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Ocean noise recorded during a typhoon is dominated by wind-generated noise sources, and can be used to monitor the typhoon and investigate the mechanism of the wind-generated noise. An analytical expression for the typhoon-generated noise intensity is derived as a function of wind speed. A “bi-peak” structure was observed in an experiment in South China Sea during which typhoon-generated noise was recorded. Strong wind speed dependence and frequency dependence were also observed in the frequency range of hundreds to thousands of Hertz. The model/data comparison shows that results of the present model are in reasonable agreement with the experimental data, and the typhoon-generated noise intensity has a dependence on frequency and a power-law dependence on wind speed.Ocean noise recorded during a typhoon is dominated by wind-generated noise sources, and can be used to monitor the typhoon and investigate the mechanism of the wind-generated noise. An analytical expression for the typhoon-generated noise intensity is derived as a function of wind speed. A “bi-peak” structure was observed in an experiment in South China Sea during which typhoon-generated noise was recorded. Strong wind speed dependence and frequency dependence were also observed in the frequency range of hundreds to thousands of Hertz. The model/data comparison shows that results of the present model are in reasonable agreement with the experimental data, and the typhoon-generated noise intensity has a dependence on frequency and a power-law dependence on wind speed.

In this study, I present an acoustic analysis of contrast between pulmonic and ejective stops in the phrase final coda position in Yucatec, a Mayan language. Ejective consonants are found in about 16% of the world’s language, and there are a relatively large number of acoustic studies about these sounds. However, a significant empirical shortcoming of the previous studies is their exclusive focus on the acoustic realization of ejective consonants in the syllable onset position. This is partly due to a cross-linguistic tendency that ejective consonants are prohibited to occur in the syllable coda position. Therefore, data from Yucatec, which allows ejective consents to occur in the syllable coda position, fill the empirical gap. This study compared pulmonic stop /k/ and ejective stop /k’/ in the phrase final coda position taking a number of acoustic measurements. The results showed (1) stop release is shorter for the ejective, (2) stop closure duration is shorter for the ejective, (3) stop release noise intensity is higher for the ejective, and (4) the contrast between pulmonic and ejective stops affects the voice quality of the preceding short vowel (H1-H2 is lower for the short vowel preceding the ejective).

Ocean noise is an important topic in underwater acoustics, which has been paid much attention in last decades. Ocean noise sources may consist of wind, biological sources, ships, earthquakes and so on. This paper discusses measurements of the ocean noise intensity in deep sea during strong wind periods. During the experiment, shipping density is small enough and the wind generated noise is believed to be the dominated effect in the observed frequency range. The analyses of the recoded noise data reveal that the wind generated noise source has a strong dependence on the wind speed and frequency. Based on the data, a wind generated noise source model is presented. [Work supported by National Natural Science Foundation of China, Grant No. 11125420.]

Monorail transport as all other city transport vehicles is the source of high noise and vibration levels. It is less widespread than cars or underground transport but its influence in modern cities enhances. Now in Moscow the first monorail road with trains on tires is designed, therefore the problem of vibration and noise assessments and prediction of its impact on the residential region appears. To assess the levels of generated vibration a physical model of interaction in the system wagon‐tire‐road coating‐viaduct‐soil has been proposed and then numerically analyzed. The model is based on the known from publications facts of automobile transport vibration and our own practice concerning underground trains vibration generation. To verify computer simulation results and adjust model parameters the series of measurements of noise and vibration near experimental monorail road was carried out. In the report the results of calculations and measurements will be presented and some outcomes of possible acoustical ecologic situation near monorail roads will be proposed.

A high fidelity acoustic simulator has been developed to enable realistic simulation of array time series in order to test sensing/processing algorithms. This simulator, capable of generating calibrated hydrophone or vector sensor array data, is fully integrated into a three-dimensional hydrodynamic array model, generating sensor time series for dynamically evolving array shape, location, and orientation. Furthermore, the simulator handles a changing number and configuration of acoustic sources, targets, and receivers while utilizing the legacy ray tracing code BELLHOP to account for ocean multipath effects. Properly modeling ambient noise is particularly important when determining the effect of noise on sensor/processing performance, e.g., array gain can vary significantly based on the directionality of ambient noise. Embedded in the simulator is the capability to efficiently generate broadband noise for an arbitrary noise intensity distribution as a function of depth and elevation angle (azimuthally sym...

