Microphone Research Articles

Pressure from the lips on the teeth during speech.

Pressure on the teeth from the labial soft tissues during the articulation of a given sentence was measured in 24 children, 8 to 14 years old, with normal incisor relationships. The points of measurement were labial in the midlines between the maxillary and mandibular central incisors and between the right maxillary canine and first premolar (the modiolus point). A mouthpiece was attached to the teeth at these three positions and connected via a water-filled system to an extraoral pressure transducer. A microphone recorded the volume and speed of articulation while the activity of the lip muscles was surveyed by electromyography. The maximal pressure during pronunciation of the consonant /p/, the pressure at rest (RP), the speech posture pressure (SPP), the time pressure integral (TPI), and the mean speech pressure (MSP) during articulation were analyzed. Maximal pressure during pronunciation of /p/ and TPI were highest at the modiolus, second highest at the lower midline, and lowest at the upper midline. RP and SPP were highest at the lower midline. SPP was 2 to 3 times higher than RP, and MSP was 4 to 7 times higher than RP. The pressures during articulation recorded at the lower midline were closely correlated with those at the modiolus, with weaker correlations between the upper and lower midlines and between the upper midline and modiolus. There was a close correlation between RP and SPP. SPP, MSP, and TPI may, along with RP, contribute to the positions of the teeth.

A hybrid passive/active system for control of the noise radiated by a small generator

The aim of this work was the design and implementation of a hybrid passive/active system to control the noise radiated by a small generator. The fundamental frequency of the periodic radiated noise depends on the electrical load plugged into the generator. Passive control is afforded by a rectangular enclosure with dimensions 1000×710×530 mm3. The wall panels of the enclosure (steel 1.5 mm thick) are lined with a 30-mm layer of sound absorbing material. Special attention is paid to technical aspects such as air refreshing and temperature inside the enclosure. The measured insertion loss is higher than 20 dB above 500 Hz. Low-frequency noise escapes the enclosure via intake and exhaust openings. Active control is applied to the exhaust noise. The reference signal is supplied by an accelerometer over the air filter case of the generator. A high-temperature loudspeaker is used as control source. The error signal is picked up by a cheap electric microphone. Since noise along the exhaust is too loud, the microphone sensitivity had to be reduced by taping its diaphragm. A commercial system is used to implement active noise control. [Work supported by CICYT, Project AMB97-1175-C03-01.]

Using unannounced standardized patients to assess the HIV preventive practices of family nurse practitioners and family physicians.

Measuring health risk assessment and counseling recommendations can be challenging. In this study, unannounced standardized patients (lay individuals trained to replicate a clinical encounter consistently) were used to evaluate HIV preventive performance of 22 family nurse practitioners (NPs) and family physicians. Standardized patients were trained to present an identical scenario of a heterosexual individual at risk for HIV exposure. Audiotaping via a hidden microphone and recorder was used to validate the reproducibility of clinical encounters and accuracy of standardized patient assessment. Standardized patients were highly accurate in both case portrayal and assessment activities with an indexed Kappa coefficient of 0.82. Determining risk, including condom use, sexual orientation, and number of past sexual partners, was performed less often than experts advise by both physicians and NPs (done between 9% and 63% of encounters). Providing patient education to reduce risk, including educating about abstinence, mutual monogamy, and limiting sexual partners, was also done in only 9% to 36% of encounters. The methodology used was innovative. There is room for improvement in the provider participants' clinical performance of HIV risk assessment, patient education, and counseling. However, the results of this case study cannot be generalized.

A measurement of flow noise spectrum of an axisymmetric body

The pressure fluctuation on the surface of a submerged body has been recognized as a dominant noise source. There have been many studies concerning the flow induced noise on a flat plate. However, the noise over an axisymmetric body has not been well reported. This paper addresses the way in which we have investigated the mechanism of noise generation due to an axisymmetric body. The associated experiments and signal processing methods are introduced. A 3-dimensional axisymmetric body whose length and diameter were 2 m and 10.4 cm, was prepared as a test specimen. The wall pressure on the surface of the body was measured in a large scale low noise wind tunnel at KIMM(Korea Institute of Machinery and Metals). To measure the wall pressure, we used two microphone arrays which were tangential and normal to the flow. Based on the measured signal, frequency-wavenumber spectrum which explains the structure of turbulence noise, was estimated. Tangential to the flow, there exists convective ridge at a relatively higher wavenumber region; this can cause spatial aliasing. To circumvent this problem, the cross spectrum was interpolated. The interpolation has been performed by unwrapping the phase and smoothing the cross spectrum. The phase unwrapping was done based on the Corcos model; the phase of cross spectrum decreases linearly with the distance between microphones. Aforementioned signal processings are possible by employing the experimental results that the estimated wavenumber spectrum quite resembles the Corcos model. We try to modify the Corcos model which is applicable to the flat plate, by altering the magnitude of cross spectrum to fit the experimental data more accurately. We proposed that this wavenumber spectrum model is suitable for the 3-dimensional axisymmetric body. Normal to the flow, there exists a little correlation between signals of different microphones. The circumferential wavenumber spectrum contains uniform power along the wavenumbers.

