Efficiency Of Sound Production Research Articles

Effect of the characteristic time on the system performance of a three-stage looped traveling-wave thermoacoustic engine

A three-stage looped traveling-wave thermoacoustic system with high efficiency thermoacoustic conversion and acoustic power transmission potential is studied through computational fluid dynamics simulation. ωτ, an important dimensionless parameter representing the heat exchange efficiency of the system, is related to the efficiency of sound production and depends on the frequency, hydraulic radius and temperature of the regenerator. The influence of resonance tube radius on the system performance is analyzed, while the acoustic impedance and exergy loss of main components are given. The proposed unequal-radius resonance tubes help with the realization of acoustic power amplification and impedance matching. After parameter evaluation, the proportion of traveling wave in the whole system increases, and the impedance amplitude of some resonance tubes also becomes higher. The mechanism and effect of ωτ on the system performance are expounded. The simulation results show that when the ωτ is 5.7, acoustic power of 8.9 kW and relative Carnot efficiency of 53.1% are obtained, which are higher than the performance of the baseline model.

Prevalence of Benign Vocal Fold Lesions in Ear, Nose, and Throat Outpatient Unit of Dr. Soetomo General Hospital, Surabaya, Indonesia

Introduction: Benign vocal fold lesions reduce the efficiency of sound production. Reports of dysphonia cases caused by vocal principles in Indonesia are still very limited. This study aimed to determine incidence and prevalence of benign vocal fold lesions, namely vocal cord nodules, cysts, and polyps.Methods: A descriptive retrospective study was conducted using patient’s medical record of Ear, Nose, and Throat (ENT) Outpatient Unit. Dysphonia patients with benign vocal cord abnormalities were identified. The data analyzed using descriptive analytic.Results: There were 20 patients with benign vocal fold lesions, consisting of 13 patients (65%) with nodules, 3 patients (15%) with polyps, and 4 patients (20%) with cysts. The ratio of male and female patients was 1: 1. Most patients belonged to age group of 20-59 years (12 patients; 60%). In term of occupation, most patients belonged to group III, which is a group of workers who are not professional voice users (12 patients; 60%). Most vocal fold lesions were found in the 1/3 of bilateral anterior (17 patients; 85%). Most therapy was non-operative in 13 patients (65%). Conclusion: Benign vocal fold lesions, including vocal cord nodules, polyps, and cysts, are found in all patients with dysphonic complaints. The prevalence of dysphonia symptoms is quite high every year, but only a small portion are diagnosed with benign vocal cord lesion.

Investigation of sound generated by a DC biased rectangular AC current arc in ambient air

In order to investigate the characteristics of arc sound and observe the physical process for the generation of arc sound, the effect of arc parameters including the arc current, arc frequency, and arc length on the arc sound was experimentally investigated. It was found that the power efficiency of sound production varied with the arc length and was relatively low for a short arc. Based on this phenomenon, it was found in the experiment and confirmed in the numerical simulation with a modified physical model that the sound pressure was proportional to dH/dt rather than dP/dt, where H and P are the change rates of internal energy and electric energy of the arc, respectively. In the experiment, the time-resolved arc channel and arc temperature were measured. By correlating the waveform of the arc sound with the time-resolved arc channel and arc temperature, as well as the waveform of arc current and arc power, the physical process for the generation of arc sound is clearly shown.

Tree cricket baffles are manufactured tools

AbstractTree crickets use sound to attract mates and make acoustic baffles to increase their sound production efficiency. It has been recently discovered that these insects use a flexible yet inherited behavioural programme to make acoustically optimal baffles. Whether these baffles qualify as tools, however, remains controversial. Here, baffle‐using and baffle‐making behaviours are analysed using the most current and authoritative definition of tool use. The current definition of tool use does not require the tool to be detached from the substrate and includes attached but manipulable external objects. Given this schema, tree cricket baffles, which are attached but manipulated prior to use, must be considered tools. The mode of manufacture for a baffle is “Subtract,” and the mode of use is “Drape”.

