Infrasound, sound at frequencies below the normal threshold of human hearing
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Subsonic aircraft, a flying machine that flies at air speeds lower than the speed of sound
McNamara further proposed that a SAC variant of the new F-111, to be designated FB-111A, along with improvements in the Air Force Minuteman and Navy Polaris missile systems and modernization of the subsonic Boeing B-52, would enhance strategic deterrence and make the B-58 superfluous to the needs of the USAF.
The second is his "Whisper" family of cartridges, intended to cause maximum damage at subsonic speeds, making them nearly silent when used with a firearm silencer.
LRASM-A is a subsonic cruise missile based on Lockheed Martin's 500 nm-range AGM-158 JASSM-ER - Lockheed Martin was awarded initial development contracts.
The energy range of sonic boom is concentrated in the 0.1–100 hertz frequency range that is considerably below that of subsonic aircraft, gunfire and most industrial noise.
Techniques learned from studies of the original supercritical airfoil sections are used in designing airfoils for high-speed subsonic and transonic aircraft from the Airbus A300 and Boeing 777 to the McDonnell Douglas AV-8B Harrier II.