For a modern person, it’s hard to imagine life without a car. We drive to work, to supermarkets, to our friends, to business trips. We spend minutes, hours and days behind the wheel or on a passenger seat. During all this time we are exposed to noise and vibration.
Unfortunately, noise is a highly negative factor which can damage our health. Based on the latest research data, we can say that noise can cause cardiovascular diseases, problems with hearing, and damage the nervous system. Even a vibration disease can develop. The most harming is long-term exposure to vibration at frequencies of 1 to 80 Hz and to over 80 and 115 dB noise.
Inside a vehicle, a driver and passengers are affected by different types of noise: the engine noise, the traffic noise and airborne noise. Moreover, airborne noise can overlap any other sources especially when you’re standing in a traffic jam while the other lane is moving. We found this problem interesting in terms of a possibility to solve it using vibration insulating materials, and we decided to conduct an experiment.
We took two 2013 Ford Focus cars with hatchback body type. The automobiles had equal power stations, as well as all other parameters. We’d soundproofed one of the cars with vibration insulating materials, then went to a highway and had the two cars parked by the side of the road. We used a long-haul truck Volvo FH 42 TB as a source of airborne noise. It passed by our cars at speeds of 80 km/h and 100 km/h. So we managed to create equal experimental conditions for both cars. To measure noise and vibration levels in the cars, we used first accuracy class microphones MPA201, vibration sensors AP37 and the eight-channel frequency spectrum analyzer ZET A17-U8. To record and process measurement results, we used a laptop with professional software: ZETLAB and ZETView. To achieve maximum accuracy, we measured noise and vibration 5 times at each speed. We tested noise level within the range from 20 to 10000 Hz, and the vibration level - from 5 to 2500 Hz.
To start with, we measured sound pressure.
The first gauging was at a speed of 80 km/h. We placed the mics between the front seats on a level with the arm support. On the average, the gauged noise level was 59 dBA in the soundproofed car and 65 dBA in the non-soundproofed one.
For the second testing, we placed the mics at the back seats and increased the truck’s speed to 100 km/h. At such speed, the air flow spawned by the truck overlaps all other sources of noise. The registered values were 61.6 dBA in the soundproofed car, and 65.5 dBA in the untreated one.
Based on the acquired results, we made conclusions about the noise pressure level and measured its changes in a wide range of frequencies. For the first gauging, the difference was 6 dBA, and for the second - 3.9 dBA. According to the measurement results analysis, in the driver seat of the soundproofed car noise level reduces two times, and in the front passenger seat - 1.6 times. These are quite large numbers, and such changes can be felt without any equipment.
We couldn’t help measuring the vibration level in both cars together with the noise level. The most reasonable value to gauge in that situation was vibration acceleration.
It is the vibration value which is directly related to the force spawning vibration.
We set up the detectors on the plastic panel of the rear left door and the floor of each car. After testing, we converted the values to decibels.
According to the results, vibration levels in both cars was more than 100 dB: 103.1 in the soundproofed one, and 106.4 dB in the non-soundproofed one. Though both values are high, the vibration level in the treated vehicle was reduced by approximately 1.5 times.
Our experiment helped to prove the hypothesis that sound and vibration insulating materials can help to decrease sound pressure and vibration 1.5 - 2 times at average compared to the car without additional soundproofing thus minimizing their impact on human health.