??? I have a question about speaker wattage ???

Discussion in 'Amps and Cabs' started by thesooze, Feb 17, 2008.


  1. thesooze

    thesooze Supporting Member

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    Hey, I've got a Z Maz 38 head-- if I get a cab with speakers that are rated at 30 watts or lower (say a 25w Greenback, 15w Blue, 30w G12H30) does that present any problem to running the head like it should?

    Will it break up sooner than, say, running it into a cab with Vintage 30s (rated at 60w??). Not sure how it all works.

    BTW, since I've got you here-- is it correct to say that 4 ohm most breakup, 8 ohm less breakup, and 16 the cleanest?
     
  2. rockon1

    rockon1 Member

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    Speaker impedance values shouldnt change the break up characteristics . Ive noticed slight changes in tone though when running amps at different impedances-some amps more than others.

    Running a lower wattage speaker than the amps output poses a threat to the amp if you blow the speaker while playing. This can damage the output transformer. Its better to have a speaker rated 50 to 100 % higher than the amps output to minimize this from happening.

    The G12H-30 is one of the few speakers I would mate ith a 30 watt amp as I know from first hand experience its rated conservatively. That said its better to err on the side of caution and keep the speaker match up to 50 to 100% higher than the amps rated output. Bob
     
  3. Steve Dallas

    Steve Dallas Supporting Member

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    A good rule of thumb is 1.5 times the output of the amp. The reason is your amp's output rating (if it is done correctly) is measured with 10% THD, which means clean. That's usually around 9-10:00 on the dial. When you crank an amp, you can increase its output to almost twice its rating in some cases.
     
  4. thesooze

    thesooze Supporting Member

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    So with a 38 watt amp, would you not recommend using Blues or Greenbacks which are rated below 30 watts each? Maybe use a Vintage 30 that's rated at 60 watts?
     
  5. Steve Dallas

    Steve Dallas Supporting Member

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    No, you'll blow those in a heartbeat unless you are talking about running 2 in parallel.
     
  6. thesooze

    thesooze Supporting Member

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    parallel? Can you explain how/why that changes things?
     
  7. thesooze

    thesooze Supporting Member

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    I have no idea. I get an "F" for that quiz.
     
  8. GCDEF

    GCDEF Supporting Member

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    If you're running two speakers, multiply the power handling of the lowest rated speaker by 2. If the answer is greater than the power of the amp, you're safe.
     
  9. StompBoxBlues

    StompBoxBlues Member

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    Couple of things, but first your question...

    Answer: Watts = volts x amps, in a parallel circuit the current (amps) splits according to the impedance/resistance. Since this is EQUAL, it splits in half. The voltage is the same at the tops (plus side) for each "leg"...so in your example each leg would need to have a speaker at 25 watts (not taking into account the tolerances).

    In a series wiring, the current is the same through both elements, but the voltage divides, but again..EVENLY, so that half drops over the first element half over the other, so because watts = volts x amps, it is still two 25 watt speakers or better.

    BUT...I think this is the wrong tree you are barking up. I could be totally wrong, but my understanding is that the EFFICIENCY of the speakers has WAY more to do with them sounding OD'ed or not. More efficient speakers give you more headroom, you want speakers to be pushed hard, I think you need less efficient speakers.
     
  10. thesooze

    thesooze Supporting Member

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    So back to the original question-- If I run a 38 watt amp through two speakers (one rated at 60w, one rated at 30w), neither will blow (because 30x2=60) but one will break faster than the other??
     
  11. GCDEF

    GCDEF Supporting Member

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    You'll be fine. If the efficiencies aren't the same, one may sound louder than the other though.

    As far as the speakers breaking up, in general a lower wattage speaker will break up before a higher wattage one, but that's just in general. I doubt you'd get a whole lot of breakup out of either of them, which IMHO is a good thing.
     
  12. eru

    eru Member

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    You also have to take into account that the impedance of series vs. parallel wiring for speakers is different. 2 8 ohm speakers in parallel would be a combined load of 4 ohms, while wired in series, they'd be 16 ohms. And (drum roll) the output power of the amp can change based on the impedance load its running into depending on exactly how the taps on the output transformer are wired.

    This last part is funny coming from the pro audio world, since I had to think about this with every sound system I designed, hooked up, or sold (worked in live sound at GC), and I have not once heard about this in the context of guitar amps/cabs except when I mention it.
     
  13. GCDEF

    GCDEF Supporting Member

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    Not exactly sure what you're saying here. Can you explain.
     
  14. rhythmrocker

    rhythmrocker 1966 Battle of the Bands Supporting Member

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