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Volume : Speaker size vs. Power rating (watt)

Discussion in 'Amps and Cabs [BG]' started by Inconnu, Feb 18, 2013.

  1. Hi!

    I'd like to sort this out and maybe some people here could help. I know that volume as to do with 2 factors :
    1. the power to make a speaker move
    2. the quantity of air that speaker can move

    So, well, I'm wondering. In theory (because I know, the design of a cab and of the speaker itself, among other things, have an impact), what would be louder : a bigger (say 15 inch) speaker with less (say 100 watt) power or a smaller (say 12 inch) speaker with an higher (say 150 watt) power rating?

    Purely in theory... I know what I' comparing here is not absolute.
  2. There are other specs that would come into play to make this kind of call.
  3. Depends on the efficiency of the speaker and the efficiency in the given cabinet design, to say the least.
  4. The advertised power ratings for speakers are usually thermal limits, which aren't really useful because most speakers will be limited by excursion (how far it can move in and out) way before they reach the thermal limit. That is, it may take 100 watts to burn up the voice coil, but 50 watts will move the cone as far at it will physically go.

    I think you can get an approximation of how loud a speaker will play by calculating the volume of air it will move, i.e. pi x r^2 x the excursion limit. Some small speakers have very high excursion limits and can therefore be louder than much bigger diameter speakers.
  5. BogeyBass


    Sep 14, 2010
    Your somewhat one the right track speaker sensitivity has the most to do with it.

    If you had a 12" speaker rated at 94db and a 15" rated at 98dB
    and you applied 50 watts to both then yes the higher sensitivity 15" would be louder.

    And for the most part yes larger speakers typically do have the most sensitivity. So a 15inch is usually the best option.

    there is other instances were a speaker is designed to handle more power and will have a longer magnet gap or more xmax. Usually the trade off for more xmax is lower sensitivity. Likewise the trade off for having more sensitivity is a shorter magnet gap or less xmax. The speaker will have incredible sensitivity but will have less power handling or bass response.

    same trade off with larger speakers is they require more volume, so its gonna be a larger enclosure. Also the resonant frequency of larger speakers typically gets lower and lower. So more bass response is available with a lower resonant frequency. And also again to get more bass you need a larger airspace/cabinet as well.

    typical sensitivity ratings for a single 3 to 5mm xmax speakers are

    10" 92 to 94dB
    12" 94 to 96dB
    15" 96 to 99dB

    typical resonant frequency of single pro audio drivers are

    10" 65 to 50hz
    12" 55 to 40hz
    15" 45 to 30hz
  6. Total generalizations. A Quick search of Emenence, B&C and even Dayton drivers disprove your typical ratings.
    There is much to more speaker engineering and performance achieved.
  7. When calculating the cone area remember to subtract 1 inch or 2.54cm from the radius to account for the surround and frame.
  8. BogeyBass


    Sep 14, 2010
    yes total generalizations but typical, and yes there is always a exception. and remember most manufactures average/overate sensitivity ratings
    and dayton drivers are not for pro audio they are home stereo/car audio drivers

    I dont care to argue and not here to post fraudulent information
    and if you feel its necessary to discredit me then go ahead.

    Find a pro audio 10" with 99dB sensitivity and a 30hz resonant frequency that is impossible.

    but yet a 15inch will be able to do that in a decent price range.
    as said a 15inch usually has more sensitivity when compared to a another speaker with equal xmax of any diameter. And its very typical for larger speakers to have lower resonant frequency.
  9. Not looking to "discredit" anyone. I am pointing out these are generalizations not hard facts.
    A low Fs is only one small parameter, more important to a sealed enclosure than a ported for usable instrument use.
    So again no intent to argue the fine points as the OP has not taken any important parameters into consideration. Basically a question so general it can only lead to many pages of facts/garbage and ending in Mod lock?
  10. BogeyBass


    Sep 14, 2010
    most likely

    But i tried to answer it in a general sense as well and close to real world answer.

    such as the difference between a 100 watt 15 and a 150 watt 12"
    yes very hard to answer because there is so many other things that would have to be included to answer that.

    and for the most part I dont know if there is such a thing
    a 15 that could handle 100 watts and a 12" that could handle 150watts would almost get you to the same place.
    Knowing that most 15's have more sensitivity it would only take 100watts to reach the same level as a 12inch with a 150watts.
    those are typical numbers for 3 to 4mm drivers but for a 12inch to beat the 15" it would be a huge jump in power rating and xmax.
    so yes a 12" could get louder but because of the low sensitivity of higher xmax speakers, you would have to double the power
    not just a extra 50 watts. Even with say a 5 to 7mm xmax speaker with a 450 watt rating comparing a "450 watt" 12" to a "400watt" 15" most likely the larger diameter speaker is still gonna have more sensitivity

    but to clue him in on something more realistic in the real world in the mid to low budget range when comparing a 12 to 15inch
    drivers in the 3 to 4mm range. the 15" is gonna be louder.
    and power handling will be in the 100 to 150 watt range before 10% distortion.

    Otherwise no a 12inch could get louder than 15" but the power range would be much different than 50watts and depends on sensitivity. It would usually take much more power than a extra 50watts to get "louder"
  11. will33


    May 22, 2006
    When people talk about "moving air", as it pertains to loudness they are talking about only low frequencies, where output hinges on displacement,....ie: what volume of air can be displaced by the cone moving back and forth. Once you get above a couple hundred hz, it's not about displacement anymore, but rather how well the unit can turn electrical wave into physical motion and this sound. It's ability to accelerate quickly has large effect on higher frequency response. So, I would answer your question with multiple more questions.

    There are 30 or so different measureable parameters to a speaker. The physical size of the cone is one of these. You change one single spec you affect all the others, so there really are no direct comparisons.

    Obviously a larger cone will displace more air than a smaller one if they both travel the same distance, but that is just one aspect to consider in what can be thousands of different combinations of speaker parameterse

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