Impulsive Sound Source Research Articles

Effects of exposure to pile-driving sounds on the lake sturgeon, Nile tilapia and hogchoker

Pile-driving and other impulsive sound sources have the potential to injure or kill fishes. One mechanism that produces injuries is the rapid motion of the walls of the swim bladder as it repeatedly contacts nearby tissues. To further understand the involvement of the swim bladder in tissue damage, a specially designed wave tube was used to expose three species to pile-driving sounds. Species included lake sturgeon (Acipenser fulvescens)--with an open (physostomous) swim bladder, Nile tilapia (Oreochromis niloticus)--with a closed (physoclistous) swim bladder and the hogchoker (Trinectes maculatus)--a flatfish without a swim bladder. There were no visible injuries in any of the exposed hogchokers, whereas a variety of injuries were observed in the lake sturgeon and Nile tilapia. At the loudest cumulative and single-strike sound exposure levels (SEL(cum) and SEL(ss) respectively), the Nile tilapia had the highest total injuries and the most severe injuries per fish. As exposure levels decreased, the number and severity of injuries were more similar between the two species. These results suggest that the presence and type of swim bladder correlated with injury at higher sound levels, while the extent of injury at lower sound levels was similar for both kinds of swim bladders.

Reduction of underwater sound from continuous and impulsive noise sources using tethered encapsulated bubbles

Arrays of encapsulated bubbles have been shown to be very effective in reducing underwater sound radiated from various sources [J. Acoust. Soc. Am. 131, 3356 (2012); J. Acoust. Soc. Am. 131, 3506 (2012) ]. These arrays have been used to treat both sources of noise and to protect a receiving area from external noise. The system provides noise reduction using the combined effects of bubble resonance attenuation and acoustic impedance mismatching. Results are reviewed from experiments where tethered encapsulated bubble arrays were used to reduce underwater sound levels from both continuous and impulsive sound sources. In one set of experiments, the encapsulated bubble array attenuated continuous wave sound from a compact electromechanical source. In the other set of experiments, the continuous source was replaced by a combustive sound source [IEEE J. Oceanic Eng. 20, 311--320 (1995)], which was intended to simulate real-world impulsive noise sources such as impact pile driving or airguns used in seismic surveys. For both the continuous and impulsive sources, the encapsulated bubbles provided as much as 45 dB of reduction in the 10 Hz to 600 Hz frequency band. [Work supported by Shell Global Solutions and ARL IR&D program.]

An under-ice Arctic geophysical exploration sonar system concept to resolve international territorial claims.

A consequence of the shrinking polar ice cap is the increased interest in commercial shipping. Therefore, several nations are surveying the continental slopes and Arctic basin to better define the political boundaries. Under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS), the boundary between territorial and international waters is defined where the sub-bottom basement extends l km from the seafloor. Therefore, icebreakers and air guns are currently implemented for deep sub-bottom profiling. However, there still remains older and thicker ice that leads to inaccessible areas for geophysical surveys from surface ships. Submarines can easily navigate below the Arctic ice, but a safer sound source must be identified to avoid air guns or explosives. An analytic formulation was developed to predict the maximum basement detection depth of an under-ice sound source. This formulation was implemented to compare candidate underwater transducers and impulsive sound sources. Results from this study will be presented with discussions on additional constraints affecting the selection process. A workable submarine system for defining territorial boundaries would also help increase our understanding of the Arctic environment and facilitate exploration for potential natural resources. [Funding provided via UAF sub-award under NOAA Grant No. NA09NOS4000262.]

Effect of Inhomogeneous Sub-Bottom Layering on Broadband Acoustic Propagation

In this paper, the effects of range inhomogeneities in the seabed layering on low-frequency broadband sound propagation in a shallow-water ocean environment are examined. Acoustic measurements generated by an impulsive sound source were made on the New Jersey continental shelf over propagation paths where previous geophysical analyses provide information on the seabed layering structure. Additional information on the physical properties of the sediment layers, such as sound speed and attenuation, was obtained from previous analyses of continuous wave tow experiments. The seismic and the geophysical information, the inferred geoacoustic information for the sediment layers, and sparse water-column sound-speed measurements provide inputs for a finite element parabolic equation propagation model. For the three propagation paths considered in this study the seabed layering structure for two of the paths is range dependent and the other is approximately horizontally stratified. With this information modeled, time series are produced and are compared in the 35-265-Hz band to the measured received times series from impulsive sources deployed at ranges between about 70 and 350 water depths. Further, simulations of the received time series are performed for each of the three paths using modified sub-bottom layering structures for the purpose of quantifying the acoustic field effects associated with deviations of the seabed structure from horizontal stratification.