Acoustic limits in habitable space enclosures are required to ensure crew safety, comfort, and habitability. Noise control is implemented to ensure compliance with the acoustic requirements. The purpose of this paper is to describe problems with establishing acoustic requirements and noise control efforts, and present examples of noise control treatments and design applications used in the Space Shuttle Orbiter. Included is the need to implement the design discipline of acoustics early in the design process, and noise control throughout a program to ensure that limits are met. The use of dedicated personnel to provide expertise and oversight of acoustic requirements and noise control implementation has shown to be of value in the Space Shuttle Orbiter program. It is concluded that to achieve acceptable and safe noise levels in the crew habitable space, early resolution of acoustic requirements and implementation of effective noise control efforts are needed. Management support of established acoustic requirements and noise control efforts is essential.

The effects of noise in learning experiments vary considerably, depending on the characteristics and duration of the noise, and the behavior through which learning is being measured. There can also be considerable individual differences in animals’ responses to noise, even between members of the same species. Acute, mild noise is typically no more than a distractor. As noise intensity increases, behavioral effects increase, ranging from increased rates of responding in lever‐pressing experiments to freezing in radial‐maze tasks. Some paradigms are relatively unaffected by noise, including purely appetitive tasks, such as solving mazes for food reward, and tasks such as the water maze, where the aversive properties of water immersion outweigh the aversive effects of noise. Individual differences in animals’ responsiveness to noise can predict learning performance, with stronger responses to noise being associated with more effective learning. Research using rats in our own laboratory shows that chronic exposure to mild but unpredictable noise can attenuate latent inhibition, the capacity to ignore a stimulus that has previously been conditioned to be irrelevant.

This study was performed to evaluate the differences in noise level produced by an eccentric press, during the manufacturing of metallic clo‐ sures for steel cans. The primary objective of the study was to establish a rank of sound‐intensity level and sound‐power level as well as the global noise level emitted by this particular press. Ten different areas in the surface surrounding the press were evaluated regarding both the sound power and the sound intensity of each measurement. Each site was measured twice to increase accuracy. The ten areas sampled were sweeping using intensity probe. We have found the surface area to demonstrate the lowest noise level was at S1 and the highest one was at S10 (p value 0.0005). In conclusion, our study demonstrates adequately the global noise level as well as in specific sites, indicating areas requiring special treatment for noise reduction in this environment.

Predicting indoor noise in industrial facilities is a vital part of designing industrial plants. The predicted levels are used in the design process to determine compliance with occupation noise exposure limits, and to estimate levels inside the walls as starting point for predicting community noise radiated by buildings. Once levels are predicted, the noise controls needed can be developed. Special methodologies are needed, because normal room acoustics found in architectural acoustics texts is valid only for nearly empty rooms with limited absorption and ranges of room dimensions. The fittings inside industrial spaces can profoundly affect the propagation of noise and the resulting noise levels. In an industrial space, such as a power plant, there is no such thing as a reverberant field, except in isolated areas. In industrial spaces, including factories, predicting noise levels by summing free and reverberant fields gives erroneous results that are usually overly conservative. This paper discusses norm...

Evaluating the noise levels to which the bus drivers of Curitiba are exposed to during their working days is the main scope of this study. The city is served by an internationally known public transportation system featuring 1902 buses, which attend 1.9 million people per day. Two measurements have been taken inside each one of the 60 buses surveyed, one close to the driver and another one at the back of the bus. The results have showed that the dose levels the drivers are exposed to were below 50% in 92% out of the buses, but the normalized exposure levels were over 65 dB(A) in all cases. This level is considered as the threshold of comfort according to the Brazilian legislation on occupancy health NR‐17—Ergonomics. The surveyed buses have been divided into three categories, according to their characteristics: feeder, rapid, and bi‐articulated. A total of 20 buses within each category have been surveyed. Among the different categories, it has been found that the feeders have presented the highest noise l...

