## Piston Excursion calculator

This calculator can solve for one piston excursion parameter while changing the other variables.  For example: tell the calculator the number of drivers, cone diameter, desired volume level, a frequency and it will calculate how much driver excursion (Xmax) is required to achieve this assuming a sealed box or infinite baffle alignment.

Solve for

number of drivers
driver diameter (inches)
Hz
dB SPL @ 1m
Xmax (mm)

Notes:
• basic piston formula:
• SPL = 112 + 10 * log(4 * pi^3 * Ro / c * (num * Vd)^2 * f^4)
• Vd = (.83 * diam)^2 * pi / 4 * Xmax
• This calculator is only valid for sealed box or infinite baffle alignments.
• Xmax excursion is center to peak ("one-way") which is usually half of the peak to peak value.
• These are excursion limited numbers.  It is assumed that amplification and driver power handling are not a factor.
• Vented alignments will typically have double the driver's Xmax values at F3, this shows the efficiency inherent in the vented alignment.
• Isobariks should be calculated with half the number of drivers, since all we are interested in is how large the radiating surface is and how much air it can move.  Isobariks change effective box volume and that is not what is of interest here.
• If you're interested in some basic dB doubling laws then check out my dB laws, misc formula, and tidbits page.
• These equations don't follow the max 194dB limit in 1 atm.  They track nicely until you get to the extremes (example: 10000 drivers or an Xmax of 300 feet or a driver with a diameter of a quarter mile).  As things get huge the point source model falls apart.

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