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difference between ported and sealed cabinets??

Discussion in 'Amps [BG]' started by thrashermatt, Mar 6, 2006.


  1. thrashermatt

    thrashermatt

    Joined:
    Jan 26, 2006
    Location:
    western mass
    i'm hearing a lot of people talking about ported and sealed cabs and i was wondering whats the difference between the both... i've only been able to get at that ported can handle lower notes... clarification would rule!
     
  2. fdeck

    fdeck Supporting Member

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    Well-designed ported cabs can have lower frequency response and higher power handling at the lowest frequencies. Those are really the only serious differences.
     
  3. Alex

    Alex

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    Nov 7, 2005
    Location:
    Hinsdale, IL - outside Chicago
    don't sealed cabs have like a tighter low end or something, and aren't they also faster than ported cabs?

    Just passing on word of mouth, not really sure.
     
  4. Boomer

    Boomer

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    Hollywood, FL
    Sealed cabinets control cone excursion much more than a ported cab so generally it is a bit more controlled. They are also less efficient than a ported cab and generally are more directional than a ported cab. I'm not sure that in the world of bass that the narrower field of dispersion is important.
     
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  6. fdeck

    fdeck Supporting Member

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    Yes and no. "Tighter" may simply be the qualitative word that describes the typically higher cutoff frequency of a sealed cab. "Faster" could be the same thing.

    The physical speed of the cone, and of the air in the port, are both directly proportional to sound pressure at any given frequency, thus I think it remains the case that frequency response accounts for any perceived differences between sealed and ported cabs.
     
  7. fdeck

    fdeck Supporting Member

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    At the frequencies where sealed vs. ported is important, speakers are non-directional.
     
  8. Lowtonejoe

    Lowtonejoe

    Joined:
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    West Richland, WA
    But...but...but...

    Hmph!

    Yep.

    :D

    Joe.
     
  9. fdeck

    fdeck Supporting Member

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    Perhaps a bit more explanation would help. In a sealed speaker, sound pressure at a given frequency is proportional to the cone excursion amplitude times the square of the frequency. (Fletcher Munson curves aside). Thus you need more cone excursion to produce the same amount of sound as you go lower in frequency. Eventually, at a given power level, you hit the excursion limit of the driver. I think the non-technical term is "farting." The speaker produces audible distortion. If it is a high quality driver, it only produces distortion and not schrapnel.

    To prevent this from happening, you have to limit the frequency response of the speaker by imposing a cutoff frequency, below which the response curve goes down by 12 dB per octave. This is what keeps a correctly designed sealed box from farting out. It is why typical sealed speakers have a relatively high cutoff frequency.

    You can also protect the speaker by reducing its overall sensitivity. Therein lies the rule of thumb that you give up sensitivity in order to have extended low end response.

    In a ported speaker, the "plug" of air in the port moves in and out, coupled through the air pressure in the box to the motion of the cone. This plug produces sound, as if it were a cone of the same diameter. When correctly designed, the port takes over in the last octave. At the lowest frequencies, the port can actually be producing most of the sound, and there is a resonant frequency where the cone is actually at a near-standstill.

    What's nifty is that the port has no physical excursion limit (or at least, any limit can be avoided by correct design), and it is working in the frequency range that the driver is happy to avoid. The end result is a speaker that can have higher sensitivity, lower frequency response, or some combination thereof.

    Naturally, a ported speaker is a bit more complex than a sealed box, but the complexity is practically a non-issue now that speaker design modeling software is widely available.

    An interesting aside is that a guitar speaker, by virtue of working at higher frequencies, can have a much smaller excursion limit. This is typically the case, and it is the reason why you have to be careful playing bass into a guitar amp.
     
  10. Lowtonejoe

    Lowtonejoe

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    The first time I visited your website I knnew you were a geek.

    This just nails the coffin shut.

    :D

    Joe.

    P.S. Don't take this as an insult, I envy you your intelleigence and knowledge. But not your experience YET punk! Heh heh. :)
     

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