Sound Field In The Enclosure With An Aperture And The Sound Field Radiated From The Aperture

Usually an enclosure is a closed and rigid cover.But most enclosures require some form of ventilation and access of passing materials in and out.Such necessary permanent openings must be treated.Otherwise the effectiveness of the enclosure can be very much reduced by the presence of the apertures.Based on the previous studies by others the effects of apertures,flexible plane on the sound field in an enclosure,sound field radiated from the aperture are investigated in this dissertation.For reducing snoring noise the active partition is proposed.The effects of apertures on the sound field of an enclosure are investigated.First,the acoustic model of the enclosure with apertures is developed based on the modal expansion approach by considering the vibrating air in the aperture as an equivalent point source,and then the proposed model is used to calculate the higher-order resonance frequencies of the enclosure and the sound pressure distribution at resonance frequencies.The results demonstrate that having an aperture is equivalent to reduction of the acoustical mass at the location of the aperture and generally makes the resonance frequencies of the enclosure increase.If the aperture is located at a modal node,the mode is not coupled with other modes over the aperture,so its resonance frequency remains unchanged.Reduction of sound pressure in the region near the aperture is also observed,which is due to the opposite phases between the modal sound pressures corresponding to the resonance frequency and the sum of the other modal sound pressures.In conclusion,the sound field in an enclosure is affected by the presence of the aperture and the variation degree of the sound field characteristics depends on the location and the size of the aperture.The forced response of an acoustic-structural coupled system has been modeled to analyze the resonance frequency shift of a cavity controlled mode.Theoretical analysis and simulations show that unlike the infinite acoustical mass of the approximately rigid wall with a slight damping,the finite acoustical mass of the plate allows the plate-cavity couple,resulting in the resonance frequency shift of the cavity controlled mode.The degree and direction of the shift are affected by the modal coupling coefficient,the acoustical mass of the plate and the resonance frequency of the plate.Using finite element method the enclosure with an aperture is modeled.In the free field sound pressure,intensity and power are calculated in the theories and the simulations and compared.By mode analysis and forced vibration analysis by a point source,the normal frequencies and resonant frequencies in simulations are compared with the results in the theories.The model is verified.By the simulation analysis it is found that:there are clear peaks in sound power spectral,and it is caused by the cavity modeSnoring noise around the ears of the partner on the other side of the bed can be reduced by the specialized ear plugs or the active headsets.Nevertheless prolonged or frequently repeated use of ear plugs can result in infection(otitis externa or otitis media),hearing loss,discharge or meningitis etc." and the active headsets with broad bandwidth of attenuation noise are not suitable for the sleepers on the bed.An active partition is proposed that can be placed between a snorer and a non-snorer on a bed to reduce the snoring noise around the non-snorer ears by integrating a rigid finite size passive peartition with a two channel active noise control system.The noise reduction performance of the passive partition on a bed with a headboard is studied first,where the effects of the height and the width of the partition are discussed.Due to the limited partition size,the attenuation for the low-frequency diffracted noise is not sufficient,so two loudspeakers are proposed to be installed on the partition as the secondary sources to increase the overall noise attenuation.Both numerical simulations and experiments are carried out to demonstrate the feasibility of the proposed integrated snoring noise control system,and the results show that the proposed active partition can achieve over 10 dB noise attenuation at non-snorer ears in the 1/3 octave bands from 80 to 1000 Hz.