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open back vs sealed vs vented?

Discussion in 'Amps and Cabs [BG]' started by SirPoonga, Feb 7, 2005.

  1. SirPoonga


    Jan 18, 2005
    I've been reading through loudspeaker design books and websites. I see many bass cabinets with open backs. I have yet to see anything in speaker design books and sites about open backs. How do you design one of these?

    Also I've noticed calculations for vented and sealed cabinets seem to be a bit larger than what the open backs appear to be. Though that's just an observation.
  2. embellisher

    embellisher Holy Ghost filled Bass Player Supporting Member

    Where did you see an open back bass cabinet? If there is such a thing, it must have been made before 1970.
  3. Petebass


    Dec 22, 2002
    QLD Australia
    I think you'll find those open back speakers are for guitar, not bass. When you're dealing in the frequencies that a typical bass guitar needs to reproduce, on open back cab will do nothing to prevent losses due to diffraction.

    At high frequencies the speaker is radiating into "half space" i.e. it is only radiating into the forward hemisphere. No significant energy is radiated to the rear of the speaker. At low frequencies generated by a bass guitar, the speaker is radiating into both the forward hemisphere and the rear hemisphere. That is, at low frequencies the speaker radiates into "full space". Because the "energy density" at low frequencies is reduced there is a loss of bass. In short, speaker systems designed for radiation into half space (mounted flush on an infinite plane) exhibit a loss of bass when implemented in typical speaker enclosures. The same goes for cabs with an open back. That's how sealed and vented enclosures came into existence in the first place.

    For kicks have a look at JBL's website and have a look at the first ever Theatre subs they manufacturered. A row of 18" speakers with no cab, all trying to radiate low frequencies into the theatre. That design didn't last long, and with good reason.
  4. DubDubs


    Aug 23, 2004
    Los Angeles
    Where? I didn't know open backed bass cabs existed. Bass cabs are always sealied or ported/vented for the reasons mentioned above.
  5. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    im sure there are others but the onlyest bass "Cabs" i recall were fender combos that turned out to be better for guitar.
    sealed cabs can generally handle more power and sound "tighter" with bettter control over speaker excursion (there's a lot more to it than just that) lots of cats who use tube amps like them as they kind of make up for the "looser" sound and lower damping factor of a lot of tube amps. ported and vented cabs tend to a bit louder but can't handle as many watts and have less speaker control but are frequently tuned to lower frequencies. this can get a bit dangerous as some vented boxes cant handle frequencies much below their tuned low frequency. however, these remain the most popular of the bass cabs you'll see.
  6. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I had a Fender Musicmaster Bass amp -- 12 Tube Watts (must have been equivalent to 1200 solid state watts :bag: ). It had an open back cabinet. The day I sold it to a guitarist was the happiest day of his life, and the happiest day of mine.

    Seriously, it was a great two-knob guitar amp, but useless for bass.