Primary Resonance Frequency Research Articles

Influence of Outer Ear Resonant Frequency on Patterns of Temporary Threshold Shift

Noise-induced hearing loss following a broadband noise exposure has been characterized by a notch in the audiogram in the 3.0 to 6.0 kHz range. It has been postulated that loss of sensitivity in this frequency range is related to the primary resonant frequency of the external auditory meatus. In order to further explore this hypothesis, 31 normal-hearing subjects provided measurements of acoustic gain of the external ear and temporary threshold shift (TTS). Subjects completed sweep frequency Bekesy tracking procedures prior to and immediately following a 30-minute broadband noise exposure (95 dBA). The frequency maximally affected by the noise exposure (Max TTS) was correlated to primary resonant frequency of the outer ear (Max RF). A significant positive correlation between these two measures was identified. A 100 Hz difference in Max RF resulted in approximately a 140 Hz change in Max TTS. Thus, the external ear plays a significant role in the frequencies affected by a broadband noise exposure.

Design of wide range piezoelectric microphones.

A wide range ceramic microphone using a round flat type diaphragm is described in this research report. Use of the ceramic electrode diameter as the parameter is proposed for setting of the upper frequency limit. A concentric mode of vibration will appearin the vicinity of the secondary and tertiary resonance frequencies in the range above the primary resonance frequency of the diaphragm. Since the generated voltagewill be the highest at this center (inside the inflection point), the maximum power can be obtained by determining the electrode diameter according to the frequency. When high voltage obtained from this maximum power is supplied to the FET, a large output voltage can be obtained with the optimum signal-to-noise ratio. The performancecharacteristics which were realized by this prototype capsule of ∅23.77 are Sensitivity:-40.2 dB/Pa. 1 kHz; Electrostatic capacity: 118 pF, and Frequency response:±2.5dB at 20Hz to 20kHz.

Bifurcation of Harmonic Solutions of an Integro-Differential Equation Modelling Resonant Sloshing

This paper proves the existence of multiple solutions $( \mu ,u )$ of \[ u^m ( t ) - \lambda u'( t ) - 2u( t )u'( t ) = \mu _1 ( {{\bf D}u'} )( t ) + \mu _2 \sin t, \] such that u has period $2\pi $ and mean zero. ${\bf D}$ is a singular integral operator. The equation models steady gravity waves on the surface of a shallow tank, oscillating near the primary resonance frequency. It is shown here that for each $\lambda > - 1$, the equation has one, two, or three solutions, depending on the position of $\mu = ( \mu _1 ,\mu _2 )$ in a neighbourhood of zero in $\mathbb{R}^2 $. This extends previous work, which required that $\lambda $ be close to $-1 $. The method depends on the existence of cnoidal solutions when $\lambda > - 1$ and $\mu = 0$. The Lyapunov–Schmidt procedure is used to reduce the problem to a single bifurcation equation, which is analysed using some results of Hale and Taboas.

Wide band acoustic receiver transducer

For use in an acoustic logging tool having a sonde adapted to be lowered in a borehole, an improved acoustic transducer comprising a pyramidal frustrum is disclosed. The preferred embodiment incorporates fifteen sides. Each side mounts a piezoelectric crystal for receiving. Mechanical resonant frequencies of the transducer are outside the receiver band width which is about 25 kHz. The resonant frequencies are above 25 kHz, thereby avoiding primary resonant frequencies within the band width.

Measured Lateral Response of Mass on Single Pile in Clay

The results of dynamic lateral load tests on a cantilevered mass supported by a single 10.75‐in. (273‐mm) diameter steel pipe pile embedded in stiff, overconsolidated clay are presented. These tests were conducted to provide a basis for evaluation of mathematical models that predict the relatively low‐frequency dynamic pile response that is representative of systems in which the primary resonance frequency is controlled by the mass and stiffness of the superstructure. Frequency sweep shear forcing functions were applied at the top of the mass, which simulated a simple structure. The responses of the pilesupported mass, points on the embedded pile, and points in the supporting soil were recorded to determine frequency response functions. Frequency response functions between the applied load and pile cap‐mass were then examined to aid in the identification of the pile‐soil system parameters which most strongly influence response. The measured pile cap frequency response function peak amplitude was 0.0022 in./lb (0.0126 mm/N), or about ten times the static flexibility, and the resonance frequency was approximately 2.2 Hz.

