Speakers swap 8 ohm or 4 ohm ?

Discussion in 'Amps and Cabs [BG]' started by mercuryman, Mar 14, 2018.


  1. mercuryman

    mercuryman

    Dec 4, 2017
    I have a vented 2 15 cab and i wonder about buying 2 8 ohm speaker who give 4 ohm total or buying 2 4 ohm speakers who give a 8 ohm cab .

    I know the 4 ohm cab is easier to drive but witch one will sound better ?

    I can choose Eminence or Celestion in 4 or 8 ohm .

    Thank's
     
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    What amp(s) are you using
     
  3. I think you are taking an overly simplistic view of this project.

    Impedance alone has no bearing on how a cab will sound.
    Nor does brand name.

    There is a lot more to all of this than just picking a couple of speakers and bolting them into a box.
    Are you familiar with Theile/Small speaker parameters?

    What do you mean "the 4 ohm cab is easier to drive"?
    An amp has to work harder to drive a 4 Ohm cab, at least a solid state amp does.
     
    agedhorse likes this.
  4. mercuryman

    mercuryman

    Dec 4, 2017
    I am using a GK as pre amp and QSC MX1500a as power amp .

    Need less power to drive in 4 ohm . Am i right ?
     
  5. No.
    The speaker (Impedance) in use determines how much power the amp will deliver.
    Think of the job of a speaker to be to convince the amp how hard it will work.
    A 4 Ohm speaker will cause the amp to deliver more power than an 8 Ohm.

    When you discuss how a speaker might need less power to drive it, you are looking at the efficiency of the speaker.
    One of the parameters to consider is the speaker's SPL rating. (Sound Pressure Level).
    But the impedance (Ohms) by itself is not a determining factor in how easy it is to drive a speaker.
     
  6. Rick James

    Rick James Inactive

    Feb 24, 2007
    New Jersey
    It takes less voltage swing for the same output with 4 ohm, but it also takes more current. More current puts more demand on the amp, not less. You don't see it referred to with bass cabs, but some home stereo speakers are called difficult to drive, and it's because they are low impedance.
    +1.
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    For power matching with that amp, I would be looking at an 8 ohm cabinet. Iirc, that amp does 1500 watts RMS at 4 ohms bridged and about 900 watts at 8 ohms bridged. 900 watts is a safer and better match imo.

    There were 2 versions of that amp, the earlier one may not have been rated for 4 ohms bridged. Also, there are parts that are no longer available for that amp (rail commutator pens) that often fail catastrophicly. Be very careful with your experiments.
     
  8. Just because you can doesn't necessarily mean you should...
    I agree with the above that [email protected]Ω would be the wiser choice. Less heat... Cool good. Hot not.
    If 900w won't get it done, it won't get done....
     
    saabfender likes this.
  9. BassmanPaul

    BassmanPaul Inactive

    What’s wrong with the drivers that are already in the cabinet?
     
    mbelue and agedhorse like this.
  10. mercuryman

    mercuryman

    Dec 4, 2017
    They are finish and i dont want to recone . I was playing and they start to smell electric burn .....
     
  11. All the more reason to keep your cab at 8, or even go to 16 Ohms.
    If the speakers are smelling of an electrical burning smell, you are running too much power.
    The smell would be the insulation of the voice coil wires burning.
    You have exceeded the thermal power limits of those speakers.
    They likely are compromised now.

    Having two 15" speakers with a total load of 8 ohms will put a max of 450 watts on each one.
    That's assuming clean audio. If you are driving into distortion, you can put even more power to the speakers.
    As it is, 450 watts seems to me to be lot to ask of a single 15" driver.
    And there is the question of what the speakers are actually rated to handle and is that rating in peak or RMS or what? If it's peak, for instance then they won't handle nearly as much power on a continual basis as you might think they will. Hence the burning smell.
     
  12. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    What does "finish" mean?

    Why not recone? What's wrong with that?
     
  13. I think he has an issue with the country of origin. :woot:

    On a serious note. If he has burned the coils, is a re-cone a good idea or just throwing good money after bad?
    I really don't have a good handle on how bad the smell of burning speakers is for the future usability. Can they recover from something like that?
    It seems like a pretty bad thing to me.
     
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Generally, burned could are not a problem for reconing but sometimes additional cleaning might be required.
     
    Old Garage-Bander likes this.
  15. Good to know. Thanks.
     
  16. BassmanPaul

    BassmanPaul Inactive

    they are from Finland? :)

    If they started to smell you used too much power. What is the cabinet?
     
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Wouldn't that be Finnish?

    Even so, there are Peavey authorized dealers all over that part of Europe.
     
  18. BassmanPaul

    BassmanPaul Inactive

    T'was just a play on words Andy. :D
     
    agedhorse likes this.
  19. They have fins?
     
    agedhorse likes this.
  20. mercuryman

    mercuryman

    Dec 4, 2017
    These speakers are very old ( 1990 ) and it's more expensive to rebuilt them then bought a new one .
     
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