Calculation and Analysis of Free Sound Field Deviation of Tones in Anechoic Room

It is introduced firstly that the caculation principle of the free sound field deviation of the tones in the anechoic room, there are three caculation methods, and the differences among them are discussed. And then based on the size of the anechoic room in the Nanjing University, the free sound field deviation of the tones with different frequency have been calculated.The conclusions have been drawn from the results that the free sound field deviation in the high frequency range are larger than those in the low frequency range if the sound absorbtion indices of all frequency are 0.99, so the sound absorbtion of the high frequency in the anechoic room should been more attention, and the instruct significance of the cut-off frequency in the anechoic room is absent.