Explaining the acoustical behavior and the soundscape quality of Tabriz Bazaar based on the objective and subjective assessments

Soundscape is a subfield of urban studies that deals with the quality of sound heard and perceived in urban spaces. Numerous characteristics affect the quality of urban space soundscapes, and the acoustic behavior of the space is thus an influential factor which depends on its environmental characteristics. The acoustic behavior of the space indicates that the physical body of any environment amplifies or attenuates sound waves in the face of sound. As the environment body intensifies sound once created in space, sound waves stay in the environment longer, and increase sound intensity. Conversely, when the acoustic behavior of space attenuates, sound waves are destroyed in space shortly after created by sound sources. In this case, the intensity of the sound heard in the environment can be relatively stable, provided that the audio sources are constant.

The amount of time it takes sound to drop to 60 decibels after created by a sound source is called Reverberation Time (RT), which is measured in seconds. In soundscape studies, Sound Pressure Level (SPL) is also a physical component in decibels, which is used to measure sound loudness. Thus, Sound Pressure Level and Reverberation Time are two components that can specify the acoustic behavior of a space. In addition to acoustic assessments, soundscape studies address how people perceive the sounds around them and how desirable and pleasant they are. In fact, acoustic measurements are a tool that can help to create the desired soundscape, because sonic comfort depends to a large extent on the SPL. However, what greatly matters in soundscape studies is the perceptual loudness and subjective sonic comfort. Therefore, it is necessary to clarify the factors affecting these subjective components. The perceptual quality of urban soundscape is specified through subjective assessments.

This research discussed the effect of environmental features on the acoustic behavior of Rasteh-Bazaars, in Tabriz Grand Bazaar, and on the quality of the soundscape therein. Based on the objective evaluations, the acoustic behavior of the Rasteh-Bazaars and the factors affecting it were specified, and the desirability of the Rasteh-Bazaars soundscape was clarified using subjective evaluations. Objective assessments were made to specify the acoustic behavior of the Rasteh-Bazaars based on the measurements of SPL and RT. The B&K 2260 set of equipment and ACAM100 acoustic camera were used to measure RT and SPL. Both of these values were evaluated in frequency spectra. Subjective assessments were made based on a descriptive soundscape questionnaire, where a total of 165 people answered the questions. The questionnaire assessed sound loudness, sonic comfort, sound preferences, and soundscape descriptors through the Likert scale. Based on the results, it could be found how the people present in the Rasteh-Bazaars of Tabriz Bazaar felt about and perceived the space soundscapes.

The findings demonstrated that spaces such as Rasteh-Bazaars, which are identical in form and material, exhibited consistent acoustic behavior. If accompanied by physical changes such as ones in the space axis and spatial integration as cavities, this homogeneity could change the acoustic behavior and the heard sound. This finding could add a new concept called homogeneous spaces to the field of soundscape design. This means that homogeneous urban paths can be designed so that the soundscape is perceived almost uniformly along them, and diversity and distinction can be provided through physical changes in the urban soundscape that can be perceived during movement. The findings also indicated that sonic comfort did not necessarily increase as sound intensity decreased. Even in tranquil urban spaces with low SPLs, the tranquility and quality of the soundscape decreased as the phenomenon of difference in SPL occurred. This important finding demonstrated that a new component called urban soundscape clarity should be evaluated in the study of soundscapes in tranquil urban spaces to investigate the occurrence of difference in SPL in tranquil urban spaces.

Based on the comparison of the objective and subjective findings of the research, it was found that it was not sufficient for provision of sonic comfort to simply follow the standard values of SPL and RT. This is because the phenomenon of difference in SPL could have a negative effect on environmental and sonic calmness, as mentioned earlier, in a silent space. The subjective perception of the soundscape depended on factors other than the physical quantity of the sound. In fact, the values of SPL and RT, which indicate the acoustic behavior of the space, could not serve as the sole basis for assessment of the quality of the soundscape although somehow involved in people’s perceptions thereof. The environmental characteristics and qualities of spaces, such as lighting and congestion and supplied goods appeal at the Rasteh-Bazaar were found to have direct effects on the favorability of the soundscape.AcknowledgmentThis article was extracted from Bita Shafaei’s doctoral thesis under the supervision of Dr. Abbas Ghaffari and Dr. Morteza Mirgholami at Tabriz Islamic Art University.