Explanation of basic terms for acoustics

The physical characteristics of sound
Sound: A pressure wave generated by vibration in an elastic medium.
Wave: The form of transmitting energy from one point to another.
Wavelength: The length of time a cycle occupies in space.
Frequency: The number of cycles completed in one second. The unit is Hz.
Period: The time required to complete a cycle.
Velocity: The speed at which the wave moves.
Wave velocity = wavelength * frequency
The speed of sound is related to the medium
Density: Usually in a denser medium, the faster the speed of sound.
Elasticity: Usually in a medium with higher elasticity, the faster the speed of sound.
Energy: In the air, the higher the temperature, the faster the speed of sound, the formula is as follows:
Vs = 331 m/s + 0.6t
Therefore, at 20 degrees C, the speed of sound is 331+20*0.6=343 m/sec.
Amplitude: A measurement of the displacement of a molecule in a medium, used to indicate the volume of sound.
RMS (Root Mean Square) square mean root value is 0.707 times the maximum amplitude
Average: 0.637 times the maximum amplitude
Resonate Frequency: The natural frequency at which objects vibrate.
Free Field: No obstacles, no sound field/space that reflects sound waves.