Are existing speech-rating criteria adequate for characterizing speech in an unamplified soundscape?

A number of metrics are currently in use to evaluate and plan room design for music or speech reproduction, such as Clearness, STI and Bass Ratio. These criteria originally derived from surveys analyzing the correlation between the auditory perception of concert halls and physical measurements. A room's Reverberation Time has been found to be key, playing a significant role in several of these criteria calculations. However, similar comprehensive research has yet to be conducted for speech in exterior settings. In considering outdoor acoustic fields (consisting of free field conditions), Reverberation Time does not characterize the sonic character of the space, particularly in unamplified conditions. Therefore, it is necessary to investigate whether existing parameters for characterizing speech transmission in interior settings can be applied productively in outdoor settings or whether a new psychoacoustic indicator may be needed. Because of the critical role that speech has and continues to play in human communication and interaction, the concept of soundscape, which describes the (exterior) sonic environment as perceived and interacted by humans in context, will serve as the basis for this analysis. Some psychoacoustic indicators such as loudness and sharpness , which can also serve as consistent parameters for speech transmission assessment, will be considered. Both of these models (room acoustics and psychoacoustics) point to limitations in evaluating speech in an open field, namely the difficulty in describing perception and the difficulty of measurement, respectively. This paper will explore which parameters from each of these models best fit for characterizing speech transmission in soundscape and how they might be combined. A proposal for field-testing, including consistent measurement and analysis, will be laid out. The importance of further research is also stressed, since human communication through unamplified speech and its perception was, is and most likely will be of major importance for humanity and quality of life.