Tone Low B, Bb vibration

[JamesOxford]

Took a while to settle on a setup for my Tenor, lockdown hasn't helped. I ended up with a D'addarrio Select Jazz mpc to replace the Rouseau it came with and settled on Vandoren Reds after trying several and now am getting a somewhat clear tone. I have eliminated the nightmarish squeaks and can play to high F# okayish. (btw I think reeds were only a small part of the puzzle for squeaks; mostly it was down to me being too tense and trying to force notes out, when I made a conscious effort to relax everything started getting better.)

However when I play low B, Bb the sound shudders. According to a tuner it is (mostly) in tune, but it seems a somewhat raspy tone. Not sure how to describe it. I don't think it's right though.
I expect it's to do with my embouchure/breathing or something, any ideas/advice? Should I be doing something with my mouth, jaw for lower notes? I find it difficult to play long tones down there too, but expect that is because I don't have the stamina yet.

 

[Stephen Howard]

Very kind comments, thank you.
I just write it like I'd say it - and I suppose I imagine someone stood at the end of the workbench with a puzzled look on their face.