Peak Sound Pressure Research Articles

Instrumentation techniques for the measurement of gunfire (Part 3)

This paper is the third in a series concerning near-field measurement of sound pressure from small arms gunfire. It has been long established that exposure to gunfire events can lead to permanent threshold shift for an unprotected shooter. Close to a shooter's ear, the peak sound pressure level from a rifle or pistol can be 155-to-160 decibels with a pulse rise time on the order of ten microseconds. The U.S. Department of Defense has considered two approaches for assessing exposure limits from small arms gunfire - one involves the unweighted peak sound pressure and the other a series of A-weighted sound exposure events integrated to obtain an equivalent eight-hour dose. This dose is then compared to hearing damage risk criteria established for continuous noise signals. The first approach places great demands on the measurement system since the necessary bandwidth extends well into the ultrasonic range, thereby requiring fast slewing from the amplifiers combined with high sampling rates from the digitizer. The second approach requires the A-weighting filter to have specified time and frequency domain properties in the ultrasonic region. The paper discusses some laboratory experiments using actual gunfire signals to simulate the outcome from both approaches.

The Noise Exposure of Urban Rail Transit Drivers: Hazard Classification, Assessment, and Mitigation Strategies

Prolonged exposure to high-intensity noise environments in urban rail transit systems can negatively impact the health and work efficiency of drivers. However, there is a lack of comprehensive understanding of the noise pattern and, therefore, effective mitigation strategies. To control the noise in urban rail transit systems, this study proposes a comprehensive noise assessment framework, including metrics such as average sound pressure level, peak sound pressure level, percentile sound pressure levels, dynamic range, main frequency component, and cumulative time energy to evaluate the noise characteristics. We also employ a density-based spatial clustering of applications with noise (DBSCAN) method to identify the noise patterns with the evaluation of their hazard to urban rail transit drivers. The results have revealed that: (1) The equivalent continuous sound pressure level (Leq) in the cab of Lanzhou Urban Rail Transit Line 1 averages 87.12 dB, with a standard deviation of 8.52 dB, which reveals a high noise intensity with substantial fluctuations. (2) Ten noise patterns were identified, with frequencies varying from 14.47 Hz to 69.70 Hz and Leq varying from 60 dB to 115 dB. (3) The major noise sources from these patterns are inferred to be the train’s mechanical systems, wheel–rail interaction, aerodynamic effects, and braking systems. Combined with the noise patterns and urban rail transit’s operation environment, this study proposes tailored mitigation strategies for applications aimed at protecting drivers’ hearing health, enhancing work efficiency, and ensuring driving safety.

Surgeons Who Perform Total Hip Arthroplasty Are at Risk for Noise-Induced Hearing Loss, Especially When Using Automated Broaching.

Noise-induced hearing loss (NIHL) is a serious concern for orthopedic surgeons. The National Institute for Occupational Safety and Health (NIOSH) sets the safe exposure limit at 85 dB for 8 hours, yet operating rooms often surpass this limit. This study investigated if using an automated broaching system exposes orthopedic surgeons to dangerous decibel (dB) levels. A prospective study analyzed 138 intraoperative sound recordings from 92 total hip arthroplasty (THA) surgeries and 46 baseline measurements at an academic-affiliated private practice, using the NIOSH Sound Level Meter (SLM) application and a microphone. The surgeries were categorized into manual and automated broaching. Key metrics measured included maximal dB level (MDL), peak sound pressure (LCpeak), average continuous sound (LAeq), and average weighted sound in an 8-hour period (TWA), along with dose representations, to identify hazardous noise levels. Of the 92 THA sound recordings, 50 used manual broaching and 42 employed automated broaching. Automated broaching exhibited higher noise levels, with an average MDL of 109.92 dBA, a LAeq of 86.09 dBA, a TWA of 76.48 dBA, and a projected noise dose of 137.74%. In contrast, manual broaching exhibited an average MDL of 105.87 dBA, a LAeq of 83.06 dBA, a TWA of 72.82 dBA, and a projected noise dose of 82.02%. This study highlights the auditory risks from automated broach and manual THA surgeries that orthopedic surgeons experience. Manufacturers should focus on reducing instrument noise when designing surgical tools and orthopedic surgeons and operating room staff should take measures to protect themselves from NIHL during surgery. [Orthopedics. 202x;4x(x):xx-xx.].