Active noise control with the active muffler in automotive exhaust system

This study experimentally demonstrates the use of active muffler attached to the automotive exhaust system to reduce exhaust noise. For improving the signal to noise ratio in the process of estimation of secondary path transfer functions, the on-line algorithm that conventional inverse modeling is combined with adaptive line enhancer is used as the control algorithm. Active muffler is designed that the primary noise and the control sound are propagated as a plane wave in the outlet. Therefore, the error microphone could be placed out of the tail pipe center of a high temperature and the radiation noise to the outside could be reduced in the whole area around the outlet. The control experiment for reducing exhaust noise with active muffler is implemented during run-up at no load. From the experimental results presented, compared with the conventional off-line method, the proposed on-line method is capable to acquire a reduction of exhaust noise above 5 dB in overall sound power level.

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Photoacoustic detection of trace gases with an optical microphone

An alternative to the electrical microphone for photoacoustic detection of trace gases is presented. This new microphone is made of standard monomode optical fibers wound and glued on a thin plate and is one of the arms of a Michelson interferometer. A detection scheme with a Sagnac interferometer has also been used and has given better results. Three cells working with different resonance modes and different microphone configurations have been tested.

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A phase-modulating microphone utilizing integrated optics and micromachining in silicon

Abstract A proposed new integrated optical microphone, in which micromachining and integrated optics in silicon are combined, is described. It is an interferometric sensor with a hollow parallel-plate waveguide as the phase modulator. One of the walls of this hollow waveguide is the gold-coated silicon nitride diaphragm. If the membrane is displaced by sound pressure, the phase of a light wave propagating in the waveguide is modulated. All-silicon waveguides are used for good coupling of light between glass fibers and the modulator. The fabrication process will be very short and compatible to standard semiconductor technology. An equivalent noise level of 45 dB assuming a bandwidth of 10 kHz can be estimated for the microphone, which has not yet been realized. The sensor has dimensions of 10 mm×3 mm×0.56 mm with a 1 mm×1 mm membrane area.

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Auditory brainstem responses in the normal beagle.

The latencies of the peaks in brainstem responses and the threshold response were determined in 18 healthy beagles. In the first series of measurements the dogs were sedated and the stimulus was delivered via an in-the-ear transducer. The latencies, the threshold levels, and the influence of the stimulus repetition rate on the latencies were measured. Using a miniature electric microphone in the outer ear canal near the tympanic membrane, it was found that at a level setting corresponding to 0 dB human level (HL) the major peak in damped oscillation during condensation reached a sound pressure level (SPL) of about 27 dB and the secondary rarefaction peak reached 24 dB SPL. In the second series of measurements the dogs were not sedated and the stimulus was delivered via a headphone. The wave forms, the mean latencies for peaks I to V as a function of the stimulus level, and the threshold of each wave are presented from both series. In the first series the latency values at 80 dB HL (107 dB SPL) were 1.21, 1.97, 2.67, 3.12 and 3.61 ms for peaks I, II, III, IV and V, respectively. The thresholds for peaks I to V were 47.5 +/- 9.5, 47.5 +/- 11.5, 41.3 +/- 13.0, 63.3 +/- 17.4 and 28.0 +/- 9.7 dB HL, respectively. The difference in peak latency between the first and the second series was 0.065 ms. This difference corresponded to the difference in length of the acoustic pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Nocturnal cough in patients with chronic bronchitis and emphysema.

Patients with respiratory disease commonly report that their sleep is disrupted by nocturnal cough. We have recorded cough during the night in 10 patients with severe chronic bronchitis and emphysema (forced expiratory volume in one second, 1.0 +/- SEM 0.1/L) who complained of nocturnal cough and correlated cough with electroencephalographic sleep stage and arterial oxygenation. Cough was recorded using a directional microphone and an auto-editing tape recorder system. Each cough was subsequently verified by a listener. There was a mean of 14.6 +/- 4.5 bouts of coughing per patient per night, each bout lasting on average 3.9 +/- 0.2 s. Eighty-five percent of coughing bouts occurred during electroencephalographically confirmed wakefulness (p less than 0.02 versus sleep), and coughs during true sleep were rare, with only 1 patient coughing during rapid eye movement sleep and none during Stages 3 and 4 sleep. Cough was only once followed by arousal. There was no correlation between cough and either apneas or hypoxemia during sleep. We conclude that spontaneous cough is suppressed during sleep and only rarely awakens patients.