The Brazilian Silence Program, created in 1990 by the Brazilian Ministry of Environment, advocates the production and use of equipment with lower noise level. The subcommittee of Noise Labeling of the Brazilian Committee of Certification is composed of INMETRO acoustic specialists to organize and implement the Brazilian Labeling Program. This subcommittee elaborated the label form and test procedure. The noise‐labeling program will first concentrate on the following household devices, both manufactured in Brazil or imported from abroad; mixers, blenders, hairdryers, refrigerators, and vacuum cleaners. The label should contain the sound‐power level in dBA. INMETRO or other credited laboratories are responsible for the measurements. The ISO 4871, 3740 (1 to 5), ISO 8960, and IEC 704 (1 to 4) and also the equivalent Brazilian standards are used for the measurements, such as ABNT NBR 13910‐1. The main objective of the label is to inform the consumer about the emitted noise level. The label offers the noise parameter to be used by the consumer when comparing devices, considering price, performance, and now also noise. No restriction for noise level was established.

Active noise control techniques can provide significant reductions in aircraft interior noise levels without the structural modifications or weight penalties usually associated with passive techniques, particularly for low frequency noise. Our main objective in this presentation is to give a review of active control methods and their applications to aircraft cabin noise reduction with an emphasis on recent advances and challenges facing the noise control engineer in the practical application of these techniques. The active noise control method using secondary acoustic sources, e.g., loudspeakers, as control sources for tonal noise reduction is first discussed with results from an active noise control flight test demonstration. An innovative approach of applying control forces directly to the fuselage structure using piezoelectric actuators, known as active structural acoustic control (ASAC), to control cabin noise is then presented. Experimental results from laboratory ASAC tests conducted on a full‐scale fuselage and from flight tests on a helicopter will be discussed. Finally, a hybrid active/passive noise control approach for achieving significant broadband noise reduction will be discussed. Experimental results of control of broadband noise transmission through an aircraft structure will be presented.

Original positions of the interstate standard GOST 30691‐2001 are considered, in which the requirements are established to declaration and verification of noise emission values of machinery and equipment, being manufactured in Russia and imported there from different countries. The comparison of the standard with the International standard ISO 4871:1996 is conducted. The main differences are marked. The suggestions for standards revision are made.

Studies of acoustic conditions are planning tools on which we can diagnose the problem of noise pollution in the cities. The first study on noise pollution made in the city was made by the University of Guadalajara in 1995 and updated in 1998 covering with measuring points the city center. This paper discusses the problem of noise pollution by motor vehicles at critical points and covers a total of 105 points. The study also analyzes the problem of noise pollution base on the community annoyance from which a regulation policy should derive. Results of the study show that the most critical points are located within zone 1 (center) where Leq levels within the range of 70–85 dB were found. Such levels exceed by far the international standard of 65 dB as recommended for ambient noise by the World Health Organization.

A standard psychometric measurement is response time, the interval elapsing between a stimulus and a response. While studies of response time have been published for humans and other terrestrial mammals, this study marks the first report of response times for odontocete cetaceans at threshold in an audiometric task. Two white whales (Delphinapterus leucas) and four Atlantic bottlenose dolphins (Tursiops truncatus) were given audiometric tests to determine masked hearing thresholds. Animals were tested at 26 frequencies over a range from 200 Hz to 100 kHz using pure tones. The test tone amplitudes covered a range of 20 dB re 1 microPascal including the hearing threshold of the animal at that frequency. Hearing thresholds varied from 87.5 dB to 125.5 dB depending on frequency, masking noise intensity and individual animal. Data was analyzed to determine characteristic relationships between response time and amplitude of test tone for each frequency and animal. The two whales responded significantly slower (640 ms, 0.001) than the four dolphins (430 ms). As in terrestrial animals, reaction time became shorter as stimulus strength increased. At threshold, median response time across frequencies within each animal varied about 150 ms.

