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Determining Loudness...

Discussion in 'Amps and Cabs [BG]' started by Ionic Eye, Jul 16, 2002.

  1. Ionic Eye

    Ionic Eye

    May 13, 2002
    Columbus, OH
    What, generally speaking, determines how loud a certain cabinet will be? For instance, say you have two 15" cabinets, both at 8 ohms, with one rated at 200 W RMS and another rated at 600. Now say you run them at their max RMS ratings: is the 600W one going to be louder than the 200? Or is this really just a matter of speaker and design quality?

    Another question I've wondered about is if a 400W RMS 8 ohm cabinet would be less loud than a 400W RMS 4 ohm cabinet, if both were run at max RMS.

    I've been reading a LOT of posts here, but am still left wondering about this. If these are silly musings, please ignore me entirely. Thanks... Matt
  2. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    Ok,, their are alot of other factors to, SPL, Size of box, all that crap. But here is the truth. TECHNECILY SPEAKING More watts = more loudness. the idea is, more power, more loudness. Technicily speaking, if you ran 600 watts thru a 15 cab, it would be louder than running 200 watts to the 200 watts rms 15' cab. Their are so many other factors though, and i would explain them all if i didn't have a band practise in less than an hour that i need to get ready for. Someone should help you out with everything else. Also, no, a 4 ohm cab run at the same power as a 8 ohm cab would be no diffrent. it's just a diffrent wireing system. if you plan on running more than 2 or three cabs, 8 ohm cabs would be better, because ... well, someone help him, i'm damn late for practise.:eek:
  3. geshel

    geshel Supporting Member

    Oct 2, 2001
    Depends on the base sensetivity rating of each cab (usually listed as something like 101dB / 1w / 1m). This means how loud the cab plays with one watt input power, from one meter away.

    To come up with a total SPL for a single cab, you convert the power to dB and add it to the base rating. Some handy conversions are:

    2x power -> 3dB
    3x power -> 5dB
    4x -> 6dB
    5x -> 7dB
    10x -> 10dB

    When you multiply on the left, add on the right. So 600w = 2x3x10x10 w = 3+5+10+10 db = 28dB louder than 1w.

    So in your case, you're adding 23dB to the first cab's base SPL and 28dB to the other one's. All other things being equal, the second cab will be 5dB louder. But if they have different sensetivity ratings that won't necessarily be the case.
  4. 44me


    Jun 17, 2002
    Bedford, NH USA
    Here’s another point to consider. If you have an 8 ohm cabinet and you add a second one, you get a 6dB boost in volume, assuming your amp puts out twice the power at 4 ohms as 8 ohms. 3dB comes from the efficiency improvement you get when you double the number of speakers, and the other 3dB comes from doubling the output power. This is why adding that second 8 ohm cabinet makes such a big difference.
  5. Ionic Eye

    Ionic Eye

    May 13, 2002
    Columbus, OH
    OK, cool; thanks for the info! I completely forgot about the sensitivity thing; if I had remembered, I would have said, "And both at 100 db SPL." So, the info (esp. the "formulas", Geshel) given has definitely helped out; thanks for taking the time! Also, thanks for the "2 cab" explanation; that helps me out as well, as I am planning on running a 2 cab set-up, and wondered how much of a difference one could expect doubling up. Thanks again... Matt

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