Evaluation of acoustic environmental effects and improvement method of ecological fish-nest bricks in the Yangtze River Basin: A model-based case study

With the rapid development of the Yangtze River Basin, the issue of underwater noise pollution has become increasingly severe, which has adversely affected aquatic creatures, particularly fish. Ecological fish-nest bricks (EFNBs), a new type of eco-friendly revetment, can provide a favorable habitat for fish. However, its effects on the acoustic environment remain unclear. The finite element numerical simulation method of acoustic-structure coupling is adopted to explore the acoustic environment of EFNBs, analyzing the impact of sound source frequency (within 300 Hz), structural forms, and arrangement of these bricks on the internal sound pressure level. The sound pressure level distribution of A-EFNBs were also analyzed at a distance of 0–0.5 m from the opening. A method of acoustic environment improvement is proposed, which utilizes porous polyurethane sponge (PPS) sound-absorbing material to establish a conducive acoustic environment for fish in EFNBs. The study results indicate that at low frequencies of sound source (f ≤ 150 Hz), the sound pressure level within EFNBs slightly decreases compared to the adjacent areas without EFNBs. The sound pressure level variation within the bricks increases with sound source frequency. The peak sound pressure increases with the number of openings. Interval arrangements can in general decrease sound pressure by less than 20 dB. At higher frequencies(f＞200 Hz), the sound pressure level at the opening of the A-EFNBs tends to increase. However, the PPS sound-absorbing material substantially reduces the sound pressure level by 15 –55 dB, rendering it an effective method for improving the acoustic environment for fish. The PPS sound-absorbing material is more suitable for habitat improvement of black carp (Mylopharyngodon piceus) and grass carp (Ctenopharyngodon idellus) with relatively low hearing thresholds among the four famous Chinese carps. The research findings can serve as a reference for designing and implementing river ecological restoration projects.

Power saw noise levels during steel stud cutting tasks on commercial construction sites: a tool characterization from a worker exposure standpoint.

Construction framers who cut and install steel studs as part of their daily tasks are exposed to hazardous noise levels during their work shift in large part due to the power saws they use to cut steel studs. This investigation characterized the sound pressure levels of power saws used to cut steel studs on active construction sites. Further, the length of time it took to cut various studs on a construction site was investigated to understand worker exposure times to saw noise. In general, power saws used on the study sites to cut steel studs had a mean A-weighted equivalent continuous sound pressure level (LAeq) of 107.2 dB and a C-weighted peak sound pressure level (LCpeak) of 120.1 dB. Three of the saws-the chopsaw, the cut-off saw, and the grinder-had similar noise levels, whereas the cordless circular saw had higher noise levels. It took an average of 13.2 s to cut each stud, and workers in the study used power saws to cut steel studs for an average of 371.5 s per day. This average exposure time at the average recorded sound pressure levels (SPLs) suggests these saws can increase the risk of occupational noise-induced hearing loss, according to National Institute for Occupational Safety and Health (NIOSH) recommendations.

Noise-Induced Hearing Loss: Should Surgeons Be Wearing Ear Protection During Primary Total Joint Arthroplasty?

The risk of noise-induced hearing loss (NIHL) to orthopedic surgeons due to occupational exposures is unknown. A level of 85 decibels (dB) over an 8-hour time-weighted average (TWA) is considered hazardous. We sought to identify whether manual and/or robotic arthroplasty procedures increase surgeons' risk of developing NIHL. At our institution, we prospectively collected intraoperative recordings with a microphone attached to the surgeon during manual total knee arthroplasty (TKA), manual total hip arthroplasty (THA), and robotic-assisted total knee arthroplasty (RTKA). Recordings taken in the operating room without operating room staff present served as baseline controls. The 172 recordings consisted of 46 baseline, 42 THA, 40 TKA, and 44 RTKA recordings. Decibel levels were reported as "maximum dB level" (the highest sound pressure level using an A-weighted dB scale), "LAeq" (the equivalent continuous sound level), "LCpeak" (the peak sound pressure level using a C-weighted dB scale), and "TWA" (the average dB level projected over an 8-hour period). The percentage of allowable daily noise dose was reported as "dose" and the measured dose projected over 8 hours as "projected dose." The recordings of surgeries had average maximum dB levels ranging from 106.0 to 108.0 dB, all significantly greater than controls. Robotic-assisted total knee arthroplasties had the highest average dose (18.7%) and average projected dose (252.0%). Our review of recordings at a single institution found that noise levels of RTKAs surpassed projected doses of 100%. Orthopedic surgeons performing more than 2 RTKAs per day may be at increased risk of NIHL. Further research is needed to assess the effectiveness of measures such as ear protection to minimize surgeons' exposure.

