An effective silencer design for artificially air conditioned environment

An effective silencer for an air conditioning duct is studied. A duct with an acoustically soft boundary is employed as an effective silencer. On the acoustically soft boundary the sound pressure is zero and it is impossible to realize such boundary in the air-borne sound field, because of the non-existence of a much lighter medium than the air. In this study, the arrangement of one-quarter wave-length acoustic tubes is employed as a soft boundary. This acoustic tube has frequency dependence, but the sound pressure becomes nearly zero at the tube mouth around the odd resonance frequency. The relation between the noise reduction efficiency and this acoustically soft boundary is examined experimentally and more than 40 dB noise reduction is obtained in a one-half octave band around the first resonance frequency. It is also made clear that more than one wave length of soft boundary is required to get enough reduction compared with the reduction obtained in the case of quite a long soft boundary.     

Mapping of soil insect infestations sampled by excavation and acoustic methods.

Geostatistical analysis was used to map traditionally and acoustically sampled populations of soil invertebrates at two different times in a hayfield at Grove Hill, AL, and once in an Auburn, AL, hayfield. The distributions of nearly all the soil invertebrates and their sounds were nonrandom in all three mapping studies. The maps constructed by excavation and acoustic sampling methods were compared by correlating the estimated (kriged) soil invertebrate counts with the estimated (kriged) counts of sounds per minute (pulse rate). Acoustic and traditional estimates were positively correlated in the Auburn study. Kriged estimates for green June beetle grub counts overlapped significantly with kriged estimates of sound pulse rate (R2 = 0.47). Overlap with sound pulse rates increased slightly when other soil organisms were counted along with green June beetle grubs: estimates of sound pulse rates were significantly correlated with counts of all white grubs (R2 = 0.50), all white grubs with earthworms (R2 = 0.52), all white grubs with earthworms and earwigs (R2 = 0.59), and total invertebrates (R2 = 0.59). The correlation between acoustic and traditional estimates was not significant at Grove Hill in either year, possibly because of a lack of experience in signal analysis or because the soil invertebrates may not have generated enough sounds to be detected above the background noise levels. These results suggest that acoustic technology is a promising tool for detecting insect pests in soil, but that further study and additional analysis are needed to improve interpretation of acoustic data obtained in the field.     

Mechanical properties of the frog ear: vibration measurements under free- and closed-field acoustic conditions

The acoustically induced motion of the eardrum of the frog was measured by an incoherent optical technique. When free-field sound stimulation was used, the eardrum vibration had a band-pass characteristic with maximum amplitude at 1-2.5 kHz. However, when the sound was presented in a closed-field acoustic coupler the response was low-pass (cut-off frequency about 2.5 kHz). We demonstrate that the motion is the result of the mechanical properties of the eardrum and the sound pressure acting upon it. The net pressure is due to a combination of sound incident directly on the front of the drum and of sound conducted to the rear via internal (resonant) pathways. The frog ear therefore acts as a pressure-gradient receiver at low frequency and a pressure receiver at high frequency. A model is proposed and analysed in terms of its electrical analogue. This model accounts for both our own experimental observations and those of previous studies.     

Acoustical expression of arousal in conflict situations in tree shrews (<Emphasis Type="Italic">Tupaia belangeri)</Emphasis>

Empirical research on human and non-human primates suggests that communication sounds express the intensity of an emotional state of a signaller. In the present study, we have examined communication sounds during induced social interactions of a monogamous mammal, the tree shrew. To signal their unwillingness to mate, female tree shrews show defensive threat displays towards unfamiliar males paralleled by acoustically variable squeaks. We assumed that the distance between interacting partners as well as the behavior of the male towards the female indicates the intensity of perceived social threat and thereby the arousal state of a female. To explore this hypothesis we analyzed dynamic changes in communication sounds uttered during induced social interactions between a female and an unfamiliar male. Detailed videographic and sound analyzes revealed that the arousal state predicted variations in communication sound structure reliably. Both, a decrease of distance and a male approaching the female led to an increase in fundamental frequency and repetition rate of syllables. These findings support comparable results in human and non-human primates and suggest that common coding rules in communication sounds govern acoustic conflict regulation in mammals.     

