The negative sound intensity in sound field

The sound intensity distribution in the sound field of two closely spaced simple harmonic point sound sources have been studied in this paper. It was found that the normal component of the sound intensity over a plane surface above the source can be negative in certain areas. An experiment was conducted to map the distribution of the mormal component of the sound intensity over a surface above a loudspeaker, and it was also found that there are some surface areas where the normal sound intensity component is negative. It can be concluded that the negative sound intensity measured in a real situation does not necessary indicate extraneous noise sources outside the measurement surface, or sound absorption inside the measrement surface, or measurement mistakes.