Abstract
This study examined a method for evaluating air discharge sound quality in the
development of automotive air-conditioning systems. As the first step, the evaluation factors
for expressing air discharge sound quality were extracted, and evaluation indexes were
examined on the basis of subjective evaluation data. As the second step, an examination was
made of evaluation factor differential thresholds and customer preferences concerning air
discharge sound quality, which serve as standards for setting specific development targets for
engineering the sound quality of air-conditioning systems. The conditions examined in this
study were engine idling, air-conditioner use and the maximum fan speed.
In order to extract the evaluation factors of air discharge noise, subjective evaluations were
conducted using the semantic differential method. A cluster analysis was performed on the
results, and only the data of clusters that yielded effective responses were extracted for use in
identifying the factors. As a result, "quiet," "gentle to the ear" and "indistinct" showed high
factorial loadings for Factor I, and "clear" showed a high factorial loading for Factor II. The
first and second principal factors will be referred to in the following discussion as the
powerful factor and aesthetic factor, respectively.
Subjective evaluations were conducted using adjective pairs for comparison, and a subjective
evaluation score was calculated for each factor. A multiple regression analysis was conducted
on the scores and the physical quantities used in this study. It was found as a result that the
powerful factor and the aesthetic factor could be expressed with the index equations.
The possibility of using this method in vehicle design work was then examined. Subjective
evaluation tests were conducted using the magnitude estimation method to clarify customers´
preferences. Listening tests were performed in which the powerful factor and aesthetic factor
customers found most pleasing were varied, and the results revealed the following preferences.
oWhen the powerful factor is large, customers react sensitively to the aesthetic factor,
making it necessary to tune the balance between high- and low-frequency sounds to a suitable
tone quality for each operating mode of the air conditioner.
oWhen the powerful factor is small, a tone quality with strong low-frequency sounds and
weak high-frequency sounds is preferred.
oNo differences in preference tendencies were seen between genders or among different age
groups.
Subjective evaluation tests were then conducted using the Limit Method to clarify differential
thresholds for perceiving improvements in each factor when customers change vehicles. The
ability to differentiate each factor was first confirmed in a listening room under an ideal state.
The differential thresholds were then confirmed in actual vehicles under conditions assumed
for their use by customers. In the vehicle tests, a forgetfulness operation was applied between
test sessions under the assumption that customers changed vehicles. As a result, target values
were clearly defined for the perception of the degree of improvement in the air discharge
sound quality of air-conditioning systems when customers change vehicles.
Keywords - Air conditioning, Sound quality, Evaluation, Audition, Discrimination