Muscle sound frequencies of the frog are modulated by skeletal muscle tension.

The purpose of this study was to determine the relationships among muscle sound frequencies, muscle tension, and stiffness. Time-frequency transformations of nonstationary acoustic signals provided measures of resonant frequency during isometric contractions of frog (Rana pipiens) semitendinosus and gastrocnemius muscles. A mathematical expression for muscle transverse resonant frequency, elastic modulus and tension, based on elastic beam theory, was formulated by the Rayleigh method adapted for muscles. For thin muscles, the elastic modulus was found to have negligible influence on transverse muscle resonant frequency. Changes in muscle tension were the major determinants of changes in transverse resonant frequency. Consequently, for thin muscles, the time course of muscle tension, but not elastic modulus, can be monitored acoustically during the early phase of contraction when muscles give rise to sounds. Muscles were found to be anisotropic with a modulus of elasticity, EL, measured via length perturbations near 0.1% muscle length peak-to-peak, that was much larger than the modulus of elasticity, Eb, that resists the lateral bending that causes sound production. The elastic and resonant behavior of a thin muscle is similar to a tensioned fibrous cable with distributed mass.     

Intense ultrasonic clicks from echolocating toothed whales do not elicit anti-predator responses or debilitate the squid Loligo pealeii

Toothed whales use intense ultrasonic clicks to echolocate prey and it has been hypothesized that they also acoustically debilitate their prey with these intense sound pulses to facilitate capture. Cephalopods are an important food source for toothed whales, and there has probably been an evolutionary selection pressure on cephalopods to develop a mechanism for detecting and evading sound-emitting toothed whale predators. Ultrasonic detection has evolved in some insects to avoid echolocating bats, and it can be hypothesized that cephalopods might have evolved similar ultrasound detection as an anti-predation measure. We test this hypothesis in the squid Loligo pealeii in a playback experiment using intense echolocation clicks from two squid-eating toothed whale species. Twelve squid were exposed to clicks at two repetition rates (16 and 125 clicks per second) with received sound pressure levels of 199-226 dB re1 microPa (pp) mimicking the sound exposure from an echolocating toothed whale as it approaches and captures prey. We demonstrate that intense ultrasonic clicks do not elicit any detectable anti-predator behaviour in L. pealeii and that clicks with received levels up to 226 dB re1 microPa (pp) do not acoustically debilitate this cephalopod species.     

Acoustic characteristics and variations in grunt vocalizations in the oyster toadfish <Emphasis Type="Italic">Opsanus tau</Emphasis>

Acoustic communication is critical for reproductive success in the oyster toadfish Opsanus tau. While previous studies have examined the acoustic characteristics, behavioral context, geographical variation, and seasonality of advertisement boatwhistle sound production, there is limited information on the grunt or other non-advertisement vocalizations in this species. This study continuously monitored sound production in toadfish maintained in an outdoor habitat for four months to identify and characterize grunt vocalizations, compare them with boatwhistles, and test for relationships between the incidence of grunt vocalizations, sound characteristics and environmental parameters. Oyster toadfish produced grunts in response to handling, and spontaneous single (70% of all grunts), doublet (10%), and trains of grunts (20%) throughout the May to September study period. Grunt types varied in pulse structure, duration, and frequency components, and were shorter and of lower fundamental frequency than the pulse repetition rate of boatwhistles. Higher water temperatures were correlated with a greater number of grunt emissions, higher fundamental frequencies, and shorter sound durations. The number of grunts per day was also positively correlated with daylength and maximum tidal amplitude differences (previously entrained) associated with full and new moons, thus providing the first demonstration of semilunar vocalization rhythms in the oyster toadfish. These data provide new information on the acoustic repertoire and the environmental factors correlated with sound production in the toadfish, and have important implications for seasonal acoustic communication in this model vocal fish.     

