At 130 and 140dB air is starting to behave rather nonlinearly. That means you will actually start hearing it.
Remember that the OSHA ultrasonic recommendation is more about "Will it permanently harm you" than comfort. At 140dB you'd hear probably rather substantial audible whine due to first and second order harmonics.
On the other hand a brutal whine at 15kHz is perfect for keeping those kids off my lawn when I charge my phone!
Edit:
I tried to find some information about the receiving end transducer losses. I bet they're going to be insane as it basically any impedance mismatch with air is going to cause the power to just reflect away, the bigger the mismatch the bigger the wasted power.
Remember that the OSHA ultrasonic recommendation is more about "Will it permanently harm you" than comfort. At 140dB you'd hear probably rather substantial audible whine due to first and second order harmonics.
On the other hand a brutal whine at 15kHz is perfect for keeping those kids off my lawn when I charge my phone!
Edit:
I tried to find some information about the receiving end transducer losses. I bet they're going to be insane as it basically any impedance mismatch with air is going to cause the power to just reflect away, the bigger the mismatch the bigger the wasted power.