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Why do people place boards under their cabs?

Discussion in 'Amps and Cabs [BG]' started by namuxtree, Jan 26, 2012.

  1. I've seen a ton of pics uploaded by TBers with a solid board under their cabs. Does it have something to do with the resonance of having a solid foundation as opposed to (let's say for example) a hollow stage? Any insight to this? Does it help THAT much?
  2. will33


    May 22, 2006
    They're probably Gramma Pads. A thick foam pad to try to isolate the rig from vibrating stages. Without a page full of arguing mechanicsl vs. acoustic coupling.....some say it seems to work.:smug:
  3. oinkbanana


    Oct 20, 2011
    some people don't like coupling.
    the frequency response (of the stage vibrating) from one stage to another can never be the same.
    the foam helps cut that down some. i'm not sure how effective that is.
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    A hollow stage will vibrate, sympathetically resonating in response to the acoustical output of the speaker. A pad will help keep that vibration from rattling the cab and amp. But a parametric EQ notch filter works better, eliminating the resonant frequency at the source.
  5. Vandy

    Vandy Banned

    Dec 24, 2011
    With all due respect to a loudspeaker designer / audio expert, I'm not adept enough to "isolate" a specific sympathetic frequency. Then be able to afford a parametric EQ notch filter to soothe the stage?
    If a placebo pad is available, I'll use it, but I'm usually just happy to be there . . .
  6. DBCrocky


    Oct 18, 2011
    Cary, NC
    Yeah, I pretty much saw those pads as something to keep guitar player's spring reverbs in their amps from rattling when the bass player drops the floor-rattling bombs.
  7. will33


    May 22, 2006
    The pad is a solution because a fully parametric eq is not a feature found on most bass amps. The knowledge required to properly use one isn't a feature found in a lot of bass players either, but it can be learned, isn't too dificult. Technically though, the pad is a mechanical band-aid for an acoustic problem.
  8. DWBass

    DWBass The Funkfather

    Had a gig once at the Windows Of The World Restaurant (top floor of the no longer standing World Trade Center) and no amount of eq worked! That resonance would not go away. I ended up turning the amp off! Had to utilize my DI box & the monitors to hear myself.....barely! NOT a fun gig that night!
  9. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    All you do is turn a knob. And a parametric works just as well at notching out a boom frequency that can be present even when the stage is not the cause.
    The cause was said windows. What's best for the eyes is usually the worst for the ears.
  10. 4-stringB


    Jun 10, 2010
    Will33, thanks for the insight...LMFAO...
  11. Biggbass


    Dec 14, 2011
    Planet Earth
    wow...40+ years of playing and I've yet to either see or use such a device.
    hmmm...wonder if that's part of the concept behind putting little rubber feet on the bottom of an amp cab?
  12. moles


    Jan 24, 2007
    Winnipeg, MB
    As an example of a low cost parametric eq, the Presonus EQ3B can often be had for under 70 bucks used.

    As far as not knowing how to use one...The learning curve really isn't that hard if one actually puts forth the effort to learn... :meh:
  13. NWB


    Apr 30, 2008
    Kirkland, WA
    I put a solid board underneath my cabs to keep them from falling into the gates of hell.:D:ninja:
  14. The only amp, that I know of, that has a feature that remotely comes close to this "parametric EQ notch filter", as Bill said, is Acoustics "B" series stuff. Theirs is called a "Sweepable Frequency Notch Filter". Same thing?
  15. will33


    May 22, 2006
    Not sure. A parametric has three adjustments, one for boost and cut, one to select the center frequency and one for the Q width. It may be a "semi-parametric", those have the first 2 adjustments but not the Q width, sometimes called a "sweep". The only bass amps I've seen with a true parametric are some older Peavey's, there might be others.
  16. GrowlerBox


    Feb 10, 2010
    Nude Zealand
    That's almost certainly a centre-frequency adjuster with a fixed deep cut and a very narrow Q, most often used for cutting a feedback-causing frequency when amplifying acoustic instruments. Or, in this case, an amp-chassis rattle-causing frequency.
  17. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Makes as much sense as any reason.
  18. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Almost. A full parametric will boost or cut, and has a variable bandwidth (Q).
    Signal Processing Fundamentals
  19. ack

    ack Why Can't We All Get Along?

    Nov 19, 2006
    Somewhere near Raleigh
    My Peavey Pro500 has a "Q" section within the Parametric EQ's.
    I always wondered what those knobs did...
  20. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You could have read the manual, but then you'd have had to turn in your Man Card. :crying:

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