frequency vs impedence?

Discussion in 'Home Theater Projects' started by RaphaelZ, Mar 13, 2005.

  1. RaphaelZ

    RaphaelZ Agent

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    Hi,

    I have 3-way DIY speakers that I built a few years back using all Radioshack componetnts. I'm using their standard, convertible 3-way cross-overs, and the crossover points are 800, and 5000. The whole system is 8 ohm, including all thre drivers. My question is how would the crossover frequency change if I replaced the 8ohm midrange with a 4ohm midrange? Also, what happens if you use 8-ohm drivers in a 4-ohm crossover? How does driver impedence affect crossover frequency on a pre-built crossover?

    Thanks


    8" woofer
    6" mids
    1" dome tweeter
     
  2. Jason Dalton

    Jason Dalton Stunt Coordinator

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    The crossover frequency will depend on the impedance of the midrange in the crossover region. The impedance of the drivers differs depending on the frequency. Look at the bottom plot in this link:

    http://www.partsexpress.com/pdf/296-145g.pdf

    That's the the impedance profile of a typical driver. a "4-ohm" driver may have an impedance of 5 ohms @ 800Hz and an impedance of 13 ohms @ 5000Hz.

    Also, there is really no such thing as an 8-ohm or 4-ohm crossover. You can hook whatever drivers you want to it, but the crossover frequencies will just be different.
     
  3. RaphaelZ

    RaphaelZ Agent

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    Ok

    That makes sense. Now, in principal will the midrange frequency increase or decrease with a decreased impedance, and is there a rule of thumb or formula? Regarding 4ohm or 8ohm crossovers: will my receiver see any difference in the total speaker resistance after I change one of the drivers, or does the crossover still maintain 8ohms at the terminals?

    Thanks
     
  4. Jason Dalton

    Jason Dalton Stunt Coordinator

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    The amplifier will (probably) see a lower impedance when reproducing frequencies in the midrange.
     

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