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19th April 2009, 12:53 AM  #1 
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Join Date: Jan 2004
Location: Toronto, ON, Canada

SPL and excursion
I have no idea how to solve this sort of problem, so I'm falling back on you guys. This is not homework, by the way.
An acousticallysmall driver that fires into halfspace plays a fullspectrum sound (that is, equal energy at all frequencies between 20 Hz and 20 kHz) but is 4thorder LR bandpassed at 150 Hz and 600 Hz. The Cweighted (flat) SPL at 1 m is measured to be 110 dB. What is the peaktopeak excursion of the driver? 
19th April 2009, 04:49 AM  #2 
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Join Date: Jan 2002

Model the particular driver in Unibox and look at the Xcurs curve.
Here is a curve for the required volume displacement for a given spl and freq. Extrapolate to fit your requirements. 
19th April 2009, 05:24 AM  #3 
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I can do that with either WinISD or SL's spl_max spreadsheet, but AFAIK the numbers are only valid for single tones. Any given SPL that is comprised of various frequencies should have less amplitude per freq, right?

19th April 2009, 06:07 AM  #4  
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Quote:
For a given SPL the LF requirements dominate xcurs. 

19th April 2009, 06:39 AM  #5  
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19th April 2009, 08:58 AM  #6 
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What the graph shows is the calculated amount (volume) of air needed to be displaced at a given frequency to produce a certain SPL. HOW you do that is irrelevant. How much error between a measured result for a given driver and the calculated will depend upon the driver and it's linearity. That you need to MEASURE.

19th April 2009, 01:29 PM  #7  
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The excursion is the vector sum of the excursions at each frequency. I know of no analytic expression for noise, or music, so you will have to approximate it by brute force. You could start at 20Hz and go up at 1/12 octave intervals.
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19th April 2009, 09:50 PM  #8  
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19th April 2009, 11:25 PM  #9 
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Don't get me wrong, There are a number of ways to approximate this.
The simplest is to calculate the excursion at each frequency and add them up. The excursion at F1 = X1 Excursion at time t, due to F1 = X1*sin(2*pi*F1*t) Do this for every frequency...This is brute force. You could also generate a model and apply a stimulus. For your example, you have the added complexity of a bandpass filter. I could do this, but not for free, what is it worth to you to know the answer?
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Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. Carl Sagan Armaments, universal debt, and planned obsolescencethose are the three pillars of Western prosperity. —Aldous Huxley 
19th April 2009, 11:37 PM  #10  
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