The construction of multiple use theatres is becoming more common due to the need to accommodate different kinds of performances at the same space. In order to acoustically adequate this space to concert music, the inclusion of an orchestra shell becomes necessary. The main objective of an orchestra shell is to improve the acoustic quality on stage, both for musicians and for the conductor. The goal is to improve balance of the group allowing musicians to hear themselves and the orchestra better. However, the orchestra shell can also improve the acoustic quality for the audience. The objective of this study is to analyse the difference of the acoustic performance perceived at the audience area with the inclusion of a light orchestra shell with diffuse surface in a proscenium theatre. Measurements were done using the impulse response technique according to ISO 3382-1. Measured parameters were Reverberation Time, Early Decay Time and Clarity Index. Results showed that the orchestra shell improves the acoustic performance at the audience area, although by a small difference. It increased the Reverberation Time and Early Decay Time at high frequencies and decreased clarity, improving spaciousness and group balance to the audience.11 89678977 International Institute of Noise Control Engineering (I-INCE),Acoustical Society of America (ASA),SAE InternationalBarron, M., (2003) Auditorium Acoustics, , 2° ed. Spon PressPasseri Jr., L., (2008) Subsídios para o Projeto de Teatros e Auditórios Multifuncionais: Recursos de Variabilidade Acústica, , USPBradley, J.S., Some effects of orchestra shells (1996) The Journal of the Acoustical Society of America, 100 (2)Farina, A., Fausti, P., Pompoli, R., The acoustical shell of the 'Nouvo teatro comunale' in cagliari (1995) Proceedings of the 15th International Congress on Acoustics, 2. , Trondheim, NorwayJaffe, C., Design considerations for a demountable concert enclosure (Symphonic shell) (Reprint) (1974) J. Audio Eng. Soc, 22 (3)(2009) ISO 3382-1: Acoustic Measurement of Room Acoustic Parameter Part 1: Performance Spaces, , International Organization for StandardizationSchultz, T.J., Acoustics of the concert hall (1965) IEEE Spectrum, 2 (6), pp. 56-67. , (junho)Han, J., Stage sound-reflectors in hangzhou theatre (1988) Applied Acoustics, 24 (3)Bradley, J.S., Review of objective room acoustics measures and future needs (2011) Applied Acoustics, 72 (10)Meng, Z., Zhao, F., He, M., The just noticeable difference of noise length and reverberation perception (2006) International Symposium on Communications and Information Technologies, 2006, pp. 418-421. , ISCIT '06 IEEEBarron, M., Bass sound in concert auditoria (1995) The Journal of the Acoustical Society of America, 97 (2)Kahle, E., Jullien, J.-P., Some new considerations on the subjective impression of reverberance and its correlation with objective criteria (1994) ASA Conference, , CambridgeBeranek, L.L., (2003) Concert Halls and Opera Houses: Music, Acoustics, and Architecture, , 2nd ed. SpringerBradley, J.S., Some further investigations of the seat dip effect (1991) The Journal of the Acoustical Society of America, 90Giacomoni, C., Jasinski, C.M., Edwards, S., Ignatiuk, D., Ormsbee, C.I., Wells, A.P., Vigeant, M.C., Celmer, R.D., (2011) Final Report: Just Noticeable Difference of Clarity Index (C80), , Phase 2. University of Hartford Acoustics