Measurement of Acoustic Impedance

Mawardi, Osman K.

doi:10.1121/1.1906486

Cited by 17 publications

(2 citation statements)

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“…Figure 2 shows the real and imaginary parts of the radiation impedance of the unoccluded ear, the mean occlusion impedance of nine circumaural HPDs (earmuffs), and of nine intraaural HPDs (earplugs). These impedances were measured on a special acoustic test fixture (ATF) equipped with pinna and circumaural and intraaural flesh simulation using the "short-tube method" described in detail in Poesselt (1982Poesselt ( , 1985, which has been used before by several others (e.g., by Cook, 1947;Mawardi, 1949;Singh and Schary, 1978;Salava, 1980Salava, , 1981 impedance of the earmuffs also gives a first-order estimate for the occlusion impedance of headphones. It can be stated that in order to measure the sensitivity level of circumaural headphones the influence of the eardrum impedance is also negligible (see Hudde and Schroeter, 1980, Fig.…”

Section: Ps O = Ps O and Z•o --Zro (12)mentioning

confidence: 99%

The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part II: Modeling the external ear, simulating bone conduction, and comparing test fixture and real-ear data

Schroeter¹,

Poesselt²

1986

The Journal of the Acoustical Society of America

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This paper investigates two main features of the human head which influence the measured attenuation of circumaural and intraaural hearing protection devices (HPDs): the external ear and the different pathways of bone conduction. A theoretical model for the external ear shows that its influence on the insertion loss of HPDs, on the sensitivity level of headphones or earphones, and on the insertion gain of hearing aids, all can be described by one equation. While it is not necessary to simulate the eardrum impedance in order to measure the insertion loss of earmuffs and the sensitivity level of headphones with acoustical test fixtures (ATFs), the required accuracy of an ear simulator is more stringent when the same measurements are performed on intraaural devices. For the evaluation of HPDs, bone conduction plays an important role. We have developed a model to estimate HPD-dependent bone conduction effects. The model includes two bone conduction sources: one in the external ear and one in the middle ear. The model explains, for example, the occlusion effect of HPDs and the masking error at low frequencies due to physiological noise that arises when real-ear attenuation at threshold (REAT) measurements are made. Consequently, objectively measured insertion loss can now be used to predict REAT with improved accuracy. ATF and REAT data are compared using nine earmuffs and nine earplugs. In the majority of cases, the two sets of data agree well. Discrepancies are discussed.

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Section: Ps O = Ps O and Z•o --Zro (12)mentioning

confidence: 99%

The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part II: Modeling the external ear, simulating bone conduction, and comparing test fixture and real-ear data

Schroeter¹,

Poesselt²

1986

The Journal of the Acoustical Society of America

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“…Two main shapes have been used: cavities and tubes. Cavities can be used for low frequencies only, because for higher frequencies higher modes must be taken into account: the amplitudes of these modes are di$cult to determine theoretically [2,48]. Straight tubes are most often used.…”

Section: The Choice Of the Known Loadsmentioning

confidence: 99%