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Are 2 low watt amps running in dual mono as loud as a bigger amp?

Discussion in 'Amps and Cabs' started by The Whiz, Oct 27, 2005.

  1. The Whiz

    The Whiz Member

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    For example, all else being equal (speaker types, preamp, tube types etc). Are running 2 20 watt 1x12 combos together approximately as loud as running a 40 watt 2x12 combo? I've always assumed it more or less is. Am I wrong?

    :confused:
     
  2. electronpirate

    electronpirate Member

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    Jumping in trying to use logic as not a 'sound techie'.

    I would think it would be louder. A 100 watt amp is only a few DB's louder than a 50w, not intuitively 'twice as loud.' Thus, a 20 watt amp is only a few DB's quieter than the 40 watt. Two of them would make it a bit louder than the dbl-spkr 40.

    I think the speakers are a detail as well, a single speaker 40 watt combo I think puts out about the same amount of DB's, but a double pushes more air, so it *sounds* louder.

    But (as my wife tells me) I have been wrong before....

    EP
     
  3. GCDEF

    GCDEF Supporting Member

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    2 x 20 = 40. All other things being equal, they would be the same.
     
  4. Roccaforte Amps

    Roccaforte Amps Member

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    Seeing how some 20watt amps sound like they're only 10,
    some sounding like they're 30, no.
     
  5. pcutt

    pcutt Member

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    No, this is wrong. For the human ear, doubling the power does not produce a doubling of apparent loudness. You would need ten of the lower watt amps cranked to have the same apparent loudness as a single bigger one.
     
  6. GCDEF

    GCDEF Supporting Member

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    No. Doubling apparent volume doesn't apply to his question. He asked if 2 20 watt amps will produce the same volume as 1 40 watt amp. The answer is all other things equal, you still have 40 watts through 2 speakers. The fact that it's two amps instead of one is irrelevent.

    One 20 watt amp will be 3 dB quieter than one 40 watt amp. Add in another 20 watt amp, you add back the missing 3 dB and have equal volume again.
     
  7. bob-i

    bob-i Member

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    It's really difficult to quantify volume. Bottom line.. all things being equal yes, 2 small amps would equal one big amp.
     
  8. amper

    amper Member

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    This is a fallacy, and I'm not sure where this factoid came from, but a doubling of volume is 6 dB, or four times the power, not 10 dB or 10x power.
     
  9. GCDEF

    GCDEF Supporting Member

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    Volume is a perception. Most people perceive volume to have doubled somewhere between 6 and 10 dB. 10 is the figure usually used.
     
  10. amper

    amper Member

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    Also, you have to account for coupling of the speakers. If the two speakers are in separate cabinets, they are loosely coupled and will produce +3 dB. If they are in the same cabinet, they are tightly coupled and will produce +6 dB.

    So, if you're running 2 watt into a single speaker which has a 100 dB@1 watt sensitivity, you'll be at 103 dB.

    If you're running 1 watt into a tightly coupled 2x12 with two speakers of the same sensitivity as above, you'll produce 103 dB. If it's two separate cabs, you'll produce 100 dB.

    One 1 watt amp into one 1x12 cab = 100 dB
    Two 1 watt amps into two cabs = 103 dB
    One 2 watt amp into one cab = 103 dB
    One 1 watt amp into 2x12 = 103 dB
    One 2 watt amp into 2x12 = 106 dB

    [edit] whoops, dreaded math mistakes...I keep forgetting to half the power into each speaker in the two speaker setups.

    [edit again] oh yeah...the point...two 20 watt amps into two 1x12 will be slightly less loud than a single 40 watt amp into a tightly coupled 2x12.
     
  11. amper

    amper Member

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    Ten is frequently used, and just as frequently *wrong*. Ask any competent acoustician or engineer.
     
  12. OOG

    OOG Member

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    so Papa
    are you clear now?

    ;)
     
  13. riffmeister

    riffmeister Gold Supporting Member

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    Make sure the two amps are in phase.........out of phase will be perceptibly less loud than in phase.
     
  14. JamesPeters

    JamesPeters Member

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    This is the first thing that crosses my mind when someone asks this question. There are too many amps (especially nowadays) which aren't designed to have higher headroom even for their supposed power rating. Until you try the amps, ensuring they're properly set up of course (biasing etc.), you won't know what's louder.
     
  15. drbob1

    drbob1 Silver Supporting Member

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    Let's change the picture a bit to try and sort this out: for the sake of argument, use two identical 112 combos vs a similar topology of 212 combo. We've successfully identified that the power output will be the same, coupling will be an issue (both for volume and spread of the sound). Other factors that may tie in: assuming transformers that are just large enough to give 20w or 40w clean output before breaking up, the transformers in the 40w amp will be bigger and likely able to tolerate higher distorted output before saturating-so that amp should sound louder and hit harder. Mostly the 212 cab will be bigger, giving more bass, although you could control for that. Tube type, class and bias method will make a big difference (since tube response isn't linear, I don't think there's any way to make a 20w amp respond like a 40w amp, or at least no ones doing it). So, bottom line, they'll sound different and my guess is the 40w will be louder.
     
  16. JamesPeters

    JamesPeters Member

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    Separate 1x12s won't exhibit the same phase cancelling effect that occurs in a single multi-speaker enclosure, and some 1x12s can sound pretty bassy. I imagine using two 1x12s side by side might sound bigger/bassier than a single 2x12, at least in some cases.
     
  17. amper

    amper Member

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    The cancellation only takes place at higher frequencies, where the distance between the driver centers is a significant fraction of a wavelength. Also, for a wider horizontal dispersion of the treble frequencies, the two speakers should really be stacked vertically. Side by side placement will degrade the horizontal dispersion, exactly the opposite of what is generally wanted on stage.
     
  18. reachjkh

    reachjkh Member

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    Somebody go try it and let us know
     
  19. mad dog

    mad dog Silver Supporting Member

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    I've done this a fair amount. Not an expert opinion, but I'd say two 20 watts it's not as loud as one 40. Example: I like running my BFDR with a Gibson Les Paul GA40. That adds up to around 38 watts. Running not quite flat out (say 8 out of10 on volume knobs) it's definitely louder than the louder amp (the DR) alone, but not as loud as my 35 watt Clark Tyger running at equivalent settings.

    Apart from the physics, different amp/speaker setups seem to interact in ways that affect volume. The DR and Gibson are voiced very differently. The sound gets fuller as that solid DR bass and smooth highs mixes with the rawer, darker Gibsons sound. That's why I run them together, not for volume, but because the sound blend is so tasty. If I was running two similar amps, I bet the combination would sound quite a bit louder. That seemed to be the case when I ran a BFDR with a SFDR, another really great combination. What a big sound that was!
     
  20. pcutt

    pcutt Member

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    Oops, I'm wrong! I misread the question and gave an answer that doesn't pertain. Thanks to GCDEF and amper for pointing out my mistake.
     

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