Acoustic comfort improvement of simultaneous heating and cooling heat pumps using control logic for flow-induced noise reduction

Acoustic comfort in buildings can be achieved by minimizing unwanted noise generated primarily from heating, ventilation, and air-conditioning systems. However, research on noise reduction in simultaneous heating and cooling heat pumps (SHCHP) is limited. This study proposes a novel noise reduction control logic (NRCL) based on experiments on flow-induced noise through electronic expansion valves (EEVs) in an SHCHP. The flow-induced noise through EEVs was measured and analyzed regarding the degree of subcooling, differential pressure between indoor unit and evaporation (ΔPindoor), EEV opening speed (Vo), and opening (Oeev) while switching operation mode in an SHCHP. For all the operating and controllable variables, the peak sound pressure level (SPLpeak) was decreased by evenly distributing sound energy (SE). The sensitivity analysis indicated that Oeev and Vo were the most significant variables for achieving uniformly distributed SE. Therefore, a novel NRCL was proposed in terms of the initial EEV opening (Oeev,i) and dimensionless control time (CT) derived from the relationship between Oeev and Vo. The optimal CT for EEVs in SHCHP with NRCL was 1. At this point, the difference between SPLpeak and average SPL decreased by 46.2%, and the converging time for ΔPindoor to 0 increased by 17.8% compared with those of baseline.

Study on impact of robotic-assisted orthopaedic industrial noise (SIREN).

The aim of this study was to evaluate noise exposure to the operating room staff consisting of the surgeon, assistant, anaesthetist and Mako Product Specialist (MPS) during Mako robotic-arm assisted total knee arthroplasty (TKA) and total hip arthroplasty (THA). We aimed to determine whether employees were exposed to noise at or above a lower exposure action value (LEAV) set out by the Noise at Work Regulations 2005, Health and Safety Executive (HSE), UK. We prospectively recorded intra-operative noise levels in Mako robotic-arm assisted TKA and THA over a period of two months using the MicW i436 connected to an iOS device (Apple), using the Sound Level Meter App (iOS) by the National Institute for Occupation Safety and Health (NIOSH). Data obtained was then used to calculate "worst case" daily exposure value to assess if sound levels were compliant with UK guidelines. Comparison between operating room staff groups was performed with ANOVA testing. A total of 19 TKA and 11 THA operations were recorded. During TKA, for the primary surgeon and the assistant, the equivalent continuous sound pressure level (LAeq) was over 80 dB, exceeding the LEAV set out by the Noise at Work Regulations by HSE. During THA, the average LAeq and peak sound pressure levels did not exceed the LEAV. The calculated daily exposure for the primary surgeon in TKA was 82 dB. A Tukey post hoc test revealed that LAeq was statistically significantly lower in the anaesthetist and MPS (p < .001) compared to the primary surgeon and assistant in both TKA and THA. Operating room staff, particularly the primary surgeon and assistant are exposed to significant levels of noise during Mako robotic-arm assisted TKA and THA. Formal assessments should be performed to further assess the risk of noise induced hearing loss in robotic-arm assisted arthroplasty.

Comparison of two acoustic test fixtures for measuring impulse level dependent attenuation

In the American National Standards Institute (ANSI) S12.42-2010 standard for measuring insertion loss of hearing protection devices (HPDs) in impulsive noise, the range of peak sound pressure levels for the impulses is 132 to 168 dB peak sound pressure level (dB pSPL). The specification of the acoustic test fixtures (ATFs) included an IEC 60318-4 ear simulator fitted with a microphone. The microphones typically used are a ¼” cartridge and have a dynamic range up to about 169 dB pSPL. For most small caliber firearms, the peak SPLs are less than 170 dB SPL at the location of the shooters ear (Schulz et al. 2013). For some military weapon systems that produce impulses greater than 170 dB pSPL, impulse insertion loss cannot be assessed without exceeding the microphone maximum dynamic range. Some condenser microphones have maximum dynamic ranges of 190 dB pSPL. This paper compares insertion losses for HPDs measured on two GRAS 45CB ATFs with microphones with maximum dynamic ranges of 169 and 193 dB pSPL. Waveform distortion, field probe to unoccluded transfer functions between the ATF and field probe will be examined for distortion and accuracy when estimating the impulse level dependent attenuation.

