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  • 4ohm drivers with 8ohm crossover?

    Which way do the numbers shift... up or down? For instance if I have a 3 way 8ohm 800hz/5000khz crossover but I hook it up to three 4ohm drivers what would the numbers be?

    Sorry, noob question :o

  • #2
    Re: 4ohm drivers with 8ohm crossover?

    You can fiddle with the numbers using Erse Audio's Crossover calculator. I'm assuming that's one of PE's premade crossovers?

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    • #3
      Re: 4ohm drivers with 8ohm crossover?

      Originally posted by greywarden View Post
      You can fiddle with the numbers using Erse Audio's Crossover calculator. I'm assuming that's one of PE's premade crossovers?
      No, not PE's premade. I figure its gonna shift one one or the other. Just not sure which way

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      • #4
        Re: 4ohm drivers with 8ohm crossover?

        Originally posted by nonsuchpro View Post
        Which way do the numbers shift... up or down?
        Neither, unless it's only 1st order. Otherwise they just won't work at all.
        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

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        • #5
          Re: 4ohm drivers with 8ohm crossover?

          Originally posted by nonsuchpro View Post
          Which way do the numbers shift... up or down? For instance if I have a 3 way 8ohm 800hz/5000khz crossover but I hook it up to three 4ohm drivers what would the numbers be?

          Sorry, noob question :o
          As Bill indicated...
          It's not as simple as that.
          A complex crossover becomes - for lack of another phrase - "non-symmetrical"
          Best way to see the effect is to "jam" a crossover calculator and note what the component values are for one impedance and then vary the impedance.
          "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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          • #6
            Re: 4ohm drivers with 8ohm crossover?

            Originally posted by billfitzmaurice View Post
            Neither, unless it's only 1st order. Otherwise they just won't work at all.
            It's 2nd order. when i hook a 4ohm tweeter to it, it does cut the low frequencies. so it is working, i just don't know at what frequency it's being cut off at.

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            • #7
              Re: 4ohm drivers with 8ohm crossover?

              The same components are used to build a 4ohm or 8ohm crossover. It's just the values of each component that differ. I don't understand when you say it wont work. It's just no longer at the stated crossover points.

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              • #8
                Re: 4ohm drivers with 8ohm crossover?

                Bill doesn't mean it won't function, just that its performance will be way off from anything approaching good, much less optimum. The problem is not simply a change in crossover frequency.
                Paul

                Originally posted by nonsuchpro View Post
                The same components are used to build a 4ohm or 8ohm crossover. It's just the values of each component that differ. I don't understand when you say it wont work. It's just no longer at the stated crossover points.

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                • #9
                  Re: 4ohm drivers with 8ohm crossover?

                  Originally posted by Paul K. View Post
                  Bill doesn't mean it won't function, just that its performance will be way off from anything approaching good, much less optimum. The problem is not simply a change in crossover frequency.
                  Paul
                  Right, well I got the impression he meant it wont function period. I don't plan on using it this way.

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                  • #10
                    Re: 4ohm drivers with 8ohm crossover?

                    Originally posted by nonsuchpro View Post
                    It's 2nd order. when i hook a 4ohm tweeter to it, it does cut the low frequencies. so it is working, i just don't know at what frequency it's being cut off at.
                    I followed greywarden's advice and used the Erse calculator
                    http://www.erseaudio.com/Second-Order-3-Way

                    Using the Butterworth scheme, if I call for 2nd order 8 ohm high pass at 5000 Hz I get a capacitance of 2.81 microfarads and an inductance of 0.36 millihenries. If I lower the impedance to 4 ohms and raise the frequency to 10 000 Hz, I get the same capacitance of 2.81 microfarads, but the inductance is now only 0.09 millihenries.

                    This is what greywarden meant by playing around with the Erse calculator.

                    The impedance of a capacitor (measured in ohms) is inversely proportional to the frequency. So in this case, if we halve the impedance (lower it from 8 ohms to 4 ohms), we double the frequency (raise it from 5 kHz to 10 kHz).

                    This is what Bill meant when he said it'll work only for a first order, because a first order high pass consists of only a single capacitor.

                    What is it you're trying to do? Take an existing design and replace the 8 ohm drivers with 4 ohm drivers?

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                    • #11
                      Re: 4ohm drivers with 8ohm crossover?

                      Originally posted by Herman Trivilino View Post
                      I followed greywarden's advice and used the Erse calculator
                      http://www.erseaudio.com/Second-Order-3-Way

                      Using the Butterworth scheme, if I call for 2nd order 8 ohm high pass at 5000 Hz I get a capacitance of 2.81 microfarads and an inductance of 0.36 millihenries. If I lower the impedance to 4 ohms and raise the frequency to 10 000 Hz, I get the same capacitance of 2.81 microfarads, but the inductance is now only 0.09 millihenries.

                      This is what greywarden meant by playing around with the Erse calculator.

                      The impedance of a capacitor (measured in ohms) is inversely proportional to the frequency. So in this case, if we halve the impedance (lower it from 8 ohms to 4 ohms), we double the frequency (raise it from 5 kHz to 10 kHz).

                      This is what Bill meant when he said it'll work only for a first order, because a first order high pass consists of only a single capacitor.

                      What is it you're trying to do? Take an existing design and replace the 8 ohm drivers with 4 ohm drivers?
                      Thank you!!! This is the answer I was looking for. I'm not trying to do anything. Just asking the "pros" a question.

                      Rob

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                      • #12
                        Re: 4ohm drivers with 8ohm crossover?

                        As you see the components work in conjunction ( but their action is reciprocal ), it's like a multiple variable equation increasing with filter complexity.
                        It's also the reason why off-the shelf crossover don't work optimally because the assumption of a nominal value of driver impedance being constant across it's operating range.
                        "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."

                        Comment


                        • #13
                          Re: 4ohm drivers with 8ohm crossover?

                          Originally posted by Sydney View Post
                          As you see the components work in conjunction ( but their action is reciprocal ), it's like a multiple variable equation increasing with filter complexity.
                          It's also the reason why off-the shelf crossover don't work optimally because the assumption is the driver impedance is fixed across it's operating range.
                          Yes, it's making more sense to me now. I've used a few off the shelf crossovers in projects before... results varied obviously. Honestly, I haven't found many premade crossovers for sale other than a few sites, this one included. I would never do what I'm asking. I'm still learning internals. I'm great at telling you if a speaker sounds good or not once I've heard it. I currently have good speakers and have heard great speakers. I live at this place Gramophone

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                          • #14
                            Re: 4ohm drivers with 8ohm crossover?

                            I'm great at telling you if a speaker sounds good or not once I've heard it
                            Not everyone can do that, though I do believe that ears/brains can be trained to become more discriminating.
                            Knowing the internals may not essential but I truly believe it helps immensely to understand the relationships.
                            "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."

                            Comment


                            • #15
                              Re: 4ohm drivers with 8ohm crossover?

                              Originally posted by Sydney View Post
                              Not everyone can do that, though I do believe that ears/brains can be trained to become more discriminating.
                              Knowing the internals may not essential but I truly believe it helps immensely to understand the relationships.
                              I agree. That being said, most guitar builders suck at playing guitar ;)

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