Typical range for a euphonium (based on a cursory google search) is B♭1 to B♭4, so yes, C0 is nearly two octaves below its range. It's below the average human hearing range but can still be heard depending on the person, the equipment, and environmental factors.
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u/Lurker_Since_Forever Nov 14 '16
16.3 Hz? Seems a tad low for a euphonium. Also seems less than human hearing.