I've recently become a dealer for VMPS after having used their speakers for the last decade. Their passive subs are extremely musical and powerful not to mention bargains for the money. They come pre built or can be ordered as kits. Check out the reviews on audioreview.com and also check out the Vmps forum at audiocircle.com. Also I thoroughly understand why you'd want a passive sub as it can be much more versatile and you can use a much better amp than a plate amp.
Another option is to build your own. On the madisound and partsexpress boards there's alot of knowledgeable people that are very helpful. A sub is relatively simple compared to a multiway speaker and is fairly easy to build.
Not too many speakers in my opinion can do a truly thorough job without at least one sub. I run my speakers which are full range(Vmps RM 40's) with a sub. The Rm 40's are running full range and I've got the sub crossed over at about 45hz. Others do the same with similarly powerful speakers and there's a thread here with some info on that. Then there's people who don't care for bass as much as many of us. To me the bottom octave must be produced accurately and this means it must be well articulated, have power and weight. Best of luck to you.
Another option is to build your own. On the madisound and partsexpress boards there's alot of knowledgeable people that are very helpful. A sub is relatively simple compared to a multiway speaker and is fairly easy to build.
Not too many speakers in my opinion can do a truly thorough job without at least one sub. I run my speakers which are full range(Vmps RM 40's) with a sub. The Rm 40's are running full range and I've got the sub crossed over at about 45hz. Others do the same with similarly powerful speakers and there's a thread here with some info on that. Then there's people who don't care for bass as much as many of us. To me the bottom octave must be produced accurately and this means it must be well articulated, have power and weight. Best of luck to you.