When CV syllables have longer vowels following a stop /b/ or glide /w/, the duration of transition necessary to perceive a stimulus as /w/ is longer as well. Perceived continuity/duration of following vowels was manipulated by exploiting the phenomenon of auditory induction. All syllables were 315 ms in duration, and transition duration was varied from 15–65 ms for four series of syllables. After the first 100 ms of each syllable (transition + vowel), broadband noise either replaced or was added to the second 100 ms of syllable. Noise was either the same intensity as or 12 dB greater than the intensity of the vowel. Results from a signal detection task indicated that listeners could reliably report when the signal was deleted and replaced by the less intense noise; however, they could not reliably report whether the vowel was deleted when the noise was more intense (+12 dB). Listeners were asked to label these four series of stimuli as beginning with /b/ or /w/, and there was no effect of either the presence or absence of the vowel or of noise intensity. Even when subjects’s phenomenal experience was one of intact continuous syllables (+12‐dB noise with vowel present or absent, or equal intensity noise with vowel present), subjects’ labeling boundaries were virtually identical to those for syllables perceived as interrupted (equal intensity noise with vowel absent) or for syllables of only 100‐ms total duration. Theoretical implications and results from follow‐up experiments will be reported. [Work supported by NIDCD Grant No. DC‐00719 and NSF Grant No. DBS‐9258482.]

A method and apparatus for reducing noise originating in a flowing stream of gases in which the noise is progressively absorbed from the flowing stream to provide noise of reduced intensity relative to noise intensity at the upstream end of the stream, and the noise of reduced intensity actively attenuated with controlled sound energy. To facilitate the active attenuation of noise, the flowing stream is preferably divided into a plurality of smaller streams after a level of reduced intensities is attained and the active attenuation performed independently in each of the smaller streams. The apparatus is in the nature of a conduit (10) which defines a single duct extending from the inlet end (14) for a portion of the length of the conduit. Downstream, the single duct joins with a plurality of ducts (32,34) extending to the outlet end (16). An active noise attenuating device is preferably provided in each of the plurality of ducts.

Noise‐intensity discrimination was studied as a function of both signal and masker bandwidth. Five bandwidths of noise—ranging from 100 to 10 000 Hz—were employed. Maskers were presented at each of three spectrum levels (5, 25, and 45 dB re 0.0002 μbar). Discrimination thresholds were relatively unaffected by changing bandwidth over a two‐decade range when the signal and masker were filtered together, with either continuous or gated presentation of the masker. When the masker bandwidth was greater than that of the signal, the reciprocity between signal power density and signal bandwidth was found to be 5 dB per log unit of bandwidth with continuous maskers and 5–10 dB (depending upon level) with gated maskers. The results were compared with predictions of energy‐detector models of noise‐intensity discrimination. Modifications of simple energy‐detection schemes were discussed.Subject Classification: [43]65.58, [43]65.75, [43]65.50; [43]50.70.

An account on the development of a directional microphone system for jet‐noise‐source strength distribution measurements is given. The system selected is based on the imaging principle of a spherical concave reflector. As expected, the system is diffraction limited; a loss of resolution results. A special technique is discussed to recover the axial‐source strength distribution from the diffracted data. Sample experiments are presented to show the successful application of such a system for jet noise measurements.Subject Classification: [43]28.65; [43]50.55; [43]85.62.

Our understanding of community reaction to helicopter noise is incomplete and inadequate. While A‐weighting appears to work outdoors and at modest noise levels, and the community response in terms of percentage of population highly annoyed can be correlated with respect to the day/night average sound level (DNL) descriptor, questions remain as to the role of perceived building vibrations and rattle in human response to helicopter noise. Does hearing windows, ceiling tiles, or objects in the room rattle or does the general perception of building vibration increase the public’s adverse response to helicopter noise? To answer these questions, this study examined the role of vibration and rattle in human response to helicopter noise. Results showed that the A‐frequency‐weighting is generally adequate to assess community response to helicopter noise when no vibration or rattle is induced by the noise. When rattle or vibrations are induced by the helicopter noise, however, A‐weighting does not assess the commun...