The modulated double diffusive system: Chaotic behaviour near the convection threshold

We show that chaos through period doubling can be induced in a parametrically modulated double diffusive system near its oscillatory (of frequency ω 0) convection threshold. This happens on modulation with the primary parametric resonance frequency (ω ≅ 2ω 0) at a critical amplitude of modulation. The onset of period doubling is preceded by a symmetry-breaking bifurcation. Convection experiments on binary fluids should reveal this effect.

Mechanical properties of the vocal folds of fresh excised human larynxes

A compulsory sinusoid wave vibration ranging from 30 to 300Hz was induced to the vocal fold of fresh excised human larynxes by pressing a vibrator on the midline of the thyroid cartilage. The vocal fold vibration, thus created, was measured and recorded as a function of frequencies and Q-values of the resonance using Ultrasonic Pulse Methods.The resonance pattern of the vocal fold was measured and recorded under the loading of mass and longitudinal tension.From the resonance characteristics, damping ratio, effective mass, and effective stiffness of the vocal fold were estimated.The results obtained were as follows:1. The resonance characteristics were almost equal before or after vertical incision of the midline of the posterior wall of the larynxes. The mean value of the resonance frequency was approximately 100Hz, while the Q-values ranged from 2.0 to 3.0.2. Under the loading of longitudinal tension posterioly, as the tension increased, so did the appearance rate of the secondary resonance wave. And the secondary resonance frequencies and Q-values also increased in proportion to the tension given to the vocal fold. On the other hand, the primary resonance frequency was always constant (about 100Hz), regardless of the given tension. The Q-values of the primary resonance wave were also constant, ranging from 2.0 to 3.0.3. Under mass loading, as the mass increased, the resonance frequencies and the Q-values of resonance decreased. When the mass was over 60mg, the resonance frequency had a trend to be leveling off, probably because of the change in the stiffness of the vocal fold.4. Damping ratio, effective mass, and effective stiffness were estimated as follows:Damping ratio:0.21±0.04Effective mass:0.13±0.02gEffective stiffness:51±8k dyne/cm

Performance of external ear as a sound collector

The overall performance of an acoustical antenna system can be expressed in terms of its absorption cross section which, for a diffuse sound field, is defined as the cross-sectional area A of the perfectly absorbing sphere which would absorb the same sound power from the field as the system under study. The limiting value of A is λ2/4π. For the external ear A can be expressed in terms of the eardrum impedance ZA, the impedance looking outward from the eardrum Za, and the radiation efficiency η all of which can be measured or estimated. The analysis shows that the ear is a very inefficient sound collector at low frequencies but performs well at its primary resonance frequency (2.7 kHz) where A attains a peak value of 5 cm2 compared with theoretical limit of 13 cm3. The cross section almost attains the limiting value at 9 kHz and remains within 6 dB of the limit up to 15 kHz. However, when allowance is made for the energy loss in the eardrum and middle ear it is clear that the cochlea receives no more than 10% of the power available in a diffuse field at any frequency.

Diffuse field sensitivity of external ear based on reciprocity principle

The reciprocity principle defines a general relationship between transmission and reception in an acoustical system. By applying this principle, the transformation of sound pressure level from a diffuse sound field to the eardrum can be expressed in terms of the frequency. the radiation impedance Zrad of the external ear looking outward from the eardrum position, and the load impedance Zd presented by the eardrum. The formula, which contains no assignable constants, has been used to calculate the diffuse field response curve for a physical model of the external ear combined with an eardrum impedance simulator. An impedance tube was used to measure Zrad and Zd. The magnitude of the response and the frequencies of the resonance peaks are in excellent agreement with other measurements. The diffuse field pressure gain at the primary resonance frequency (2.7 kHz) is approximately 18 dB.

Eardrum impedance and ear canal geometry

A consistent description of the human external ear must take into account a diversity of data concerning (a) the transformation of sound-pressure level from the free field to the eardrum, (b) the transfer functions from the ear-canal entrance and insert positions to the eardrum, (c) the pressure distributions in the ear canal and concha, (d) eardrum impedance, (e) insert earphone response. (f) ear-canal length and volume (directly measured), and (g) sex differences. A cylindrical canal 23 mm in length and 7.5 mm in diameter satisfies most of the data fairly well but places the primary resonance frequency of the complete external ear at a frequency 5%–7% higher than the observed value. The discrepancy is probably associated with the connection between the canal and the concha.