Zoo soundscape: Daily variation of low-to-high-frequency sounds

Most studies assessing the impact of noises on zoo animal welfare did not measure sound frequencies outside of the human-hearing range (infrasounds and ultrasounds). Many nonhuman mammals can hear these frequencies, and because loud and variable soundscapes are potentially detrimental for animal welfare, this overlooked aspect of their acoustic environment could have important consequences. This study evaluated the soundscape of an urban zoo in a large frequency range (17.5–90,510 Hz) by measuring its average sound levels (L_eq) and variability (the difference between highest and lowest peaks). Sound data were collected for 24 hr in 25 locations (e.g., indoor, outdoor, near the amusement park). The soundscape was not considered problematic for animal welfare when looking at the average sound levels in most locations (<77-dB sound pressure level [SPL]), except for a few indoor areas and near the water park. Ultrasounds were rare, had low average sound levels, and were less variable in time. Infrasounds were always present and were the loudest and most variable sound frequencies. The soundscape was louder and more variable during the day and when visitors were present, suggesting that human-related activities were the sources of these augmentations. Indoor environments were generally louder than outdoor environments and touristic features; however, the water park was near 85-dB SPL during the day. On the basis of results, we suggest a series of mitigation actions to minimize noise-related stress in captive animals.     

A description of defensive hiss types in the flat horned hissing cockroach (Aeluropoda insignis)

Acoustic communication can inform studies of behaviour and phylogeny in insect species. Despite there being 4600 described species of cockroach, few studies have focused on their ability to communicate acoustically. Cockroaches have been found to produce sound in a variety of ways. Species within the tribe Gromphadorhini produce sound through modified spiracles, often referred to as hisses. Sound parameters have been described for the species Gromphadorhina portentosa and Elliptorhina chopardi. Aeluropoda insignis, within the same tribe, produces sound and is morphologically similar to these two species, but no research has been published describing its acoustic signals. Our study explores the defensive acoustic signals of this species and indicates that A. insignis is capable of producing three classes of acoustic signals (whistles, whistle–hisses and hisses) associated with defensive behaviour. Sexes differed in the entropy and the frequency of their signals, with males producing signals with lower entropy and at higher frequency than females. Future studies on acoustic communication within Blattodea could give more insight into the complexity of signals and their relationship to behavioural context.     

Measurement and theory of wheezing breath sounds

We measured the time and frequency domain characteristics of breath sounds in seven asthmatic and three nonasthmatic wheezing patients. The power spectra of the wheezes were evaluated for frequency, amplitude, and timing of peaks of power and for the presence of an exponential decay of power with increasing frequency. Such decay is typical of normal vesicular breath sounds. Two patients who had the most severe asthma had no exponential decay pattern in their spectra. Other asthmatic patients had exponential patterns in some of their analyzed sound segments, with a range of slopes of the log power vs. log frequency curves from 5.7 to 17.3 dB/oct (normal range, 9.8-15.7 dB/oct). The nonasthmatic wheezing patients had normal exponential patterns in most of their analyzed sound segments. All patients had sharp peaks of power in many of the spectra of their expiratory and inspiratory lung sounds. The frequency range of the spectral peaks was 80-1,600 Hz, with some presenting constant frequency peaks throughout numerous inspiratory or expiratory sound segments recorded from one or more pickup locations. We compared the spectral shape, mode of appearance, and frequency range of wheezes with specific predictions of five theories of wheeze production: 1) turbulence-induced wall resonator, 2) turbulence-induced Helmholtz resonator, 3) acoustically stimulated vortex sound (whistle), 4) vortex-induced wall resonator, and 5) fluid dynamic flutter. We conclude that the predictions by 4 and 5 match the experimental observations better than the previously suggested mechanisms. Alterations in the exponential pattern are discussed in view of the mechanisms proposed as underlying the generation and transmission of normal lung sounds. The observed changes may reflect modified sound production in the airways or alterations in their attenuation when transmitted to the chest wall through the hyperinflated lung.     