Ultrathin thermoacoustic nanobridge loudspeakers from ALD on polyimide

The recent development of low-temperature (<200 °C) atomic layer deposition (ALD) for fabrication of freestanding nanostructures has enabled consideration of active device design based on engineered ultrathin films. This paper explores audible sound production from thermoacoustic loudspeakers fabricated from suspended tungsten nanobridges formed by ALD. Additionally, this paper develops an approach to lumped-element modeling for design of thermoacoustic nanodevices and relates the near-field plane wave model of individual transducer beams to the far-field spherical wave sound pressure that can be measured with standard experimental techniques. Arrays of suspended nanobridges with 25.8 nm thickness and sizes as small as 17 μm × 2 μm have been fabricated and demonstrated to produce audible sound using the thermoacoustic effect. The nanobridges were fabricated by ALD of 6.5 nm Al2O3 and 19.3 nm tungsten on sacrificial polyimide, with ALD performed at 130 °C and patterned by standard photolithography. The maximum observed loudspeaker sound pressure level (SPL) is 104 dB, measured at 20 kHz, 9.71 W input power, and 1 cm measurement distance, providing a loudspeaker sensitivity value of ∼64.6 dB SPL/1 mW. Sound production efficiency was measured to vary proportional to frequency f 3 and was directly proportional to input power. The devices in this paper demonstrate industrially feasible nanofabrication of thermoacoustic transducers and a sound production mechanism pertinent to submicron-scale device engineering.

Negligible energetic cost of sonar jamming in a bat–moth interaction

Energetic cost can constrain how frequently animals exhibit behaviors. The energetic cost of acoustic signaling for communication has been the subject of numerous studies; however, the cost of acoustic signaling for predator defense has not been addressed. We studied the energetic cost and efficiency of sound production for the clicks produced by the moth Bertholdia trigona (Grote, 1879) (Grote’s bertholdia) to jam the sonar of predatory bats. This moth is an excellent model species because of its extraordinary ability to produce sound—it clicks at the highest known rate of any moth, up to 4500 clicks·s–1. We measured the metabolic cost of clicking, resting, and flying from moths suspended in a respirometry chamber. Clicking was provoked by playing back an echolocation attack sequence. The cost of sound production for B. trigona was low (66% of resting metabolic rate) and the acoustic efficiency, or the percentage of metabolic power that is converted into sound, was moderately high (0.30% ± 0.15%) compared with other species. We discuss mechanisms that allow B. trigona to achieve their extraordinary clicking rates and high acoustic efficiency. Clicking for jamming bat sonar incurs negligible energetic cost to moths despite being the most effective known anti-bat defense. These results have implications for both the ecology of predator–prey interactions and the evolution of jamming signals.

Low frequency sound produced by a ventilated supercavitating vehicle

An analytical investigation is made of the low frequency noise produced by gas jet impingement on the gas–water interface of a ventilated supercavity. Enclosure within a supercavity enables an underwater vehicle to attain high-speed forward motion. Whereas high frequency components of the cavity self-noise can interfere with the vehicle guidance system, low frequency sound tends to radiate in the water to large distances from the cavity. A canonical mathematical problem is examined that extends a previous study by Foley et al. ( Journal of Sound and Vibration329 (2010) 415–424.) of sound generation by a specially modified, model scale supercavitating vehicle involving gas jet impingement at normal incidence to the interface. Our analysis determines the influence on low frequency sound production of cavity aspect ratio and the manner in which the efficiency of sound production increases with decreasing distance of the jet impact region from the circular ‘cavitator’ at the vehicle nose, where the supercavity is formed.