Field experiment on vibration and acoustic responses of building to sonic booms using impulsive sound source.

Annoyance related to sonic boom is believed to be enhanced in indoor spaces by vibration of building walls, window rattles, room acoustic effects, and so forth. For investigating such vibration and acoustic effects of sonic booms in buildings, both laboratory and field experiments have been conducted. Although propagation of sonic booms in space and relative phenomena such as diffraction around a building can be reproduced in field experiments, it is sometimes not straightforward to generate sounds similar to sonic booms in open space. In this study, an easy-to-handle, portable device suitable for simulating sonic booms in field experiments is developed. A device developed by some of the authors to generate impulsive sound with fair level of infrasonic components by using compressed air is modified to simulate the negative overpressure of sonic booms. The improved device is used in a field experiment to investigate vibration and acoustic responses of a small house. Results of this preliminary experiment will be reported.

An investigation of the combustive sound source.

The combustive sound source (CSS) is a versatile impulsive underwater sound source with an adjustable bandwidth and output amplitude. Unlike typical impulsive acoustic sources, CSS can maintain a wide bandwidth at low amplitude; hence, it is a more environmentally friendly impulsive source for ocean acoustics experiments and surveys. The CSS consists of a submersible combustion chamber, open to the water, which is filled with a combustible fuel/oxidizer mixture. The mixture is ignited and a combustion wave propagates through the mixture. During this process the ensuing bubble expands due to an increase in temperature and can collapse to a smaller volume than before ignition. This bubble activity radiates acoustic pulses. The CSS can be used as a source for low-frequency sediment characterization and TL measurements, and when deployed on the bottom can produce seismic interface waves. In addition to stationary deployments in the water column, CSS can be deployed in a tow body and as an array. Discussion will focus on the latest CSS design including functionality, acoustic output, long-term operational stability, and future development plans.

Analytical Expression for Sound Transmission Loss Calculation: An Improvement to the Existing Method after Singh and Katra

An analytical expression for measuring of sound transmission loss (TL) has been developed by using two microphones, an impedance tube and an impulse sound source as a proposed improvement to the existing procedure after Singh and Katra (1978). The calculation procedure is based on the autospectrum of short‐time signals captured by the two microphones placed on two opposite positions from test sample while the sound source is on its surface. No spectral decomposition is required and the TL is calculated directly from the autospectrums of captured signals.

Prediction of radiation characteristic of intermittent exhaust noise generated via pneumatic value

A mechanism for intermittent exhaust noise (IEN) generation mechanism, and the existing pressure shockwave with the standing-wave variation resulting in the impulse characteristic sound source that sequentially develops the airflow-induced IEN with the much high-frequencies content, is proposed. The shockwave impulse acoustic source (SIAS) describes the impulse sound source caused by the shockwave, conceptually and aerodynamically. Upon analysis of the exhaust noise source distribution in the pneumatic exhaust system via the pneumatic valve, this paper proposes that the SIAS with the maximum amplitude is located at the exhaust outlet; a relation of the noise source and both mass flux and flow speed is set up. With the piston acoustic source approximating the SIAS radiation at the outlet, formulae for calculating the sound pressure (SP) and sound pressure level (SPL) are given. Experiments support the proposed IEN-generation mechanism. The analytical results are in a good agreement with the experimental results in the octave bands, with the difference between the measured and calculated overall A-weighted sound level less than 3 dB. Especially for the octave bands from 250 Hz to 16 kHz, the differences between the measured and calculated A-weighted sound level are less than 3.5 dB.