Impedance of the chest wall during sustained respiratory muscle contraction

We measured total chest wall impedance (Zw), "pathway impedances" of the rib cage (Zrcpath), and diaphragm-abdomen (Zd-apath), and impedance of the belly wall including abdominal contents (Zbw+) in five subjects during sustained expiratory (change in average pleural pressure [Ppl] from relaxation = 10 and 20 cmH2O) and inspiratory (change in Ppl = -10 and -20 cmH2O) muscle contraction, using forced oscillatory techniques (0.5-4 Hz) we have previously reported for relaxation (J. Appl. Physiol. 66: 350-359, 1989). Chest wall configuration and mean lung volume were kept constant. Zw, Zrcpath, Zd-apath, and Zbw+ all increased greatly at each frequency during expiratory muscle contraction; increases were proportional to effort. Zw, Zrcpath, and Zd-apath increased greatly during inspiratory muscle contraction, but Zbw+ did not. Resistances and elastances calculated from each of the impedances showed the same changes during muscle contraction as the corresponding impedances. Each of the resistances decreased as frequency increased, independent of effort; elastances generally increased with frequency. These frequency dependencies were similar to those measured in relaxed or tetanized isolated muscle during sinusoidal stretching (P.M. Rack, J. Physiol. Lond. 183: 1-14, 1966). We conclude that during respiratory muscle contraction 1) chest wall impedance increases, 2) changes in regional chest wall impedances can be somewhat independent, depending on which muscles contract, and 3) increases in chest wall impedance are due, at least in part, to changes in the passive properties of the muscles themselves.     

Soil aeration capacity,an index for soil structure,tested against yield and root development of apple trees at various soil treatments and drainage conditions

Summary Under Dutch climatic and drainage conditions soil aeration, particularly of loam and clay soils, is an important factor in crop production. It is determined by soil structure and ground water level. A soil aeration capacity has been developed to quantify soil structure. This SAC has been based on a schematic concept of aeration in proportion to the interface between water and air in the soil. Assuming certain capillary properties of soil pores, it can be derived from the pF curve as the wall area of air-filled pores at field capacity.Experiments carried out in apple orchards in the western and south-western part of the Netherlands and in Lake I jssel Polders revealed that SAC is a valuable parameter for soil aeration, soil structure and therefore gives sound relations with root development and yield of apple trees. It is found that SAC can be basic for quantifying classification of soil structure.     

Beat Processing Is Pre-Attentive for Metrically Simple Rhythms with Clear Accents: An ERP Study

The perception of a regular beat is fundamental to music processing. Here we examine whether the detection of a regular beat is pre-attentive for metrically simple, acoustically varying stimuli using the mismatch negativity (MMN), an ERP response elicited by violations of acoustic regularity irrespective of whether subjects are attending to the stimuli. Both musicians and non-musicians were presented with a varying rhythm with a clear accent structure in which occasionally a sound was omitted. We compared the MMN response to the omission of identical sounds in different metrical positions. Most importantly, we found that omissions in strong metrical positions, on the beat, elicited higher amplitude MMN responses than omissions in weak metrical positions, not on the beat. This suggests that the detection of a beat is pre-attentive when highly beat inducing stimuli are used. No effects of musical expertise were found. Our results suggest that for metrically simple rhythms with clear accents beat processing does not require attention or musical expertise. In addition, we discuss how the use of acoustically varying stimuli may influence ERP results when studying beat processing.     

