Noise control - sound pressure level calculation?

In a conference room (35dB), measure sound pressure levels in dB re 20渭Pa for the octave bands between and including 63Hz and 8kHz are 46, 41, 38, 40, 43, 46, 49, 50.





a) calculate the overall A-weighted sound pressure level





I've read through my notes and text book but I can't work out how to do this? Can anybody please help?Noise control - sound pressure level calculation?
The sound levels for the octave bands between 63 Hz and 8kHz are:





63 Hz - 46dB


126 Hz - 41dB


252 Hz - 38 dB


504 Hz - 40 dB


1 kHz - 43 dB


2 kHz - 46 dB


4 kHz - 49 dB


8 kHz - 50 dB





Examine the graph of an A-weighting curve such as the one here:





http://en.wikipedia.org/wiki/A-weighting





For each frequency band, you'll need to add or delete dB in order to properly weight the average. I happen to have an A-weighting table handy:





Freq (Hz)Level (dB)


31.5-39.4


63-26.2


125-16.1


250-8.6


500-3.2


10000


20001.2


40001


8000-1.1


16000-6.6





So, just add and subtract those values from the values given to obtain the weighted values:





63 Hz - 19.8dB


126 Hz - 24.9dB


252 Hz - 29.4 dB


504 Hz - 36.8 dB


1 kHz - 43 dB


2 kHz - 47.2 dB


4 kHz - 50 dB


8 kHz - 48.9 dB





Now just average all those values as your textbook tells you to, and you'll have the answer.

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