TubeNet

You could try pulling the corners of your mouth into a frown. I find this helps focus the sound as well. Some sticking out of the chin will help this.

First I could get the pedal BBb.
Then I could but the air came out just like it is happening to you.
Now I can do it with all the air going in the tuba. and in tune.
Do you make "drastic" changes in your embouchure to get there? If you do, there must be the problem.
The air must pass very constant and slow.
You must try to do a seal without loosing the note.

I can get a pedal F (below that BBb) but with "dubious" intonation.

I'd much prefer having a good tone and play well in a 2 or 3 octave range. I still dont...

hey I just thought of something..... Do you puff out your cheeks at all when you play that low? That could possibly be causing the problem.... but I would hope your teacher would have already addressed this.

Support the economy: buy 8 different mouthpieces. That should solve it. If it doesnt, you can fool yourself into thinking it did because you spent so much money on them!

I like the eight mouthpieces theory!! Buy so that you support as many manufacturers as possible.

But seriously....you are part way there. There is no reason for your corners to be floppy just because you're playing a pedal tone. Your corners should always be firm, or at least "stable." I don't know what you're doing to play the pedal....but try looking up Roger Lewis's technique posts from a while back. If your embouchure works the way mine does (but it might be upside-down to mine) you can protrude your lower lip WAY into the cup for the pedals, while leaning the bell of the tuba towards you. THey should come out easily. If you're upside down, it would be your upper lip that protrudes. I remember somebody did a joke recently on the sound of one lip flapping....!

My horn embouchure is upside-down from my tuba embouchure, which makes life very interesting.

And.... I puff my cheeks for all but the highest notes. On tuba cheek puffing is not the horrible flaw that it is in, say trumpet playing. I've seen Sam Pilafian's cheeks puff too, on low notes, so that should end any and all controversy on THAT subject.

MA

***

Funny how different we all are from each other...In my case it was the high notes where I had the problem with air leaking out the sides. In the low register the corners of my mouth seem to come forward and seal up the leaks. Puffing out the cheeks a little bit seems to help in the low register, but not up high.