This paper is part of a PhD work, dealing with the acoustics of the public squares (‘Agorá Acoustics’), especially when music (amplified or not) is played. Consequently, our approach will be to evaluate public squares using the same set of acoustics concepts for subjective evaluation and objective measurements as applied for concert halls and theatres. In this paper the acoustical effects of arcades will be studied, in terms of reverberation (EDT and T30), clarity (C80), intelligibility (STI) and other acoustical parameters. For this purpose, also the theory of coupled rooms is applied and compared with results. An acoustic modelling program, ODEON 7.0, was used for this investigation. Three different sizes of public squares were considered. In order to evaluate the ‘real’ effects of the arcades on the open square, models of all three squares were designed both with and without arcades. The sound source and the receivers were positioned in the open square as well as in the arcades (making four different combinations).The results show that, when adding arcades to an open square, an increase in reverberation time is observed: a criterion is studied to predict in which cases arcades have this effect. Arcades can also cause a decrease in Clarity (C80), Strength (G) and STI in the main open area. Arcades cannot be considered responsible for double decay in the open area; however the open square can cause a double decay under the arcades, if both sound source and receiver are positioned in the same arcade. Finally, the distribution of energy through the coupling surface is discussed using Statistical Energy Analysis (SEA).