Characteristics of phonation onset in a two-layer vocal fold model

Characteristics of phonation onset were investigated in a two-layer body-cover continuum model of the vocal folds as a function of the biomechanical and geometric properties of the vocal folds. The analysis showed that an increase in either the body or cover stiffness generally increased the phonation threshold pressure and phonation onset frequency, although the effectiveness of varying body or cover stiffness as a pitch control mechanism varied depending on the body-cover stiffness ratio. Increasing body-cover stiffness ratio reduced the vibration amplitude of the body layer, and the vocal fold motion was gradually restricted to the medial surface, resulting in more effective flow modulation and higher sound production efficiency. The fluid-structure interaction induced synchronization of more than one group of eigenmodes so that two or more eigenmodes may be simultaneously destabilized toward phonation onset. At certain conditions, a slight change in vocal fold stiffness or geometry may cause phonation onset to occur as eigenmode synchronization due to a different pair of eigenmodes, leading to sudden changes in phonation onset frequency, vocal fold vibration pattern, and sound production efficiency. Although observed in a linear stability analysis, a similar mechanism may also play a role in register changes at finite-amplitude oscillations.

In vitro evaluation of a double‐membrane–based voice‐producing element for laryngectomized patients

A sound generator based on a double-membrane design that fits into a regular tracheoesophageal shunt valve may improve voice quality after total laryngectomy in patients rehabilitated with surgical voice prostheses. Voice-producing element (VPE) prototypes were manufactured using medical grade biocompatible materials and tested in vitro under physiological conditions. Basic sound, containing multiple harmonics, was successfully produced under physiologic air pressure and airflow conditions. The fundamental frequency and sound pressure level (SPL) is controlled by changing the driving pressure, thus enabling sufficient intonation for day-to-day speech. The obtained frequency range (190-350 Hz) is appropriate for producing a female voice. The low noise-to-harmonics ratio (mean 0.15) and also the efficiency of sound production (5.5 x 10(-5) at 80 dB(A) and 0.15 m microphone distance) is comparable to that of normal vocal folds. Functional restoration of the voice after laryngectomy with a double-membrane VPE appears to be a feasible concept for female laryngectomized patients with a hypotonic, or atonic pharyngoesophageal segment.

Measuring the Efficiency of Sound Production

Sound production efficiency is a complex phenotypic trait that incorporates biochemical and mechanical events beginning with substrate oxidation and ending with the radiation of sound. Its accurate measurement is significant in understanding the mechanisms and energetics underlying acoustic signaling and sexual selection. I show that in the short-tailed cricket Anurogryllus arboreus Walker, acoustic performance is apparently the same in acoustic free fields and in the reverberant conditions of a respirometry chamber. I present three methods for simultaneous and nearly simultaneous determination of calling metabolic rate and acoustic power output. The new methods yielded metabolic rates 3%-6% lower than matched controls using traditional flow-through respirometry (mean=8.1 mW); however, none of theses differences were statistically significant. I also evaluate four methods for determining the efficiency of sound production. The means of an individual's efficiencies calculated using these methods vary between 0.50% and 0.60%, with no statistically significant differences between the methods. I conclude with a critical evaluation of these techniques.

Simultaneous measurement of metabolic and acoustic power and the efficiency of sound production in two mole cricket species (Orthoptera:Gryllotalpidae)