Inverse modeling of dog airway and respiratory system impedances

Mechanical parameters of the respiratory system are often estimated from respiratory impedances using lumped-element inverse models. One such six-element model is composed of an airway branch [with a resistance (Raw) and inertance (Iaw)] separated from a tissue branch [with a resistance (Rt), inertance (It), and compliance (Ct)] by a shunt compliance representing alveolar gas compression (Cg). Even though the airways are known to have frequency-dependent resistance and inertance, these inverse models have been composed of linear frequency-independent elements. In this study we investigated the use of inverse models where the airway branch was represented by a frequency-independent Raw and Iaw, a Raw that is linearly related to frequency and an Iaw that is independent of frequency, and a system of identical parallel tubes the impedance of which was computed from the tube radius and length. These inverse models were used to analyze airway and respiratory impedances between 2 and 1,024 Hz that were predicted from an anatomically detailed forward model. The forward model represented the airways by an asymmetrically branched network with a terminal impedance representative of known Cg, Rt, It, and Ct. For respiratory impedances between 2 and 128 Hz, all models fit the data reasonably well, and reasonably accurate estimates of Cg, Rt, It, and Ct were extracted from these data. For data above 200 Hz, however, only the multiple-tube model accurately fitted respiratory impedances (Zrs). This model fitted the Zrs data best when composed of 27 tubes, each having a radius of 0.148 cm and a length of 16.5 cm.     

Low-cost acoustic design of a bat test room

Experiments with captive bats need a flight room that is acoustically neutral, especially when recording and analysing bat calls or the response of bats to certain sound stimuli. Our aim was to identify an isolation material with the best quality–price relationship to acoustically coat such a flight room. For this, we built a flight room divided into two compartments that were to be acoustically isolated from one another. Audible and infrasonic waves are difficult to attenuate with low-cost materials but the attenuation of ultrasounds is rather straightforward. We evaluated the absorbing capacities of different low-cost materials – felt fabric, polystyrene, egg boxes, egg boxes coated with felt fabric, absorbing pyramidal foams, polyurethane foams and cork. The material that showed the best quality–price relationship was the polyurethane foam of open cells (5 cm thickness), which was able to attenuate approximately 20 dB at ultrasonic frequencies.     

Improved frequency response of pneumotachometers by digital compensation

To measure impedance one measures or estimates flow, which is commonly done by measuring the pressure drop across a pneumotachometer. The frequency response characteristics of standard pneumotachometer/pressure transducers (PPT) limit their use to relatively low frequencies. Also, the frequency response of PPTs has been reported to be "load" dependent. Thus, the frequency response characteristics measured under "no-load" conditions, which theoretically could be used to compensate subsequent measurements, may not be appropriate for measurements made under loaded conditions. Another method of measuring impedance exists which depends on a reference impedance element other than a pneumotachometer. In this method, an oscillatory flow signal with known amplitude is generated and used to force the system being tested. Unlike PPTs, this oscillatory flow generator (OFG) is a closed system that allows measurements to be made only during breath holding. Our objective was to determine whether the frequency response of a PPT could be compensated using measurements made under no-load conditions, such that it accurately measured an impedance load. The frequency response of the PPT under no-load conditions was measured by the OFG and used to compensate the output of the PPT in subsequent impedance measurements. The compensated PPT was used to measure the impedance of a mechanical structure and the impedances of four human subjects. The impedances of the mechanical structure and the subjects were also measured using the OFG.(ABSTRACT TRUNCATED AT 250 WORDS)     

SOUND PRODUCTION BY THE LUSITANIAN TOAD FISH,HALOBATRACHUS DIDACTYLUS

ABSTRACT

Several batrachoidids have been known to produce sounds associated with courtship and agonistic interactions, and their repertoires have been studied acoustically and behaviourally. In contrast, sound production of the Lusitanian toadfish Halobatrachus didactylus, although often noted, has not been acoustically studied.

This sedentary predator of Northeastern Atlantic coastal waters is usually found in sandy and muddy substrates, under rocks or crevices. Sound recordings were made in Ria Formosa, a lagoon complex in southern Portugal. The sound producing apparatus was studied in adult individuals of both sexes captured by local fishermen.

