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What issues arrise when using multiple amps

Discussion in 'Amps and Cabs [BG]' started by Blankandson, Oct 20, 2010.

  1. If I use two Fender Rumble 350s on stage would I be perceived by the audience as any louder (or cleaner sounding) than if I use one? Would my perceived volumn be the same as if I were using one 700 watt stack? Just wondering because two Fenders would be less expensive and probably easier to transport.
  2. Doubling the speaker surface area makes +3dB. Doubling the power only +1.5dB.
    These are only theoretical values, but the essence is that it's more effective to increase the speaker surface area than power.
  3. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    true, but if you increase both, it will definitely be noticeable. i think it's a good way to go.
  4. PSPookie

    PSPookie Supporting Member

    Aug 13, 2006
    Lubbock, TX
    I was under the impression that you got a 3dB boost from doubling either speaker surface area or power, provided that the drivers in question can handle the additional power with similar efficiency.

    Either way, adding a second, identical combo will noticeably increase your available stage volume.
  5. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    nope, not power. to get double the perceived volume from an amp, you have to use 10x the power.
  6. jmac


    May 23, 2007
    Horsham, Pa
    Jimmy speaks the truth.
  7. PSPookie

    PSPookie Supporting Member

    Aug 13, 2006
    Lubbock, TX
    Right, but you're saying no 3dB boost from doubling power?
  8. Doubling the wattage give approximately a 3db boost

    Correct - doubling speaker area + doubling wattage = 5 - 6db gain

    While this is true, doubling percieved volume is +10db
  9. scottbass

    scottbass Bass lines like a big, funky giant

    Jul 13, 2004
    Southern MN
    I think it will work better to stack one on top of the other than to have them side by side. Something about apparent phase cancellation. You definitely don't want them separated (like one on each side of the stage).
  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You'll get the same result by adding another cab with the same driver complement as the Rumble 350, if the amp will allow it. Halving the impedance will double current, for 3dB, while mutual coupling of two cabs gets you another 3dB.
  11. James Judson

    James Judson

    Jul 16, 2009
    Lots of misleading "opinions" on this forum regarding decibels. How do we find out who has the right info (nearly impossible)??? Most musicians do not know the definition of decibel.

    Example: 10X the watts = 2X SPL.

    Engineering school had tons of equations. This one is not one of them. I challenge anyone to put a 10 watt amp next to a 100 watt amp and report back. My experience is a 100w amp it about 10 times louder. I own 28 amps and have done this test many times. I just can't make that equation work.

    Decibel is a ratio of 2 to 3. When Alexander Graham Bell invented the cell phone he needed to know how loud the other end of was compared to the input. Sound is not linear it is logrythmic. When you turn up an amp til it sounds twice as loud then measure it. The output will measure three times. Decibels gets applied to electronics a lot as in input to output gains. It also gets applied to SPL (sound pressure level). Then musicians try to mix and match to confuse the issue. Watts, gains, speakers, etc do not easily equate to SPL.

    Running two cabinets in phase will not cause a problem. If it did the sound man would have to shut off half the FOH speakers. You will get cancellation issues if one speaker is wired backwards (out of phase). You will notice this as you walk around the room. One speaker is pushing while the other is pulling. Sound will get louder and quieter as you walk around the room.

    You don't have to believe me. Go to engineering school.

    Running two of the same amps simultaneously is a good idea. Twice the watts, twice the speakers, exact same sound (tone). Very predictable. Calculating the SPL, near impossible. To many variables.

    This forum is an excellant place to get opinions and real experiences. Technical data, not so much. There is a reason for a school just to learn all this crap.

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