Charles A. Laszlo

Modeling of the cat eardrum as a thin shell using the finite‐element method

A finite-element model of the cat eardrum is presented which includes the effects of the three-dimensional curved conical shape of the drum. The model is valid at low frequencies (below 1-2 kHz) and within the range of linear vibration amplitudes. The material properties used are based on a review of the literature. The critical material parameters are the stiffness (2 times 10(8) dyn cm(-2)) and thickness (40 micrometer) of the pars tensa. The model exhibits a vibration pattern and amplitude very similar to those observed experimentally using laser holography. A number of parameters are varied in order to study their relative importance in the model.

A critical review of experimental observations on ear-drum structure and function.

This paper presents a review of the experimental data available concerning ear-drum structure, properties and behaviour, in order to provide a basis for quantitative modelling and to identify areas where further information is required. The review of anatomy and structure indicates a lack of quantitative data about thickness, fibre distribution, three-dimensional curvature, and post-natal development. The mechanical properties of the ear-drum and attached structures are very poorly known, particularly with respect to isotropy, uniformity and damping. A historical review of observations of ear-drum vibration patterns shows general agreement that at low frequencies the displacements of the manubrium are smaller than those of the surrounding drum. Possible reasons are suggested for the apparent incompatibility of Békésys capacitive-probe measurements with this picture.

Dependence of middle‐ear parameters on body weight in the guinea pig

The dependence of several anatomical and functional parameters of the guinea‐pig middle ear on body weight, and thus on age, has been investigated. In particular, the volumes of the tympanic and epitympanic cavities are found to increase with age, with the tympanic cavity growing somewhat more slowly. The acoustical impedance of the passage between these two cavities also varies with age, while the weight of the incus appears to be independent of body weight. These results are important for establishing the values of parameters used in mathematical models of the middle ear. They are also relevant to theoretical considerations of the significance of middle‐ear resonances. [Supported by the Medical Research Council of Canada.]

The Acoustical Impedance of the Guinea‐Pig Middle Ear and the Effects of the Middle‐Ear Muscles

The acoustical input impedance of the guinea‐pig middle ear was measured in the frequency range 100–10 000 Hz, using a highimpedance volume‐velocity source and a probe‐tube microphone. The impedance was measured both in the normal ear and with the tympanic membrane removed; the latter measurement permits accurate characterization of the middle‐ear cavities themselves. The data was compared to a slightly modified version of the middle‐ear model of Zwislocki [J. Acoust. Soc. Amer. 35, 1034–1040 (1963)], and new parameter values were calculated to match the present data. We also measured the time couraes of transient impedance changes caused by spontaneous contractions of the middle‐ear‐muscles of the anesthetized animals. These transient changes were compared to the middle‐ear‐muscle effects predicted by the model. [Supported by the Medical Research Council of Canada.]

The Role of the External Ear in the Hearing of the Guinea Pig

The acoustic transmission characteristics of the outer rim of the pinna (flap), the concha, and the external auditory meatus of the guinea pig were measured in the frequency range 100 Hz–15 kHz using a PDP‐12 computer. The experiments were performed on anesthetized guinea pigs suspended in a sound field. The orientation of the field relative to the experimental animal was varied and the localization properties of the pinna recorded. To measure the amplitude and phase of the input and transmitted sound, two identical acoustic probes were used. One probe was placed at the entrance to the ear canal, and the other probe was surgically implanted in front of the tympanic membrane. The results of ten experiments indicate: (1) that the flap does not provide any significant amplification in the frequency range of measurement, (2) that the concha provides a significant amount of boost (10 dB) in the 5–9 kHz region, (3) that the ear canal itself can be represented by an open‐ended tube of appropriate dimensions, and...

