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Can I Use A Passive Woofer?

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  • Can I Use A Passive Woofer?


    Noob question here. I've been thinking about building a passive floor standing speaker using a 32cm woofer for the below 100hz sounds and other similarly rated SPL (about 90SPL) drivers for the mid and tweeter. My question is, is it ok to have such a large woofer without additional power in a normal speaker setup or is that going to drain too much power?

    Thanks in advance.

  • #2
    No reason why you can’t do this, two things to consider though, sensitivity of true subwoofers tend to be fairly low which will drag down the overall sensitivity of the speaker meaning more power is needed overall and secondly a passive crossover at 100hz is likely to need big inductors and lots of capacitance which may get pretty expensive and also big to package eating up internal volume in the box so needs to be taken account of. You say the woofer is rated at 90SPL, not sure what this means, speaker sensitivity is usually quoted in dB/W/m, if sensitivity is 90dB/W/m then this is pretty high for a 12” woofer and suggests a pro audio driver that is likely to have a fairly high fs and not play much below 50hz so cutting at 100hz may not be idea.

    What driver are you thinking of and also what drivers are you looking to cross over to, if it’s the traditional 5-6” mis and then a tweeter it may be better to go sealed box on the mid and the crossover at 200-300hz to the woofer.

    Just a couple of thoughts to get things going.


    • #3
      There's no need to separately power the woofer in a three way speaker. There's also no need for nor necessarily any benefit from crossing over at only 100Hz. Doing so puts a lot more stress on the midrange than crossing over well above that. 800Hz to 1kHz is common with a twelve inch woofer. Crossing at 100Hz or lower is SOP with separate subs/mains, which, BTW, is a much better option than a full range three way.


      • #4
        Here's such a speaker currently under development by an experienced designer.


        • #5
          Thanks guys, you've given me a number of things to think about so i can go away and research / learn. Very helpful.