Quantum mechanics

Noise reduction coefficient

Materials science

Tube (container)

Absorption (acoustics)

Range (aeronautics)

Ultrasonic sensor

Economics

Acoustics

Porosity

Acoustic impedance

Electrical impedance

Physics

Optics

Position (finance)

Attenuation coefficient

Composite material

Finance

The Journal of the Acoustical Society of America

A hybrid passive-active sound absorption structure is experimentally investigated in a water-filled impedance tube. The surface impedance of the passive material is manipulated by active parts to match the impedance of medium, and consequently to improve sound absorption performance at low-frequency range. Parameters such as boundary, material thickness and position of secondary source are optimized by numerical analysis to achieve high absorption coefficient. Experimental results show that the developed hybrid structure has potential to improve sound absorption at low frequency range.

An investigation on passive-active absorption system in a water-filled impedance tube