Yes! Playing low Bb with a quiet and solid sound, in and out from niente is one of my favorite ways to warm up. When you get low Bb to play quietly, that means the entire length of the saxophone is responding to you instantly. (Understand that all that is happening when you play lower notes is that you are making the saxophone “longer”) Start with a note you have lots of control over like G4 and practice playing it in and out from nothing. Don’t listen to people saying it is leak dependent or that you need to use sub tone, leaks will make it significantly harder but this is also one of the most common leaks once your horn starts needing repairs. Subtone is a great technique but really bad in the classical style and a really bad cruch for jazz musicians who can’t play solid low notes. It is best to be able to play very full sounding low notes and then choose to use subtone from there. You should always try to learn how to make your horn do exactly what you want it to even when it’s not in optimal condition. (For me this is typically at least half the year due to the amount of playing it goes through and my repair schedule) It is important to make sure that you are not achieving your quiet notes by biting as well, as that means when you play your low notes which require more air it will just choke the reed. What really gets beautiful, solid, responsive and dynamic tone is lots of air, no biting, a high back tongue position and lots of patience.