First I should start by saying my goal is to build a dual tempest sub (already have the drivers) for less then the cost of a 20-39CS+, of which I already own one. With $300 left to build the enclosure I think this is reasonable. I am looking for a similar sound quality and at least equal output as a dual 20-39CS+ setup with my current Samson 1000 amp (500 watts x 2 @ 4ohms). If I can also get lower extension it would be great, but it's not a requirement (actual in room response is flat to 18 HZ). After searching through past posts it seems that my choice is between a sonotube or an IB. Having aan svs I have a good idea of the potential of a sonotube and realize that a dual tempest (single tube) would be about my height if properly sized. I am also aware of the benefits and tradeoffs of an IB. My only deterent to an IB is the fear it will be too loud for the rest of the house. One thought was that since I have a walk in attic next to me hometheater room I could place my current sub in there to get an idea of how it would sound in the rest of the house. My assumption is that this would actually be worse then an IB because all the bass would be focused in the attic. Does anybody know if this is a reasonable line of thought? I am also looking for a program that can give me an idea of how the two compare. Can an IB manefold be modeled? If so what program? I would prefer the program be able to model sonotubes as well to get a more accurate comparison. If the performance is roughly equal I may just build the sonotube.