questions
 

i have one 12" type r sub in a ported box. when i turn it up i can hear a kind of fluttering air noise coming from the port. is that normal or can it be fixed? and what should i put the lpf and subsonic filter at? around 30hz? the amp is only powering the sub. not really sure what the box is tuned to.

What name brand of box is it? LPF would be around 80hz and the Subsonic around 30.

The noise is probably "port whistle". Too much power is being put through that port, causing that sound. Either put less power through or get a better box.

Or router the port edge if you can (or get a larger diameter port.) that sub moves alot of air so if its pushing that through a 3" port that is not rounded, you may have some port noise.

it says alpine bass engine ready on the box. the port is 4" but the edge isnt rounded. is the box too small?

Prefabbed boxes aren't usually the best.

Port noise is quite common. I find most ported enclosures with traditional ports tend to have more noise. Focal made some boxes specifically for their subs with rounds edged ports and it still had a little port noise.

Maybe try a custom built slot port box

Exactly!