Measurement of sound absorption coefficients of flat surfaces in a workshop

To improve the acoustic treatment of facings and provide appropriate solutions for noise control at workplace, it is necessary to develop methods of acoustic characterization of the walls in industrial halls. Sound absorption coefficient measurement in industrial rooms is however quite a difficult task because of the partially reverberant conditions. This work describes the measurement of the sound absorption coefficient of flat panels subject to small angle sound incidence, in an industrial hall using an experimental device equipped with an acoustic array. The directivity of this array has been optimized so that the major part of the received acoustic energy would come from one portion only of the investigated facing, this, in turn attenuating the reflected beams due to the reverberation. This new device includes an impulse sound source targeting the panels. The present article focuses mainly on the sound source design and implementation. It also describes some sound absorption measurements carried in a semi-anechoic chamber and in an industrial hall in order to examine the performance of the device. Sound absorption coefficients of several standard liners obtained through this device have been compared to those resulted from the two microphone technique.

Impulsive sound source localization using distributed elevated acoustic sensors.

For detecting and localizing impulsive sources in the daytime, distributed elevated acoustic sensors with large base line separations have distinct advantages over small ground-based arrays. First, during the day, the signal levels are generally higher at altitude than on the ground. Second, the large base lines provide improved localization accuracy. Results are reported from a distributed array of acoustic sensors deployed during an experiment in Bourges, France during June of 2008. The distributed array consisted of microphones and global positioning system (GPS) receivers attached to the tether lines of several widely separated balloons. The sound sources were various impulsive devices. Data from the experiment are presented and discussed. In particular, the localization error is analyzed as a function of the GPS accuracy and the motion of the balloons. Possible ways to improve the localization accuracy are suggested. [Research supported by the U. S. Army TACOM-ARDEC at Picatinny Arsenal, NJ.]

New method for measuring sound absorption coefficients in an industrial hall

Predicting the sound pressure level at a workplace requires in‐situ characterization of the facings. This work describes a new method for the measurement of the sound absorption coefficient of flat panels present in industrial halls. In such room, it is necessary to separate the echo coming from the studied panel from the others due to the entire reverberation. This separation has been achieved in space by an acoustic array and in time by an impulse sound source. The array processing uses a multipolar weighting to achieve a directivity constant with frequency and with attenuated side lobes. This weighting requires a limited number of microphones. The impulse source has been designed using the inverse impulse response from the emission system (equalizer, amplifier, loudspeaker). This inverse filtering technique allows equalizing the response of the emission system in order to radiate very short pulses. Sound absorption coefficient of several flat facings have been evaluated by mean of this new device in a ...

Beam‐forming and dispersion measurements at the edge of a pine forest

Beam‐forming analyses were performed on four‐microphone linear arrays placed just within the interior of a pine forest to separate signal arrivals by direction from an impulsive sound source in an open field. The arrays were deployed in three configurations: transverse, longitudinal, and vertical. The arrays spacings were organized in a pattern that provides six baselines with four microphones. Longitudinal and transverse configurations show arrivals scattered from trunks, and the vertical configurations indicate some refraction and scattering by the canopy. Signal dispersion curves developed using the four‐microphone arrays had greater variation in trace velocity at higher frequencies in each configuration.

Lightning: A Hard Real-Time, Fast, and Lightweight Low-End Wireless Sensor Election Protocol for Acoustic Event Localization

We present the Lightning Protocol, a hard real-time, fast, and lightweight protocol to elect the sensor closest to an impulsive sound source. This protocol can serve proximity-based localization or leader election for sensor collaboration. It utilizes the fact that electromagnetic waves propagate much faster than acoustic waves to efficiently reduce the number of contending sensors in the election. With simple RF bursts, most basic comparison operations, no need of clock synchronization, and a memory footprint as small as 5,330 bytes of ROM and 187 bytes of RAM, the protocol incurs O(1) transmissions, irrespective of the sensor density, and guarantees hard real-time (O(1)) localization time cost. Experiment results using UC Berkeley Motes in a common office environment demonstrate that the time delay for the Lightning Protocol is on the order of milliseconds. The simplicity of the protocol reduces memory cost, computation complexity, and programming difficulty, making it desirable for low-end wireless sensors.

A simple impulse sound source for measurements in room acoustics

This paper deals with the construction and characteristics of a specially designed wooden clapper intended to operate as an impulse sound source for measurements in rooms. It is to be used as an alternative impulse sound source for experimental estimations of impulse responses of rooms located at remote and specific places where none of the standard sound sources – an omnidirectional loudspeaker system, etc. – can be used. The paper describes the spectral characteristics and directivity of the clapper impulse. Its features are compared with other impulse sources.

