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how crucial are the dimensions of a cabinet?

Discussion in 'Amps and Cabs [BG]' started by mlwarriner, Sep 27, 2005.


  1. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA
    let's say i have a bass cab with a volume of xx cubic feet. if i were to build a cabinet of similar volume, with different dimensions, how much would it affect overall sound? are there general guidelines to follow?

    please and thanks!
     
  2. K Dubbs

    K Dubbs Just graduated from OSU, Go Bucks!

    Mar 16, 2002
    Toledo, Ohio
    The ways in which the sound would be effected are less drastic than changes in total volume and/or port dimensions, but still to some degree noticeable. The variables that would effect the sound are resonation in the cabinet structure, echoic effects from improper or insufficient absorption material, and from how easily/well you can internally brace the different dimensioned enclosures.

    For the first one, the bigger each panel is, in the absense of bracing, the more energy will be displaced from air movement via the drivers into vibrating wood. Depending on the size of each panel in question, you'll have a certain frequency range/peak of resonance. At these frequencies, "tone" and SPL will experience inconsistency from the rest of the frequencies produced, and usually in an unpleasant way.

    For the second one, when a speaker cone vibrates, it kicks of sound in both directions of its movement axis. This means that there's energy being transfered into the air in FRONT of the cabinet as well as INSIDE it. If the kinetic energy of the air inside the cabinet isn't handled properly (usually handled via absorption with foam, wool fiber, glass fiber, etc) it'll reflect all over inside the cabinet before it gets outside of the cabinet through either the port hole/s or the thin paper/plastic speaker cones themselves. This is a problem because it makes for super muddy sound. To further explain it ianother way, when the speakers produce a certain tone at time "t," that tone gets to your ears at time "t*(speed of sound)" as well as time "t*(speed of sound)+(however much time the sound waves spent bouncing around in your unproperly damped/insulated box before escaping through the port holes and/or speaker cones)"

    So going back to the point, properly insulated and damped enclosures minimize these echo effects that muddy up sounds, but if the enclosure isn't so well insulated and damped, the dimensions of the enclosure effect how and how long the air energy inside the enclosure bounces around before it hits your ear drums and makes you hear mud.

    The third point regarding bracing means just that as a panel gets bigger it resonates more easily and energetically. The most common method for reducing this sort of sound-altering resonance is by bracing the panel in question to increase stiffness. Likewise to the panels, the longer the brace goes without being attached to something, the less effective it is and more likely that it'll produce unwanted vibration as well.


    Hopefully a lot of that blabbing helps answer your question
     
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The volume is critical, the shape doesn't matter much, although the preferred dimension ratio is around 2:3:5.
     
  4. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA
    kdubbs and bill, thanks for the input. k - yours went a little over my head, and beyond what i was looking for, but hella thanks. i'd rather have too much than not enough.


    what i'm pondering is reloading a peavey 412tvx with aguilar speakers. i'm just not getting as much love out of the peavey as i'd like to.

    or are there better alternatives to the aggie speakers for about the same price?


    please and thanks.
     
  5. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    I wouldn't assume that putting the Aguilar spec'd Eminences in that Peavey cab will make too big a difference, and you will most likely have to alter the port tuning to compensate, which can be a hassle if its a shelf port.

    That being said, the Eminence Kappa Pro's and Deltalite 10's are in the same price neighborhood using partsexpress.com, but again, each different speaker will necessitate different port tuning.
     
  6. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA

    thanks for the info, and the suggestions. much appreciated :cool: