Among the petitions submitted in recent years, many have been complaining against the big noise made by modified vehicles and motorcycles roaring past during the night, causing serious disturbance of tranquility and sleep. To pursue the fad, many young people modify their cars or motorcycles by taking off the silencer, causing a big noise when they whistle past. Whether it happens during the daytime or in the night, the noise is very annoying. Particularly when it is late at night, the annoying noise disturbs people’s sweet dreams. A lot of complaints or petition calls have been received, complaining against the big noise made by modified cars and motorcycles (with silencer taken off or other modifications) for seriously disturbing people’s sleep, while they are whistling past during the nighttime. Therefore, it is necessary to assess the effect of applying the detection camera system to in-use motor vehicles in order to enhance the execution efficiency of screening of high-noise motor vehicles and “block checks” through “excessive noise camera” technology, so as to achieve our goals of improving the living environment quality of the public, people’s health and lifestyle, and sustainability. The main achievements of this year are as follows:
1. Completed collection of the noise sources of in-use motor vehicles and related information on the noise meter.
(1) Traditionally, engine noise is the main source of noises generated by in-use motor vehicles. However, with the improvement of pavement conditions, tire noise has become another noise source when vehicles are running at high speeds. Generally speaking, when vehicles run at lower speeds and the pavement is dry, the engine noise constitutes the main portion of the overall noise. On the other hand, when vehicles run at higher speeds and the pavement is wet, the tire noise constitutes the main portion. However, the proportion of noise accounted for by each noise source varies from vehicle to vehicle.
(2) In terms of spectral features of the noise and propagation properties, the overall noise of the vehicle increases due to the increase of transmission system noise as the gear is lifted to a higher level. The spectrum of the overall noise is also related to such factors as vehicle speed, gear position, load, and vehicle type. The mid-high frequency noise increases with the decrease of gear level and increase of engine speed. With the increase of vehicle speed, the spectral curve rises, particularly at mid-high frequency bands. In terms of motor vehicle noise control, other than taking control measures at the noise source and propagation path, such as improving the engine structure and installing the exhaust muffler, noise control measures can also be taken at the receiving end, such as soundproof windows.
(3) The rationale of array microphones and application examples:
In a microphone array, dozens of microphones are usually deployed to collect sound signals simultaneously, which will be turned into “sound pictures” and “sound videos” by rear-end signal processing algorithms in order to show the location of noise sources in a real-time and intuitive manner. In terms of application examples, “NoivelCam”, an independent integrated vehicle noise tracing system designed and developed by Nanyang Technological University, has been used to monitor single-lane noise on expressways. In addition, in order to regulate illegal horning, China has adopted the sonar camera (source location) system in cities such as Shanghai, Nanjing, Shenyang, and Shenzhen to help the police deal with traffic violations of such kind with high technologies.
(4) The rationale of non-array directional microphones and application examples:
Collected a bunch of directional microphones, including interference and overlying type, planar reflection type, parabolic reflection type, ellipsoid reflection type, sound lens type, and horn type. In mid to high frequency bands, directional microphones work pretty well. However, in low frequency band, in order to get better directional features, you have to have a very big microphone, which is not very convenient in actual use.
2. Completed collection and analysis of the noise measuring methods, control standards, and regulations for in-use motor vehicles adopted in foreign countries.
(1) Please see Section 4.1 for noise measuring instruments, sound source identification systems, and measuring methods for in-use motor vehicles adopted in foreign countries. Currently, the stationary noise test regulations for motor vehicles widely used in Taiwan and other parts of the world are mainly formulated by the Chinese National Standards (CNS), Society of Automotive Engineers (SAE), International Standards Organization (ISO), and Japanese Industrial Standards (JIS). After analysis and comparison, it is found that there is no significant difference among the stationary noise test regulations for motor vehicles formulated by CNS, SAE, JIS, and ISO.
(2) Please see Section 4.2 for noise measuring methods, calculation models, and noise control SOPs for motor vehicles under driving conditions adopted in foreign countries. Regulations on noise measuring for motor vehicles under “driving” conditions are all specified in the “Motor Vehicle Noise Measuring Methods” and CNS5799 “Motor Vehicle Noise Level Test Methods” currently adopted in our country. However, for motor vehicles under “driving” conditions, there are no inspection standards for in-use vehicles in our country, other than standards for new vehicle type approval and new vehicle inspection.
3. Completed studying and planning of noise detection, snapshot, and measuring methods for in-use motor vehicles and proposed recommendations.
(1) Completed collection of the rationales of speeding camera systems for motor vehicles (such as radar, infrared, ground induction coils, and video), rationale of radar speed detection, and rationale of laser speed detection.
(2) Solved the problem of difficult evidence collecting for noise generated by vehicles with “excessive noise camera” technology. The speed and noise level of the vehicle can be detected simultaneously (license plate recognition system to be integrated in the future). The speeding vehicles will be fined directly by the police and the excessive noise vehicles will be recorded by the Environmental Protection Bureau for further inspection. To strengthen control of in-use motor vehicles, it is recommended to use a microphone array, integrate the license plate recognition system, and implement the excessive noise detection and camera measuring system for motor vehicles.