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Why is a 8x10 louder than a 4x10

Discussion in 'Amps and Cabs [BG]' started by CombatWombat, May 30, 2002.


  1. CombatWombat

    CombatWombat

    May 5, 2002
    If you give an 8x10 and a 4x10 300 watts, the 8x10 will be louder. Is this only because of sensativity, with more speakers your sensativity is higher or is it something else?
     
  2. more speakers = more moving air.
     
  3. If you look at common speaker sizes and compute their respective areas you end up with a chart sort of like this...
    1x10=79
    1x12=113
    2x10=157
    1x15=177
    2x12=226
    3x10=236
    4x10=314
    3x12=339
    2x15=353
    4x12=452
    3x15=530
    8x10=628
    4x15=707
    8x12=905
    8x15=1,414

    From this chart it's easy to see the obvious... like a 15" speaker pushes way more air than a 10... but it also shows some more subtle things... like 2 12" speakers push almost the same amount of air as 3 10's.

    Obviously it's way more complicated than this... but it's a start... hope this helps!:D
     
  4. CombatWombat

    CombatWombat

    May 5, 2002
    So it's all about air volume being moved? So sensativity is how a speaker responds to the power it is given?
     
  5. geshel

    geshel

    Oct 2, 2001
    Seattle
    Well of course bigger speakers only push more air than 2 if they move the same distance. . . :)

    Sensitivity is related to a number of things. But, it does work out that if you have 8 of the same driver the output will be higher at the same power (esp. at low frequencies) than if you have 4 of them.

    Technically, when the speaker is smaller than the wavelength of the sound, it gets more efficient as you make it bigger. And at low frequencies, a few speakers next to each other driven with the same signal effectively become one bigger speaker.

    There's a limit to that somewhere of course, or diminishing returns at least. Otherwise a 128x10 or something would be > 100% efficient. :)
     
  6. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    This is only the case if the drivers and the cabinet parameters are comparable. A 4-10 with highly efficient drivers in an optimally designed cab can sound louder than an 8-10 with inefficient drivers in a poorly designed cab.
     
  7. BigBohn

    BigBohn

    Sep 29, 2001
    WPB, Florida
    It might seem logical that more square inches present on the speaker face will push more air but it does not matter at all. It's, like others said, the parameters, dimensions, porting, etc., of the cabinet.
     
  8. geshel

    geshel

    Oct 2, 2001
    Seattle
    :confused:

    "doesn't matter at all" ?? It's just as important as all the other factors you mentioned (or, more properly, it's part of them - the "parameters").
     
  9. Thanks geshel... I didn't mean to imply that the area of the speaker was the ONLY factor. As with most anything, there's way more to it than originally meets the eye. The original question was basic... I mistakenly thought a basic answer would suffice... as usual, there is a wealth of info at TB. :D
     
  10. BigBohn

    BigBohn

    Sep 29, 2001
    WPB, Florida
    I'm not trying to question your information on this topic because I'm sure that you are very knowledgeble about this. My understanding is that when a bass frequency is put out by a cabinet, note I said bass frequency meaning lower than around 100 Hz, the movement of the speaker cone creates a vacuum or suction of the greater part of the inside volume of the cabinet, thus projecting bass frequencies out of the ports, not the speaker face. Now for higher aural frequencies, 100 Hz and higher, are given by the speaker directly, not the entire cabinet air volume as a whole. If I am incorrect in some way or another, I will gladly resign my position and accept the correct explanation.

    edit: add a missing word
     
  11. Just goes to show that you CAN teach an old dog new tricks... thanks... I guess I never understood the importance of ports before. :D

    Still, speaker size/area must have something to do with it or we'd all be using a single 4" speaker cabs! :p
     
  12. geshel

    geshel

    Oct 2, 2001
    Seattle
    No, no, no. :) Say the box is tuned to 50 Hz. At frequencies higher than that (say 60Hz and up), to the speaker the box looks sealed - the air in the port can't vibrate that fast (or, the impedance of the port rises with frequency :) ). In this case the speaker is effected by the springiness of the air inside the box, and the speaker produces most all of the sound.

    Below the tuning frequency (say 40Hz and lower), as the speaker moves it more or less pushes air in and out of the port in sync. But the output of the port is out of phase with the woofer (as the cone moves in, the port air moves out), and so the two tend to cancel each other out. Hence, below tuning frequency ported boxes have a steeper rolloff (24dB/octave v. 12dB/octave) than sealed boxes.

    At the tuning frequency, the speaker+box+port all resonate together - what happens here is that the speaker doesn't move much at all and the port produces most of the sound. If you sweep a signal through this frequency you'll see the woofer movement start high, get very small, then start getting really high as frequency gets lower (watch out you don't damage it).

    The thing to keep in mind however is that the speaker is driving the whole thing. More speaker area means, even at resonance, it's moving more air with each push and pull.
     
  13. rickbass

    rickbass Supporting Member

    Is it appropriate for someone more knowledgeable than I to bring up acoustic coupling in this thread???
     
  14. BigBohn

    BigBohn

    Sep 29, 2001
    WPB, Florida
    Alright, geshel, thanks for your clear and definitive explanation to correct my wrong concept of speakers and cabinet size. I totally understand what you mean now about the pulling action of a higher square inch area of a speaker to the whole inner air volume of the cabinet. Thanks for clarifying.
     
  15. geshel

    geshel

    Oct 2, 2001
    Seattle
    No problem. :) I was thinking, a good analogy might be: you know that game with the cheap wood paddle that has a rubber ball attached to it with elastic? And you hit the ball over and over again? If you take one of those, and hold it out so the ball hangs down. Then move the paddle up and down slowly - the ball pretty much moves up and down same as the paddle. That's like the speaker in a ported box below the tuning frequency. Next, move the paddle up and down really fast (though not too far) - the ball will more or less sit still while the elastic stretches and contracts. That's like the speaker above the tuning frequency. Finally, find the happy medium where the ball actually comes up and hits the paddle over and over again - that's the resonant frequency. You don't have to move the paddle very far to get the ball to go flying.

    That's really a pretty close analogy because in a ported speaker, the air in the box acts almost exactly like a spring and the air in the port acts just like a mass connected to the end of it (with the driver connected to the other end).

    The really cool thing is that the whole thing can be modeled with an electrical circuit too - capacitors are like springs and inductors are like masses. So in a funny way an EE background can help you understand speaker boxes, even the mechanical parts! :)
     
  16. BigBohn

    BigBohn

    Sep 29, 2001
    WPB, Florida

    Good analogy! That clearly demonstrates how a speaker would work within a cabinet. Good job! I'm sure that would help others about the basic physics of a speaker inside a cabinet. Great. :cool: