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Tweeter and Ohms????

Discussion in 'Amps and Cabs [BG]' started by jrpark, Sep 28, 2009.


  1. jrpark

    jrpark

    May 6, 2009
    In most of the research I've done on repairing my 210 cab, people only talk about the main drivers when calculating Ohms. I thought that having an 3rd 8 Ohm speaker, the tweeter, would factor into this, but then It seem like the crossover comes into play here.


    So what is happening here? I am wiring two 8 ohm speakers in parallel to make 4 ohms, but the the crossover shuts off a speaker and uses the tweeter instead when the frequency is high enough, thus remaining at 4 ohms. Am I getting that right?


    Thanks
     
  2. seamonkey

    seamonkey

    Aug 6, 2004
    Sure you want a tweeter? There's not a lot of bass content up that high.
    Most bass amps just hiss up there.
    I'm thinking you want a midrange
    Search the fEarfull threads for driver and crossover ideas.
     
  3. PBass101

    PBass101

    Jul 3, 2008
    Illinois
    +1. Never heard a bass cab with a tweeter that I didn't want to take a shotgun to the tweeter. If you want that upper harmonic content and can't get it with a regular bass driver, use a smaller midrange driver in your cabinet design.
     
  4. jrpark

    jrpark

    May 6, 2009
    Well, I'm repairing a cab I already have, and it has a tweeter. I am trying to replace the two drivers that are blown, but the tweeter is already there and working.

    I am mostly trying to figure out how having three 8ohm speakers essentially still adds up to 4ohms, I know they are wired parallel, so I can only assume that the tweeter and one of the speakers take turns so to speak.
     
  5. hbarcat

    hbarcat Supporting Member

    Aug 24, 2006
    Rochelle, Illinois
    It is my understanding that any speaker that has a crossover which filters out frequencies above a certain area (such as a tweeter around 3-4kHz) can be considered negligible for the purpose of calculating total impedance. For all practical purposes, just ignore it. Your cabinet has two 8 ohm speakers wired in parallel for 4 ohms total and you ignore the tweeter because the crossover makes it's resistance negligible in the circuit.

    If any of the cabinet designers/engineers on this forum wants to correct me on this, please chime in.
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
  7. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    You got it.

    Below the crossover point, the crossover raises the impedance of the tweeter so high that its effect on the overall net impedance is negligible. Also, up near the crossover point each of your "8 ohm" woofers probably has an impedance close to 20 ohms or so, or in other words around 10 ohms when they're paralleled - so that gives you a bit more leeway still.

    Duke
     
  8. jrpark

    jrpark

    May 6, 2009
    sweet. I am glad to finally have that final piece of my puzzle solved. I can now buy replacement speakers with piece of mind.

    Thanks everyone.
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    jrpark you didn't say exactly what repairs you're doing to your cab. Is a tweeter replacement on the cards? If so, the tweeters impedance suddenly becomes a potential issue. If the existing tweeter is 8 ohms, make sure the replacement is also 8 ohms. Changing the impedance of the tweeter will cause problems with the functionality of your crossover.
     
  10. Bassman203

    Bassman203

    Mar 29, 2008
    Chicagoland
    He said the the two drivers were blown, and the tweeter was fine.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    ahhh he did too. sorry!
     

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