Box tuning and SSF?

[mikeyboc]

I need some clarification: For example, if the box is tuned to 30 HZ, would I want to wet the SSF at 30, or below 30? I was thinking to set it at 30, but have read that you can set it below (wouldn't that damage the sub?)

[squeak9798]

A general rule of thumb is to set it to approximately 1/2 octave below tuning frequency.