Vol.2 No.4 2010

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Research paper−258−Synthesiology - English edition Vol.2 No.4 pp.258-269 (Feb. 2010) In many cases, the magnitude of the sound pressure is expressed as sound pressure levelTerm 1. Decibel and dB is used as its unit and symbol, respectively. If two types of test sounds have the same sound pressure level but different frequency (pitch), they are recognized as different loudness because our hearing is dependent on frequency. Frequency weighting which imitates our hearing is named frequency weighting A and the sound pressure level considering frequency weighting A is named A-weighted sound pressure level, or more generally, the sound level. The unit of the sound level is decibel, the same as the sound pressure level. (In the past, the unit of the sound level was phon but it is internationally standardized to decibel now.) The sound level is used to evaluate the environmental noise or the noise from instruments[3].As shown in Fig. 1, the sound pressure level or the sound level is measured by acoustic measuring instruments such as measurement microphones[4] or the sound level meters[5,6]. The sound pressure can be got from the output voltage of the measurement microphone which is used as a sensor of the sound pressure. The sound level meter can directly display sound pressure levels or sound levels to be measured because it works as a sensor of the sound pressure and calculates those quantities.Typical end-users of sound level meters are as follows; (1) providers who officially verify the environmental measurement results by a certificate of the measured sound level or the environmental measurement specialists who constitute the providers, (2) local autonomies who measure the environmental noise in various districts, (3) manufacturers who measure acoustic characteristics of their products, (4) scientists in universities or institutes who conduct acoustic measurements.1 IntroductionIn some way or another, we are exposed to sound in our daily life. Sound disturbing our conversation or uncomfortable sound is regarded as noise. Noise affects our daily life in many ways such as sleep disturbance or inefficiency in working and in some cases will result in serious health damage of hearing loss.The Japanese Basic Environment Law provides basic principles of environmental preservation and the measures for its realization to secure our healthy and cultural life, and to contribute to the welfare of human beings. The law deals with environmental problems such as noise pollution and air pollution, and gives regulations and standards on the environmental noise. The Noise Regulation Law provides regulations for the noise from specific plants, construction machines and cars. Environmental quality standards to be achieved by the government are set for traffic, Shinkansen (Bullet train) and airplane noise. NMIJ/AIST has been requested to solve technical problems necessary for the reliable environmental noise measurement and thus to sustain high quality in our daily life from the standpoint of environmental noise.Physically speaking, sound wave is a phenomenon in which the vibration of a sound source causes the vibration of a medium (air) surrounding it and the vibration of the medium is spatially transmitted[1]. The vibrational transmission causes change in time and spatial distribution of medium density, resulting in pressure fluctuation. Sound pressure is defined as pressure fluctuation from static pressure caused by the sound wave. Sound pressure is a main physical quantity in acoustics and thus its precise measurement is essential[2].- Development of acoustic standards and a new calibration service system -Ryuzo HoriuchiNational Metrology Institute of Japan, AIST Tsukuba Central 3, Umezono 1-1-1, 305-8563, Japan E-mail : Original manuscript received June 18, 2009, Revisions received September 24, 2009, Accepted September 25, 2009To ensure the reliable results in acoustic measurement such as environmental noise measurement, NMIJ/AIST has developed essential calibration techniques and established a traceability system based on the Japanese Measurement Law with acoustic standards at the highest level of accuracy. A new calibration service for reliable acoustic measurements under this system realized a minimum uncertainty in the environmental noise measurements, indispensable to sustain high quality of our daily life.How the reliable environmental noise measurement is ensuredKeywords : Environmental noise measurement, laboratory standard microphone, pressure sensitivity, coupler reciprocity method, measurement microphone, sound level meter, free-field sensitivity, anechoic chamber[Translation from Synthesiology, Vol.2, No.4, p.288-298 (2009)]

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