I made myself a active subwoofer using Rockford fosgate driver(car 12'' subwoofer 150W) in downfire configuration using MONO Toshiba 2SA1943 / 2SC5200 150W amplifier running through 50-0-50 (5 Amp) with auxiliary 15-0-15(1 Amp ) transformer and using this
DIY Dual NE5532 Subwoofer Processing Circuit Low Pass Filter Circuit Board Kit - Blue - Free Shipping - DealExtreme Low pass filter.
i also have
Wintek - 200W Mono (2SA1943 / 2SC5200) but its 200W at 8 ohm and mostly car sub woofer is of 2 or 4 ohm in my case its 4 ohm so its over powered for my sub woofer.
I bought my 150W amp from a guy from Kerala and he also custom made that transformer for me.
apart from that i am using 2 more circuit board build myself.
1.) A realy circuit to switch the output to the Driver from amp on and off to delay instant on and off of subwoofer to save driver from initial and post-off surge(without this circuit subwoofer have powerful thud sound as soon as you power it up and turn it off from mains).
2.) I found a circuit from internet and after little modification build a circuit which automatically cut power to the transformer and put subwoofer in Stand-By mode if there is no audio signal for 1 -2 minutes and restore it to on as soon as audio signal is back. To power this circuit i am using cheap 12 volt 500 mah SMPS board ( commonly found with LED strip lights) the power light turn to red when subwoofer is in stand-by mode and white when its on.
The body/cabinet of subwoofer is home made wooden (its very heavy even without anything installed) with 3 inch flare port.
the subwoofer sounds damn good. and i think its good looking too.
the only problem i am facing right now is that other wooden furniture specially racks mostly have thin plywood at backside and this thin plywood and glass sheets in windows and furniture rattles with subwoofer. so mostly i put it below medium volume level fortunately its more that enough.
Some Outside pics