Thresholds for the detection of a decrement in noise intensity between repeated bursts of noise were determined as a function of the duration of the interval between successive bursts. The results indicate a critical duration (55 milliseconds) between successive noise bursts: (1) above which, the differential threshold is constant and independent of the interval between successive bursts and (2) below which, the differential threshold increases proportionately as the interval between successive bursts decreases. Since an equivalent critical interval has previously been obtained by several different independent measures of auditory persistence, the observed deterioration of differential sensitivity is interpreted in terms of the overlap or addition of auditory persistence with the direct effects of stimulation.

The concepts and methods of estimating the perceived noisiness of sounds from subjective and physical measurements are described. A general method, called Effective Perceived Noise Level (EPNL), of estimating the perceived noisiness of a single sound or a total sound environment taken over a 24‐hour period is proposed, and its relations to the Effective Composite Noise Rating (ECNR) scheme are discussed. It would appear that the average threshold of general noisiness or annoyance for the sound environment of a typical residential area occurs at about 50 PNdBt for sounds measured indoors and at 70 PNdBt for sounds measured outdoors; these threshold values can be utilized to advantage in conjunction with EPNL and ECNR. The virtue of using EPNL and ECNR, which in essence, are the same in certain applications as “CNR,” “NNI,” and “Q” quantities developed in the U. S. A., Great Britain, and Germany, respectively, is that they can combine the variable factors of duration, number of occurrences, spectrum and in...

This paper reports some preliminary results of an attempt to apply the equalization and cancellation (EC) model of binaural unmasking to data on interaural just‐noticeable differences (jnd's). The interaural dimensions that are considered are time, amplitude, frequency, and decorrelation.

In a recent paper, Sheehy derived optimum processing structures for use in detection of signals in additive non‐Gaussian noise. An analytical form was postulated for the distribution of the noise intensity level and found to be in good agreement with experimental data. Since this data was not presented in the article, it is the intent of this letter to clarify the nature of the experimental data previously reported.

The noise of utterance initial/f/ and /θ/ in naturally spoken syllables /fi/ and /θi/ was replaced by splicing‐in both /s/ and /f/ noise cut away from spoken /si/ and /∫i/ syllables. The intensity of the replacing noise had been attenuated to the level of the original /f/ and /θ/ noise. A natural sounding /f/ or /θ/ resulted depending upon whether the original fricative had been /f/ or /θ/, respectively. This procedure was previously utilized by the author in relation to intervocalic fricatives (J. Acoust. Soc. Am. 63, S21(A) (1978)] with similar results. These results suggest that the lower noise intensity of spoken /f/ or /θ/ distinguishes them from /s/ and /∫/. The range of noise spectrum variation which is physically manifest in spoken /f, θ, s, ∫/appears to have no perceptual significance for /f/ and /θ/, which are distinguished from each other by the formant transition cues of the vocalic portion of the syllables. However, noise spectrum differences are important cues in the distinction between /s/ and /∫/. This evidence favors the categorization of both /f/ and /θ/ as nonstrident in distinctive feature terminology.

Critical bands (CB) for antiphasic tonal stimuli (noise zero phase, signal out of phase—N0Sπ) were determined in a band limiting, two‐alternative forced‐choice paradigm. Signals were 100‐msec tone bursts at either 500 or 2000 Hz. Masking noise was at sound pressure spectrum levels of 15 or 45 dB. For each combination of signal frequency and noise intensity, a signal level was determined, which produced average probability correct of 0.54 for the three observers. Band limiting of the noise disclosed the characteristics of the critical band for each stimulus condition. CB for N0Sπ were wider for a noise spectrum level of 45 dB than for a spectrum level of 15 dB. For any given conditions, the CB for N0Sπ was from 18% to 30% wider than the CB determined earlier for N0S0. [Work supported by U. S. Navy Office of Naval Research, Physiological Psychology Branch.)

