Shouldn't that video say, "Kids, don't try this at home"? That gas is heavier than the familiar mix of nitrogen and oxygen we love to breathe.
Funny thing, my Dayton-Wright ESLs are sealed in that gas. It is used by some kind of specialty welders and not cheap.
Don't gasp in disbelief, but my one-meter-square ESLs play strong down to 70 Hz and below. And vastly cleaner than you can ever get shaking large hunks of cardboard around using the right hand rule. Join two, and not sure you need any sub except for movies.
I am not sure if the designer, a person of rare hifi genius, had diaphragm resonance in mind. For sure he did know that these ESLs greatly benefit in linearity and efficiency from super-high bias voltage and these speakers can be run at 15 KV. No kidding... at least in dry weather.
My speakers have held their gas without needing a top-up, as far as I can tell, since 1984. Whazzat... 26 years?
.... but then, I don't have any cats.