I has been 30 years since I last wired together some hi-hi amps and built several different speaker enclosures. I have assembled a few electronic projects (either kits or followed articles)over the years and have done a fair amount of carpentry and have all the necessary tools. I have decided to part with time, energy and $$$$ and put together my own powered subwoofer - however in the previous 30 years things have changed some what and I would like some clarification on a couple of things. If I have a powered sub with it's own say a 300 watt amp do I also need a Linkwitz Transform Circuit in sealed sub? Will the subwoofer output on the AV amp supply only the required low end frequencies to the sub amp or will some sort of filter be required? Sorry if they are dumb questions but to a 55 year old who learnt about transistors in first year Physics it's been a long time!!!