adding a crossover to an active subwoofer

[Saltuk]

Hi , I got an active subwoofer from a friend and I am willing to use it in my second system , the sub is a part of a Sony 5.1 package "Sony SA-VE155/S" http://www.zigzag.am/productinfo.html?id=172156&l=am
as you can see in the link the satellites are very small and has no bass so the sub starts to take role from 150hz down to 28hz(actually the sub has a 6.5" driver it peaks around 50hz and barely audible lower than that )
What I am planning to do is build a proper cabinet , get a high efficiency driver ( at least 12" ) and use the amp of the sony's to build a new sub , because in my second system ( it is a stereo ) I am using Sonic impact T-amp and for speakers a 25x30x30 cm cabinet made of 30mm mdf with JVC CS-XV620 car audio fullrange drivers ( 6.5" 35-25000hz ) , so I want the subwoofer to work under 80hz or lower , I came across cheap low pass filters for subs on ebay like :http://cgi.ebay.com/PYRAMID-CR66-SUB...QQcmdZViewItem
The subwoofer has no lowpass settings just an analogue input , power button and a volume knob , can I add the lowpass elektronic crossover between the sub amp and the driver , any suggestions?
Regards Saltuk

[Destroyer OS.]

Well if you are using the same sony amplifier then it should still have the lowpass in it....

[Saltuk]

I am afraid you have mis understood me.

[richie00boy]

No, you have misunderstood him

There must already be a low-pass filter on the amp somewhere as you say it cust off about 150Hz. Therefore, find the bit that does this then replace resistors and/or capacitors to change the frequency to what you desire.

Unless of course the Sony is a bandpass box design.

[Saltuk]

Sorry , I think I should have mentioned that I have no idea about
resistors and/or capacitors and modifying them , ofcourse there is a lowpass filter in the sony but the point is that it is not low enough and not adjustable ( at least from the control panel ) as I have no idea how to modify the resistors and/or capacitors I am willing to add another lowpass filter between the sony's amp and the driver to have the roll of starting from atleast 80hz or below ,

[pinkmouse]

I'd sell the Sony, and start from scratch with the new driver and get a plate amp with the required crossover if I were you. You have much more chance of a successful result.

[richie00boy]

Modding the Sony is no harder than adding (building) an additional filter.

I agree with Pinkmouse though, a plate amp will be a better result all round.

[Saltuk]

Thanks for your answers but I didnt have my question answered still , can I add the "passive subwoofer low pass filter(the link to the item is at the first post of my thread)" to the sony by connecting the two cables that come out from the sony amp( which feeds the driver with 45 watts of power with the signal of 150hz to 28 hz) to the extra lowpass filter and from that filter to the subwoofer driver ? I just wish to know that ,
Regards,
Saltuk.

[richie00boy]

The eBay item is not a passive filter, you cannot connect it between the amp and drive unit. However, you can connect it between the source and the amp.

[Saltuk]

Thanks alot , that was what I needed to know.