Yoshiharu Soeta

The impact of external environments on noise inside a train car

Trains travel through various environments typically on tracks above ground or in tunnels. There are three main types of tunnels, which have different cross-sections according to their excavation methods. When trains pass through different environments, the perceived noise inside a train car can change. To consider appropriate acoustic treatment, the effects of the environment on noise inside train cars were investigated in this study. The noise inside a train car traveling through tunnels had a salient sound energy around 250 Hz, and came from the doors and windows of the train car. This suggests the effectiveness of acoustic treatment in the side walls of the car for the low frequency band. More reflections enter the train cars from tunnels with a circular cross-section in tunnels constructed by a boring machine, which drills tunnels before the insertion of lining segments. Acoustic treatment is likely to be needed in tunnels constructed using this method

Auditory evoked responses in human auditory cortex to the variation of sound intensity in an ongoing tone

In daily life, variations of sound intensity, frequency, and other auditory parameters, can be perceived as transitions from one sound to another. The neural mechanisms underlying the processing of intensity change are currently unclear. The present study sought to clarify the effects of frequency and initial sound pressure level (SPL) on the auditory evoked response elicited by sounds of different SPL. We examined responses approximately 100 ms after an SPL change (the N1m). Experiment 1 examined the effects of frequency on the N1m. Experiment 2 examined the effects of initial SPL on the N1m. The results revealed that N1m amplitude increased with greater SPL changes. The increase in N1m amplitude with increasing SPL was almost constant for low frequency sounds (250 and 1000 Hz); however, this increase was reduced for high frequency sounds (4000 Hz). The increase in N1m amplitude was reduced with high initial SPL. The pattern of amplitude change may reflect a difference in activation in the auditory nerve and/or primary auditory cortex.

Interior Noise Characteristics in Japanese, Korean and Chinese Subways

The aim of this study was to clarify the characteristics of interior noise in Japanese, Korean, and Chinese subways. The octave-band noise levels, A-weighted equivalent continuous sound pressure level (LAeq) and parameters extracted from interaural cross-correlation/autocorrelation functions (ACF/IACFs) were analyzed to evaluate the noise inside running train cars quantitatively and qualitatively. The average LAeq was 72-83 dBA. The IACF/ACF parameters of the noise showed variations in their values, suggesting they are affected by the characteristics of the trains running, wheel-rail interaction, and cross-section of the tunnels.

Listening level of music through headphones in train car noise environments

Although portable music devices are useful for passing time on trains, exposure to music using headphones for long periods carries the risk of damaging hearing acuity. The aim of this study is to examine the listening level of music through headphones in the noisy environment of a train car. Eight subjects adjusted the volume to an optimum level (L(music)) in a simulated noisy train car environment. In Experiment I, the effects of noise level (L(train)) and type of train noise (rolling, squealing, impact, and resonance) were examined. Spectral and temporal characteristics were found to be different according to the train noise type. In Experiment II, the effects of L(train) and type of music (five vocal and five instrumental music) were examined. Each music type had a different pitch strength and spectral centroid, and each was evaluated by φ(1) and W(φ(0)), respectively. These were classified as factors of the autocorrelation function (ACF) of the music. Results showed that L(music) increased as L(train) increased in both experiments, while the type of music greatly influenced L(music). The type of train noise, however, only slightly influenced L(music). L(music) can be estimated using L(train) and the ACF factors φ(1) and W(φ(0)).

The Impact of External Environments and Wheel-Rail Friction on Noise inside a Train Car

Trains travel through various environments typically on tracks above ground or in tunnels. When trains pass through different environments, the perceived noise inside a train car can change. For example, there are three main types of noise caused by wheel-rail interaction, namely, rolling, impact, and curve squeal. Each type can be perceived differently. To consider appropriate remedial measures, the effects of the external environment and wheel-rail interaction on noise inside train cars were investigated. Spectral analysis of noise from inside a train car traveling through tunnels featured a noticeable sound frequency around 250 Hz. More reflections enter train cars from tunnels with circular cross-section, namely those constructed by a boring machine. Impact noise had larger components at lower frequencies. Curve squeal noise had larger components at frequencies between 125 and 500 Hz.

Effects of reverberation and spatial diffuseness on the speech intelligibility of public address sounds in subway platform for young and aged people

This paper investigated how young and aged people response differently on the public address sounds in subway platform according to various reverberation and diffuseness. Both word intelligibility (WI) and listening difficulty (LD) tests were adopted as experimental method. Twelve simulated sound fields at the same position were prepared according to the combination of four different reverberation times (RT) and three different interaural cross-correlation coefficients (IACC). Auralized sounds with anechoic test words of actual station names were presented to young and aged subjects at the fixed sound pressure level. As results, LD results showed significant correlation with RT for both young and aged subjects, whereas significant correlation of WI results and RT was found only in aged subjects. Aged subjects showed worse speech intelligibility performances on public address sounds than young subjects due to their worse hearing level. RT was found as the most important factor to determine speech intelligi...

Autocorrelation function mechanism for pitch salience and cross-correlation function mechanism for sound localization revealed by magnetoencephalography

A model of primary sensations and spatial sensations is proposed by Ando (2001). The model of the auditory-brain system includes the autocorrelation function (ACF), the interaural cross-correlation function (IACF) mechanisms. At present, environmental noises are evaluated by sound level such as equivalent continuous A-weighted sound pressure level (LAeq). However, we sometimes feel annoyed with sound with low sound level because of the quality. Sound quality can be characterized by factors obtained from ACF and IACF of sound. For example, pitch and pitch strength can be characterized by delay time and amplitude of the maximum peak of the ACF. Directional sensation can be characterized by delay time and amplitude of the maximum peak of the IACF. To verify the model, we investigated how ACF and IACF factors are coded in our human brain. The results indicated that delay time and amplitude of the maximum peak of the ACF and IACF are coded by the latency and strength of brain activity.

Temporal and spatial characteristics of noise in train stations

The train noise in station (TNIS) can annoy passengers and reduce the speech intelligibility of the public address system in a station. Thus clarifying the acoustical characteristics of TNIS is important for the comfort and safety. Noise level was evaluated the equivalent continuous sound pressure level (LAeq). The sound diffuseness was evaluated by the interaural cross-correlation coefficient (IACC) from the interaural cross-correlation function. The pitch and pitch strength was evaluated by the delay time (t1) and amplitude (f1) of the first peak of the autocorrelation function. The LAeq and IACC of the TNIS in the underground station were higher and lower, respectively, than those in the ground station. The t1 and f1 of the TNIS in the underground station were stable and lower, respectively, than those in the ground station. When the train came into the station, the LAeq of the TNIS at the island platform were higher than that at the side platform. The result suggests that the underground island platfo...

Dynamic analysis, psychological and physiological evaluations of the visual environment

Attempts are made to apply preference theory for sound fields to visual fields. To investigate how the periodical flicker and movements in vertical and horizontal directions are preferred, preference judgments were conducted by paired-comparison tests. Results show that each stimulus has each pereference period. The scale value of preference is formulated approximately in terms of the 32 power of the normalized period of stimulus. It is interesting that this formulation corresponds to that of temporal factors in sound fields. Next, relationships between the subjective preference and the factors extracted from the autocorrelation function (ACF) and the cross-correlation (CCF) of the EEG and MEG alpha waves were investigated. Remarkably, preferred stimulus shows a significantly longer effective duration of the ACF, τe, of the alpha waves than that of less preferred stimulus. This tendency was also found in previous studies that varied the delay time of a single sound reflection and the reverberation time of...