Sound Insulation Performance Evaluation Of Hood Based On Near-Field Acoustic Holography And Partial Coherence Analysis

Among various noise-controlling measures,it is probably the most common way to cut the influence of noise through its propagation path,sound insulation components are widely applied in the production and daily life.Therefore,it is indispensable to evaluate the sound insulation performance.Taking the engine front hood as an example,when the sound insulation parts work in the actual working condition,its sound insulation performance is affected by the combined influence of vibration-radiated noise,sound transmission and sound reverberation in the environment etc.thus bringing great difficulty to the sound insulation performance evaluation.The different sound insulation performance testing methods currently used are either confined in the professional and expensive experimental environment for only static components,or set too high requirements for the on-site testing equipment?while simulation methods based on different theories can only focus on one aspect of radiation noise or transmission noise to get the evaluation parameter such as transmission loss(TL)etc.,through simplified model or assuming a simple boundary condition.Therefore,the evaluation accuracy and its application range are greatly limited.The results of the sound insulation performance evaluation obtained through the above two ways are only applicable to understand the sound insulation capacity of the sound insulation components,having little guidance on the performance improvement,besides they are only applicable to the evaluation of simple working conditions.In this paper,the advantage of near-field acoustic holography for sound source reconstruction is analyzed.Combining with the characteristics of partial coherence analysis,an innovative sound insulation performance evaluation method is proposed.Then the theory is applied to the sound insulation performance evaluation of the engine hood of a bus which is equipped with pre-positioned engine,under idle condition,which is rarely researched at home and abroad.First of all,conventional testing methods such as sound pressure test and sound transfer function test method are applied to evaluate the idle the overall sound insulation performance of hood under the idle condition and in the meantime to determine the concerned frequency range for the sound insulation performance evaluation;afterwards the comprehensive sound field around the source area in the concerned frequency range is reconstructed through the innovative application of the research results on the inverse problem of near-field acoustic holography,instead of using the simulation method,and the sound pressure signal of the node is extracted from the sound field above the surface of the sound insulation component,reverberation interference excluded.according to the mutual relationships amid the sound source noise signal,the radiated noise signal caused by the hood surface vibration and the near-field sound pressure signal,this paper take the results of partial coherence analysis between the engine noise and the near-field sound pressure on the surface of the hood as transmission noise,the results of the partial coherence analysis between the surface vibration acceleration signal and the surface near-field sound pressure of the hood as the radiation noise,referring to the test method using acceleration measurement when evalating the sound insulation performance.The frequency range and intensity of the influence of radiation noise and transmission noise at different locations on the sound insulation components were determined,and so the analysis of the contribution of transmission noise and radiated noise was completed once in the sound insulation evaluation.The results show that the method can simultaneously evaluate the influence of transmission noise and radiated noise at different positions on the surface of the hood,and adopt comprehensive sound insulation measures such as vibration reduction and noise absorption at different parts according to the obtained results,thus completing the hood sound insulation performance of the regional control.