The ceramic fiber blanket has good sound absorption performance for high frequency in sound.
The main factors affecting the sound absorption performance of ceramic fiber blankets are thickness, density and air flow resistance. Density is the weight of material per cubic meter. The air flow resistance is the ratio of the air pressure to the air flow rate on both sides of the material per unit thickness. Air flow resistance is the most important factor affecting the sound absorption performance of ceramic fiber blankets. The flow resistance is too small, indicating that the material is sparse, the air vibration is easy to pass through, and the sound absorption performance is degraded; the flow resistance is too large, indicating that the material is dense, the air vibration is difficult to be introduced, and the sound absorption performance is also lowered. For centrifugal glass wool, the sound absorption performance has the best flow resistance.
In actual engineering, it is difficult to measure the air flow resistance, but it can be roughly estimated and controlled by thickness and bulk density.
- As the thickness increases, the sound absorption coefficient of the middle and low frequency increases remarkably, but the high frequency does not change much (the high frequency absorption is always large).
- The thickness is constant, the bulk density increases, and the sound absorption coefficient of the middle and low frequency also increases; but when the bulk density increases to a certain extent, the material becomes dense, the flow resistance is greater than the optimal flow resistance, and the sound absorption coefficient decreases. For ceramic fiber blankets with a bulk density of more than 5 cm and a bulk density of 16 kg/m3, the low frequency 125 Hz is about 0.2, and the sound absorption coefficient of medium and high frequency (>500 Hz) is already close to one.
- When the thickness continues to increase from 5cm, the sound absorption coefficient of the low frequency gradually increases. When the thickness is more than 1m, the sound absorption coefficient of the low frequency 125Hz will also be close to 1.
When the thickness is constant and the bulk density increases, the low-frequency sound absorption coefficient of the ceramic fiber blanket will also increase continuously. When the bulk density is close to 110kg/m3, the sound absorption performance reaches the maximum value, 50mm thick and the frequency is close to 0.6-0.7 at 125Hz. - When the bulk density exceeds 120kg/m3, the sound absorption performance decreases, because the material becomes dense, and the mid-high frequency sound absorption performance is greatly affected. When the bulk density exceeds 300kg/m3, the sound absorption performance is greatly reduced.
The thickness of the sound-absorbing ceramic fiber blanket commonly used in architectural acoustics is 2.5cm, 5cm, 10cm, and the bulk density is 16, 24, 32, 48, 80, 96, 112kg/m3. A 5 cm thick, 12-48 kg/m3 ceramic fiber blanket is usually used.
The sound absorption performance of ceramic fiber blankets is also closely related to the installation conditions. When there is an air layer behind the ceramic fiber blanket, the sound absorption effect of the ceramic fiber blanket with the same thickness and no air layer is similar.
In particular, the sound absorption performance of the middle and low frequency is much higher than that of the material on the hard bottom surface, and the sound absorption coefficient will increase as the thickness of the air layer increases, but the effect is not obvious after increasing to a certain value.
Source : http://www.ceramic-fiber-blanket.com/