I'm building a subwoofer for my friends art film theater. I'm trying to figure out how much amplifier power I need to drive the drivers to Xmax, but my calculations do not match those made by Win ISD. If Win ISD is right I need about 1000 W and can expect about 121 dB at one meter. If my calculations are right then I can expect about 116 dB at one meter and I need about 500 W to achieve it.
I'm using two Titanic Mk III drivers in a 15 ft³ box tuned to 19 Hz.
Vas= 5.46 ft³ * 2 = 10.92 ft³ (5.46 ft³ per driver)
Xmax= 20.5 mm
Vd≈ 77 in³ * 2 = 154 in³ = 0.00252 m³ (I estimated that the Vd was about 77 in³ per driver since Vd isn't given)
f3≈ 19 Hz
ƞₒ= ( (2.7 * 10^-8) ( fs^3 * Vas) ) / Qes = 0.00784 W
where Vas is in ft³
112 + 10 * log 0.00784 = 91 dB SPL 1 W/1m
Par= 3 * f3^4 * Vd^2 = 2.48 W
where Vd is in m³
112 + 10 * log 2.48 = 116 dB SPL @ 1m
Max Input Power:
Per= Par / ƞₒ = 317 W
where Par and ƞₒ are in Watts
Win ISD calculated efficiency at 91 dB 1W/1m which is exactly what I calculated.
Win ISD calculated Max SPL to be about 120 dB which is about 4 dB more than I did.
WIn ISD calculated Max Input Power to be about 875 W which is about 560 W more than what I figured.
What is going on here? Those seem like big discrepancies.