Perhaps I am missing something, but "designed distortion for home theater" does not make any sense to me. If the track contains distortion, say in the form of noise of some sort, any great sub should reproduce it very accurately. If that is not the case, then the sub is adding something that is not in the soundtrack to begin with (which you would never want).
Also, I should point out that the SongSub is not a sealed design. It uses a 12" passive radiator to accomplish basically the same response as a ported design, but without the potential for port noise (chuffing), which can be considerable at lower frequencies.
On a side note, I should also point out that performance claims of some subs can be misleading. Most speaker manufacturers rate frequency response in terms of +/- 3db. This is because only -3db and above is considered usable bass response. There is output lower than that, but it is not "usable."
Subwoofer manufacturers, to the contrary, often quote low end bass response of -6db or even -10db, factoring room gain into the equation. (We typically quote performance based on the F3 (-3db) of the design.)
So any frequency listed (20Hz, 15Hz, etc.) is really meaningless unless you know if it represents the F3, F6 or F10 of a given design.
Very often I see subwoofers marketed at having extension to 20Hz or below. The problem is, there is no way the drivers, cabinet, etc. could possbily acheive an F3 of 20Hz. It would defy the laws of physics. But there is no law preventing them from claiming 20Hz if that is the F10 of the design (and they often fail to mention that it is F10). So they do. Buyer beware!
On a related note, we just got in a batch of 12" drivers and very well-engineered passives from TC Sounds. These will make for some very capable subs. We have enough on hand for 10 subwoofers and can easily get more. 15" drivers and passives are also available. With a good plate amp, these drivers and passives will make unbeatable subwoofers with great low end extension, extremely low distortion, no port noise and very musical to boot! (And they will reproduce all the distortion designed into HT tracks in the first place.)
- Jim