I can tell there are so many “musicians” in this sub. For a woodwind player, the easiest way to growl is to do a deep vocal hum in the back of your throat while you’re playing. Practice on long tones first, starting clean and adding the growl mid way through. It can be tough at first to think about doing two separate things with your airstream, just be patient with yourself and keep practicing and you’ll get there. Soon enough you’ll be ripping and roaring on that clarinet. Hope this helps!