Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

cabinets decibels and all that craic

Discussion in 'Amps and Cabs [BG]' started by theshadow2001, Jul 3, 2004.


  1. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    This is something that i've been thinking about in the past few minutes it seems to me that people think that when you put a second cabinet on to your head(amplifier that is not the thing on your shoulders) that its going to be louder simply because your moving more air. Now i think that this might not be a very correct way of thinking. If you had say two exactly the same amps and cabinets beside each other putting out 80dBs each the increase in in the over all sound level would be only two or three dBs if even that although you are moving more air there isnt a huge increase in sound level. From reading manufacturers specs when you hook two cabinets in to your head in parallel(again not the thing on your shoulders)your reducing the impedance and the wattage of the amplifier increases. For example an ampeg B-5R running with one cab at 4 ohms has 350 watts but when you put a second 4 ohm cabinet in you reduce the impedance to 2ohms and the wattage magically becomes 500 watts and i think this increase in wattage is how you get a higher sound level out of your amp with a second cab not because your simply moving more air. So what do you think am i right or have i just wasted my time typing all this out?
     
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    Doubling amp power gives a 3 dB boost.

    Doubling speaker surface area also gives a 3 dB boost.

    http://www.talkbass.com/ampfaq/

     
  3. cjgallen

    cjgallen

    Oct 19, 2001
    You are correct in stating that the increased wattage has as much to do with it as simply adding more speakers. The additional speakers move more air, yes, but more POWER allows them to move even MORE air.

    It's a combination of the increased speaker area and increased power that allows you to "move more air."
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    You're kinda correct but now quite. Yes you get more watts from your amp, but how much? An extra 30% maybe. As mentioned, to get an extra 3dB you need an extra 100%. If anything you get more headroom from your amp, but any increase in SPL has more to do with increasing your speaker cab area and therefore efficiency.
     
  5. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You get up to 3 dB extra from the doubling of the speaker area if you set them up in a way that takes advantage of that phenomenon, such as putting them side-by-side and pointing in the same direction. If you put the cabinets spaced far apart or facing opposite directions, you'll get little or no additional boost from acoustic coupling.
     
  6. Yup.

    Kind of like when the wife and I crawl into bed... when we are spaced far apart or face opposite directions, we get little or no 'boost' (in dB ) from 'coupling'.
     
  7. well it do sound much more from a 8x10 than from a 1x10 playing with the same amp. :)
     
  8. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    :D :D Damn you, I've got the giggles now................
     
  9. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    If you run a 115 4ohm cab and then a 215 4 ohm cab you keep the same wattage. However, you will have the 3db increase from the second speaker. As mentioned above, if they are "coupled" you will definately notice the volume increase.