Wide‐spectrum acoustic transients were presented simultaneous with continuous white noise. In study one, click intensities ranged from 20 to 60 dB nHL, in 10‐dB increments, with noise intensities ranging from a no‐noise condition to a perceptually based 0‐dB signal‐to‐noise ratio. In study two, click intensity was held constant at 50 dB nHL, with noise intensities similar to those cited above, and stimulus repetition rates of 15, 40, 65, and 90 Hz. The primary dependent variable in both studies was wave V latency. These studies indicate that the effect of continuous masking noise on wave V latency is a function of absolute noise intensity, rather than signal‐to‐noise ratio. Further, the effect of noise intensity on wave V latency appears to be additive with click intensity and repetition rate. Preliminary data on the interaction of signal frequency and noise masker will also be presented. [Work supported by NIH.]

A fricative identification test was administered to native French speakers. Test stimuli had been edited from naturally spoken fricative‐vowel utterances: /s,∫,f,θ/ − /i,α,u/. See [J. Acoust. Soc. Am. Suppl. 1 70, S33 (1981); and 73, S30 (1983)] for prior use with English and Spanish speakers. The results indicated that both noise segment intensity and spectrum were major acoustic cues for the French fricatives. These cues were redundant for the /f/, either low intensity noise or nonsibilant spectrum sufficed. A much weaker cue due to the original fricative, sibilant or nonsibilant, of the vocalic portion of the edited syllables must be taken into account. By comparison, Delattre had concluded using synthetic speech stimuli [Phonetica 18, 198–230 (1968)] that noise spectrum was necessary and noise intensity was redundant as cues for all French fricatives. Results implicate the specific language experience of the subjects, e.g., French lacks /θ/; the impact of natural or synthetic speech as sources of stim...

The current OSHA noise standard permits maximum occupational noise exposures equivalent to an 8‐h, A‐weighted level of 90 dB. Since equivalency is defined in terms of the 5‐dB halving rule (i.e., for each 5‐dB increase in noise intensity, exposure duration is halved), this standard permits a 15‐min noise exposure at 115 dBA. Higher intensity exposures, however, are considered hazardous and, consequently, are not permitted no matter how brief the exposure duration. Is 115 dBA for 15 min safe? Probably not. TTS2 data collected in a recent study by the second author (Schori, 1976) suggest that a 115‐dBA exposure for 15 min may be quite hazardous. Forty subjects (80 ears) were exposed to pink noise at 115 dBA for only 2.7 min. Yet this relatively brief exposure produced a TTS2 in one ear of one subject of 47 dB and produced TTS2's greater than 20 dB in six ears (five subjects). The median TTS for both ears combined was 8 dB. On the other hand, data from the same study suggest that all noise exposures above 11...

Calculated engine core noise levels, based on NASA-Lewis prediction procedures, for five representative helicopter engines are compared with measured total helicopter noise levels and proposed FAA helicopter noise certification requirements. Comparisons are made for level flyover and approach procedures. The measured noise levels are generally significantly greater than those predicted for the core noise levels, except for Sikorsky S-61 and S-64 helicopters. However, the predicted engine core noise levels are generally at or within 3 db of the proposed FAA noise rules. Consequently, helicopter engine core noise can be a significant contributor to the overall helicopter noise signature and, at this time, will provide a limiting floor to a further decrease in future noise regulations.

The effects of aircrft noise on human activities was investigated by developing a battery of tasks (1) representative of a range of human activities and (2) sensitive to the disruptive effects of noise. The noise used were recordings of jet aircraft and helicopter sounds at three lvels of loudness--60, 70, and 80 dB(A). Experiment 1 investigated 12 different cognitive tasks, along with two intelligibility tasks included to validate that the noises were being effective. Interference with intelligibility was essentially the same as found in the research literature, but only inconsistent effects were found on either accuracy or latency of performance on the cognitive tasks. When the tasks were grouped into four categories (Intelligibility, Matching, Verbal, and Arithmetic), reliable differences in rated annoyingness of the noises were related to the task category and to the type of noise (jet or helicopter).

