If that really is the range they are targeting, this product is doomed. That will be one heck of a noise to cancel. "Soundproof box" is right up there with perpetual motion, zero-point energy, and spherical chickens in vacuums.
A 'soundproof box' is hard because most of those boxed things we want to quiet down (say, pets) still need to be a part of our environment, breathing air and the like.
A clothes dryer, meanwhile, is a near-ideal case for vacuum isolation + elastic dampening. Build a box with a door; hang an airtight motorized barrel in the box from a bungee cord, with a second door, and electrical connection; and then, whenever both doors are sealed at the same time, [slowly] evacuate the air from the box.
If you are going to go through all the effort to create a proper vacuum, and then isolate all the little penetrations needed to maintain whatever is inside, just throw the wet clothes into the vacuum and call the thing a freeze dryer. No sonic required. A heat lamp inside a vacuum chamber would probably dry stuff using much less energy than either sonic of hot air.
I'm not sure whether organic materials would be very happy with all their water content getting sublimated out of them due to the sudden drop in pressure. The result would probably look more like cotton jerky than fluffy towels. (If anyone has a Youtube link of such a reaction, though, I'd love to be proven wrong!)
A clothes dryer, meanwhile, is a near-ideal case for vacuum isolation + elastic dampening. Build a box with a door; hang an airtight motorized barrel in the box from a bungee cord, with a second door, and electrical connection; and then, whenever both doors are sealed at the same time, [slowly] evacuate the air from the box.