Survey of interior noise characteristics in various types of trains
Introduction
The sound quality in train cars is an important concern for the railway industry since many people use trains for long periods of time. For example, approximately 40% of commuters use trains, with an average commuting time of more than 140 min (round trip), in a typical metropolitan area of Japan such as Tokyo. The fundamental issue is to create a comfortable acoustic environment in a train car for the passenger. The train industry has succeeded in lowering the equivalent sound-pressure level (SPL) in train cars to a mean of less than 70 dBA [1], [2], [3]. However, lowering the SPL is not enough for a comfortable acoustical environment. Even when the SPL is only about 35 dBA, people may feel annoyed by conditions such as fluctuations of pitch and a localized sound source [4].
People hear various types of noise in train cars. Researchers have studied mechanisms for generating different types of noise such as rolling, impact, curve squeal [5], [6], [7], [8], [9], motor (fans) [10], [11], and aerodynamic noises [12], [13]. Some studies have modeled the noise in train cars to help predict and reduce it [14], [15], [16], [17]. Although some studies have quantitatively [1], [2], [3], [18], [19], [20], [21] and qualitatively [2], [3] investigated the noise characteristics inside running train cars, the effects of noise sources on the noise characteristics have not been evaluated qualitatively. This should be clarified to improve the acoustical environment in a train car for the passenger.
The aim of this study is to clarify the effects of noise sources on the noise characteristics inside running train cars. In particular, we focus on the effects of the rolling, impact, curve squeal, and motor (fans) noises inside train cars. Acoustic treatment (i.e., sound absorption, insulation, and active noise control) is an effective solution for improving the sound environment inside train cars. To consider an appropriate acoustic treatment, it is necessary to clarify the characteristics of the noise inside train cars.
Section snippets
Measured trains
We continually measured noise in a train car traveling from one terminal station to another terminal station on 15 lines. Different types of train car were run on each line. Table 1 lists the location, main motor, maximum speed, average speed, number of intervals, and number of curves measured. Active noise control is not installed in the train car. We classified trains according to location (surface and underground), main motor (linear or three-phase induction motor), and speed (normal and
Effect of wheel rail interaction (rolling, impact, and curve squeal)
Fig. 2 shows the averaged LAeq and octave band levels for rolling, impact, and curve squeal noises in running surface and underground trains. Impact noises had larger components at lower frequencies (less than 500 Hz) compared with rolling noises in both underground and surface trains. Curve squeal noises had larger components at frequencies higher than 125 Hz in underground trains and at frequencies between 125 and 500 Hz s in surface trains compared with rolling noise. Underground trains often
Conclusions
We analyzed the effects of the rolling, impact, curve squeal, and motor (fan) noises on noise inside train cars. The results show the following:
- 1.
Impact noises had larger components at lower frequencies (less than 500 Hz) compared with rolling noises.
- 2.
Curve squeal noises had larger components at frequencies above 125 Hz, which have stronger pitch, in underground trains and at frequencies between 125 and 500 Hz in surface trains compared with rolling noises.
- 3.
Curve squeal noises had longer τ1 values
Acknowledgments
We thank the railroad staff who cooperated in our measurements. This work was supported by a Grant-in-Aid for Young Scientists (A) from the Japan Society for the Promotion of Science (No. 23686086).
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