This paper introduces a measuring method of early lateral energy fraction in the scale model experiments. According to the interference principle of half wave length making the high frequency figure-8 directional micr...This paper introduces a measuring method of early lateral energy fraction in the scale model experiments. According to the interference principle of half wave length making the high frequency figure-8 directional microphone. With the signal-processing technique, a receiving and analyzing system, for the measurements of lateral energy fraction in the scale model is realized.展开更多
In the normal-mode theory of Morse, it gives a series of normal modes as the solution of forced vibration in a room. But actually there is always the direct radiation besides the normai modes which represent the rever...In the normal-mode theory of Morse, it gives a series of normal modes as the solution of forced vibration in a room. But actually there is always the direct radiation besides the normai modes which represent the reverbrant sound field only. The reason is that the normai modes were assumed only in the source, and naturally normai modes only are obtained in the solution. A theory of double source is proposed, that the sound source is both the source of the direct radiation as if in free space before the boundary surfaces were reached by the direct radiation, and after the first reflection from the boundary surfaces, the source of the reflected wavelets, randomly distributed both in space an in time on the boundary surfaces that build up the normai modes after further reflections. The wave equation is formed accordingly, and the solution of the wave equation, the sound field in a room, contains explicitly both the direct radiation and the reverberant sound formed of normai modes. The approximate mean square sound pressure is found to be the dircet sound determined by the sound power of the source, and reverberant sound determined by the sound power reduced by a factor of 7T/2, different slightly from the result obtained from energy consideration, if the source is pure tone. There is essentially no difference for a source of band noise.展开更多
In order to cut down excessive experiments, acoustic response of the different fan ducted discharge (equipment) was studied based on numerical method. The sound pressure level(SPL) in each component of a duct-plenum-r...In order to cut down excessive experiments, acoustic response of the different fan ducted discharge (equipment) was studied based on numerical method. The sound pressure level(SPL) in each component of a duct-plenum-reverberant room model was drawn and SPL deviation was analyzed. The trends of the curves were explained by the diffracti on and end reflection at the duct discharge. Models with different room dimensions, duct lengths, duct cross sections, duct locations and duct elbow were constructed, and their response was analyzed and compared. The results show that the SPL curves are smooth in the duct discharge cross section, but seriously fluctuant in the reverberant room; SPL in the duct discharge is only sensitive to duct dimensions, while that of the reverberant room is regularly influenced by all the dimension and arrangement factors. Small room and short duct help to increase room SPL. Elbow has an indistinct influence on all the components’ sound field. Finally, suggestion to reduce the deviation of experiment results was proposed.展开更多
文摘This paper introduces a measuring method of early lateral energy fraction in the scale model experiments. According to the interference principle of half wave length making the high frequency figure-8 directional microphone. With the signal-processing technique, a receiving and analyzing system, for the measurements of lateral energy fraction in the scale model is realized.
文摘In the normal-mode theory of Morse, it gives a series of normal modes as the solution of forced vibration in a room. But actually there is always the direct radiation besides the normai modes which represent the reverbrant sound field only. The reason is that the normai modes were assumed only in the source, and naturally normai modes only are obtained in the solution. A theory of double source is proposed, that the sound source is both the source of the direct radiation as if in free space before the boundary surfaces were reached by the direct radiation, and after the first reflection from the boundary surfaces, the source of the reflected wavelets, randomly distributed both in space an in time on the boundary surfaces that build up the normai modes after further reflections. The wave equation is formed accordingly, and the solution of the wave equation, the sound field in a room, contains explicitly both the direct radiation and the reverberant sound formed of normai modes. The approximate mean square sound pressure is found to be the dircet sound determined by the sound power of the source, and reverberant sound determined by the sound power reduced by a factor of 7T/2, different slightly from the result obtained from energy consideration, if the source is pure tone. There is essentially no difference for a source of band noise.
文摘In order to cut down excessive experiments, acoustic response of the different fan ducted discharge (equipment) was studied based on numerical method. The sound pressure level(SPL) in each component of a duct-plenum-reverberant room model was drawn and SPL deviation was analyzed. The trends of the curves were explained by the diffracti on and end reflection at the duct discharge. Models with different room dimensions, duct lengths, duct cross sections, duct locations and duct elbow were constructed, and their response was analyzed and compared. The results show that the SPL curves are smooth in the duct discharge cross section, but seriously fluctuant in the reverberant room; SPL in the duct discharge is only sensitive to duct dimensions, while that of the reverberant room is regularly influenced by all the dimension and arrangement factors. Small room and short duct help to increase room SPL. Elbow has an indistinct influence on all the components’ sound field. Finally, suggestion to reduce the deviation of experiment results was proposed.
