简介：Quantitativeestimationofsoundtransmissionattenuationbydifferentmiddle-earprotectingmecha-nismswasmadewiththeuseofacomputer-basedCM-cogramanalyzingmethod（FFTofcochlearout-putinresponsetowhitenoise）andotheraudiometricmeans.Strongreflexcontractionofthemiddle-earmusclesinguineapigsmaycausea5—20dBtransmissionattenuationindifferentfrequencyranges.Forimpulsenoiseexposure,thepresenceofaneffectivereflexatthelashingofeveryimpulsemayreducethepost-exposurehearingthresholdshiftin15dBonanaverage.Increasingtensionofthetympanicmem-branebyapplyingpressuretotheear-canalisalsoefficacious,especiallyforfrequenciesbelow500Hzwhereattenuationofmorethan10dBmayresultatapressuredifferenceofabout200mmH2Obetweenthetwosidesofthemembrane.Simulatedopeningoftheeustachiantubehelpsonlyveryinsignificantly,withattenuationlessthan5dB.Destructionofthemiddle-earstructures(drumperforation,ossiculardisruption