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Help! No-name Cab. How Do I Find Ohms?

Discussion in 'Amps and Cabs [BG]' started by Bluesbreaker5, Apr 17, 2006.

  1. Bluesbreaker5


    Mar 24, 2006
    OK....Impulse buy. Nice "home-made"? 2x10" bass cabinet. Sounds great! But afraid to daisy-chain it with a 8 ohm cab since my head is 4 ohms and I have NO idea what ohms it is. Bought at pawn shop. How in the heck can I find out how many ohms? I know chances are it is 8 ohms, but is there any way I can tell for sure?

  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Measure the resistance with a DMM, it will be about .6 times the impedance.
  3. Bluesbreaker5


    Mar 24, 2006
    DMM ??
  4. Bassic83


    Jul 26, 2004
    Texas, USSA
    Digital Multi Meter. Available for real cheap at Radio Shark.
  5. Bluesbreaker5


    Mar 24, 2006
    ok....then where do I stick it? Thanks...
  6. Bassic83


    Jul 26, 2004
    Texas, USSA
    Um....let's not go there...;) :D

    Put one probe on the tip, the other on the sleeve. Or, if you have a crappy cord, cut it, strip some insulation off the wires, one probe on one wire end, the other probe on the other. Set to Resistance, it should give you a fairly accurate reading. Instructions are usually included in the box as well.
  7. Bluesbreaker5


    Mar 24, 2006
    Well I went to Radio Shack and got the meter. Tried it in my amp to make sure I had things right...yep, 4 ohms. Then I did the no-name cab and got no reading. So I try my Ampeg 4x10 and no reading either! Same cable. What am I doing wrong? Thanks!
  8. jake_tim


    Jun 28, 2005
    North Carolina
    if your lucky, look at the speakers, they "should" state thier independance(hope i spelled that correctly). and then just do the proper calculations to determine the resistance of the cab.

  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    While you're at it, if the cab is home-made, then the drivers may be off-the-shelf. Write down the make & model, and make your best measurement of the internal dimensions, along with the dimensions of the port. Using WinISD, you can get a pretty good picture of how the cab behaves.
  10. Bassic83


    Jul 26, 2004
    Texas, USSA
    Bad cord with intermittent short, perhaps? Your amp shouldn't be giving you a 4-ohm reading. Your cabinet, maybe. Unless you have a combo amp and were taking the reading off the speaker? That would work. Now, take one of the speakers in your 210 out. Check that one. If it reads 16 ohms, it'll likely be an 8 ohm cab (16+16=8). If it reads 8 ohms, it'll likely be a 4 ohm cab (8+8=4). If you can get to the other one, get it's reading as well.

    If your amp reads 4 ohms on the internal speaker, and you connect your 4 ohm cab, your total load is 2 ohms(4+4=2). If your cab is 8 ohms, and you connect it to your 4 ohm internal, you'll have 2.6 ohms(8+4=2.6). Either way, I don't see a lot of combos that can push a 2 ohm load without letting the magic smoke out. Some see 2-something ohms and just get real quiet.
  11. RobertUI

    RobertUI Thumper Supporting Member

    Apr 7, 2005
    Herndon, VA - NoVa
    I'm curious by what you mean with "Tried it in my amp ... yep 4 ohms". I read this as you're putting this into the output of your amp, I am not sure what that's going to be telling you. If it's not working on with the cable you've got, you should really disassemble the cab, and test each speaker to check the rating. Like others have mentioned, you are likely to find that the ohms are written on the speaker somewhere.


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