If you want real 20Hz response at low distortion you're going to need a fair-sized sub. Your room size in total volume is a big factor. To have a worthwhile discussion we'd need to know that, along with your budget. For example, the larger JL Audio subs (113, 212, 213) are nice, as are the Velodyne DD15+ and 18+, but these are all rather pricey. If you have the money, cool, but without a budget we can't tell.
There are several internet direct brands that are interesting, and a lot of people swear by. For example, the Funk Audio 18.0 and 18.3. The 18.0 is comparable to the Velodyne DD18+, but lacks some features, some design integration, although it has nicer cabinetry and finishes. The 18.0 and 18.3 are also available with neodymium drivers, which means they weigh a lot less, and can be moved around by one person.
Lower in the budget range is the SVS PB13 Ultra, which has prodigious 20Hz output in its ported mode. You might also look at Rythmik and the Hsu. The drawbacks to these subs are that they are somewhat less good looking, being simple boxes, and they have less powerful and sophisticated amps, but they get the job done at far lower prices than JL and Velodyne. All have low distortion and good time-domain performance, so they're fine for music.
Lots of people claim you get better results from multiple subs than just one sub, due to mitigating the effects of room modes. My advice is to start with one and see if it works well, like it did for me, but don't be surprised if two subs work a lot better in some rooms.
More than main speakers, subs work best when they have a lot of headroom, meaning you're not stressing them much at all. If you want decent sub-30Hz bass forget subs with a single 12" or smaller driver. A smaller driver and a big ported cabinet, like the SVS PB13 Ultra, can get remarkable output, but then you've got to put up with a huge box in your listening room.
I have a Velodyne DD18+, and it's a remarkable device, but lately Velodyne has been taking pricing lessons from JL Audio. Funk Audio has just released an improved version of the 18.3, and I'd probably go that way if I were in the market today. If you really want 20Hz bass and have $2K to spend the SVS is the way to go. For about $1K the Hsu is remarkable value.
I think all of the subs from mainstream high-end speaker brands are over-priced for what you get. Especially B&W. Revel is little better, IMO.
There are several internet direct brands that are interesting, and a lot of people swear by. For example, the Funk Audio 18.0 and 18.3. The 18.0 is comparable to the Velodyne DD18+, but lacks some features, some design integration, although it has nicer cabinetry and finishes. The 18.0 and 18.3 are also available with neodymium drivers, which means they weigh a lot less, and can be moved around by one person.
Lower in the budget range is the SVS PB13 Ultra, which has prodigious 20Hz output in its ported mode. You might also look at Rythmik and the Hsu. The drawbacks to these subs are that they are somewhat less good looking, being simple boxes, and they have less powerful and sophisticated amps, but they get the job done at far lower prices than JL and Velodyne. All have low distortion and good time-domain performance, so they're fine for music.
Lots of people claim you get better results from multiple subs than just one sub, due to mitigating the effects of room modes. My advice is to start with one and see if it works well, like it did for me, but don't be surprised if two subs work a lot better in some rooms.
More than main speakers, subs work best when they have a lot of headroom, meaning you're not stressing them much at all. If you want decent sub-30Hz bass forget subs with a single 12" or smaller driver. A smaller driver and a big ported cabinet, like the SVS PB13 Ultra, can get remarkable output, but then you've got to put up with a huge box in your listening room.
I have a Velodyne DD18+, and it's a remarkable device, but lately Velodyne has been taking pricing lessons from JL Audio. Funk Audio has just released an improved version of the 18.3, and I'd probably go that way if I were in the market today. If you really want 20Hz bass and have $2K to spend the SVS is the way to go. For about $1K the Hsu is remarkable value.
I think all of the subs from mainstream high-end speaker brands are over-priced for what you get. Especially B&W. Revel is little better, IMO.