Simulation of Acoustic Variables for Auditory Satisfaction in Metro Stations by Using ODEON Software (Case Studies: Metro of Tehran, Tabriz, Isfahan)

Considering the importance of sound comfort and speech intelligibility in determining the acoustical quality of a space, especially functional spaces, the important indexes of these two factors should be considered. In this research, acoustics in metro stations have been studied, which are functional in crowded and busy spaces, and structurally and physically have disproportionate geometry (long length) and materials with low sound absorption coefficient, thus, a noisy environment with sound disorders. Relatively high noise, which in addition to the background noise (noise of equipment and ventilation systems, etc.), in the effect of other sound sources (trains, brakes, engines, People talking, etc.), noise in metro stations is one of the most annoying issues that can cause discomfort and physical damage in the long run. Excessive sounds and repeated reflections disrupt the hearing of the audience's safety messages and verbal communication and cause fatigue, confusion, decentralization, and illegibility of the environment.

This research is quantitative because it has quantitative data that has been obtained from field measurements and simulations. simulation in this research is a method for describing acoustical behavior in metro stations. Simulations have been performed to investigate and compare acoustic variables with international standards to devise solutions for auditory satisfaction in metro stations. The case studies were selected from Tehran, Tabriz, and Isfahan and classified into two types and three different volumes. Then, by entering the three-dimensional case studies in ODEON software and determining the surface material, sound source, and background noise based on the data obtained from field measurements, specifying the receiver points and settings related to the impulse response length, simulation is performed and effective acoustic variables are extracted. Variables such as SPL, RT, EDT, STI, ALCons, C, and D concerning the subjects of noise in the environment and speech intelligibility are essential.

The results of simulations show that the maximum sound pressure level in all stations is higher than 85 dB(A) and the maximum reverberation time is more than 2s, which is far from international standards. These effects sound comfort as well as speech understanding, which is the most important factor in creating safety and performance of the space and is directly related to the user`s auditory satisfaction. Quantitative measurement and assessment of acoustic variables were also proof of this claim.

It can be concluded that the type of platform, volume, proportions, and different materials used in the stations are the reason for the heterogeneity of acoustical behavior among stations and the effect of environmental elements, especially space architecture on acoustical conditions and audio dissatisfaction is undeniable.
It is also suggested to study the sound absorption capacity at different frequencies to optimize the acoustic conditions for providing auditory satisfaction to increase the absorption capacities at low frequencies and frequencies of human speech and auditory range by creating cutouts, corners, and cavity-like functional spaces.