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bdawson72

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Posts posted by bdawson72

  1. Posted

    I made this analogy in a thread earlier....

    A single speaker (no enclosure) is simply a diaphragm with mass on a spring that is driver by an electromechanical motor. The motor is obvious: the voice coil, it's interaction with the flux from the top plate, magnetic stack, backplate, and pole piece. The spring is the spider and surround. The diaphragm with mass is the diaphragm itself (plus the mass of the other moving parts).

    Now a bass-reflex enclosure behaves on the same kind of principle. The air inside the port is the mass, the air inside the enclosure is the spring, and the motor is the speaker itself. If you imagine this visually, it should be easier for you to understand the answer.

    The enclosure itself behaves as a low-pass filter. Just like any filter, it has a Q factor, resonance frequency, rate of rolloff, etc. It's the combination of Q factor and resonance frequency that is really the question here, as the rate of rolloff for most bass reflex enclosures is around 24dB/octave (4th order). By introducing two ports with different frequencies at which they resonate, you essentially end up with two different diaphragms with two different masses. Yes, this is in fact a LOT like putting two different speakers in the same enclosure and having them share airspace. It's not a particularly efficient use of the air spring.

    Note: An aperiodic bi-chamber (ABC) enclosure does work. Using the above analogy, can you explain why?

    Hopefully one day i will be able to write a post like this one.

    :)

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