Acoustic and electromagnetic noise from lighting in classrooms

Following complaints by hard‐of‐hearing students using assistive‐listening devices, and their teachers, the hum‐like noise generated by fluorescent lighting was investigated in classrooms and the school library in a typical school. This hum is caused by vibrations in the core of the magnetic ballasts. Measurements were made in several rooms without students present. Noise levels increased between 7 and 15 dB when fixtures using magnetic ballasts were switched on. Spectral analysis showed the presence of 30, 60, 120, and 240 Hz components. In rooms where electronic ballasts were installed, there was no increase in noise level when the lights were switched on. Since hearing aids and assistive‐listening devices worn by students may also be influenced by magnetic fields, these were also surveyed in these classrooms. The magnetic fields generated by the lights were not significant, but near some wiring and electrical panels the interference was strong. In rooms with electronic ballasts some infrared assistive‐...

Modeling the eardrum as a doubly curved shell using the finite‐element method

The eardrum was earlier modeled as a plane membrane under tension using the finite‐element method [J. Acoust. Soc. Am. 56, S3 (1974)]. It has now been modeled as a curved shell, taking into account the actual three‐dimensional shape. The effects of the embedded malleus, and of the stiffness of the ossicular suspension, are included. The model is strictly static, or low‐frequency. Calculations have been done for the cat, guinea pig, and human, and the results were compared with recent experimental data on eardrum vibration. The model is able to match measurements of peak drum displacement and of manubrial‐tip displacement. We have studied the effects of variations of several parameters, including the curvature of the sides of the eardrum. We have also calculated the effect of the type of anisotropy assumed by Helmholtz. [Supported by the Medical Research Council of Canada, The Quebec Department of Education, and the McConnell Foundation.]

Simulating the behavior of the eardrum by the finite‐element method

The eardrum has been modelled as a plane, isotropic membrane. We have included the effects of the embedded malleus, the frequency‐dependent reactive and resistive forces exerted on the malleus by the rest of the ossicles, and the closed middle‐ear air cavity. The variations in the form of the drum and malleus among different species have also been considered. The simulation is done using an adaptation of the finite‐element method, in which the two‐dimensional continuum is divided into a number of arbitrarily shaped triangles. The results obtained are compared to recent servations of eardrum vibration in the cat and guinea pig, as well as to middle‐ear impedance data. [Supported by the Medical Research Council of Canada, the Quebec Department of Education, and the McConnell Foundation.]

The Acoustic Behavior of the Outer‐Middle‐Ear Complex of Man and Guinea Pig

In this study, the acoustic‐transmission characteristics of the human and guinea‐pig ear canals were compared. According to Wiener [J. Acoust. Soc. Amer. 18, 401–408 (1946)], the pressure response of the human ear canal is similar to that of a tube open at one end and rigidly terminated at the other. This indicates that in man, the middle ear acts as a high‐impedance termination and hence it does not load the ear canal. In the guinea pig, however, we have found that the pressure response of the ear canal is affected by the loading of the middle ear [J. Acoust. Soc. Amer. 50, 92 (A) (1971)]. In particular, two maxima were observed in the experimental curves and these were found to correspond to two peaks in the impedance curve of the guinea‐pig middle ear. To facilitate the interpretation of the experimental results, a computer simulation study of the outer‐middle‐ear complex was performed for the human and guinea‐pig ears. The responses predicted by the simulated electroacoustic models were very similar t...

Computer Simulation of Cochlear‐Microphonic Potential Augmentation During Intracochlear Perfusion

In previous studies, “start‐stop” perfusion of scala tympani by artificial solutions produced temporary augmentation of the CM recorded by differential electrodes. The significance of hydrodynamic changes in scala tympani and the differential action of the artificial and natural perilymph on the hair cells in this phenomenon was investigated by computer simulation. In particular, it was determined from fluid‐dynamic and experimental considerations that the artificial perilymph perfusate could be spontaneously replaced by natural perilymph at a rate of 0.8 μliter/min. The effect of this replacement was simulated on a computer model of the mechanoacoustical and mechano‐electrical transduction process of the guinea‐pig ear [C. A. Laszlo, J. Acoust. Soc. Amer. 38, 93(A) (1971)]. After simulated injection of a solution whose action was to suppress the CM generated by individual hair cells, the modeled gross CM was temporarily augmented by 40% above the preperfusion control, comparable to that observed in our p...