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helmholtz resonator question

Discussion in 'Amps and Cabs [BG]' started by K Dubbs, Mar 26, 2004.

  1. K Dubbs

    K Dubbs Just graduated from OSU, Go Bucks!

    Mar 16, 2002
    Toledo, Ohio
    This is a question I've had for some time now. I know it is possible to tune a cabinet to a certain frequency using specific internal volumes and port arrays. I also know that tuning an enclosure to slightly lower than the lowest frequency that will be input to the enclosure is a good idea to keep woofers from exceeding xmax at low frequenencies. Something I have noticed, however, is that when an enclosure is tuned lower than 80hz or so, the woofers inside tend to exceed xmax and experience extreme loss of power handling capability from the tuning frequency to around 150 hz.

    My question is this: Short of horn loading (which doesn't qualify as a helmholtz resonator, anyway), is it possible to create an enclosure with two tuning points?

    (using two enclosures tuned to different frequencies is not an option due to phase cancellation problems and still would produce the same loss of power handling)
  2. This is a bandpass type design. The woofer chamber looks into two separate chambers, each vented, and tuned to a different frequency.

    Very difficult to design.

    As for the tuning, a generic rule of thumb does not apply. Every driver is unique, and its parameters determine a set of tuning alignments.

    Cone movement is the least at tuning frequency, but it rises very rapidly as the frequency goes up. Some drivers offer more power under the Xmax curve using a higher tuning. The Eminence Magnum 18LF is an example of this.

    In SBB4 tuning at 32 Hz, the 18LF will accept 497 watts before exceeding Xmax. In QB3 tuning at 39.6 Hz, it will accept 648 watts before exceeding Xmax. The QB3 is great for 4-strings, but SBB4 is better for 5-strings.
  3. K Dubbs

    K Dubbs Just graduated from OSU, Go Bucks!

    Mar 16, 2002
    Toledo, Ohio
    is a dual tuned cab possible without a bandpass design? I'm suggesting the idea of a single chamber with two different lengths of port arrays inside that single chamber. is this possible?
  4. No.

    The concept is like a Coke bottle that makes noise when you blow across the opening.

    The cabinet has a certain amount of air volume inside. The combination of the port(s) have a certain amount of total air volume that is the sum total of the ports. Multi-size ports still operate like a single larger one, just a whole lot harder to calculate.

    This is why the bandpass is different. It uses two chambers, one on each side of the driver, and each is tuned differently.

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