We here report the first simultaneous measurement of metabolic cost of calling, acoustic power and efficiency of sound production in animals--the mole crickets Scapteriscus borellii and S. vicinus (Gryllotalpidae). We measured O(2) consumption, CO(2) production and acoustic power as the crickets called from their burrows in an open room. We utilized their calling burrow as the functional equivalent of a mask. Both species had a respiratory quotient near 0.85, indicative of metabolism based on a mix of carbohydrates and fats. The metabolic rate was significantly higher in S. borellii (11.6 mW g(-1)) than in S. vicinus (9.0 mW g(-1)) and averaged about eight- to fivefold greater, respectively, than resting metabolism. In some individuals, metabolic rate decreased by 20% during calling bouts. Costs of refurbishing calling burrows in S. borellii were less than calling costs, due to the behavior's short duration (ca. 15 min) and its relatively low average metabolic rate (4 mW). Acoustic power was on average sevenfold greater in S. borellii (21.2 vs 2.9 microW) and was more variable within individuals and across species than the metabolic rate. The efficiency of sound production was significantly higher in S. borellii (0.23 vs 0.03%). These values are below published estimates for other insects even though these mole crickets construct acoustic burrows that have the potential to increase efficiency. The cricket/burrow system in both species have an apparent Q(ln decrement) of about 6, indicative of significant internal damping caused by the airspaces in the sand that forms the burrow's walls. Damping is therefore an important cause of the low sound production efficiency. In field conditions where burrow walls are saturated with water and there is less internal damping, calls are louder and sound production efficiency is likely higher. File tooth depths and file tooth-to-tooth distances correlated with interspecific differences in metabolism and acoustic power much better than with wing stroke rates and plectrum-to-file tooth strike rates. To further investigate these correlations, we constructed two models of energy input to the tegminal oscillator. A model based on transfer of kinetic energy based on differences in tegminal velocity and file tooth spacing showed the most promise. Related calculations suggest that if there are no elastic savings, the power costs to accelerate and decelerate the tegmina are greater than the predicted power input to the tegminal oscillator, and that they are similar in the two species even though S. vicinus has a nearly threefold higher wing stroke rate.

Modelling self- and shear-noise mechanisms in inhomogeneous, anisotropic turbulence

A statistical jet noise model which includes the effects of mixing layer inhomogeneity and anisotropy is presented. The model adapts the spatial and temporal correlation function models frequently used in jet noise prediction, so that the axial, radial and lateral integral space and time scales are included to model flow anisotropy, the spatial structure of the Reynolds stress field being used to account for flow inhomogeneity. These flow properties have been estimated from single and multi-point LDV measurements performed in the mixing layer of an isothermal jet with a Mach number of 0.75. The model is used to assess acoustic contributions from the constituent self- and shear-noise quadrupoles. Results highlight the very different nature of the self- and shear-noise source mechanisms and identify those aspects of the flow structure on which their sound production efficiency depends. The dependence of the shear noise on the radial distance over which the turbulence is correlated illustrates how an isotropic model will overestimate this term. The model demonstrates how sound generation is largely dominated by axially aligned longitudinal quadrupoles and shows the self-noise mechanisms to dominate the shear by a factor of about 2.5 when the flow is anisotropic. A moving-axis temporal correlation model is used to derive expressions for the acoustic spectra of the component quadrupoles, the inclusion of whose time scales allows the temporal manifestation of the flow anisotropy to be modelled. Model predictions are compared with acoustic measurements performed on the same jet and good agreement is found for emission angles between 30° and 100°.

Wall-Cavity Acoustic Green's Function at Low Mach Number

Analytical approximations are developed for the low Mach number, aeroacoustic Green's function for a rectangular or circular cylindrical open cavity in a plane, rigid wall. The formulae can be used to predict the sound radiated into the main flow from a knowledge of the hydrodynamic flow near the cavity. At low Mach numbers the sound is a small by-product of the main flow, whose hydrodynamic properties can first be determined from observation or from a numerical treatment of the incompressible Navier-Stokes equations. Detailed predictions are made of the lowest order, open cavity resonance frequencies, and it is shown how a resonance is excited by the unsteady drag, and also by the lift or drag force experienced by a small bluff body placed in the flow close to the cavity. The cavity resonance frequencies are complex, with imaginary parts depending primarily on radiation damping, which can be sufficiently large for a shallow, open cavity, that a distinct resonance peak is absent from the acoustic spectrum – for a square cavity such peaks are predicted only when the cavity depth exceeds about half the cavity length. For very shallow cavities the efficiency of sound production by volumetric pulsations within the cavity is comparable to that of free field turbulence quadrupoles, and therefore negligible at low Mach numbers.

