SPL question

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  • James W. Johnson
    Member
    • Jun 2001
    • 68

    SPL question

    The JBL HLA 4895 3-way combined with the 4897 bass module are JBLs top of the line tour sound products, they are capable of producing 140dB from 34Hz on up from 1 meter....can a pair of these fill up a football stadium with sound? The reason I ask is that my current set-up can produce around 100dB from one meter so they are only 40dBs away from being able to fill up a football stadium with sound?
    Basically what I have now is not loud enough for me, but I am pretty close , it seems to me that if I could turn up my volume knob just a couple of notches more I would be satisfied.
    So how does SPL perception work, is it that once you get to a certain point each decible becomes more powerful?..In other words does the sound seem twice as loud for each additional decibal after a certain point? How does this work?


    (BTW I like your guys sneak peek feature where you can look into the thread without actually clicking on it)
    pics
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    they are capable of producing 140dB from 34Hz on up from 1 meter....can a pair of these fill up a football stadium with sound?
    Absolutely not. They'd do a pretty good job in the local high school gym though...

    Sound pressure levels decrease at a logarithmic rate as you move away from the source. So the sound level decreases by approximately 6 dB every time you double the distance from the source of the sound. So if you're 2ft away from a speaker and it's playing at 120db, that drops to 114db @4 ft away, 98db @8 ft away etc, etc.

    An increase in SPL from 120 to 130db is perceived by the human ear as doubling the loudness. Now to do this takes a ten times more amplifier power. Going to from 120 to 130 db output takes the amp from 10 watts output to 100 watts output. To go from 120db to 140db SPL takes 1000 watts of power if we're using the same amps in the example and this is perceived by the human ear as being 4 times louder

    Your Adire MTM towers are "radiation resistance" limited in their output by the area of the cones. 2-8" drivers simply lack adequate excursion and surface area. This is one reason why you see 15" woofers and compression drivers for pro use.

    The trick to high SPLs is using large diameter drivers or many, many smaller diameter drivers driven by a reasonably large amps. Any of the drivers should have relatively high efficiency. But using alot of medium efficiency drivers can also result in high output. The 12 Shiva IB is an example of this.




    theAudioWorx
    Klone-Audio

    IB subwoofer FAQ page


    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

    Comment

    • James W. Johnson
      Member
      • Jun 2001
      • 68

      #3
      Thanks for the reply Thomas.
      What is the math to figure a speakers output, say you have an 88dB, 92dB and a 97dB speaker driven with 100 watts. It seems it is easier to find a high sensitivity speaker and use alot of wattage then to find a low efficency speaker and have tons of wattage.
      I have not found a single 88dB speaker than can get near 120dB output, mostly because they cannot handle the needed power to get those SPLs.
      Like you said I have two options either use alot of small drivers or use a few large drivers , so what is the math to figuring out driver radiating area? For example , would 12 6.5" drivers have more radiating area then 1 or 2 15" drivers? To complicate things further what if the 6.5" drivers were only 89dB sensitive and the 15" drivers were 97dB sensitive, what if the 6.5" drivers could only handle 100watts ea and the 15" drivers could handle 500watts ea....whew! this can get kind of confusing.
      pics

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      • ThomasW
        Moderator Emeritus
        • Aug 2000
        • 10934

        #4
        James

        No body said speaker design was easy....

        The math is the same. Any speaker will have a stated efficiency, say 88db. This usually means 88db output when driven by 1 watt RMS and measured at a distance of 1 meter. So to get 96db out takes 10 watts, 102db out 1000 watts. That's why a speaker that's 88db 1w/1m can't play 120db. But everytime you add an additional driver you get an additional +3db of output. That equals a fair amount of free amplifier power.

        All drivers have Theile/Small parameters. Here's a list of what they are and what they mean.


        On the list note the one labeled 'Sd'. You add up the Sd of the small cones to see if/when they equal the Sd of the big one, (Vd also comes into play but that's a lession for another day). The efficiency of a small cone system increased by +3db for each driver added into the group. So if you start with one 89db driver, then add 3 more you've got a 98db system. It's actually not quite this simple, but this info is close enough for you to get the general idea.




        theAudioWorx
        Klone-Audio

        IB subwoofer FAQ page


        "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

        Comment

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