possible bad speaker ohms question

Discussion in 'Amps and Cabs [BG]' started by Stay Gold 1337, Jan 14, 2009.

  1. okay so lets say i have potential bad speaker (it makes my power amp shut off after a couple minutes of playing) and i took it out and tested the resistance. it's an 8ohm speaker and it tests at 6.4 ohms. would that be indicative of a bad speaker? also, when a speaker is being used i imagine there's some heat generated, would this have an effect on the power draw it has if there's something wrong with the speaker?

    thanks guys -Jake
     
  2. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    The measurement you take with an ohm meter is a measure of resistance, not impedance. 6.4 ohms resistance is a normal, expected reading for a speaker rated at 8 ohms impedance.

    I could be mistaken here, but I think there is no way the speaker is causing your amp to shut down. Unless you're running an all-tube amp it is unlikely that having a problem with a speaker would be of any consequence to the amp.
     
  3. T-Bird

    T-Bird Guest

    Hi, Jake.

    I'm with Bongo on this one, it's unlikely that Your speaker is faulty.

    Impedance (AC) measuring equipment most definitely exists, but like said above, You measured resistance (DC) and the figure you got was the usual reading from an 8Ohm speaker.

    I think it's a tech time for Your amp if the problem occurs with another cable and/or another cab.

    Regards
    Sam
     
  4. oops sorry guys i got my terms mixed up there! i fixed it. anyhoo, it only happens with that cab. i tested all other variables... cables, side of the amp (stewart world 2.1), cabs. it only happens with this cab. my 410 doesnt do it. it will happen with either side of the amp as long as it's this cab... so that's what leads me to believe there's gotta be something wrong with the speaker.
     
  5. T-Bird

    T-Bird Guest

    Hi.

    No problem, that resistance/impedance confusion happens A LOT, no need to worry.

    Does the cab in question have any cross-overs, L-pads, anything, or is the speaker directly wired to the jack? Does the jack itself look ok?

    Never in my 25 or so years with speakers and amps have I encountered one that behaves the way You described. That won't obviously mean that the speaker can't be faulty ;).

    Regards
    Sam
     
  6. no crossovers or anything, just 1 15 inch speaker wired to a pair of speakons. everything looks great.
     
  7. billfitzmaurice

    billfitzmaurice Guest Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    If the speaker is OK then the cable probably isn't.
     
  8. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Is there a way that a faulty speaker cable could cause a Stewart World power amp to shut down?
     
  9. Rando McNally

    Rando McNally Guest

    May 21, 2008
    20106
    I had a world 1.2 that shut down like this. There was a little moisture on the circuit board. My tech fixed it for $50.

    On another occasion I had an amp power down with only one speaker cabinet. Turns out that a mouse had made a little nest right behind my inputs, and had use a foil wrapper that shorted out my amp when I plugged it in, engaging the protection circuit.
     
  10. I actually have had a speaker do this, on tear down the voice coil former was warped. The voice coil had two spots where the varnish had worn off. It was a used speaker and did not know the history of use, but it appeared the voice coil former bottomed in the magnet stucture.
     
  11. stflbn

    stflbn

    May 10, 2007
    Nashville
    Not sure if you're running your Stewart through a power conditioner or not, but it's HIGHLY frowned upon by them. It will starve the power amp of power and can cause shut-downs, distortion, and potentially damage to the power amp. They want their Power Amps running straight off a plug or power strip coming straight from a wall.
     
  12. John Wentzien

    John Wentzien

    Jun 25, 2007
    Elberta, AL
    Artist:TC Electronic RH450 bass system (original test-pilot)
    That's about the same resistance I get from one of my 8-ohm 15's. Does it sound OK?
     
  13. It's on the low side for DCR (Direct Current Resistance), but that could be heavier coil wire used in winding. If the speaker works okay it's fine. The driver found with the damaged voice coil had a DCR of 6.8 ohms, so the DCR didn't tell us anything.
     
  14. Rando McNally

    Rando McNally Guest

    May 21, 2008
    20106
    +1000 very true. They hate power conditioners.
     
  15. 2x4strgkramers

    2x4strgkramers Guest

    Dec 15, 2008
    Real question. If you gently push in and out on the speaker does the Direct impedence change stay the same etc ?
     
  16. aperfectbass

    aperfectbass Guest

    Mar 17, 2008
    Minneapolis, MN
    I had the same kind of thing happen to me, I was rewiring my one cabinet and unintentionally caused a short, my power amp would clip, even at low volumes and then shut off. Maybe it is that?
    Is it a new (or new to you)? I've known guys who their power amps and speakers have had different wirings when using the speakon connectors.
     
  17. T-Bird

    T-Bird Guest

    Hi.

    I would still redo all the wiring and perhaps measure the speakon connector(s) before buying a new speaker. I still have a hard time believing that the speaker sounds all right up until the amp switches off if it's faulty.

    ?? You mean measuring resistance of a circuit and feeding the meter AC from that same circuit at the same time ??

    A moving wire (a coil in this case) in a magnetic field will create AC. Because of the input impedance of the meter no harm is done, but the reading will be something jibberish.

    Regards
    Sam
     
  18. i don't use a power conditioner. how does one measure a speakon connector?

    thanks