Definition

1. Noun:
   • Acoustic Reactance: The imaginary component of acoustic impedance, representing opposition to the flow of sound energy through a medium or at a surface due to the inertia (mass) or elasticity (springiness) of the medium, not due to energy loss. It causes a phase shift between sound pressure and particle velocity.

Usage

• Technical Context: The term is used almost exclusively in physics, engineering, and acoustics to analyze and design sound systems, noise control materials, and musical instruments.
  • The engineer calculated the acoustic reactance of the enclosure to optimize the speaker's bass response.
  • At certain frequencies, the acoustic reactance of the air in the neck of the bottle causes it to resonate.

Advanced Usage

• Mathematical Representation: In complex number notation for acoustic impedance (Z), acoustic reactance (X) is the imaginary part: Z = R + jX, where R is acoustic resistance and is the imaginary unit.
• Frequency Dependence: Acoustic reactance varies with frequency. Mass-like reactance increases with frequency, while stiffness-like reactance decreases with frequency.
• "Reactance Cancellation": A condition where inductive (mass) and capacitive (stiffness) reactances are equal in magnitude but opposite in sign, resulting in resonance.
  • The system was tuned to achieve reactance cancellation at 100 Hz.

Variants and Related Words

• Acoustic Impedance (n): The total opposition a medium presents to acoustic flow, a complex quantity of which acoustic reactance is a part.
• Acoustic Resistance (n): The real component of acoustic impedance, representing opposition due to energy dissipation (e.g., as heat).
• Reactance (n): The broader electrical or general concept of opposition due to energy storage rather than dissipation.

Synonyms

• Imaginary Impedance (in the specific context of acoustics)

Related Concepts (Not Phrasal Verbs)

• Phase Shift: The delay, measured in degrees, between the sound pressure wave and the particle velocity wave caused by reactance.
• Resonance: A peak in vibration that occurs when the reactance is zero, meaning the impedance is purely resistive.

Noun

1. opposition to the flow of sound through a surface; acoustic resistance is the real component of acoustic impedance and acoustic reactance is the imaginary component