This page will show how to use the subwoofer from the Altec Lansing ACS295 2.1 speaker kit as a stand alone active subwoofer without using the satellite speakers. The speakers are controlled from one of the satellites (as seen in the picture below, the controls are on the left satellite speaker) so if the satellites are lost the subwoofer is dead in the water..
We (me and Fredrik) found two of these subwoofers at a second hand hifi shop and wanted a active subwoofer for a home cinema. There where no sattelites and searching the web we only found other people wanting to know how to use the subwoofer stand alone and that Altec Lansing isn't exactly handing out datasheets :P Thus, we took the subwoofer apart and analyzed/traced the circuit board. Here are some high resolution photos of the board:
The speakers are controlled by a TDA7433 audio processor that speaks I2C with the controls on the satellite. This is a pinout of the connection to the satellite (red connector in the picture above from Dells support page):
After studying the datasheet for TDA7433 and this page about I2C I wrote a controller program for a Atmel Mega8 using avr-libc and connected it to SDA and SCL together with 4.7kOhm pull-ups (there are no pull-ups on the circuit board inside the ACS295). Power the amplifier on by connecting the power pin to ground as shown in the pinout above, send the right parameters via I2c and eureka, we have a working subwoofer! :D Unfortunately Altec chose a cheap plastic to cover the back of the subwoofer and this plastic vibrates and makes a noise when the base is pumping :( Let me know if you find a solution to this (we are thinking of replacing it with wood).
I've made the source code for the AVR I2C controller available at google code:
http://code.google.com/p/acs295 (google is closing down code so the source has moved to github: https://github.com/larsenglund/acs295)
I´d be happy of you post a comment if any of this is useful to you, happy hacking!