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Replacing a 4 ohm woofer with a 8 ohms one

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  • Replacing a 4 ohm woofer with a 8 ohms one

    Hi,

    Just a quick question:

    I am helping a friend with a replacement of a broken 4 ohms woofer and the woofers I have available are 8 ohms Focals.

    The system is not designed with todays modern tools, more like ”Steal a XO from a commercial system and use different drivers” (Strange, I know but the system is built in early 70-ies….)

    What do you think? Should I replace the woofers and hope for the best? I do not look forward to a complete design-work on this system.

    What can be expected to happen when you replace a 4ohms woofer with a 8 ohms one? I realize that the crossover-points are moving…..

    Regards//lasse
    Stockholm, Sweden
    Perry Mason talking to his dentist:

    "Do you swear to take the tooth, the whole tooth and nothing but the tooth, so help you God?"

  • #2
    The sensitivity will also drop. Of course the wacky frequency response might make that the least of your problems. Don't expect the best.
    Francis

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    • #3
      Hi,

      Actually I made a quick-and-dirty in-check measurement and this unit (with a non-broken woofer) measures quite decently I think, considering the history... (100 cm tweeter level)


      Click image for larger version

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      Regards//lasse
      Perry Mason talking to his dentist:

      "Do you swear to take the tooth, the whole tooth and nothing but the tooth, so help you God?"

      Comment


      • #4
        Yes, the tweeter shold be padded down like 5 dB but the owner wants it to be like this.
        Perry Mason talking to his dentist:

        "Do you swear to take the tooth, the whole tooth and nothing but the tooth, so help you God?"

        Comment


        • #5
          If the box is vented, then odds are that the box/tuning will end up not good. Less of a problem with a closed box (maybe).
          (Can you get T/S parms off the old and new woofers?)

          IF the 8n(ohm) woofer has approx. the same FR, just -3dB less sensitive, then I'd add 3 more ohms of series resistance in the tweeter filter somewhere.

          Also, changing the low-pass filter load (4n to 8n) only changes the Fc for odd-order filters.
          If they're even-order, the Fc remains approx. the same, but the filter "Q" will change.

          Comment


          • fpitas
            fpitas commented
            Editing a comment
            Yes, the higher Q will produce a lump in response.

        • #6
          I am not sure that this build merits itself for a build-thread but a few pictures.....
          Click image for larger version

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          Perry Mason talking to his dentist:

          "Do you swear to take the tooth, the whole tooth and nothing but the tooth, so help you God?"

          Comment

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