Evaluation of the Effect of Different Absorbent Materials on Sound Reduction in Armored Personnel Carriers

Recently, the sound level of military vehicles has increased significantly. Verbal communication is very important for the personnel working in these vehicles. The exchange of information between soldiers inside the vehicle as well as with the outside world, which is done using radio channels and internal communication systems, requires the ability to speak and hear properly. In military environments, armored personnel carriers (APC) are one of the most practical vehicles used, and the health and exposure to the sound pressure of the people inside the cabins of these tanks are very important. Therefore, the present study was conducted to evaluate the effect of different adsorbents on noise reduction in armored personnel carriers.

The present study was a cross-sectional and interventional study on 3 armored personnel carriers (BMP1) in 2018. Sound pressure level inside the cabin was measured (according to BS6086 -1981 [ISO5128-1980] standard) in 3 states include a. on and off mode of the tank with engine speed of 100 to 1200 rpm, b. standby mode with engine speed of 1400 rpm and c. moving mode at a speed of 15 km/hr tank with engine speed 1600 to 2000 rpm. In order to perform the intervention and reduce costs and evaluate the efficiency of adsorbents in reducing the sound pressure level, a room made of the main body of the tank, which was made of iron, was prepared in smaller dimensions. The sound was generated inside the chamber and after installing the absorbent material, the amount of sound pressure level reduction was measured. Selected absorbent materials were included Polyurethane foam with a density of 12 kg/cm2 and thickness of 2.5 cm, Polyurethane foam with a density of 12 kg/cm2 and thickness of 4.2 cm, Glasswool with a density of 12 kg/cm2 and thickness of 3.2 cm, Polyethylene foam with a density of 20 kg/cm2 and thickness of 2 cm, and felt with thickness 0.8 cm. Data were analyzed by one-way analysis of variance (ANOVA) by SPSS software version 23 at a significance level of 0.05.

The equivalent sound pressure level increased from 93.8 dBA in a standstill to 101.6 dBA in standby mode, and in the state of motion, this level increased to 107 dBA. The corresponding total sound pressure level increased from 93 dBA in a standstill to 98 dBA in standby mode and increased at a speed of 15 km/h to 104 dBA. The equivalent level of sound exposure in the chamber without adsorbent materials was considered 110 dBA, when using the felt as an absorbent material, this level dropped to 98 dBA. When the polyethylene foam was used as an adsorbent, this level dropped to 102 dBA. When the glass wall was used as an adsorbent, this level dropped to 97 dBA. When the polyurethane foam with a thickness of 2.5 cm was used as an adsorbent, this level dropped to 95 dBA. When the polyurethane foam with a thickness of 4.2 cm was used as an adsorbent, this level dropped to 93.2 dBA.

The condition of the motor of the device and the condition of the chains are the most important factors in the difference in the level of equivalent sound pressure in the three mentioned conditions. The best material for installation inside the cabin to reduce the sound pressure level is polyurethane oval foam with a density of 12 kg/m2 and 4.2 cm thickness. This material reduces the equivalent level of sound exposure from 110 dBA to 94 dBA.