Deep enough for music reproduction from most sources. Usually the quoted specification will actually be 3dB to 6 dB less than normal at the quoted spec. , so say 38/40 Hz flat, when close miked, which is fairly common in Home speakers.. The issue is usually how loud these low tones are in comparison to higher tones the system produces, not whether or not they are there at all. It's the the point at which sounds start to be made less loudly. This is due to the slope of the roll-off, All speakers will usually continue to make lower sounds, just at less volume. Some will decline in volume faster than others. For instance, closed box speakers usually sink in volume more slowly than ported or ducted ones do using similar drivers. This is because they are "trading away" a slower decline in volume for a "hump", or extended volume in the bass at a somewhat higher frequency, though usually at a point where an equivalent closed box speaker would already have perhaps a 6dB declined bass volume, so for ported speakers its an extension of sorts, but beyond that "Hump" point, the bass volume will drop very sharply to pay for it. Some listeners prefer one type over the other, and it is very common to find ported speakers made to abuse the ducting technique in order to artificially make the sound seem more bassy, simply by picking a "hump" point at a higher frequency than needed, which, of course makes for an inaccurate, very unnatural sound. Well made ported, or ducted speakers are more labor intensive to make well, which means good ones are not cheap - and there are a lot of poor ones.
The point is, very low frequencies are not picked up by the ear as well, and making them loudly enough to be useful to listeners is very dependent on room reinforcement, hearing, and driver size (how much air the driver can shove around), Maybe this is why few instruments try to make them. I like speakers that can run down in to the upper twenties or low thirties in standard rooms, but it isn't as big a deal for music as it is made out to be, and many that spec higher can deliver plenty of bass in rooms of the proper size and shape.
My feeling is, if I am purchasing speakers for my own home use, to try and get ones that can reproduce all music types well, even types that I do not frequently listen to. Specialized "rock" or "club" types, that seem to do better in genre, are making decisions for me that I can make for myself on quality speakers by adjusting tone, balance and volume controls, without sacrifices that are built into specialized speakers getting underfoot. These days, bass enhancing modules can always be added to "Bump" Bass, or color it.
Also,lower-going speakers that spec very well in lower octaves tend to use a good deal more power to do that. So it is not provided for free, and affects the price of all the associated higher powered amps, so on, and their cost. It is more important that the sounds made are crisp, airy and accurate, in so far as a quality listening experience is concerned. I'll point out that Public Address speakers are notoriously inaccurate, trading lots of things away for volume and projection at the expense of accuracy and true to source reproduction, but then, that's not their purpose, which is to "bump the crowd"..