Not all subwoofers can be upfired or downfired. Some subwoofer drivers need to be mounted on the vertical plane, firing into the room.
Determining this is easy: just make sure the woofer's suspension is strong enough to prevent gravity from pulling the driver down less than 5% linear excursion.
The formula looks like this:
We need to know a subwoofer driver's resonant frequency and Xmax. Resonant Frequency is simply the frequency that the driver will "ring" at. Xmax is maximum linear excursion. Our goal is to not lose 5% of linear excursion.
Example of the formula using a Rockford Fosgate R2D2-12 Prime Subwoofer driver, we can use it for upfire and downfire:
Example of the formula using an early 1990s Rockford Fosgate Punch 12. We should use this one to fire into the room:
I hope this helps you with your subwoofer design!
