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How can I find impedance of a driver at a given frequency

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  • How can I find impedance of a driver at a given frequency

    Here's where I am and please correct me or guide me rather if I'm off.
    In crossover calculation. I'm using an automatic calculator. It asks for high pass impedance and low pass impedance and the crossover frequency. Both my tweeter and woofer are 8 ohms but do I put at ohms or do I put the impedance of the drivers when they are at my crossover frequency, which is 2k?

  • #2
    Re: How can I find impedance of a driver at a given frequency

    A text book xover will not produce good results...

    https://sites.google.com/site/undefinition/diy-mfaq

    What drivers are you trying to use? There is a way to design a fairly accurate xover without measuring the drivers yourself.

    https://sites.google.com/site/undefi...d-measurements
    http://jaysspeakerpage.weebly.com/

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    • #3
      Re: How can I find impedance of a driver at a given frequency

      Originally posted by Jay1 View Post
      A text book xover will not produce good results...

      https://sites.google.com/site/undefinition/diy-mfaq

      What drivers are you trying to use? There is a way to design a fairly accurate xover without measuring the drivers yourself.

      https://sites.google.com/site/undefi...d-measurements
      I am making a small PA enclosure. A 12" delta pro 8 ohm and either a selenium model ?? Or eminence ASD 1001. The whole absolute point is to only create a crossover from scratch. This is just a learning experience. I was directed to a crossover calculator. If this is not the propped rout, where do I go from here? I've been directed to sites non stop, but none of which tell me anything about crossover design.

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      • #4
        Re: How can I find impedance of a driver at a given frequency

        A good book to get you started is "Speakerbuilding 201". Let's say you wanted to design and build your own airplane (or car engine, or whatnot). There's a bit of a learning curve that's required to get good results. Probably a couple years or more.

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        • #5
          Re: How can I find impedance of a driver at a given frequency

          Originally posted by RDK View Post
          I am making a small PA enclosure. A 12" delta pro 8 ohm and either a selenium model ?? Or eminence ASD 1001. The whole absolute point is to only create a crossover from scratch. This is just a learning experience. I was directed to a crossover calculator. If this is not the propped rout, where do I go from here? I've been directed to sites non stop, but none of which tell me anything about crossover design.
          If you plan to design your own passive crossover, you will need to start with adequate measurement equipment. Avoid online calculators - they imagine "perfect" drivers with flat impedance and infinitely ruler-flat natural frequency response perfectly aligned at the same point in space. Real drivers will have a system resonance at the bottom of their passband (or more in some cases) resulting in an impedance spike, and an inductive impedance rise at the top of their passband. They will also have a rolloff at both ends as well as other resonances creating unpredictable native frequency-response as a result of all their various parts - the cone material, the spider, the surround, and the box all contribute to make drivers anything but flat until you make it flat. The tweeter acoustic center will not likely be the same distance from your ear as the woofer acoustic center.

          This means you need equipment that will measure Complex Impedance, and also Frequency Response.

          http://www.parts-express.com/pe/show...number=390-806 will give you a Z-Chart which can be used in a crossover design software.

          and

          http://www.parts-express.com/pe/show...number=390-792 will give you accurate frequency response measurements.

          Next you will need to learn how to measure correctly, and also factor in things like driver off-sets, baffle diffraction, baffle step, and power handling. You will need a crossover design software, such as Jeff Bagby's Passive Crossover Designer. You will need to learn about optimizing the phase-tracking and sound power response - not just getting flat on axis with EQ and textbook slopes.

          Can you do it if you want to? Yes. But you will need equipment and patience.

          Designing an active crossover reduces complexity slightly, but will cost more in terms of amplification and will still have a steep learning curve as far as correlating electrical crossover slopes to actual acoustic crossover slopes facting in native driver frequency response.

          If you're unwilling to make that equipment investment, then you're in over your head.
          :blues: Flat frequency response, a smooth sound power response free of resonance, careful driver-integration, and high dynamic range both upward and downward :blues:

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          • #6
            Re: How can I find impedance of a driver at a given frequency

            I think GranteedEV described how to make the best X-over. But you can probably make a "good enough" X-over with just your software and the answers to your question. Impedance plots are usually included in the manufacturer's data sheets, which, for most drivers, can be found somewhere on-line. I found the data sheet for your Eminence Delta Pro here:http://www.eminence.com/pdf/Delta_Pro_12A.pdf The impedance curve is the light grey line. Looks like it's about 18ohms at 2000Hz. The Eminence ASD-1001's data sheet is here: http://www.parts-express.com/pdf/290-525s.pdf. Looks like ~9ohms at 2000Hz. I recommend not spending a lot on top quality X-over components, as you may want to change them later. Another suggestion is to use an L-pad (http://www.parts-express.com/cat/speaker-l-pads/306) to attenuate whichever driver is louder, rather than a fixed resistor.

            Good luck and have fun!

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