Noisiness of high speed trains

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  • Journal of Sound and Vibration (1977) 51(3), 359-361

    NOIS INESS OF H IGH SPEED TRAINS

    MONIQUE VERNET AND M. VALLET

    lnstitut de Recherche des Transports, Centre d'EL'ahtation et de recherche des nuisances,

    109, avenue Salvador AIlende, 69500--Bron, France

    (Receir'ed 2 December 1976)

    The noise signatures of three types of French trains (Aerotrain 180, fast train (Rhodanien) and turbotrain) were presented in the laboratory to 24 persons who gave annoyance scores to each of them. The aim of this study was to compare the resulting comfort indices with some acoustic characteristics. The peak-level showed the best correlation with discomfort.

    1. INTRODUCTION

    Research on the effects of noise of high speed trains has been undertaken during the develop- ment of the French aerotrain. The aim of the study reported here was to identify among the different dements of the sound pattern those which are related to annoyance, the hypothesis being that the rising slope is one important factor.

    2. EXPERIMENTAL METHOD

    2.1. CHARACTERISTICS OF THE SOUNDS The noise signatures of three trains--"Rhodanien" (speed 150 kin/h), turbotrain (speed

    150 kin/h) and aerotrain (speed 300 km/h)--were recorded at 15, 30, 60 or 120 meters from

    f i i 90 (a)

    60

    m

    60

    9~ 5s t 60 I I

    I 1 I 1 1 I I I I I I f f r

    Aerot ra in Tra in Turbof ra in

    Figure L Sound level of high speed trains. (a) At 15 m from tracks; (b) 30 m; (c) 60 m; (d) 120 m.

    359

  • 360 MONIQUE VERNET AND M. VALLET

    TABLE 1 Characteristics of the train noises

    Train

    Duration longer than Increasing slope Peak (seconds) (dB(A)/s)

    Le~ level , ~, , r h 9 (dB(A)) (dB(A)) 80 dB(A) 70 dB(A) Average Max.

    Aerotrain at 30m 86.2 97 3 5.8 3.9 15 60 m 79.4 92 3.1 5.8 6"8 12-5

    120 m 73.6 85 0.6 3.5 2.7 13 Train at 15 m 93-3 93 3-5 4.6 14 20

    30 m 80.5 89 3.6 12.3 12 16 60 m 77 81 4"6 12.2 8.8 14"8

    Turbotrain at 15 m 83.2 93 3-5 5 10 Un- determined

    the tracks. The characteristics of their acoustical patterns are summarized in Table 1 and the sound levels in Figure 1.

    2.2. SUBJECT SAMPLE The test was made with 30 subjects. The results of 24 of them were used. The subjects have

    the following characteristics: 13 men and 11 women, of average age 27 (age range 18 and 50); 13 were students and 11 working people.

    2.3. TEST CONDITIONS The test chamber is a quiet room, wherethe background noise is about 35 dB(A) and the

    reverberation time less than 0.5 seconds. The tape-recorder (NAGRA IV-L) and the amplifier (SONY) are in the adjacent room; only the loudspeakers are in the test chamber. Each noise was presented three times. The 21 signals were presented according to a table of numbers. Each group of subjects heard the noise signals in a different order, to reduce any "order effect" which might bias the study. For each noise heard the subjects answered on a nine-step scale, choosing a digit going from 1 ("quite acceptable noise") to 9 ("very unpleasant noise").

    3. RESULTS

    For each noise, a comfort index was calculated, from the cumulative frequency of responses in each category. The higher the index is, the more acceptable is the noise. The resulting classification appears in Table 2.

    If one considers the average rank of each noise one may statistically differentiate the different patterns. The resulting order is the same as in Table 2. Nevertheless, the train at 30 m and the aerotrain at 120 m do not present significant differences. In spite of the small number of data (N = 504) a correlation between the annoyance scores and the values of the different elements of the sound-level pattern has been made, and the results are shown in Table 3.

    TABLE 2 Annoyance rank of the train noises

    Train Train Aerotrain Turbotrain Aerotrain Train Aerotrain 60m 30m 120m 15m 60m 15m 30m

    Peak level 81 89 85 93 92 93 97

    Comfort index 159.5 120.5 117 87 68 58.5 35.5

  • NOISINESS OF tIIGH SPEED TRAINS

    TABLE 3

    Correlation of Bravais-Pearson between the comfort index and some acoustic parameters

    Acoustic parameter Corrclation

    Peak level Leq of signal Duration of noise superior to 70 dB(A) Average increasing slope Maximum increasing slope

    r = -0.94 r = -0.43 r = +0.64 r =-0.81 r =-0"61

    361

    4. DISCUSSION

    The results presented in section 3 show that the perception of the noise of the trains is very differentiated. The acoustic parameter which permits the best differentiation is the peak-level, which presents the best correlation with discomfort. However, there is not a perfect relation between peak-level and expressed annoyance. Thus, the pattern of the conventional train at 30 m and the aerotrain at 120 m have an identical discomfort level though the two peak- levels differ by 4 dB(A). Similarly, the turbotrain at 15 m and the train at 15 m result in different annoyances although they have equal peak-levels. These differences are undoubtedly related to differences in noise spectra of these trains, in that aerotrain noise contains more high frequencies than other train noises.