It is shown that this species produces acoustic emissions similar to other batrachoidids. It produces a long, rhythmical, tonal sound, often in choruses, which is comparable to the boatwhistle or hum signals of Opsanus and Porichthys, and a complex of signals that were classified as grunts, croaks, double croaks and mixed calls (‘grunt-croak’). As in other toadfishes, H. didactylus presents sonic muscles connected to a bi-lobed swimbladder. Asynchronous contractions of the sonic muscles were detected when massaging the ventral surface of the fish.     

SOUND PROPAGATION IN SHALLOW WATER: IMPLICATIONS FOR ACOUSTIC COMMUNICATION BY AQUATIC ANIMALS

ABSTRACT

Measurements of sound propagation were made in a shallow, sloping bottomed freshwater pond. The frequency responses of the pond had a highpass characteristic with a sharp cutoff frequency. Cut-off frequency of the response was inversely related to the depth of water at the shallowest transducer (either projector or receiver) and was the same whether propagating downslope or upslope (reciprocity). The relationship between cut-off frequency and depth was significantly different from that expected for propagation in a channel with either a rigid or pressure release (gas) bottom. The highpass characteristic is due to modal propagation in the ‘waveguide’, and the effect of this environmental filtering is 30–60 dB between frequencies that propagate and those that do not. Thus, the physical constraints of this shallow-water environment on acoustic communication by aquatic animals are much greater than those measured in terrestrial environments. These constraints are discussed relative to selection for behavioural adaptations of acoustically signalling aquatic animals and are compared to similar adaptations found in terrestrial systems.     

Novel motor gestures for phonation during inspiration enhance the acoustic complexity of birdsong.

Sound generation based on a pulmonary mechanism typically occurs during the expiratory phase of respiration. Phonation during inspiration has been postulated for the calls of some amphibians and for exceptional sounds in some human languages. No direct evidence exists for phonation during inspiration in birds, but such a mechanism has been proposed to explain very long uninterrupted songs. Here, we report the first physiological evidence for inspiratory sound production in the song of the zebra finch (Taeniopygia guttata). Motor gestures of the vocal and respiratory muscles leading to the production of inspiratory phonation differ from those of silent inspirations during song as well as from those leading to phonation during expiration. Inspiratory syllables have a high fundamental frequency, which makes them acoustically distinct from all other zebra finch song syllables. Furthermore, young zebra finches copy these inspiratory syllables from their tutor song, producing them during inspiration. This suggests that physical limitations confine the production of these sounds to the inspiratory phase in zebra finches. These findings directly demonstrate how novel respiratory-vocal coordination can enhance the acoustic structure of birdsong, and thus provide insight into the evolution of song complexity.     

Discharge patterns of chicken cochlear ganglion neurons following kanamycin-induced hair cell loss and regeneration

Hair cells in the basal, high frequency region (>1100 Hz) of the chicken cochlea were destroyed with kanamycin (400 mg/kg/d × 10 d) and allowed to regenerate. Afterwards, single unit recordings were made from cochlear ganglion neurons at various times post-treatment. During the first few weeks post-treatment, only neurons with low characteristic frequencies (<1100 Hz) responded to sound. Despite the fact that the low frequency region of the cochlea was not destroyed, neurons with low characteristic frequencies had elevated thresholds, abnormally broad U-shaped or W-shaped tuning curves and low spontaneous discharge rates. At 2 days post-treatment, the spontaneous discharge rates of some acoustically unresponsive units fluctuated in a rhythmical manner. As recovery time increased, thresholds decreased, tuning curves narrowed and developed a symmetrical V-shape, spontaneous rate increased and neurons with higher characteristic frequencies began to respond to sound. In addition, the proportion of interspike interval histograms with regularly spaced peaks increased. These improvements progressed along a low-to-high characteristic frequency gradient. By 10–20 weeks post-treatment, the thresholds and tuning curves of neurons with characteristic frequencies below 2000 Hz were within normal limits; however, the spontaneous discharge rates of the neurons were still significantly lower than those from normal animals.Abbreviations KM kanamycin - BrdU bromodeoxyuridine - CF characteristic frequency - CAP compound action potential - ISI interspike interval