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Rear ported cab. should i block it up?

Discussion in 'Amps and Cabs [BG]' started by dave_bass5, Feb 2, 2005.

  1. dave_bass5


    May 28, 2004
    London, UK.
    I use a MAG307 C-115 combo for all my gigs and this has 2 round ports on the back of the cab.
    The last few gigs (and more coming up) have stages that have no rear wall and am wondering if i should block the ports so the sound doesnt get out the back and get lost.

    thanks for any advice

  2. Trevorus


    Oct 18, 2002
    Urbana, IL
    No, do not block the ports. Those allow your speakers to function properly. Without those ports, you cabinet will sound VERY different. You will lose low end, and that isn't good. Those were designed for the best efficiency of the cabinet in mind.
  3. dave_bass5


    May 28, 2004
    London, UK.
    ok thanks.
    i thought they were there to direct the sound off a back wall to increase the bass response so my thinking was if theres no wall then no increase.

  4. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    No, they're not. They're there to tune the cabinet and extend the bass response a little lower. It doesn't matter whether there's a wall behind them or not, the sound coming from them is so low that it spreads out in all directions, including forwards to yourself and the audience.

  5. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    the sound will radiate off of walls behind the cab. depending upon the distance from the wall there will be phase cancellation at mathematecally predictable frequencies when doing this, but i wouldnt get crazy thinking about it.

    bottom line, don't block them, the cab/speaker is designed to work with them.
  6. dave_bass5


    May 28, 2004
    London, UK.
    Thanks guys for the info. I wont touch them.

  7. Eric Moesle

    Eric Moesle

    Sep 21, 2001
    Columbus OH
    Also keep in mind that almost no sound radiates through the ports until the sounds to be produced approach the tuning frequency of the cab . . .
  8. The other thing to remember is do not put your cab right up against the wall behind so the ports are too close to the wall.

    I would say keep 12 " away if possible to let the cab ports do there job