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how safe is this?

Discussion in 'Amps and Cabs [BG]' started by steve-o, Apr 21, 2002.

  1. steve-o

    steve-o Guest

    Apr 17, 2002
    i bought a 8 ohm 410 cab
    i have a 4 ohm 15 cab
    i already know this makes 2.666667 ohms

    ok here is what i did.
    i plugged a cord from the 15 to the 410
    then from the 410 to the head.
    (the 410 has two inputs)
    i used an ohm tester and it said 3.5 ohms.
    the 15 alone it read 3.4 ohms
    and the 410 alone it read 7.5 ohms
    i found out that it is reading this because of a cord i am using. i used a radioshack cord from the 410 to the head.
    even though the cord ups the ohms by 1
    it doesn't sound differnt in fact it sounds awsome!!!
    everything i was hopeing for since i played a trace elliot stack.

    is this fine? would you all have any concerns?
    it won't show the pic sorry!
    and here is a pic
    the 410 is a crate. it is a sealed cab and it was only $190 at a pawn shop!!!
    can anyone identify the cab it doesn't look like the regular crate cabs it has the egg crate grill insted of the cloth. it looks better thatn the cloth
  2. yawnsie


    Apr 11, 2000

    Hope you don't mind, but I changed the name of the thread to something more specific - hopefully, this will get you some replies.

    If you're having trouble with showing pictures in your post, PM me the links and I'll see if I can get them to show up for you.
  3. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    What you were measuring was the DC resistance of the cabs. This is not the same as the impedance of the cab when a signal is applied. The impedance is a combination of resitance, inductive impedance, and capacitive impedance, all of which vary with the applied signal. So don't trust your trusty ohmmeter. It doesn't know any better, and your impedance is actually a nominal 2.67 ohms, give or take.
  4. steve-o

    steve-o Guest

    Apr 17, 2002
    it does read this with certain cords
    but if i use a radioshack cord it reads 3.5 ohms
  5. steve-o

    steve-o Guest

    Apr 17, 2002
    if i run my hartke at what i have been told at 2.6 ohms. but my ohm reader reads 3.4 ohms with a certain cords.
    if i don't turn my amp up to high will this still blow my amp.

    my ohm reader reads 3.4 on the 4 ohm 15
    it also reads 7.6 ohms on my 8 ohm 410

    but i was told not to trust my ohm reader
    if it is reading the same ohms as the 15 alone.
    and the 15 and 410 together. won't this be safe?
    i have never had a problem running this head and 15
    in three months!

    and also does anybody know why if i hook a cord to the 15 from the 410 then to the head from the 410 how this is reading 3.5 ohms?
    (the 410 has to inputs)

    do you all understand?
  6. We need to know the minimum impedence of your head first. If it's above 2.6666, don't use it, if below (2 usually) , then you're fine.
  7. steve-o

    steve-o Guest

    Apr 17, 2002
    no it is 4 ohms
    but i have never had a problem with it running the 15 and the ohm reader read 3.4 ohms
  8. Then don't do it; you're risking damaging your amp.
  9. you're 15 worked because it's 4 ohms, not 2.666.
  10. steve-o

    steve-o Guest

    Apr 17, 2002
    i am sorry maybe i am not just getting this,
    but when the two cabs are together it read the same 3.5 ohms or higher. so wouldn't this be alright?
  11. The point that Munji made is your reading is of DC resistence not impedence.
  12. You'll put your eye out kid.
  13. steve-o

    steve-o Guest

    Apr 17, 2002
    what is dc resistence?
    i took electronic class but i don't remeber anything
    but the 15 cab read the same ohms so what is the differnce about measuring the single 15 to the 15 and the 410?

  14. It works like a triangle....

    Just for **its and giggles,

    First, draw a horizontal line. That is resistance.

    Then at the right end of the line draw a vertical line up about half the length of the horizontal line.

    Now draw from the left end of the resistance line, to the top of your vertical line.

    This would be your impedence.

    Now, you don't exactly know the reactive componant, so the vertical line is not correct, but you can see how it affects the impedence.

    When you are putting your ohmmeter across the speaker, you are mesuring ONLY resistance, and not taking that vertical factor (reactance) into the equation.

    Speakers are inductive, and not purely resistive, and the signal is AC, not DC when the speaker is moving, so you can't just mesure with a meter.

    Sorry for the geek talk, but I hope it helped. (or at least conjured up memories of your electronics class!!)

  15. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    Simple answer:

    No, it ain't safe.
  16. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    I think ihixulu said it best.
  17. Ty McNeely

    Ty McNeely

    Mar 27, 2000
    If your amp will go down to 2 ohms, YES, it is OK. If your amp will NOT go down to 2 ohms, NO, it is NOT ok.
  18. It's an RLC circut

    R = Resistance. Measured in ohms
    L = Inductance. Measured in Henries
    C = Capacitance. Measured in farads

    Just using a RESISTANCE meter does you no good. You have to measure INDUCTANCE and CAPACITANCE also in order to get a value for Z (Total Impedance). If you don't understand these other terms, then you need to do some reading HERE

    But you can do whatever you want. If you've convinced yourself it's okay after everyone says no (including me), and after doing some actual research, then feel free to push your amp hard enough to cause thermal problems, and let the smoke out of the electrical components, then go ahead. I know I won't complain.

    *Capitals used for important points
  19. steve-o

    steve-o Guest

    Apr 17, 2002
    all right thanks for all the input.
    i am getting an 8 ohm speaker or an 2 ohms head
  20. punkfunkfreak


    Dec 16, 2001
    you are all either very smart, or have too much time/money on your hands.

    Not that thats a bad thing ;)

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