Physical Factors Affecting the Cost and Efficiency of Sound Production in the Treefrog Hyla Versicolor

The metabolic cost, energy output and efficiency (i.e. the ratio of energy output to metabolic cost) of sound production were compared among male grey treefrogs (Hyla versicolor) as a function of body size and temperature. The effects of call length (in notes per call) and dominant frequency (in kHz) were also considered. Cost, determined from the amount of oxygen consumed, averaged 12.1 mJ per note and was dependent only upon body mass. Acoustic energy per note, determined from oscillograms of recorded calls, averaged 0.34 mJ and was dependent only upon temperature. Conventional theory suggests that the efficiency of sound production should be a function of the ratio of the linear size of the radiating structures to the wavelength of the sound generated (i.e. efficiency is assumed to be a function of the product of mass(0.33) and frequency), but efficiency in H. versicolor was found to be a function of the product of temperature(2.1) and mass(-1.08). Adjusting for temperature and body mass, the efficiency of sound production in H. versicolor (average 2.4 %) is greater than the efficiency of other frog species for which data are available. Temperature may affect acoustic energy output because trunk muscle contraction speed increases with temperature, which increases the velocity of airflow across the vocal cords.

ON THE HYDROACOUSTICS OF A TRAILING EDGE WITH A DETACHED FLAP

An analysis is made of production of sound by low Mach number turbulent flow over the trailing edge of a hydrofoil with a single detached flap. Following the approach advocated by Professor Doak in 1960 (Proceedings of the Royal Society A 254, 129–145), an aeroacoustic Green function is derived for a hydrofoil of large chord with a detached flap at relative angle of attack α (α2⪡1) when the chord of the flap is acoustically compact. The Green function can be used with data derived from direct numerical simulations of the unsteady hydrodynamic flow, and provides an effective means of calculating the radiation from a knowledge of the incompressible component of the flow in the edge region. The results permit a comparison to be made of the separate contributions to the production of sound by turbulence interacting with the trailing edge of the hydrofoil, the trailing edge of the flap, and with the leading edge of the flap. The side-edge noise of part-span flaps is not discussed. Formulae are given for calculating the “self-noise” produced at trailing edges by boundary layer instability; the efficiency of sound generation at the edge of the hydrofoil is shown to be typically at least 7 dB larger than that produced at the trailing edge of the flap. The impingement noise generated by small-scale turbulence interacting with the flap leading edge is expressed in terms of an equivalent dipole source equal to the fluctuating flap-lift force, acting at a distance lFto the rear of the main hydrofoil;lFis determined as a function of the flap dimensions, and does not normally exceed about twice the width h of the slot separating the hydrofoil and flap. The proximity of the dipole to the edge of the hydrofoil increases the efficiency of sound production by a factor proportional to h/(lFM) where M⪡1 is the characteristic edge flow Mach number, and modifies the directivity of the sound.

Sound generated by fluid-structure interactions

A tutorial summary is given of the theory of aerodynamic sound with special reference to the generation of sound by flow interacting with rigid and elastic structures. Lighthill's acoustic analogy and the theory of vortex sound are discussed. Several applications of the theory are described that exemplify the considerable progress that has been made in the analytical treatment of flow generated sound at low Mach numbers, including the use of the compact acoustic Green's function to estimate fluid-structure interaction noise when one or more pertinent source dimensions are small compared to the acoustic wavelength. The need to take proper account of additional sources formed by vortex shedding during an interaction is emphasized, and illustrated by the example of blade-vortex interaction noise. The modification caused by surface compliance of the efficiency of sound production by an adjacent flow is discussed by reference to simple analytical models involving vortex flow near the edge of an elastic plate, and over a surface inhomogeneity on a large plate.