Two-hydrophone localization of a click source in the presence of refraction

This paper introduces a ray-theoretic method for fast localization of an impulsive sound source in a general stratified ocean environment by measuring relative times of direct and surface-reflected arrivals at two hydrophones. The localization problem is solved through ray tracing and wave-front tracking in the time domain. This method is computationally efficient and allows for fast, near-real time estimation of the source location, which is a significant advantage for operational localization. The accuracy of the ray-theoretic approach is compared with that of the straight-line approximation. Further, localization errors associated with the angular and temporal discretization as well as with the variability of the hydrophone depths and the sound-speed profile are addressed.

Predicting acoustic and seismic pulses from outdoor explosions

To support the formulation of a simple model that can be used for assessment and prediction of ground vibration levels due to above-ground explosions, a fast field program for layered air ground systems (FFLAGS), developed originally for continuous sound sources, has been extended to enable predictions of propagation from impulsive sound sources in a refracting atmosphere above layered porous and elastic ground. Using a mixture of measured and best-fit parameters, the pulse version of the code (PFFLAGS) has been found to give predictions of the air pressure spectrum above ground and the vertical component of solid particle velocity near the ground surface that compare tolerably well with published data for the spectra and waveforms of acoustic and seismic pulses at short range (60 m) in grass- and snow-covered ground and at longer range (3 km) in forested terrain. The predicted seismic pulses in the presence of the snow cover explain a phenomenon frequently observed for shallow snow covers whereby a high-frequency ground vibration is modulated by a lower-frequency layer resonance [Work supported in part by SERDP SEED Project SI-1410 and Contract Number W90C2K9887EN010001 through the European Research Office of the U.S. Army.]

A simple method to detect audible echoes in room acoustical design

A simple method to detect audible echoes is proposed as an objective criterion for room acoustics. This method evaluates the perceptibility of sound reflections that are generated by an impulsive sound source and identifies from reflectograms harmful reflections perceived as echoes. Particularly with this method, the masking effect of reverberation is taken into consideration, which cannot be treated sufficiently by the existing objective criteria. The applicability to room acoustical design is verified by evaluating the impulse responses measured in real halls where audible echoes occurred. It is shown that the proposed method detects audible echoes at an accuracy of more than 90% and would be suitable for practical use.

Gun shot digital imaging system

Disclosed is a method for recording one or more images of a source area where an impulse sound has initiated. The recording is performed by at least one of a plurality of units that include a camera, a computing device, and a connection to a network. The method comprises the steps of detecting and calculating a range and direction of the impulse sound source; slewing the camera to align its optical axis with a direction of the impulse sound; determining whether the impulse sound was a gunshot; recording images of the source area; and alerting a plurality of neighboring units to perform the recording step.

Tonal response on the stairway of the main pyramid at La Ciudadela, Teotihuacan archaeological site

This paper presents new research on the very interesting audible effects produced by the stairways of many archaeological sites in Mexico. This investigation was made at the main stairway of the pyramid at La Ciudadela, Teotihuacan archaeological site. The effect previously studied was a chirped echo reflected from the stairway at normal incidence, which resembles the singing of the Quetzal. Now it is presented with the impulsive sound source and the listeners located at different angles, where apart from the characteristic chirped sound, several musical notes could be obtained and identified, covering a range of at least one half an octave. This evaluation was made at the site, where the effect is clearly audible, and it is supported with simple mathematics.

Source levels of impulsive sound sources in underwater acoustics

Impulsive sound sources have been used extensively in underwater acoustics for many different research applications. Since the initial work by Weston in developing a simple analytical model for an underwater explosion, there have been several theoretical and experimental programs designed to determine source levels. More recently, other types of sources such as air guns and water guns have been introduced from marine seismic research, and there is renewed interest in knowing accurate source levels for assessing the impact on marine environments. In this paper the results of a series of experiments carried out to measure the source levels of several different types of impulsive sources are summarized. These included traditional 0.82-kg SUS charges, small and medium sized air guns from 5–185 cu. in., and a 160 cu. in. water gun. The SUS charges were exploded at shot depths from 18–200 m, and the air guns and water guns were fired at shallow depths from 1–5 m, corresponding to the conventional operating depths. The experiments provided high-quality shot waveforms that were processed to determine calibrated source levels in 1/3 octave frequency bands from 10–600 Hz. The measured values are compared to predictions from Weston’s simple model.