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How do you calculate (or estimate) SPL for a system?

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  • How do you calculate (or estimate) SPL for a system?

    I was telling a buddy I was looking at getting a pair of EV ZXA1s over a pair of ZXA1-Subs. He said he was considering a Peavey Triflex system for the same reasons (size, weight).



    http://www.zzounds.com/item--PEVTRIFLEXII



    The ZZounds description specs the tops at 101db and the sub at 102db. It then specs the "Complete System" at 129db. Questions:



    #1 - Are the component and 'Complete System' numbers believable? Believable as any?



    #2 - Can 'System' SPL be calculated simply based on the known SPLs of the three components (and some assumptions)?



    The EV four-bin set would reportedly have two 123dB tops over two 126dB subs. Can a similar "Complete System" number be generated for comparison? Is there a published 'System' SPL number out there for the EV set of four? I couldn't find one. Can they be believed?



    I think I remember seeing the Bose L1 specs at around 115dB (120dB peak). Is that about right?



    Thanks, all!



    -Matt

  • #2
    Most of these max output SPL numbers are "calculated" and in the real world are about 10-15 dB off from what true musical performance would actually be.



    They basically take the 1W/1M sensitivity spec and increase it by the dB gain you would get from the max power spec. This assumes a 100% transfer with zero losses and it very likely looks at the output of the highest peak in the frequency response. So if the system had a 6 dB peak (considering a +/- 3 dB spec) you would normally reduce that peak by 6dB via EQ. So there is 6 dB off the calculated figure.



    There are more losses with a speaker as you increase power so your efficiency at 100% might be only half of what it is at 1 Watt. There's another 3 dB off.



    Where's the rest? In most systems the HF driver is padded down because it is much more efficient than the woofer. If you remove that pad when to "calculate" there's another 6-10 dB possible.



    We quote a measured spec with our speakers.
    Don Boomer

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    • #3

      I don't think they're that efficient.  I have a set that I will be using as the FOH Friday night.  It's a small club and we're running 6 vocals, kick drum, and trombone through it.  They're clean and get solidly about 120 dbc.  (Don't think we usually run them that hard.  We're probably running closer to 112 db.)  

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      • WynnD
        WynnD commented
        Editing a comment
        Forgot to mention that our "I've got to be the loudest thing onstage" singer, thinks they're tinny. He will admit that he knows nothing about music except how to sing, but he's more interested in unison singing. I guessing the size is fooling him. They're small and the club is small. It's a good match. (And I've had national names on my systems over the years.)
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