Objective Acoustical Parameters Of Sports Halls Based On Speech Intelligibility

Speech intelligibility is the main aim of acoustical design in a sports hall and two factors that influence speech intelligibility are signal to noise ratio and reverberation. Above is the foundation of the writing and arrangement of this paper, which brings about the following questions: which objective index should be used to evaluate the speech intelligibility of a sports hall? How does the background noise influence speech intelligibility of a sports hall? How long the RT (or EDT) should be in order to obtain good speech intelligibility of a sports hall and how to control the reverberation in a sports hall?In order to answer these questions, experiment work in three fields has been done starting from measurements of sound field:First, the sound field of several sports halls is measured, including measurements of the background noise 10 sports halls and impulse response in 4 sports halls. The former measurement takes into account the differences between background noise when the sports hall is unoccupied, occupied and in other state, and in the latter measurement, the 01db system is utilized to obtain the impulse response of each receiver when using the loudspeaker system.Second, the sound field of some typical sports halls has been simulated. Based on the summarization of 12 typical sports halls with different shape and size, ODOEN is used for sound field stimulation. Two types of loudspeaker systems and three types of absorption material arrangements are used in the stimulation, and the acoustic parameters and binaural impulse response of each receiver is obtained.Third, the subjective evaluation test of speech intelligibility of sports halls has been conducted, including test of 9 listening positions in two sports halls and auralization test of 32 listening positions of typical sports halls.On the basis of the summarization and analysis of the experiment data, the following disccussions is made and conclusions drawn according to the acoustic parameters related to speech intelligibility.Firstly, the index of speech intelligibility of sports halls has been discussed. This paper suggest STI be used for the evaluation, because the subjective evaluation test of speech intelligibility illustrates that compared with other parameters such as %ALcons, D and C50, STI can better evaluate speech intelligibility. In addition, subject evaluation test shows that STI should be more than 0.5.Secondly, signal to noise ratio in a sports hall has been investigated. Investigation finds significant difference between background noises when the sports hall is unoccupied and occupied. For example, the background noise SPL is about 76 dB when audience exchange casually in an occupied sports hall, which is 35dB more than when the hall is unoccupied. The signal to noise ratio of sports halls generally can reach 15dB, and the background noise has little influence on the speech intelligibility under such circumstance, which subjective tests have testified. When the signal to noise ratio is 10dB, subjective tests demonstrate that the speech intelligibility is influence to some extent.Third, the reverberation index in sports halls has been discussed. RT and EDT are two main index of reverberation. Subjective evaluation tests indicate EDT is more closely related to speech intelligibility than T30, and the simulation results of typical sports halls as well as the theoretical analysis of energy decay indicates that the relationship between EDT and STI is closer. Therefore, it is more suitable to use EDT as reverberation index for acoustic design of sports halls. It's difficult to determine how long the reverberation time should be in a sports hall. In this paper, the simulation results of sound field of typical sports shows: if T30<3.5s(EDT<3s), the Chinese speech intelligibility score can be more than 75%. In order to reach the reverberation limited value demanded by standard, the ceiling and walls should be filled with absorptive material, this is rigrid for acoustical design; the inccuration of reverberation time calculated by Erying formula which suggested by stardand should be discussed in the next work.