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Passive crossover for 2x10 cab?

Discussion in 'Amps and Cabs [BG]' started by PolkaHero, May 15, 2004.


  1. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    I'm running 1000 watts through a single 15 and a 2x10 cabinet. My problem is that the 10s starting breaking up on the lower notes of my E string. Is there a passive crossover that is available to cut the lower frequencies (say 100 Hz on down) going to the 2x10? Thanks!
     
  2. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    Anyone? :ninja:
     
  3. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    The simplest way to do this is to put a capacitor in series to the 2x10's. This will give you 6dB per octave cut in the low frequencies. In other words, you're -6dB at 50Hz, -12 dB at 25Hz etc..........

    The value of the capacitor will depend on the Nominal Impedance of the cab. At 100Hz, an 8 ohm cab will need a 200uF Capacitor. If it's 4 ohms, you'll need 400uF.

    If this isn't cutting enough lows, you've got 2 options. You can either decrease the value of the Capacitor. For example use 130uF (8 ohm) or 260uF(4 ohm), bringing the crossover point up to 150Hz (ie-6dB at 75Hz, -12dB at 37.5Hz etc)

    The other option is to make up a 12dB per octave crossover. They're a bit more involved and require more parts (inductors as well as capacitors). Let me know if you need me to go into it further.
     
  4. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    Thanks for the reply! Sounds good, but will these handle 500 watts RMS of power?
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    The caps will have 2 numbers on them, the first one being the uF values mentioned earlier. The second one will be a voltage rating.

    The ones I use are rated to 100V. CLICK HERE to see an example.

    I'm not sure what that translates to in terms of watts, and the formula escapes me at the moment, but it's quite a lot. I've been pumping 400w through mine and haven't even had a hint of a problem.

    Make sure you tell the guy at the electronics store that they you need caps for Audio and that you're going to be pushing LotsaWatts.
     
  6. I' m looking to do the same thing but can you put this into more specific terms for me please? :help:

    I buy one of these caps for each speaker? And then they get wired how / where?? On the positive speaker lead, just before the speaker?? Or can I just put a single one on positive wire as it leaves the input jack heading for all the speakers. Or do I need one on both the + and the - leads?

    What's the easiest way to do this for us less electonically inlined folks??

    Thank you for any assistance with this matter, it is greatly appreciated.

    Rob
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    You'll only one one capacitor for the whole cab. The cap has to go somewhere in the positive side of the speaker wire something like this:-

    INPUT TERMINAL(+) -------capacitor--------> SPEAKERS.
    INPUT TERMINAL(-) ------------------------>

    This is a typical "series" connection.

    I guess the best place to put it is inside the cab on the positive wire that goes to the input terminal.

    I've actuslly knocked up a speaker cable that has a gap in the positive side that lets me experiment twith different capacitors. I just use aligator clips to slip caps in and out, so it's actually outside the cab at this stage. Once I find the cap I'm happy with, I stick it inside the cab permanently.
     
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    The capacitor would be wired between the positive terminal (tip of a 1/4 in., red of a banana, 1+ of a Speakon) and the wire that you removed to do this (which will go to either the crossover network or the + terminal of at least one of the woofers.)

    You'd need to calculate the maximum voltage that the cabinet will see. If it's getting 500 watts and the cabinet is rated 8 ohms, the voltage will be the square root of 500 x 8 (voltage squared divided by resistance equals power...or voltage equals the square root of resistance times power).

    The answer is just over 63 volts. You would need a capacitor with a voltage rating of twice that (for safety) but you might be able to get by with a 100 volt cap.

    If you have more than one input jack on your cabinet, you might want to install the cap on just one of them so that you also have a "full range" input if you're pushing the cabinet less or only take the 2x10 on occasion.

    Make sure you glue the capacitor down with some RTV (silicone caulk) or something similar to prevent it from breaking loose during Sonic Bombast :bassist: or transport.

    Another option would be to go to a car audio dealer and tell them that you need a "bass blocker" for the impedance and power level that you're running as well as the frequency that you want to roll off at.
     
  9. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Dang Pete, what time is it in Sydney right now? It's 5:50 pm (I mean 17:50) in Chicago.
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I posted that at about 8:30am (Tuesday morning). I like to check my emails before I start work.

    It's now 1pm and I'm eating a nice chicken pasta salad.....yuuuuummmmmmmy.
     
  11. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan

    Wow, I had about given up on this project until you mentioned this! I had decided I didn't want this as a permanent fixture, but as my cabinet does have two inputs, this might work. Thanks! :bassist:
     
  12. Sounds pretty easy, thanks a lot. My tone appreciates your assistance. I'll give it a try over the weekend.
     
  13. theinnkeeper

    theinnkeeper

    May 4, 2008
    Miami, FL
    wish i saw this before, i just bought a carvin r600 for the crossover..

    Rick