Ohm ignorance...

Discussion in 'Amps and Cabs [BG]' started by Lowendmad, Dec 29, 2007.

  1. Okay.. I admit i'm a little ignorant when it comes to this and i'd appreciate anyone that can help me out...

    I have an Eden Wt-400 Traveller (4 ohms)
    I borrowed a 15" from a friend and i doesn't state what impedence it is. Can i just plug it in and go or is it bad if its an 8 ohm cab.

  2. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    It's a solid-state amp (the tube in the preamp stage doesn't count). With solid-state amps, you can't hurt them by plugging into the wrong load rating. It's only with all-tube amps that you have to be more careful about the load rating of the speaker cab.
  3. Chazinroch


    Feb 2, 2003
    Ontario N.Y.
    If the amp is rated 4 ohms, you can use an 8 ohm cab. It just won't be as loud. If the cab is 4 ohms, then you are right on! If it's a 2 ohm cab then you have trouble. Too little resistance and the amp over works to try and supply power. You can fry an amp with too little resistance. I think you are safe however, I have not heard of any single cabinets rated at 2 ohms. If there are any 2 ohm cabs, then I am not aware of them. I believe this is the case for both solid state and tube amps.
  4. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Actually, that's a good point, I forgot about the possibility of a 2 ohm cab. It's unlikely, but possible, and it could cause harm even to some SS amps- although some amps are designed to operate well at 2 ohms.

    Pretty much any load rating over the minimum stated on the back of the SS amp is fine. So if the amp says 4 ohms, then 4, 5.3, 8, 16 ohms etc. are all fine. If it can handle 2 ohms it will probably say so on the back of the amp.
  5. Cheers guys..
    I've been studying up on it today and i was a little concerned knowing my amp has a tube pre but your post cleared that up.

    Man, i dig this site... who needs school huh??
  6. Ívar Þórólfsson

    Ívar Þórólfsson Mmmmmm...

    Apr 9, 2001
    Kopavogur, Iceland
    Moved to amps.
  7. dman_113

    dman_113 Beware the Jabberwock, my son!

    Nov 4, 2007
    Sometime the speaker its self will have the ohm rating on it, you could open it up and see.
  8. That is true, but only in theory. On a solid state amp you lose about 3dB on the top end, which can't be heard.

    It has to do with heat generation and efficiency, but I don't remember enough to explain it. Plus, when you go up in ohms you gain damping, which in a bass application more than makes up for any loss in volume.

    If we were talking about a tube back end, then it would be different.

    Also, I was told by a QSC rep once that modern SS amps will not damage themselves if you run them at too low of an impedance. The fuses and thermal overloads will shut them down long before permanent damage occurs. I would think that applies to nearly all modern power amps.
  9. greenboy


    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    In a decent design damping differences won't even be noticable.

    Decent power amps have good thermal management, but not all heads do. It's weight, cost, and engineering tradeoffs.