A8. (a) The measured sound pressure level at 1 kHz of a cinema resulting from an air conditioning system is 45 dB. With the aid of the following information, determine the required in-duct attenuation at 1 kHz if the higher acceptable NC level requirement is to be achieved. (3 Marks) SPLNCS corresponding to various NC levels NC 63 Hz 125 Hz 250 Hz 500 Hz 1k Hz 2k Hz 4k Hz 8k Hz 65 60 55 50 45 40 35 30 25 877766655 80 75 71 68 66 64 63 62 71 67 63 61 59 58 57 74 67 62 58 56 54 53 52 71 64 58 54 51 49 48 47 60 54 49 46 44 43 42 64 57 50 45 41 39 38 37 60 52 45 40 36 34 33 32 48 41 35 31 29 28 27 54 44 37 31 27 24 22 21 Function Broadcasting and recording studios Concert halls and theatres Acceptable NC level 20 20 to 25 Assembly halls and churches 25 to 30 Cinemas 30 to 35 Hospital wards and operating theatres 30 to 40 Homes and bedrooms 25 to 35 Private offices and libraries 30 to 35 General offices 35 to 45 Mechanised offices 40 to 55 Restaurants and bars 35 to 45 Department stores 35 to 45 35 to 50 Swimming baths and sports arenas (b) A ventilation system supplies air to the rooms with the following information: Volume Flow Rate (m/s) Required NC Room A 0.5 40 Room B 0.7 35 Room C 0.3 30 Room D 0.4 45 Room E 0.5 35 Determine, with brief reasons, which room(s) must be analysed in determining the noise reduction required in the system. (2 Marks)