Matching Correct Cab Impedance/Wiring with Amp Head

Discussion in 'Amps and Cabs [BG]' started by Shnosh13, Jun 7, 2020.

  1. Shnosh13


    Jun 6, 2020
    Dallas, Texas
    I have a Quilter Bass Block 800 that has One Speakon and Two 1/4" and says 4 Ohms by the outputs [see image]. The two Cabs that I have have a switch and can either set to 8 or 4 Ohms.

    My question is what is the optimum set-up/wiring for this with my amp?

    With my limited knowledge in this area, my guess that you would want a separate 1/4" cable for each cabinet and set both cabinet impedance to 8 Ohm which [I believe] will put a 4 ohm load on the amp.

    If someone awesome want's to confirm this, or tell me I am WAY off and what I need to do to fix it, it would be appreciated a TON!

    If you have any other questions you need answered to help, reach out and I will get right back to you!

    Thank you!


    Attached Files:

  2. Wasnex


    Dec 25, 2011
    What kind of speakers do you have? The only speakers that I know of that actually switch from 4 to 8 ohms are the Epifani DIST series.

    Since your amp is 4 ohms minimum, it depends upon whether you will use one cab or both. If you are going to use both cabs it is essential that you set them to 8 ohms. Two 8 ohm cabs in a parallel will provide the minimum 4 ohm load your amp is rated for. If the cabs are set to 4 ohms, the load will be 2 ohms which could potentially damage your amp.

    When you use one cab, you can make a decision based upon the power rating of the speaker, power rating of the amp at 4 and 8 ohms and the resultant sound. The amp will make maximum power at 4 ohms. If the cabs RMS rating at 4 ohms is equal to or greater than the amps rating at 4 ohms, you may want to use the 4 ohm setting if you need full volume.

    However, something to keep in mind is many speakers are excursion limited below their RMS rating for low frequencies. This is the mechanical power rating of the system versus the RMS rating, which is a thermal rating. Few companies actually publish any data related to their cab's mechanical power rating; so it's wise to use caution, especially if you really like pumping up the lows.

    If you don't need the full volume of the amp, consider setting the speaker to 8 ohms so it limits the amp's output so there is less chance of damaging a speaker by accident. The different impedance may have some subtle effect on sound quality as well.
  3. Shnosh13


    Jun 6, 2020
    Dallas, Texas
    Oh man thank you so much for taking the time to write such a clear, informative reply!

    That was my thinking, but the extra explanation, really helped me grasp the "Why", and that is the thing that I have struggled with.

    To summarize:
    Say "no" to Parallel/4 ohms and Series/8 ohms you could damage your amp and/or speakers.
    4 Ohms for optimum volume with One 4 Ohm cab, or Two 8 Ohm cabs in Parallel.
    You can also run a single 8 Ohm cab [if you can take a volume hit] to run "safe".

    How'd I do?

    Seriously, thank you for the response... Oh, and the cabs are two Hartke Hydrive HD 1x12.

    Have a good one!

    Wasnex likes this.
  4. Paulabass


    Sep 18, 2017
    I believe theres some Hartke cabs with a 4/8 ohm switch.
    Wasnex likes this.
  5. Shnosh13


    Jun 6, 2020
    Dallas, Texas
    I think you posted at the same time I posted my reply... you are correct! Hartke Hydrive HD 1x12.