Originally Posted by steve nn
EDIT> I'm referring to just the driver size part.
All things being equal, at 20Hz, a fifteen inch driver has approximately twice the SPL output of a twelve inch driver. Twice the output being a minimum SPL increase of 3db in a sealed subwoofer setting. My above does not address issues of perceived volume increase but instead, deals with SPL increase. As an example, I replaced two of our drivers with twelve inch drivers that have an Xmax of 14.5mm. Using the 14.5mm Xmax as the the standard, if one uses this calculator
, all things being equal, there is a +r4dB increase in SPL output when going from a twelve inch driver to a fifteen inch driver.
If all things are equal, going from three twelve inch drivers with an Xmax of 14.5 to three fifteen inch drivers with an Xmax of 25mm, the increase in SPL calculates out to an increase of a +r9dB or ~8x's the the output in SPL. Ten dB being the accepted threshold for the perception of the sound level being twice as loud.
Based on the above, my recommendation is when possible, all things being equal, twelve inch driver vs fifteen inch driver, due to output issues, always go with the larger driver.
(hopefully I got my above correct and what I posted above makes sense to you)