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Rear ported cabinets??

Discussion in 'Amps and Cabs [BG]' started by MrHeadfirst, Apr 18, 2010.


  1. MrHeadfirst

    MrHeadfirst

    Apr 17, 2010
    what are you experiences with rear ported cabinets...i find many stages i play, my rig ends up against the wall, which screws with the sound something awful if you have a rear ported cab. anyone ever deal with this? and wouldnt it make more sense to have that air moving forward?
    i really dont get it. i was just look at the new tc electronics stuff, and realized that the cabs are rear ported. this is a huge turn off to me. is that rational?
     
  2. James Hart

    James Hart

    Feb 1, 2002
    toms_river.nj.us
    Endorsing Artist: see profile
    I've been using rear ported cabs since the early 90s... sometimes on tiny stages or outdoors. Never had an issue making second guess the port placement.
     
  3. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    nope. port location is irrelevant as the frequencies that come out of it are omnidirectional. having a wall directly behind your cab can screw with it but it's nothing i haven't seen with front ported cabs, too.
     
  4. duderasta

    duderasta

    Feb 25, 2010
    Tampa, FL
    yeah, a little tweaking your cab orientation might be required to deal with phase-canceling if there is a wall really close, but just angle it a little one way or the other and try moving it about.. (I'd do this at home with one, and you can get an idea of how much room, what angle etc.)
     
  5. jmattbassplaya

    jmattbassplaya Looking for a gig around East Islip, NY!

    Jan 13, 2008
    All you really need is just 6 inches from the wall. I`ve never had a problem with my cab.
     
  6. Hi.

    If You have the cab more than the port diameter away from the wall it shouldn't be a problem.

    The port is not there to project sound, so it doesn't matter where it points. It's there to make a Helmholz resonator out of the box to tune the enclosure to the speaker. The frequencies coming out of the (correctly designed/placed) port are omnidirectional in nature.

    Edit:I'm slow :).

    Regards
    Sam
     
  7. duderasta

    duderasta

    Feb 25, 2010
    Tampa, FL
    FWIW my only rear-ported experience was with studio monitors... they were pretty picky about placement
     
  8. Johnny Crab

    Johnny Crab ACME,QSC,Fame/Hondo/Greco/HELIX user & BOSE Abuser Gold Supporting Member

    Feb 11, 2004
    South Texas
    ACME B2's here are rear-ported. I just keep them off the wall and ALWAYS make sure to angle them even if only slight.
     
  9. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    No, it isn't, because the port output is omni-directional, so it doesn't matter where they are. The only caveat with rear ports is that the cab should be at least 6 inches from a rear wall, so it can breathe. Otherwise the sound is identical to front ports.
     
  10. abarson

    abarson

    Nov 6, 2003
    Santa Cruz
    Not to highjack, but I came across a cabinet design for a downward ported enclosure. If the above comments are true, would the cabinet need to be at least six inches off the floor?
     
  11. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    I've built a few cabinets that are downward-ported. With a downward-ported configuration, the designer knows in advance how far away from the floor the cab will be and takes that into account when he designs the cabinet. So whatever feet the cabinet came with should be sufficient unless it's placed on a thick shag carpet or on the grass.
     
  12. My two Ampeg BA series combos are rear-ported. To my ears, the best bass response seems to be when the back is between 6 to 18" away from a wall. I believe that the low bass drops off noticeably if the distance between the back and the wall is more than 18".
     
  13. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    Billoetjen, if you're standing close a front-ported cab will usually sound like it has more bass than a rear-ported cab simply because the port is that much closer, and in the nearfield like that SPL is falling off by 6 dB per doubling fo distance. With the port on the rear, up close to the cab the port is maybe twice as far away as the woofers so its output is correspondingly less due to the added distance. This effect pretty much disappears beyond eight or ten feet and is completely gone out in the house. In the house, if anything, having the port on the rear of the cab may boost the low bass a little because the port is getting more boundary reinforcement.
     
  14. ricguy

    ricguy Supporting Member

    Jul 22, 2006
    Syracuse, NY
    I don't like and won't use rear-ported cabs anymore. They sound fine but wreak havoc on smaller stages where vocal and drum mics in close proximity pick up the sound.
     
  15. Blues Cat

    Blues Cat Payson Fanned Bass Strings Owner Commercial User

    May 28, 2005
    Katy, Tx
    Payson Fanned Bass Strings Owner
    Outdoors forget about rear ports. You have to boost the bass so much to get any low end.

    Speakers experts will disagree.
     
  16. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That has more to do with the distance of the front of the cab from the wall than the ports, as the radiation pattern from the cones is also omni-directional to at least 200 Hz. When you pull the cab away from the wall Allison Effect results in cancellation of low frequency output.
    No, they don't. Look up the definition of 'omnidirectional'
    And that's why were experts. :smug:
    With no rear wall there's nothing to reflect either port output or low frequency output from the front of the cones back in your direction. The technical term for outdoor placement is half-space, versus quarter-space indoors, and the difference in output is at least 6db, which means you need twice as many cabs to get the same result outdoors as indoors, no matter where the ports are located.
     
  17. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    that's pretty smart, duke. i knew there was a reason you went with bottom porting. i thought it was to save space on the cab, but that makes a lot of sense.
     
  18. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You can engineer a bottom ported cab so that the air volume between the cab and the floor acts as an extension of the air volume inside the port. That allows the port duct to be made shorter, and thus the cabinet interior also smaller, with no loss of performance. The downside is that if you engineer the cab to work best at a precise distance off the floor then it won't work right if you tilt it back or lift it, so most downward ported cabs aren't designed to be that fussy.
     
  19. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    always something to learn, isn't there? thanks for the explanation, bill.
     
  20. Oh jeez Bill brought up half space! I mentioned that to my band when they wanted to put me in the corner of our studio. I said, uh guys I'm alredy loud enough in quarter space, that would make me 8th-space and if you though I was loud already that will pretty much liquify your guts.
    They looked at me like I was speaking fluent esperanto.

    I find that rear ported cabs sound best when there IS a wall in proximity to them. On a big open stage they seem to dissipate more than front ported TL606 style boxes.
    I used to run a rear ported eden 15 and front ported boogie 15. Great pair of speaks. Didnt have any problems sounding loud and deep with those! So if you think the front and rear ports would fight each other, they dont.
     

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