DARPA is these days developing an “ultrasonic curtain” that is intended to lower noise levels by at least 30db in military vehicles. It’s in actual a sonic cloaking device that could shield an entire vehicle through “absorption of transverse acoustic energy through a vertically projected ultrasonic field.’ Reduction in noise levels by at least 30dB would facilitate U.S. forces to efficiently operate noticeably closer to enemy forces without being detected aurally. They will have a “field demonstration of a vehicle operating over a military test range.”