preset subsonic filter vs adjustable

[plugger]

i put this in the subwoofer section because its related to my subwoofer even though its about amps. my sub is an AQ hdc3a 15" 4.5 cu ft box tuned to 36 hz. my quiestion is if its better to have an adjustable subsonic filter or preset to a certain freq...i have a older rockford power bd1500 amp i want to use but its subsonic filter is NOT adjustable and i searched and cant find what its set at. one guy said 25 hz but cant really trust everyone. say it is 25 hz then if my box is tuned to 36 hz would that be bad?

[wickedwitt]

The need for an adjustable SSF is completely dependant on the box+power combined constraints. If you are not overpowering your sub (from the looks of it you aren't) and have proper port area for your tuning/size of enclosure, you should be perfectly safe with a 25hz filter. The need for an adjustable filter only comes into play in these two scenarios:

1. You are tuned so high, or have so little cone control that the sub will unload higher than the SSF.
2. You are tuned low enough, or have enough cone control that the SSF is actually limiting controlled bass response from your subwoofer. Not many people typically want to play full powered notes below 25hz (20 on many other amps). The few that do typically seek to find an amp in which the SSF has an "off" setting.

[plugger]

thanks i feel better about installing this amp now. i heard that you want your ssf about 5 hz lower than your box tuning, and if the bd1500 is at 25 that puts it at like 11 hz lower than the 36 hz tuning wich isnt much but i have other amp options (orion 2500d @ 2 ohms). but sounds like this is fine