Blog Forums DIY Speakers and Subwoofers Is it OK to put a resister inline with a woofer/midbass driver to increase the ohms?

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    • #13296
      willylax24
      Member

      I have built a MTM center channel with two 5″ Morel CAW538 woofers and 1 Kartesian TWt30 tweeter.  The two woofers are 8 ohms so if I put them in parallel, the impedance dips down below 4 ohms between 120 and 220Hz and hits a low of about 3 ohms at about 175Hz.  My amp, the Adcom GFA 7000 is rated down to 3.2 ohms.  Would this be a problem?  If I put seven 3.3ohms resisters in parallel and connect them in series to the woofer, it brings the impendence up to 3.6ohms at the lowest point, still at 175Hz.  Is adding resisters just a bad idea?  If I understand correctly, it does lessen the amps ability to control the woofers, but they will be crossed over by the home theatre receiver at 80Hz, so I am not sure if that is a big issue in this case??

      I know I can wire the two woofers in series, but then I end up with decreased bass, causing me to have to had a fair amount of resisters to the tweeter to bring it back down, making the speaker not very efficient, especially when compared to my front towers.  So I guess my main question is, better to wire in series and just increase the level of the center channel to match the towers (while having a very uneven impedance with multiple spikes over 20ohms ), wire in parallel with a dip down to 3ohms, or wire in parallel and add the resisters?

      I did try changing the inductors values on the woofers and changing from 2nd to 3rd order, but could not get ride of the impedance dip without ruining the frequency response.

      Thanks in advance for any help.

       

       

       

    • #13301
      123toid
      Keymaster

      @willylax24

      You never want to put a resistor on a woofer or mid if it’s playing your low notes. It will see a lot of of power and get very hot. I don’t you’d have a problem if you were at 3 ohms, if it’s rated at 3.2. that’s under a 10% tolerance. Either way, if it is an issue, your amplifier will typically cut ou. Aka self protect. I’m assuming adcom has a self-protect. If you’re still concerned about the crossover. Why don’t you post some of the files and we can take a look at it. 


    • #13306
      willylax24
      Member



      I have attached my X-sim layout, frequency repsonse and impedence graphs.  These are with the woofers in parellel.  My concern with this configuration is that the impedence drops down to 3 ohms about 175Hz.  Please let me know if you see any other problems.

      Thanks!! 

    • #13314
      123toid
      Keymaster

      @willylax24

      It does drop pretty low.  You might end up having to put hose woofers in series if your amplifier can’t take it.  Keep in mind on where you are going to cross it at.  That will make a difference with the lower frequency impedance. 


    • #13315
      123toid
      Keymaster

      @willylax24

      Why don’t you upload your xsim files on here.  You will probably just have to zip it for the forum to upload it.


    • #13316
      willylax24
      Member

      It would not let me attach a zip file or a Xsim .dxo file.  Not sure if this will work, but I changed the file extension on the Zip file to jpg, and it let me upload the file.  Hoping you can download the jpg file, then just change the file extension back to .zip to extract the files.

      Thanks,

      Willy

       

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