Future STOL aircraft may utilize engine-over-the-wing installations in which the exhaust nozzles are located above and separated from the upper surface of the wing. An external jet flow deflector can be used with such installations to provide flow attachment to the wing/flap surfaces for lift augmentation. Deflector noise in the flyover plane measured with several model-scale nozzle/deflector/wing configurations is examined. The deflector-associated noise is correlated in terms of velocity and geometry parameters. The data also indicate that the effective overall sound pressure level of the deflector-associated noise peaks in the forward quadrant near 40 deg from the inlet axis.

A number of facilities were developed which provide a unique test capability for psychoacoustics and related human factors research. The design philosophy, physical layouts, dimensions, construction features, operating capabilities, and example applications for these facilities are described. In the exterior effects room, human subjects are exposed to the types of noises that are experienced outdoors, and in the interior effects room, subjects are exposed to the types of noises and noise-induced vibrations that are experience indoors. Subjects are also exposed to noises in an echo-free environment in the anechoic listening room. An aircraft noise synthesis system, which simulates aircraft flyover noise at an observer position on the ground, is used in conjunction with these three rooms. The passenger ride quality apparatus, a device for studying passenger response to noise and vibration in aircraft, or in other vehicles, is described.

Measurements of the vertical noise intensity versus angle [W. Carey and R. Wagstaff, J. Acoust. Soc. Am. 80, 1523–1526 (1986)] show the low‐frequency distribution (≪200 Hz) to be broadly peaked about the horizontal, whereas the higher‐frequency (≈400 Hz) distribution is peaked at the SOFAR angles (≈ ± 15) near the axis with a minima at the horizontal. This effect has been attributed to the noise from ships over the basin margins [R. Wagstaff, J. Acoust. Soc. Am. 69, 1009–1014 (1981)]. However, since spectral variation along the horizontal is smooth and the effect is observed in sparsely shipped areas of the world, wind noise must be included to explain this effect. R. W. Bannister [J. Acoust. Soc. Am. 79, 41–48 (1986)] has attributed this effect to high‐latitude winds and the shallowing sound channel found in Southern Hemisphere waters. W. Carey [J. Acoust. Soc. Am. 79, 49–59 (1986)] attributed the effect to downslope propagation. Calculations between 50 and 400 Hz of the midbasin vertical directionality made with ASTRAL and PAREQ with a geoacoustic model were both found to show that the bottom behaves as a low‐pass filter as the low‐frequency energy at higher angles interacts with the bottom and is converted to low‐angle energy in the deep sound channel while, at the higher frequencies and higher angle, energy is absorbed. This low‐pass effect is consistent with experimental results. Propagation of low‐grazing angle energy from the shelf is prominent in the computational results but not apparent in measured data, perhaps due to bathy‐metric roughness.

In California, the level of integrated noise intensity‐time function (noisework), called Single Event Noise Exposure Level (SENEL), is used as an indicator of the noise impact due to individual noise sources (air and ground vehicles) passing by. For the simple case, SENEL = SPLA MAX + 10 logπR/V, where R and V are the distance to and speed of the vehicle. A previously published expression for SENEL is incorrect. Analyses of recorded samples of autos, trucks, and light aircraft show that the correct analytical expression predicts SENEL values within ±1 dB of measured values. For commercial jet aircraft landing noise samples recorded at LAX, the theoretical SENEL values were 1–2 dB greater than the experimental values, whereas similar data reported by the FAA indicated theoretical SENEL values 2–4 dB greater than the corresponding experimental values.