The Energetics of Acoustic Signaling in Anurans and Insects

SYNOPSIS. This review focuses on the energetics of advertisement calls in frogs and insects (mostly ensiferans). I also review a number of methodological questions relating to the most appropriate ways to normalize metabolic rates for calling animals and to calculate efficiency of sound production Although the mechanism of sound production is very different in these groups (vocalization vs. stridulation), net metabolic costs normalized to mass are similar among species producing the most conspicuous calls. Features of the call that interact to determine energetic cost include repetition rate, call duration, and intensity (sound pressure level). Anurans tend to produce louder (more intense) calls while ensiferans tend to produce sound during a greater proportion of the calling bout. All evidence suggests that advertisement calls are produced aerobically and the aerobic costs are similar or exceed the aerobic (but not necessarily total costs) of terrestrial locomotion The pattern of radiated sound tends to be constant within a species and can be predicted to some degree from characteristics of an animal's acoustic radiator. Efficiency of sound production (acoustic power/net metabolic power) is low (0.05 to 6%) and variable when compared to locomotion (˜ 10–20%). From the present sample it appears that frogs are more efficient than ensiferans, but as more katydids are studied this trend may not hold. Of the factors that have been identified as determining efficiency the most important are the match between the size of the radiator and wavelength radiated, the absorption properties of the environment immediately around the animal, and the presence or absence of structures such as baffles and acoustic burrows

Power output and efficiency of sound production by crickets

Male crickets produce calling songs that function to attract mates. Sound is produced when membranes of the wings are caused to vibrate during stridulation. Sound fields were measured for three species of crickets. Two species of mole crickets, Scapteriscus acletus and s. vicinus, call from within burrows constructed in the soil. Sound fields of the mole crickets were hemispherical and the power output averaged 4 μW (N = 22, range 2–22 μW). Power output was dependent upon male size and moisture content of soil surrounding the burrow. Efficiency of sound production was estimated to be less than 0.2%. Sound fields of a species of tree crickets, Oecanthus quadripunctatus, approximated that of a doublet source. Power output ranged from 2–17 μW (N = 6) and efficiency was estimated at about 1%.

Energy and Communication in Three Species of Hylid Frogs: Power Input, Power Output and Efficiency

ABSTRACT Rates of oxygen consumption for calling, rest and locomotion were measured for three species of treefrogs from the south-east United States: Hyla cinerea (Schneider), H. gratiosa LeConte and H. squirella Bosc. Anaerobic metabolism was slight during calling but large during forced hopping in H. squirella. It is assumed that calling in all three species is primarily aerobic. For all species, oxygen consumption during calling rivalled or exceeded that for locomotion in a closed chamber. Calling apparently is at least as costly as closed-chamber locomotion, if anaerobic contributions to hopping are ignored. The mass-specific costs of producing calls are similar in most species of hylids whose calling energetics have been studied. As in other species of hylids, abdominal trunk muscle masses in male H. squirella and H. gratiosa were large - approximately 10% of the total body mass. Complete sound fields (with measures of variation) were mapped for each species. Each species is an essentially omnidirectional radiator with only a slight flattening of the field behind the head. Efficiencies of sound production (acoustic power/metabolic power) were calculated for each species and compared with values from other frogs, insects and loudspeakers. Efficiencies in hylids vary between 0-8 and 4-9%. Factors that contribute to determining the efficiency of sound production are reviewed. Small animals such as frogs and insects must either use low-efficiency radiators or use high-frequency sounds that do not propagate over great distances. It is possible that low-efficiency transducers maximize the area over which an animal is heard per unit of energy expended.

Power output and efficiency of sound production by crickets

Male crickets produce calling songs that function to attract mates. Sound is produced when membranes of the wings are caused to vibrate during stridulation. Sound fields were measured for three species of crickets. Two species of mole crickets, Scapteriscus acletus and s. vicinus, call from within burrows constructed in the soil. Sound fields of the mole crickets were hemispherical and the power output averaged 4 μW (N = 22, range 2–22 μW). Power output was dependent upon male size and moisture content of soil surrounding the burrow. Efficiency of sound production was estimated to be less than 0.2%. Sound fields of a species of tree crickets, Oecanthus quadripunctatus, approximated that of a doublet source. Power output ranged from 2–17 μW (N = 6) and efficiency was estimated at about 1%.