To establish noise prevention measures for Shinkansen cars that run at speeds higher than 300km/h, it is necessary to clarify the contribution of noises generated from different sources on the car body. For this purpose, the RTRI developed a microphone-arranged ellipsoidal sound absorber (Fig. 1), measured the distribution of noise sources on a Shinkansen car, and obtained the noise source distribution over the entire car at a resolution of 50cm or less in the frequency range of 1,000Hz or more (Fig. 2).
      The RTRI also devised a technique to estimate the power of a noise source at different parts of the car based on the distribution of noise sources, and calculated the contribution of each noise source to the entire noise of a Shinkansen car when there are no noise barriers.
      The RTRI compared the noise levels estimated from the noise source distribution and measurements from an array of sound level meters for which the validity of quantitative evaluation has been proven. The relative correlation between the noise levels in different frequency ranges and a frequency spectrum trend were obtained (Fig. 3), though the absolute noise levels were different. The RTRI also performed model tests to clarify the shielding attenuation by sound barriers as well as the range attenuation. As a result, it is now possible to estimate the contribution of each noise source to the entire noise of a Shinkansen car in sections where sound barriers are installed.

Fig. 1 Microphone-arranged ellipsoidal sound absorber

Fig. 2 Shinkansen car noise source distribution, obtained using a microphone-arranged ellipsoidal sound absorber

Fig. 3 A comparison between noise levels measured with an array of sound level meters and those estimated from the sound source distribution (converted into the value at a point 6.25m from the sound source)

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