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!)
That (the 600 Hz) is the modulation of the ultrasonic signal from the transducer...I am not sure if modulating the underlying signal at that frequency has a similar auditory effect as a simple 600 Hz sine wave.
Indeed that's what it says. That's neither ultrasonic nor easy to block with reasonable quantities of sound dampening materials.
They also directly mechanically couple the transducers to the fabric. You need as much area of transducer as fabric you need to dry, unless you have some automated way to place the fabric on the transducers sequentially.
To get the effect they want they have to use high frequency 30-40kHz (as in name, ultrasound). They modulate it with lower frequency (which probably splits off bigger water globs) for better efficiency or something. You won't be able to hear the modulating signal as you are not able to hear the carrier frequency.
Yeah, maybe it's the frequency that some component runs at but not the produced sounds? Or maybe they forgot a "k" in "kHz"? Eyeballing a chart in their presentation seems to show 100kHz piezotronics. [Page 8 of https://energy.gov/sites/prod/files/2016/04/f30/31297_Momen_... ]
and 500: https://www.youtube.com/watch?v=GlEfshsoyZk
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.