Annoyance response to vehicle noise is commonly reported by many people in society. A need to improve the sound quality of vehicles is therefore apparent. The engine is one of the most predominant sources of vehicle noise causing annoyance. Judgments of annoyance due to engine noise were made by 160 subjects in five separate listening tests. An M-S "mid-side… stereo microphone was used to record engine sounds under idling and running conditions for listening Tests A-C, and E. For listening test D, two microphones were used to record engine sounds in stereo under idling conditions. All sound stimuli were presented to the subjects through a pair of loudspeakers in an anechoic room. One of the listening tests was conducted using a paired comparisons method and the other listening tests were conducted using a sequential rating method known as the method of successive intervals. A prediction model of annoyance response was developed by the use of principal component analysis and partial least-squares regression. In this case, all original annoyance scores for all five separate tests were transformed into a common annoyance scale. The prediction model was based on three psychoacoustic descriptors: loudness, sharpness, and harmonic ratio. The model was validated internally and also externally by three new sound stimuli. The prediction of annoyance for these three sounds was found to be consistent when judged by 20 additional subjects. The model gave good predictions of annoyance judgments for 6-cylinder in-line engine noise.
The effects of vibration on train passengers' sedentary activities were investigated with a questionnaire survey as well as onboard vibration measurements. Three types of Swedish inter-regional trains were studied on four different lines. 330 passengers were randomly selected for the questionnaire survey. The vibration measurements were made at five positions around a passenger seat above the bogie during normal service. The vibration data were weighted according to ISO 2631-1 and the older German (Sperling) Ride Index Wz. Two-thirds of the passengers reported difficulties in performing sedentary activities such as reading and writing due to vibration and shocks. However, the standardized measurements did not reveal any severe discomfort values due to the vibration. This reveals that ISO and Wz standards do not evaluate vibrations effect on sedentary activities correctly. This also indicates that even low levels of vibration can reduce the ability to perform sedentary activities. Both chair and table produced more vibration than the floor. The spectral analysis showed that the chair had nearly the same frequency content as the floor, below 10 Hz. This range is critical since it coincides with the most vulnerable range for reading and writing as well as the perception of ride comfort.
The sound quality of four different models of wheel loaders was evaluated using twentyeight experienced male operators as subjects. Using these human subjects, sounds were recorded binaurally and played back through headphones. Tachometer recordings were also made from the engines and transmissions in order to trace the origins of amplitude peaks in the signals. There were two sessions (viz. lift and transportation) for each wheel loader. Altogether, there were eight sessions for all four wheel loaders. Tachometer signals indicated that peaks were dominated mainly by pinion and drop box for the transport sounds, whereas the peaks of hydraulic orders (i.e., between 250 and 1000 Hz) were dominant for the lift sounds. The dominant peaks were damped by either 3 or 6 dB, thus creating new modified sounds. Both original and modified sounds were then played randomly and separately for all sessions using a paired comparisons method. The results showed that the pinion and drop box were causing annoyance for the transportation sounds, while the hydraulic orders were causing annoyance for the lift sounds. The results also revealed that damping the tonal components created by the drop box reduced the annoyance response more significantly than damping the tonal components made by the pinion. This indicates that the tonal components in higher frequencies were more annoying than the tonal components in lower frequencies. In the final part of the study, multivariate analysis was applied in order to model annoyance of noises from the four different models of wheel loaders for both sessions (i.e., lift and transportation) on the basis of the sound quality descriptors. Annoyance prediction models for all sessions were developed based on the articulation index and a newly developed descriptor, viz. tonal ratio. The new descriptor identifies the tonal components by comparing the sound pressure level of each 1/3-octave band of the peaks between 125 and 3150 Hz with the two 1/3-octave-band levels adjacent to it. © 2002 Institute of Noise Control Engineering.
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