$1.(7$ points$)$ A compressor is tested in an anechoic chamber. The measured SPL $($sound pressure level$)$ is $90$ dB when the compressor is on and $75$ B$)$ when the compressor is off$)$ It is assumed that all sound sources are uncorrelated. i$)$ Why is not the measured SPL O dB when the compressor is off? ii$)$ What is the SPL of the compressor? iii$)$ If $5$ such compressors are switched on$,$ what are the measured SPL at the same location and in the same environment? Keep your calculations to the $4$th decimal place.