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Double Cabs = Different Sound?

Discussion in 'Amps and Cabs [BG]' started by LeonD, May 15, 2001.

  1. LeonD

    LeonD Supporting Member

    I've seen people mention that they like the sound of their one cabinet but when they add an identical cabinet, the sound get deeper, fuller, bigger, etc.

    Why is this? I would think if you had two identical cabinets, you'd get twice as much of the same sound. But this doesn't seem to be the case.

    Do the sound waves coming out of the cabinets combine into a different wave with lower frequency characteristics?

  2. Nightbass


    May 1, 2001
    Seattle, WA
    It probably has to do with what is known as mutual coupling. When two drivers are within 1/4 wavelength of each other, there is a "free" 3dB gain in that frequency. For two bass cabs with 10"/12"/15" drivers, this means you get a 6dB gain in the low frequencies, at about 200 Hz and below. Why 6dB? 3 from mutual couping, and 3 from adding a second speaker and lowering the system impedance.

    Another factor is that you'll usually stack two cabs vertically, one on top of the other, and the vertical sound propagation pattern is much, much better than if you put them side by side.

    Anyone know any other reasons? I've seen this whole-is-greater-than-the-sum effect before, most notably with a pair of Bag End S15-D and a pair of Acme Low-B2.

  3. You've hit it right on the head.. excellent description. This is why a stack is louder than splitting the cabs on either side of the stage.
  4. Gabu


    Jan 2, 2001
    Lake Elsinore, CA
    I did not know this... and that is cool... One question though, the orginal post seems to be talking about tone more than volume? If that is the case could it be that the louder volume just gives you more headroom to get the nicer tone? (Just a guess)
  5. Good point. The phenominon of mutual coupling occurs below 200 Hz and is more prominent as the frequency goes lower (wavelength increases). It reinforces the low frequencies which start rolling off around 45~50 Hz in many cabinets. What is being heard/felt is the increase in the lows that are missing. The apparent loudness is also increased, and IMO this has a tendency to create the feeling of more tone.
  6. Good thread. The question I'm going to pose is related.

    Why is it that when you add a second cabinet, it kind of takes some of the growl away from the sound?

    Example: You have a 300 watt head powering a 1-15 cab that can handle 300 watts, and you're pushing it not to the point of stress, but to the point where you're getting a nice scream from it.


    You add a second cabinet (exactly the same) and you get that apparent increase in volume, but, the sound has lost some of the screaming tone that the single cab was producing by itself. Is this because each speaker is now running further from its limits? You know what I mean? It seems the same to me with lead amps. Take a 100 watt head and run it through a good 10 or 12 that can handle all the power, and it screams. Now add a second speaker, and it seems to become a good rhythm amp.

    Mike J.
  7. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Well, I dunno, but if the previous post is correct about the frequency range at which mutual coupling takes place, it oughtta emphasize the bottom rather than the mids and overtones. Makes sense.
  8. Nightbass


    May 1, 2001
    Seattle, WA
    That's how I look at it, too. But also, someone was recently describing Bergantino cabs to me, saying they are like the SWR Goliath II on steriods - the louder you play, the more growl you get. So it seems that if you use two cabs, you are playing them softer, and get less growl.
  9. MikeyD


    Sep 9, 2000
    Speakers are quite nonlinear, so I think many of the comments here have merit from the standpoint of physics. The ideal speaker would sound the same throughout its power handling range, but in reality other things happen. The harmonic distortion increases as a speaker is driven harder, and in some cases intermodulation can happen - the gross cone movement can even induce Doppler shifts of the higher frequencies (harmonics), etc. Gets messy. But it may be analogous to overdriving a tube amp to get a certain edge to the tone.

    I also agree that speakers interact acoustically - after all, a speaker is sort of a microphone in reverse! (You can sometimes use headphones as a microphone in a pinch - try it and see!) Then you have the phenomena of interference and diffraction - an array of speakers starts to develop radiation patterns quite different than a single speaker. And when cabinets are stacked, the geometry of the "system" changes, which also affects diffraction and interference patterns. All these things come into play, and it often defies easy explanation.

    An extreme example of this is comparing a single, small cabinet to a vertical stack of such cabinets that goes from floor to ceiling (or maybe 40 feet high if outdoors): at most low frequencies, the radiation "envelope" changes from approximately spherical to approximately cylindrical - so the propagation and attenuation with distance change.

    - Mike
  11. MikeyD


    Sep 9, 2000
    Not nice! Do unto others... what goes around comes around, etc. But it points out that loudspeakers can and do make useful microphones.
    - Mike

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