Twelve tokens each of /SiSi, SiSa, fifi, fifa/ were recorded by one male speaker and manipulated in a PCM system. Duration and intensity of each segment were measured. A matched pair of /SiSi, SiSa/ tokens was edited to produce additional tokens in which the intensity of /S2/ noise was reduced in 3‐dB steps. Control variables were: /S2/ noise duration; /S1/ noise present or absent; final vowel. A very strong relationship between /S2/ noise intensity and % /S2/ percepts was apparent in the data from 10 subjects who listened to the stimuli. From 100% /S2/ at natural levels, an 18 dB reduction in intensity shifted the percepts to 2% /S2/, 95% /θ, f/, 3% /p, t/. There was a nonoverlapping intensity differential between /S2/ and /f2/ noise in the measurements from the 48 original tokens. A trade‐off between /S2/ noise duration and intensity was apparent in the perceptual data, but not in the measurements from the original /SiSi, SiSa/ tokens. /S1/ present/absent had a consistent but even smaller trading value. Final vowels had no effect. See the pilot study [J. Acoust. Soc. Am. Suppl. 1 67, S39 (1980)]. [Haskins Laboratories provided valuable assistance in processing the speech samples on NICHD Contract No. NIH‐71‐2420.]

Rectangular jets of various height‐to‐width ratios have been operated over a range of exit velocities in an anechoic chamber. Each of the jets had an exit area equal to one square inch and was tested in pairs of equal height‐to‐width ratios. The noise intensity and directivity pattern were measured and evaluated as a function of the separation distance of the jets, the height‐to‐width ratios, and the jet velocity. Noting the width of the jet as w, and separation distance as s, the s/w ratio was varied from zero to two and the value was noted where the generated noise was a minimum. This optimum s/w ratio was found constant with respect to the angle of radiation and the jet velocity for all height‐to‐width ratios. The effect of forcing air through the area between the jets by means of a third jet was also studied. Results of these studies in relation to rational design of jet noise suppressors are discussed.

When a noiselike auditory stimulus is used to study the auditory nervous system, it is difficult to determine the evoked response dependency upon the transitory changes in stimulus intensity and upon its spectrum. This is particularly true when the noise intensity fluctuates, as in filtered white noise, for example. However, if a relatively long tone burst is briefly frequency modulated (FM) by noise, the tone‐noise and noise‐tone transitions occur with no SPL intensity fluctuation. The responses can then be ascribed solely to the spectral transitions. A series of experiments has been performed on awake cats subjected to such stimuli in which the noise bandwidth was varied. Responses to the tone‐noise transitions were obtained from epidural electrodes and were compared with responses to both pure‐tone bursts and FM bursts with the same envelope. Of considerable interest is the finding that for relatively large bandwidths, the response is greater to the tone‐noise transition than to onset of an FM noise burst with the same bandwidth. [Supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]

Most of our knowledge of masking is derived from experiments that used one continuous sound to mask another continuous sound. In practical situations, however, masking noises are often intermittent. The present experiments were designed to explore the effect of interruptions upon the masking effectiveness of random noise. In the first experiment, tones were masked by continuous and by interrupted noise. The noise intensity, the proportion of the time the interrupted noise was on, and the rate of interruption were varied. The principal effect of interruption is to lower the masking effectiveness. The extent to which the masking is decreased depends principally upon the duration of the silent interval and secondarily upon the frequency of the masked tone and the intensity of the noise. A computational scheme is possible which will permit a rough approximation of the masked threshold in the presence of interrupted noise. In a second experiment, articulation tests were conducted to determine the effect of int...

The high‐conductance quartz ultrasonic image converter differs from those of the Sokolov type in that the scanned element is connected to the output termination by a high‐conductance secondary electron path over which interaction can occur between the element and the termination. Conductance‐bridge measurements over this path indicate a mushroom‐shaped space‐charge cloud with the path conductance set by the mushroom‐head surface area and the ultrasonic resolution by the electron‐beam diameter. A measured equivalent noise intensity of 6×10−6 W/m2 for operation at 2.5 MHz with a 400‐kHz video bandwidth is evaluated in terms of stored‐energy retrieval and internal‐noise sources. The observed resolution approaching 20 lines/in. appears primarily set by electron‐beam diameter rather than by conversion‐plate thickness.

A sound cage with a seconds pendulum regulating the intervals between stimuli was used to determine the threshold of two‐point discrimination of the position of sound. Observations will be reported on the change in threshold with change in decibel level and absorption in the test chamber, the intensity and character of the discriminated stimulus remaining constant. Bearings of the data on annoyance, fear reaction, and “third dimensional sound” will be pointed out.