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Size of capacitor vs frequency it blocks

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  • Size of capacitor vs frequency it blocks

    I need help to figure out what size of capacitor blocks what specific frequency. Is there a chart? If not what is the formula to calculate a specific capacitance to block a specific frequency?

    Example: 4 F capacitor is a first-order Butterworth filter at 10,000 Hz

    4 F : 10K Hz

    5 F: 12K Hz

    Hopefully the example explains what I mean.

    Thank you!

  • #2
    Re: Size of capacitor vs frequency it blocks

    the larger the cap the more low end frequency it lets through.

    Comment


    • #3
      Re: Size of capacitor vs frequency it blocks

      Here is a link to some fairly simple calculators, charts etc. http://www.the12volt.com/caraudio/crosscalc.asp .

      Comment


      • #4
        Re: Size of capacitor vs frequency it blocks

        Originally posted by nick650 View Post
        what is the formula to calculate a specific capacitance to block a specific frequency?

        See "A Simple Filter"
        http://artsites.ucsc.edu/EMS/music/t...impedance.html
        Last edited by Sydney; 04-14-2011, 08:55 AM. Reason: additional link
        "Not a Speaker Designer - Not even on the Internet"
        "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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        • #5
          Re: Size of capacitor vs frequency it blocks

          You also need to know the speakers impedance !!!

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          • #6
            Re: Size of capacitor vs frequency it blocks

            Originally posted by Servicetech View Post
            You also need to know the speakers impedance !!!
            AND you really need to see a plot of the impedance vs. freq.

            An 8 ohm woofer could be 6n at 200 Hz, but 30n up at 10k, and 20n at 2k where you want to cross it. A Zobel across the woofer can help flatten this rise.

            A 8n tweeter could be 6n at 4k, and 8n at 2k where you want to roll it off, but it could be 15n at its Fs (resonant freq.) at 1000 Hz (it could be DOUBLE that if it doesn't use ferrofluid). Since the Fs may be less than an octave away from your cap, it messes with the transfer function making it less effective at rolling the power off at Fs, causing great trouble.

            That's why only a simulation using actual impedance data (and response data) can really show you what's going on. Often you'll have to change a "textbook" calculated cap (or coil) by 2X or more.

            Chris

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            • #7
              Re: Size of capacitor vs frequency it blocks

              This may be something the OP was asking for.

              These component values are only a starting point and represent approximations based on the nominal 8 and 4 ohm speaker impedances listed.

              As others here have already pointed out, more accurate impedence values are needed at the crossover point of interest to design a more accurate crossover.
              Attached Files
              Live in Southern N.E.? check out the CT Audio Society web site.

              Comment


              • #8
                Re: Size of capacitor vs frequency it blocks

                http://store.12velectronics.com/prod...eeter-Set.html

                Tweeter I'm using and under the manual is an impedance and a frequency graph.

                http://store.12velectronics.com/prod...eaker-Set.html

                Woofer I'm using and under the manual is an impedance and a frequency graph.

                I hope that helps to get an accurate measurement of what I'm looking for.
                Here is another manual if that might help:

                http://hybrid-audio.com/White%20Pape...r%20System.pdf

                Thank you very much!

                Comment


                • #9
                  Re: Size of capacitor vs frequency it blocks

                  If you're planning to build a passive crossover for these, I suggest you use 3000 hz as the target - assuming those spec. sheets are correct.

                  Use 10 ohms for the woofer impedance and 3.5 ohms for the tweeter. Those are the impedances at 3 kHz according to their plots. They recommend a 24 dB slope for the tweeter. So, a 4th order Linkwitz/Riley might work well.

                  Now you can to to a crossover calculator web site and plug in those impedances in the 4th LR for the tweeter and see what you get. You may need a 1st or 2nd order for the woofer.

                  Those drivers seem quite pricey. Where is that 12V company located?

                  Good luck
                  Live in Southern N.E.? check out the CT Audio Society web site.

                  Comment


                  • #10
                    Re: Size of capacitor vs frequency it blocks

                    I plan to do a 50Hz low pass filter (off my Zed Leviathan amp) and do a quasi active and do one cap in series with the tweeter to protect it so I get the most out of my system since crossovers eat all the power and make my speakers not sound the best.

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                    • #11
                      Re: Size of capacitor vs frequency it blocks

                      Originally posted by nick650 View Post
                      I plan to do a 50Hz low pass filter (off my Zed Leviathan amp) and do a quasi active and do one cap in series with the tweeter to protect it so I get the most out of my system since crossovers eat all the power and make my speakers not sound the best.
                      If all youre going to install in terms of passive components is a cap to protect the tweeter, then a 6.8 uF 630V should work for you.
                      Live in Southern N.E.? check out the CT Audio Society web site.

                      Comment


                      • #12
                        Re: Size of capacitor vs frequency it blocks

                        Wow, those prices are absurd. I can't imagine spending that much for a car system. That's in accuton and RAAL altitude.

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                        • #13
                          Re: Size of capacitor vs frequency it blocks

                          Originally posted by carlspeak View Post
                          If all youre going to install in terms of passive components is a cap to protect the tweeter, then a 6.8 uF 630V should work for you.
                          Cut off range of that is?

                          Note: I bought them slightly used for $275 with a slight scuff mark on the side of the woofer, so I got a great deal on them.

                          Thanks

                          Comment


                          • #14
                            Re: Size of capacitor vs frequency it blocks

                            Cut off range of that is?
                            For a 4 ohm tweeter about 5850Hz.
                            "Not a Speaker Designer - Not even on the Internet"
                            "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                            Comment


                            • #15
                              Re: Size of capacitor vs frequency it blocks

                              Would it be better to get this tweeter instead? http://store.12velectronics.com/prod...eeter-Set.html

                              I'm trying to figure out what to do since I bought the woofer but not the tweeter. I could build an X-over for this whole setup but I feel I can just get by on using some simple caps to do the filtering.

                              Thank you all for your help so far!

                              Comment

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