Measurements of anisotropic sound propagation in glass wool

Abstract

The attenuation coefficient and phase velocity of plane sound waves propagating in three perpendicular directions in glass wool were measured in the frequency range 50-10 000 Hz. For glass wool of mass density 14 kg/m 3 at the frequency 1000 Hz, the attenuation constant for propagation perpendicular to the glass wool sheets was 75 dB/m, and for propagation parallel with the sheets 57 dB/m. For mass density 30 kg/m 3 , the corresponding numbers were 140 and 100 dB/m. The measured values were compared with calculated ones taking into account the movements of the fiber skeleton. The calculations need the elastic moduli, which were measured. For density 14 kg/m 3 and deformation perpendicular to the glass wool sheets, the static modulus was 2.0 kPa, and for parallel deformation 120 kPa. The corresponding numbers for mass density 30 kg/m 3 were 16 and 390 kPa.

Measured anisotropic air flow resistivity and sound attenuation of glass wool

“…Further details of the measurements were given in Ref. 7. For the light glass wool of mean density 14 kg/m 3 , the results are shown in Fig.…”

“…The elastic modulus for compression in the X direction is approximately 50 times smaller than the one for compression in the Y and Z directions. 7 Obviously the less dense layers have a very low stiffness. The resistivity in the Y direction is smaller than for a homogeneous model because when the air flows through the glass wool in the Y direction, most air will flow between the dense layer, where the local resistivity is smallest.…”

“…Measurements by the author 7 showed that the sound attenuation of glass wool is anisotropic, and it is interesting to measure the resistivity of the glass wool used for the measurements of attenuation ͑and phase velocity͒ to see whether the usual methods used to predict the attenuation of acoustic sinusoidal waves works for the attenuation in different directions. This paper presents measurements of resistivity in three main directions in glass wool, and investigates whether these resistivities can be used to predict the attenuation of sound waves at audio frequencies.…”

Dynamic measurements of the elastic constants of glass wool

“…Rice and Göransson 8 reported a Young modulus E 1 = 17.2 kPa for glass wool of mass density 14 kg/ m 3 . Tarnow 14 found the static value 390 kPa for glass wool of mass density 30 kg/ m 3 , and the dynamic result for the real part was 1.5 MPa at 20 Hz. The strain was 2 · 10 −2 by the static measurement, and below 10 −5 by the dynamic one.…”

Modelado acústico de silenciadores con material absorbente

“…Ballagh [7] estudió las propiedades de otro tipo de lana, comparando su coeficiente de absorción acústica en función de la densidad, el diámetro de fibra y la resistencia al flujo. Tarnow [78] trabajó como Picard con lana de roca, calculando el coeficiente d e atenuación y la velocidad de fase para la propagación de ondas no isótropas. Bauer [8] a su vez abordó el estudio del comportamiento acústico en dirección normal al material de diferentes materiales porosos.…”