, 2008.

  1. Benlevy

    Benlevy Member

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    I've heard people say if you put your open back cab against the wall, it's pretty much the same as a closed back. I find that hard to believe. I though a big part of it was the air pressure trapped behind the cones in a closed back cab. :dunno What say the experts??
     
  2. m@2

    m@2 Member

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    not the same in my experience. true, up a gainst a wall will decrease the "spread" effect of an open back, but I can't imagine getting the same tones that a trully closed back would get. like you mentioned, part of it is the complression effect (especially an un-ported, closed-back cab)
     
  3. walterw

    walterw Gold Supporting Member

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    i think you're right.

    now 6-12" away from the wall, and you've got yourself a nice bass vent throwing the low end off the back of the speakers over the top of the amp and forward, fattening things up nicely.
     
  4. Tone_Terrific

    Tone_Terrific Member

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    Speaker positioning is an acoustic event related to the room, not a speaker effect, directly, even if the results happen to be similar.
     
  5. StoneAge Cabs

    StoneAge Cabs Silver Supporting Member

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    Definitely not the same. Here's an obvious comparison/example between the two:
    Try speaking with the palm of one hand placed firmly against your mouth, then, slowly remove your hand and listen to the differences. You'll find that tone of your speaking voice changes incrimentally with each repositioning of your hand.
     
  6. Rick51

    Rick51 Member

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    +1, 'Stoneage.

    An open back cab radiates a back wave that is 180 degrees out of phase with the front. So you are getting phase cancellation, much more so in the low frequencies. The upper frequencies in the back wave are bouncing all over the place, so you get a "fill" effect. As you move it close to the wall, you'll cut down the back wave and reduce the effect.

    Benlevy, why don't you just try it out and tell us what you hear?
     
  7. shane88

    shane88 Member

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    make sure it's not a combo as the air won't flow to cool the toobz
    the rest is moot :)
     
  8. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

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    Well...back when you played at Leftys Pub, we could have mounted an open back to the wall and caulked it since we had a permanent setup. :dude
     
  9. Benlevy

    Benlevy Member

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    Ahhh, the good 'ole days.
     
  10. michael.e

    michael.e Supporting Member

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    Right now I have two 4-12's against my back wall..

    The Orange has had it's back replaced with a couple of nice pieces of high quality 1/2" ply. There is a 3" space between the two panels.

    The Marshall has it's closed back.


    At low to moderate volumes the Orange has such a huge sound. The Marshall does much better when the volumes reach stage levels.

    I would not want an open back cab against a wall at rock/gig levels. I need a more focused sound, and as nice as the semi-open back sounds at controllable levels or at home levels, it gets completely indistinct and lost when the other sonics come in to play.

    Emee
     
  11. tms13pin

    tms13pin Supporting Member

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    The other difference is the wall itself, which is different than the
    closed back of the cabinet. Put *any* cab up against the wall, open
    or closed, and the pressure from the low frequencies will increase,
    simply due to the radiation into the front hemisphere rather than
    spreading all around cab, more spherical. Now couple this with the
    cabinet effects mentioned above as well.

    You can do this experiment with your stereo speakers. Put one in the
    middle of the room. Move it against the wall, then into the corner, then
    into the corner down by the floor where the wall corners meet the floor.

    --Tom
     

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