Definition

1. Adjective:
   • Relating to speeds less than the speed of sound: Describing motion, especially of an aircraft or object, that travels at a velocity slower than the speed of sound in a given medium (like air).
   • Relating to sound waves with frequencies below the range of human hearing: Pertaining to sound or vibrations with frequencies lower than approximately 20 hertz, which is the typical lower limit of human hearing.

Usage and Examples

• Adjective:
  • Most commercial airliners are subsonic aircraft. (They fly slower than the speed of sound.)
  • The new engine is designed for efficient subsonic flight. (It operates optimally at speeds below Mach 1.)
  • Scientists study subsonic vibrations to understand geological events. (They examine frequencies too low for humans to hear.)

Advanced Usage

• Technical Context: In aerodynamics, "subsonic" specifically describes airflow or flight where the local air velocity is below Mach 1 (the speed of sound). This is distinct from "transonic" (near the speed of sound) and "supersonic" (faster than sound).
  • The wing's design is optimized for subsonic cruise conditions.
• Scientific Context: In acoustics, "subsonic" refers to infrasound, which can be produced by natural phenomena like earthquakes or by large machinery.
  • Elephants use subsonic rumbles to communicate over long distances.

Variants and Related Words

• Subsonically (adverb): In a subsonic manner.
  • The plane traveled subsonically across the continent.
• Infrasound (noun): Sound waves with frequencies below the lower limit of human audibility; a technical synonym for subsonic sound.
  • The monitoring station detected infrasound from the volcanic eruption.

Synonyms

• Below the speed of sound: Pre-Mach, slower-than-sound.
• Infrasonic (specifically for sound frequencies): Pertaining to sound waves below 20 Hz.

Antonyms

• Supersonic: Relating to speeds greater than the speed of sound.
• Transonic: Relating to speeds close to the speed of sound.
• Ultrasonic: Relating to sound waves with frequencies above the upper limit of human hearing.

Adjective

1. (of speed) less than that of sound in a designated medium
   • aircraft flying at subsonic speeds