Experimental study of noise barrier boards with increased acoustic performance by utilizing Helmholtz resonator effects

Concept study of sustainable noise control solution for HVAC systems based on microperforated elements

“…By applying excitation noise from the electro-dynamic driver located at the end of the tube (see Figs 3 and 4) and by measuring the acoustic signals from two microphones, it is possible to calculate the absorption coefficient of the material tested. The plane wave acoustic pressures at the two microphones separated by distance s can be expressed as follows [15]: where p is the acoustic pressure, 𝑓 denotes the frequency, 𝑘 = 2π𝑓/𝑐 is the wave number, 𝑐 represents the speed of sound, -and + denote the pressure waves propagating in nd a , negative and positive directions along the tube axis. The reflection coefficient at microphone 1 is defined as [15] It can be shown that where 𝐻 12 = 𝑝 2 /𝑝 1 is the transfer function between induct mounted measurement microphones 1 and 2.…”

“…The plane wave acoustic pressures at the two microphones separated by distance s can be expressed as follows [15]: where p is the acoustic pressure, 𝑓 denotes the frequency, 𝑘 = 2π𝑓/𝑐 is the wave number, 𝑐 represents the speed of sound, -and + denote the pressure waves propagating in nd a , negative and positive directions along the tube axis. The reflection coefficient at microphone 1 is defined as [15] It can be shown that where 𝐻 12 = 𝑝 2 /𝑝 1 is the transfer function between induct mounted measurement microphones 1 and 2. Then the absorption coefficient of the material is calculated as follows [15]: According to the impedance tube diameter of 28 mm, the cut-of frequency is 8376 Hz, and the observation range is chosen from 200…8000 Hz, which is determined by the microphone separation (s = 16 mm).…”

“…The reflection coefficient at microphone 1 is defined as [15] It can be shown that where 𝐻 12 = 𝑝 2 /𝑝 1 is the transfer function between induct mounted measurement microphones 1 and 2. Then the absorption coefficient of the material is calculated as follows [15]: According to the impedance tube diameter of 28 mm, the cut-of frequency is 8376 Hz, and the observation range is chosen from 200…8000 Hz, which is determined by the microphone separation (s = 16 mm). In such experiments, the investigated material is placed onto the tube with varying distance from the back wall X1.…”

“…Fig.3. One-port measurement set-up for the experimental determination of materialsʼ absorption coefficient[15].…”

Numerical optimizing noise damping performances of Helmholtz resonators with a rigid baffle implemented at neck in presence of a grazing flow

“…For this, 2-dimensional computational frequency-domain model is developed by applying the linearized NS equations. [21][22] For comparison, the conventional Helmholtz resonator design is chosen to be a benchmark/ reference configuration. Before applying the model, it is validated by comparing with the previous experimental and 2D/3D numerical results reported in the literature.…”