We have supersonic jet and rocket flight now, and use ultrasound heat in physical therapy, and use other ultrasound frequencies for breaking up kidney stones. The inventor in this episode was essentially right: sounds that we can't hear are possible and can be useful. And we know that whales and elephants communicate somehow with very low frequencies; so it's conceivable that certain frequencies outside our threshold of conscious hearing could communicate something.
But anything unseen or untraceable that doesn't just communicate, but also conveys power to an individual or entity--now you're talking about something dangerous. The scientists who eventually developed the atomic bomb never originally imagined creating something that could cause horrific devastation, human suffering, and long-lasting radioactive pollution. I don't think we can really blame this violin-maker for tinkering with sound in a way that had unforeseen results. It was just a horn, a special horn that he was working with.
Maybe someday, physicists will destroy the universe as we know it by tinkering with unseen particles in a Hadron collider. You can't really blame people for wanting to know how things work, or asking "what if...?"
This series is very crude, but sometimes it makes you think. And the episodes are short, and not too gory or scary, so they're OK to watch at bedtime. Gives your unconscious/subconscious something to do besides think about your routine in the morning.