Development of an implantable hearing aid using a piezoelectric vibrator of bimorph design: state of the art.

A new, implantable hearing aid has been developed. An ultraminiature electric microphone placed under the skin of the external ear canal transduces sound waves into electrical impulses that are amplified with battery power. The amplified electrical impulses are fed into a piezoelectric vibrator directly in contact with the stapes. The vibrator transduces the electrical impulses into mechanical vibration with minimal consumption of electrical energy. Direct coupling of the vibrator to the stapes allows a high degree of fidelity in the perception of sound. The developmental process and the structure and function of each component are described together with clinical problems. Preliminary and tentative implantation of this new device during middle ear surgery indicated that it would be beneficial to patients who have suffered hearing loss from middle ear disease and whose condition does not lend itself to surgical correction.

Mechanism of production of crackles after atelectasis during low-volume breathing.

We compared the effects of shallow breathing of air (LVB-air) and oxygen (LVB-O2) at low lung volumes (below closing capacity) and tidal breathing at FRC (FRC-air, FRC-O2) on the production of crackles in 5 normal volunteers. Two microphones were attached on the right posterior chest wall in the midclavicular line 10 and 20 cm from the apex of the right lung, respectively (M10 and M20), to record crackles during various breathing maneuvers. We found that after LVB-air and LVB-O2, there were changes in residual volume as measured by the body plethysmograph. Both inspiratory and expiratory limbs of the quasi-static pressure volume curve were shifted to the right. Occasionally, some subjects coughed after LVB-air and/or LVB-O2. Inspiratory crackles occurred mostly at the upper third of vital capacity (VC) after LVB-air and LVB-O2 and were confined almost exclusively to the dependent lung zones (M20). The inspiratory transpulmonary pressure at 25% (PL25) and 50% (PL50) of VC correlated with the volume of trapped gas that was absorbed (delta Vtg) (p less than 0.001 and p less than 0.001, respectively). The quantity of crackles correlated with delta Vtg (p less than 0.01). We conclude that during low lung volume breathing airways in the dependent lung regions are closed. There is absorption of trapped oxygen which causes reversible atelectasis. Upon reinflation, inspired air will go to the lung regions with open airways first and subsequently to the closed dependent regions, producing crackles recorded by the M20 microphone at the upper third of VC. The crackles are produced by inflation of atelectatic lung.

Mesures de diffusivités thermiques par la méthode photoacoustique et par l'effet mirage

Deux experiences originales de determination de diffusivites thermiques sans l'intermediaire de thermocouples sont proposees. Dans ces deux experiences, l'echantillon etudie est excite par absorption de rayonnement en regime sinusoidal : dans l'une, la grandeur mesuree est un son detecte par un microphone, dans l'autre on utilise la deviation du faisceau laser passant au voisinage de l'echantillon parallelement a sa surface.

Determination of the site of production of respiratory sounds by subtraction phonopneumography.

The site of origin of the vesicular lung sound has long been in question. A technique (subtraction phonopneumography) is described here for determining the relative distance of a sound source from the chest wall. This technique involves the simultaneous recording of lung sounds from two different sites on the chest wall, phase inversion of one of the signals, and then mixing the signals in a summing amplifier. The degree of cancellation that results is inversely proportional to the number of sources and the degree to which each source is detected by both microphones simultaneously. A study of six normal subjects revealed little or no cancellation of inspiratory vesicular sounds with microphones separated by 10 cm. During expiration, cancellation did occur at distances well beyond 10 cm and was detectable over several homologous segments of opposite lungs. This finding is consistent with an intrapulmonic and probably intralobar source for the inspiratory component and an upper airway source for at least some of the expiratory component.

International standard for microphones is issued by the IEC

International standard for microphones is issued by the IEC

Breath sounds and distribution of pulmonary ventilation.

A phonocardiograph and microphone were used to record normal breath sounds in different lung zones at controlled lung volumes and flows and body positions. Breath sound intensity varied with lung volume, flow, body position, and the site of recording on the chest wall. At a given inspiratory flow, in various body positions, the maximal relative intensity of breath sounds was always recorded at low lung volumes over superior regions, but the maximum occurred over inferior regions of the lung at larger lung volumes. The results correlated well with the differences in regional distribution of ventilation found with radioactive gases.