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Any way to correct for low impedance when 2 woofers are run in parallel?

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  • Any way to correct for low impedance when 2 woofers are run in parallel?

    Just for practice I'm playing around with simulating different driver configurations and setups. In one instance I choose a 6 Ohm driver (Hivi L6-6R in case you wonder) and simulated a TMM speaker and of course the impedance is cut in half to 3 Ohm (see attached FR curve and impedance curve). So is there a way to raise the impedance without dropping the FR however many decibel? I assume some series resistor is really the only way of doing it, but with a loss in db levels.

    And maybe a second question, when adding the inductor to the second woofer in a TMM configuration, am I looking for some minimum difference in db to the first woofer? Or do I need a minimum drop near the crossover point?

    Thanks
    Billy

  • #2
    Originally posted by crossbound View Post
    is there a way to raise the impedance without dropping the FR however many decibel? I assume some series resistor is really the only way of doing it, but with a loss in db levels.
    Think about what you're saying. Impedance and output are directly related, you don't increase impedance without lowering output with respect to voltage. The only way is to add more speakers or choose different drivers. Putting a series resistor in series with the woofers is a bad idea, a waste of amplifier power and a fire hazard. You can keep a 6 ohm impedance by using 4 woofers, with increased sensitivity, power handling, size and cost.

    Originally posted by crossbound View Post
    And maybe a second question, when adding the inductor to the second woofer in a TMM configuration, am I looking for some minimum difference in db to the first woofer? Or do I need a minimum drop near the crossover point?
    I'm not sure what you're asking here. The series inductor for the second woofer would be to account for the baffle step, so just size the part for flat response, provided your input data includes the baffle step.

    This TMM from Zaph is a good example:
    http://www.zaphaudio.com/Waveguidetmm.html
    "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
    exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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    • #3
      Thanks dcibel that's what I figured.

      On your second response, yes all the FR curves I used have been simmed in Response Modeler and Baffle step is included.

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      • #4
        No, usually if 2 8 ohm woofers are paralled, it will remain above 4 or close to 4 ohms.

        Series resistance a bad idea.
        I have seen some speakers utilize the 2nd woofer ONLY to cover a small range of the lower bass, but then you need huge inductors to roll it off.

        You could though, parallel 2 SETS of (2) 6 ohm woofer and they combined those 2 sets in series, and get about 6 ohms...but need 4 woofers.!

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        • #5
          Thank you @kevintomb
          Exactly what I figured. But definitely not planning on putting 4 drivers in the box :-)

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          • #6
            While both responses are correct, an air core inductor with its higher dcr can often be used to increase the resistance enough as well.
            https://www.facebook.com/Mosaic-Audi...7373763888294/

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            • #7
              An "8 ohm" (nominal) woofer usually has a minima of 6 ohms (its DCR).
              An amp that's made to handle a (nominal) "4 ohm" load is expected (and almost always designed) to handle a 3 ohm minima.
              If you're maintaining a true 3 ohm Z-min (by paralleling a pair of 6 ohm nominal drivers), you should be OK (using most "4 ohm" amps).

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              • #8
                Originally posted by Chris Roemer View Post
                An "8 ohm" (nominal) woofer usually has a minima of 6 ohms (its DCR).
                An amp that's made to handle a (nominal) "4 ohm" load is expected (and almost always designed) to handle a 3 ohm minima.
                If you're maintaining a true 3 ohm Z-min (by paralleling a pair of 6 ohm nominal drivers), you should be OK (using most "4 ohm" amps).
                ​Or definitely get an amp that can handle low impedance loads! Ha. LOL

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                • #9
                  The minimum impedance in your model doesn't dip much below 4 ohms. A 4 ohm rated amp should handle your original design just fine.

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                  • #10
                    Ha! This DIY speaker building rabbit hole goes deeper and deeper. Looks like I do have to get a 4 Ohm amp sooner or later. :-) Sent from my SGH-M919 using Tapatalk

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                    • #11
                      Originally posted by Millstonemike View Post
                      ...A 4 ohm rated amp should handle your original design just fine.
                      yeah,,, my 220s have been driving 4 ohm loads for decades.

                      "Not a Speaker Designer - Not even on the Internet"
                      “Pride is your greatest enemy, humility is your greatest friend.”
                      "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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                      • #12
                        Originally posted by crossbound View Post
                        Ha! This DIY speaker building rabbit hole goes deeper and deeper. Looks like I do have to get a 4 Ohm amp sooner or later. :-) Sent from my SGH-M919 using Tapatalk
                        Scott has a few amps up for sale in the classified that might be a good start.

                        http://techtalk.parts-express.com/fo...-free-shipping
                        My "No-Name" CC Speaker
                        Kerry's "Silverbacks"
                        Ben's Synchaeta's for Mom
                        The Archers
                        Rick's "db" Desktop CBT Arrays
                        The Gandalf's

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                        • #13
                          Originally posted by Kevin K. View Post
                          Scott has a few amps up for sale in the classified that might be a good start. http://techtalk.parts-express.com/fo...-free-shipping
                          Nice Kevin. Thanks Sent from my SGH-M919 using Tapatalk

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