ABSTRACT
This chapter explores the factors and issues that affect speech intelligibility and how these aspects may affect the potential design of a sound system. The elements involved are shown to include both the physical and structural properties of the building or room as well as the system components and electronics. The factors are separated into primary and secondary status with 8 primary factors and 17 secondary issues being highlighted and discussed. It is further demonstrated that there is a human element (the listener and talker) that must also be considered, albeit outside the normal control of the sound system designer. The nature of the speech signal itself is then discussed including its waveform, dynamics and spectral content. The effects that reverberation and noise can have on the audibility and clarity of a speech signal are illustrated together with methods of mitigating these within the design of a system. Having discussed the issues that can affect intelligibility the final part of the chapter discusses how intelligibility can be quantified and measured. A number of techniques and measures are examined and in particular the Speech Transmission Index (STI) is considered as this is the most common and widely recognised measure. The practical use and limitations of STI are discussed. The chapter concludes with a bullet point summary of the 20 most important design factors required for the production of good intelligibility from a sound system.
