Im new here to the forums and to HT in general, so please forgive any obvious questions I just got a second hand entry level receiver (RCA RT2500) and now need a sub. This receiver has both a line-level RCA sub output and a built-in dedicated subwoofer amp with spring clip connectors. So I then have a choice of either a passive or active sub. Im guessing that building a passive sub will be both easier and more cost-efficient, basically get a driver and build a box around it Although I do not know how the crossover works with the internal amp, there is no adjustment I can see. The manual is not very detailed: Heres the .pdf manual The amp fed 200W into to the original 3ohm sub - a small ported enclosure (about 1 cubic foot) with twin 5" drivers. I tried the factory sub briefly, but the small dual drivers were obviously not getting as low as I would like, and there was considerable distortion above 1/3 volume. Im guessing the surrounds were well broken in - or just plain broken My front speakers (CerwinVega 200SE) already have 8" woofers, so Im thinking I will need at least a 12" sub. I will probably go for a ported design. I have never built a speaker before so I need some help with most of the details like: choosing size of enclosure/air volume/shape port length building materials method of joining panels driver model will this actually work when Im done? I have looked around at the faqs here but havent yet found anything on building passive subs, any links would be appreciated. EDIT: Sorry, just found the DIY forum, mods feel free to move this.