The speaker must be able to fit under the seat or go in the overhead. It the case of turbulence, the airline doesn’t want hard object flying around that could cause injury. You can always pack it very carefully and have it put on the airline with the oversized and special handling baggage.
Commercial air travel with a speaker
Does any member have experience flying domestic US commercially with a hifi speaker? Willing to buy a seat/ticket for it, I just don't want to be halfway across the country and have issues. TSA looks to be OK with it. Any real-world experience out there?