Active Subwoofer Circuit

Discussion in 'The Projects Forum' started by noingwhat, Dec 9, 2010.

  1. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    I am trying to find the simplest sub-woofer circuit, so that I can build it to add to my home theater system I sorta just threw together. So far, the simplest one I can find, I think I might be able to do, but I would still like to know if there is something simpler out there.

    [​IMG]

    In the page I found this it says that this circuit can be simplified and if anyone can tell me how, that would be awesome!

    This is only my second circuit (my first being a simple RC circuit with a few extra components put in) so that is why I want it so simple. Thanks to all who help!
     
  2. R!f@@

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    Apr 2, 2009
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    Buddy..That is as simple as it gets.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    That is only a filter/pre-amp for an active subwoofer, you'll still need a one channel power amplifier to actually drive the speaker.

    Here is a link to one, that would go between the circuit above and a 400W capable speaker.
     
  4. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    I already have an amplifier, I just need a super simple preamp/filter.
     
  5. thatoneguy

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    Feb 19, 2009
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    Most active subwoofers have line in, line out, speaker level in and out, gain and freq cutoff.

    What brand amplifier and active sub do you have? You may not need the circuit.
     
  6. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    Its just a regular amp, a really old one with a radio and everything in it. I just use the line in.

    And my subwoofer is an old speaker that has a big 12" woofer in it, and I cut the wires to the midrange and tweeters.
     
  7. R!f@@

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    Apr 2, 2009
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    U cannot make a sub woofer by cutting out the Mid/high end of Full range speaker.

    Sub woofers operate well below the range of normal woofers. And it requires lots & lots of power to reproduce the low frequency range, not to mention the driver and it's cabinet
     
  8. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    I don't understand, why can a regular woofer not reproduce the same frequencies given the correct filter. idk if it's normal or not, but my speaker DOES have the capability to reproduce very low frequencies, when I hook it up to my computer and audacity, it can play all the way down to 1hz, and I believe that is as low as audacity allows.

    It is a 100 watt woofer and I actually have two different amps I can use. I have the 100 watt hooked up to it right now (it is currently on a passive R/C filter for 300 hz, so I am trying to upgrade with an active filter), and I also have a 450 watt which has a blown fuse.
     
  9. R!f@@

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    Apr 2, 2009
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    Can you hear 1Hz

    Can you provide the specs of your speaker
     
  10. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    Obviously I can't hear the 1hz, it is below audible hearing range but on a 12" woofer, it is pretty easy to see it moving back and forth as long as it is below about 20hz or so.

    The best specs I can give you are the ones that came with the speaker, but all I am using is the woofer and box that came from a speaker with a woofer, tweeter and midrange.

    --------------------

    Fisher DS-178

    Min: 10 watts
    Max: 100 watts
    Impedance: 8 ohm

    Three way system with a 12" woofer, a 5" midrange and a 3" tweeter.

    ---------------------

    Sorry, but the best I have is the info on the label sticker. All I have, it is one of my dad's really old speakers from 20+ years ago.
     
  11. R!f@@

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    Ok..Does that speaker normally produce good bass when you play music?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    The circuit you found is used with a very special sub-woofer and enclosure that you do not have.
    It uses a sub-woofer in an enclosure that is too small for it so the sub-woofer operates at frequencies below its resonance in the small enclosure. It needs a lot of bass boost and the sub-woofer must be able to survive the very high power. Your low power woofer won't survive and won't produce powerful deep bass. Your amplifier doesn't have enough power anyway.

    Your woofer probably uses a big enclosure designed for it so it doesn't need the huge amount of bass boost provided by the circuit you found. But it will not produce powerful deep bass like a sub-woofer.

    A normal sub-woofer simply needs a Butterworth lowpass filter to feed its amplifier. Then the other speakers need a complimentary highpass filter to feed their amplifier.
     
  13. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    I'm not sure, I'm trying to use it for a home theater set-up built more for movies and tv shows. I used to have it hooked up to my computer and used it as a little dj kinda thing, but I used a different amp, and different speakers (to handle the higher frequencies. I had it setup to cut off around 500hz or so), and with that setup, yes, it played great music, and I would presume it would be the same with the new setup I have.

    Wow, thats all I need and that will work fine? Will it perform as well as this circuit would for a proper woofer & encloser?
     
  14. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    you can produce it, but without a resonant chamber, your power levels will be inadequate.
     
  15. thatoneguy

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    Feb 19, 2009
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    I'd strongly suggest a Sunfire sub, or a Definitive if you can afford them. They provide solid LFE down to just a few Hz.

    Check out eBay.

    LFE is THE most taxing power wise and design wise to get correct. 400 W RMS is norm, 1kW RMS or more is the norm for home theater.

    LFE channel needs to move a LOT of cubic feet of air, this can be done with a sub having high enough excursion. A typical Woofer in a home system is only good to around 30 Hz, with 20Hz being 3dB rolloff. LFE is 3dB down at 10Hz.
     
  16. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    I'm just basically trying to throw something together for real cheap using stuff I already have. Only thing I'd be buying for the preamp is a few components and a project box, totaling up to only about $5-10.
     
  17. R!f@@

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    Apr 2, 2009
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    You really have no idea what you want, do u?
    You have no idea what a Butter worth filter is and you have absolutely no idea on what an active low pass filter does and how many different levels of cutoff can be achieved from it. do Ya?

    Stop asking what you want to do and tell us what actually you are trying to achieve, together with what you have and the budget

    Oh...u did said 10 bucks....well...with that money you can go fish.
     
  18. noingwhat

    Thread Starter Member

    Jul 23, 2010
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    1st off, I will admit, I am not 100% what a butterworth filter/active low pass filter is, but from what I know, it is a filter that has a specific cutoff frequency and just about everything above that will have a massive DB drop and everything below that will either be preserved or amplified.

    I already said what I wanted to achieve in the beginning of this thread. I am trying to build a sub woofer filter, I already have the driver, speaker box and amplifier, all of which I have previously stated.

    10 bucks? yes, my electronics store has small project boxes for $1-3 breadboards for about $1 and the resistors and caps are roughly $.10 a piece. Only thing I cant find there is the op amp, and I wouldn't presume that it is THAT expensive. I believe $10 is reasonable, all I need is the filter, and not a really complex one, just a few, simple components.
     
  19. R!f@@

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    OK. then decide what you want..a passive filter or an active filter
     
  20. Kermit2

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    Feb 5, 2010
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    [​IMG]

    For a filter that works at sub woofer freqs. you would need about $50 worth of steel and copper wire for the inductor.

    Go for active filtering. :)
     
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