I have a velodyne f-1500, it's a 15" servo subwoofer. The built-in amp and power supply are toast and unrepairable and have since been reomoved and replced with an external amp and crossover. I want to take this sub and either port this box(currently sealed) or build a new ported box. I have no, and cannot get specs for the subwoofer. I know the current box is 3.25cu.ft. Is there a general ratio from sealed size to ported size? Any other suggestions would be appreciated.
There is no general rule. However, most subs ask for twice the volume than sealed if you're going ported. Also, if it's a home theater sub, it may be an 8 ohm speaker. The power output from your amp will be cut dramatically if unless you wire two of these in parallel.