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(Amp1 X Watt) + (Amp2 X Watt) = ? watt

Discussion in 'Amps and Cabs [BG]' started by NoiseNinja, Jan 8, 2017.

  1. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone

    Feb 23, 2011
    It probably have been asked before, but couldn't come up with any useful search terms that lead me to an answer, so here we go:

    What would the result be?

    Or specified a bit more:

    If we are assuming you run your bass out two amps and cabinets at the same time, both amps does not only have equal watt technically but are also playing equally loud

    How many watt would you effectively gain by this, contrary to just one of the amps?

    Let's say they both are effectively pushing 100 watt through similar cabinets, just to come with an example.

    I know this probably would make more sense to measure in decibel, but as I am not well versed in exactly how decibel works, how much 1 decibel actually is, and if perceived sound level works exponential or whatever, a number in watt would personally give me a better idea of what kind of output I should expect.
    Last edited: Jan 8, 2017
  2. Jazz Ad

    Jazz Ad Mi la ré sol

    Theorically, doubling the power gives you a boost of +3dB, assuming the speaker can handle the extra power and has a somewhat linear response.
    Practically, you will get a drastic loss of volume when both amps go south. One does not plug 2 amps into the same cab. It's an electronic sin.
  3. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone

    Feb 23, 2011
    I did say similar cabinets, not the same cabinet.

    Either way I found the answer.

    And I am a bit embarrassed to admit I found the answer in an old thread started by myself with almost the exact same headline.

    What do you know, I must be getting senile.

    Anyway the correct answer is that you do actually double up the watt doing so, so in my example it would give a power equal to 200 watt, which again in the concrete example I gave give an increased volume perceived as +6 decibel compared to only running one amp at 100 watt.

    Well, at least according to someone who seemed knowledgeable in the previous thread, for all I know he might have made it up :p
  4. Rick James

    Rick James Inactive

    Feb 24, 2007
    New Jersey
    He was right. This brings up the recurring theme that watts don't matter, because we don't hear watts, we hear decibels. How many decibels we hear is based on the displacement of the speakers, and how much air the cones displace is based on the voltage applied to them. In this case two amps providing the same voltage to two speakers results in twice the displacement as one speaker, which gives a 6dB increase in output. You would get the same 6dB if you doubled the displacement of one speaker, which takes a doubling of the voltage applied. That's a quadrupling of watts, as opposed to only doubling watts with two speakers, showing again why you can't use watts as an indicator of loudness.
    NoiseNinja likes this.
  5. Nev375


    Nov 2, 2010
    100 watts + 100 watts = 200 watts. That might mean something to the electric company's billing department, but it means nothing in terms of volume.
    andruca likes this.
  6. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone

    Feb 23, 2011
    So 200 watts coming from two 100 watt amps with similar cabinets and turned up equally, would still be quieter than a similar 200 watt amp pushing a similar cabinet?
  7. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Two cabs will move more air than just one.

    Rip Van Dan and NoiseNinja like this.
  8. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone

    Feb 23, 2011
    I might as well reveal the reason why I ask.

    I am pondering on copying my usual approach when recording "clean" bass through my sound interface running one tack clean and one track with a slight touch of chorus, reverb and a subtle low grit on as well.

    I have a setup at the moment where I run the Line Out of my main amp, a 130W Trace Elliot through the Line Out, post EQ, into a 345W active 12" PA speaker with disabled horn, just to be able to get more of the same in case 130W isn't enough.

    But what I am think of doing instead is running my Trace Elliot clean and then conect the PA speaker I got to the Tuner Out, so I just get the straight signal from my bass and signal chain before the Trace into the PA speaker, and then run a slight bit of chorus, maybe a tad of room reverb too, and then Behringer V-Tone Bass BDI21 with a bit of low grit on in between the Tuner Out and the PA speaker.
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Wattage sums. But there are potential complications.

    If the amps are the same, they will be in phase. If they are not the same, there MAY be a phase issue. If this is the case, it can be corrected by wiring one cabinet out of phase relative to the other. This is as simple as switching two wires in the cab. You want all the speakers moving outward on the leading edge of a positive going input wave.
    agedhorse, NoiseNinja and delta7fred like this.
  10. delta7fred


    Jul 3, 2007
    What beans says.

    If when you run both rigs the bottom end seems less than one on it's own try reversing the phase (swap the connections on one of the speaker leads) of one cab, doesn't matter which one.
    NoiseNinja likes this.
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Note that the 3dB contribution to SPL increase due to the acoustic coupling (increased displacement) from doubling the number of speakers only applies to very closely spaced speakers and at low frequencies only. As the spacing increases, the contribution decreases because of destructive cancellation.
    NoiseNinja likes this.
  12. BassmanPaul

    BassmanPaul Inactive

    Them destructive cancellations getcha every time! LOL


    Edit: Getcha is like gotcha only different! :)
    High Camp likes this.
  13. Your chorus will usually cause a phase mismatch in a clean blend as the returned chorus signal is reversed phase.
    NoiseNinja likes this.
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Chorus doesn't have to be inverted polarity, but there will be a modulated phase element because of how chorus works.
  15. I didn't word that very well. Afaik most chorus pedals output a signal which is inverted from their input.
    NoiseNinja likes this.
  16. What?
  17. Which what?
    NoiseNinja likes this.
  18. SactoBass

    SactoBass A retired civil engineer who likes all-tube amps! Supporting Member

    Jul 8, 2009
    Lake Havasu City, AZ
    NoiseNinja likes this.
  19. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA

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