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  1. #1

    Default 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. #2

    Default Re: Size of capacitor vs frequency it blocks

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

  3. #3
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    Default 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 .

  4. #4
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    Default Re: Size of capacitor vs frequency it blocks

    Quote 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 at 08:55 AM. Reason: additional link

  5. #5

    Default Re: Size of capacitor vs frequency it blocks

    You also need to know the speakers impedance !!!

  6. #6
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    Default Re: Size of capacitor vs frequency it blocks

    Quote 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

  7. #7
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    Default 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 Thumbnails Attached Thumbnails Click image for larger version. 

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  8. #8

    Default 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!

  9. #9
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    Default 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

  10. #10

    Default 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.

  11. #11
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    Default Re: Size of capacitor vs frequency it blocks

    Quote 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.

  12. #12
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    Default 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.

  13. #13

    Default Re: Size of capacitor vs frequency it blocks

    Quote 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

  14. #14
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    Default Re: Size of capacitor vs frequency it blocks

    Cut off range of that is?
    For a 4 ohm tweeter about 5850Hz.

  15. #15

    Default 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!

  16. #16
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    Default Re: Size of capacitor vs frequency it blocks

    Quote Originally Posted by nick650 View Post
    ... 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.
    Actually it's the same thing in function....
    Are the tweeters to be fed a filtered signal off an active crossover?

  17. #17

    Default Re: Size of capacitor vs frequency it blocks

    What I'm doing is: Connect the midbass drivers to the amplifier directly with no filters in between the amplifier and midbass speaker. For the tweeters, you can run a second pair of speaker wires from the amplifier (there are advantages to this; it’s called bi-wiring), or simply connect the tweeter
    wiring right off of the midbass or midbass’ wiring. You will then install the capacitor on the positive lead of the tweeter’s speaker wire.

    So technically all i can do is a HP filter for my midrange witch will be set at 50 Hz 24DB slope. The tweeter then needs a crossover or a capacitor. Next issue I looked at is the frequency response of the woofer; doesn't seem to do well after 1k Hz. What I'm getting at is would a crossover with all these cut off's and slops give me better quality sound then running it active in a bi-wiring mode with just a simple capacitor in series for it?

    Thanks!

  18. #18
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    Default Re: Size of capacitor vs frequency it blocks

    Next issue I looked at is the frequency response of the woofer; doesn't seem to do well after 1k Hz.
    The Legatia L1V2 tweeter has an (Fs): 1,830 Hz, and a Recommended Minimum Crossover: 3,200 Hz at 24 dB/octave highpass ( Frequency 2,500 Hz – 25,000 Hz, +/- 3 dB. )
    That leaves a response gap - above 1Khz, and below the tweeters safe bandpass.

  19. #19

    Default Re: Size of capacitor vs frequency it blocks

    Yes there is a gap and was wondering if it would be best to get a better tweeter to fill in that gap or? Then the next thing is the overlapping and if it is best for the woofer to naturally roll off or build a passive network to fix all that.

  20. #20
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    Default Re: Size of capacitor vs frequency it blocks

    IMO - yes

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