Influence of reference transducer location on hearing protector attenuation metrics for impulse noise

The ANSI/ASA S12.42-2010 standard can be used to estimate the attenuation for impulsive noises between 130 and 170 decibels peak sound pressure level (dB pSPL). The ANSI/ASA S12.42 method uses a complex transfer function between the signal received in the ear of an acoustic test fixture (ATF) and a reference transducer. The reference transducer is at the same radial distance from the impulse source and at less than 30 degrees from the ATF angle. The reference transducer is specified as a pencil-type pressure (&amp;gt; 40.6 cm long). The maximum angle and the minimum pencil probe dimensions could be incompatible near the source, or may introduce artifacts or hazards. In this study, several hearing protectors were evaluated with two rifles (A-Bolt .300 Winchester Magnum and Colt AR-15 5.56 caliber), two ATFs (GRAS 45CB), and five transducers (four ¼” microphones and one surface mount microphone). The ATFs were on opposite sides of the gun at distances for field levels between 180- and 140-dB pSPL. For each location and rifle, S12.42 metrics were calculated for all 20 combinations of ATF ear and reference transducer. Results indicated that S12.42 metrics were minimally affected by the locations of the reference transducers.

Determination of the sound level during different management measures in piglet rearing related to animal welfare and human health and safety

In the present study, sound level measurements were taken during management measures with expected high noise exposure on three German pig farms in order to quantify the noise level for pigs and farm staff. The sound level was measured during different activities, such as teeth grinding and tail docking of piglets, vaccination, castration with anaesthesia, stabling and rehousing the pigs. The equivalent continuous sound level (LAeq) was measured as well as the actual sound level (LAF) and the peak sound pressure level (LCPKmax). The latter two were assigned to specific sound events during the individual measures, such as piglet screams or using the pig paddle. Rehousing the pigs at the end of the nursery period resulted in the highest continuous sound levels (LAeq= 83.3 ± 4.9 dB(A)), followed by anaesthesia before castration (LAeq = 78.1 ± 7.4 dB(A)) and teeth grinding and tail docking of piglets (LAeq = 77.5 ± 3.6 dB(A)). The peak sound pressure level LCPKmax was more than 100 dB(A) for all measures with an absolute maximum of 129.7 dB(A) when pigs were being moved out of the nursery compartment. Furthermore, the human pain threshold of 120 dB(A) was exceeded in isolated cases when nursery pigs were being moved to the stable (LCPKmax = 121 dB(A)) and during anaesthesia before castration (LCPKmax = 125.2 dB(A)). During the individual measures, particularly high sound levels were generated when using a pig paddle (LAF = 92.1 ± 7.8 dBA)), when pigs ran over a loading ramp of a transporter (LAF = 93.8 ± 1.4 dB(A)) or when piglets screamed (LAF = 87.9 ± 7.5 dB(A)). The piglets’ screams were particularly loud during anaesthesia before castration (LAF = 90.0 ± 9.2 dB(A)), during vaccination (LAF = 89.6 ± 6.5 dB(A)) and during teeth grinding and tail docking (LAF = 89.5 ± 5.9 dB(A)).Even if the LAeq was always below 85 dB(A), i. e. the limit specified in European legislation (EU Directive 2008/120/EC) for continuous noise in piggeries, there were brief sound peaks that exceeded the pain threshold of 120 dB(A). In the interest of animal welfare and human health, noise should be reduced by a gentle handling of pigs. The use of the pig paddle should be restricted whenever possible. Additionally, farm staff should wear hearing protection when carrying out those measures that were identified as particularly noise-intensive in this study.

In-situ comparison of high-order detonations and low-order deflagration methodologies for underwater unexploded ordnance (UXO) disposal

The unexploded ordnance (UXO) on the seabed off Northwest Europe poses a hazard to offshore developments such as windfarms. The traditional removal method is through high-order detonation of a donor explosive charge placed adjacent to the UXO, which poses a risk of injury or death to marine mammals and other fauna from the high sound levels produced and is destructive to the seabed. This paper describes a sea-trial in the Danish Great Belt to compare the sound produced by high-order detonations with that produced by deflagration, a low-order disposal method that offers reduced environmental impact from noise. The results demonstrate a substantial reduction over high-order detonation, with the peak sound pressure level and sound exposure level being around 20 dB lower for the deflagration. The damage to the seabed was also considerably reduced for deflagration, although there was some evidence for residues of explosives related chemicals in sediments.

Experimental analysis of the effect of ultrasonic vibration on porosity suppression in narrow gap laser welding

Abstract The welding process has a wide range of applications in aerospace, military manufacturing, machinery, and other fields, and with the continuous improvement of welding technology requirements, the inhibition of porosity in the welding process is also increasing. This study, through the narrow gap laser welding characteristics and porosity formation mechanism of the depth of analysis, for the existing narrow gap laser welding method exists in the side wall of the weld fusion is poor porosity, poor uniformity of organizational properties and other issues, proposed ultrasonic-based welding method to achieve effective inhibition of porosity. The experimental analysis of ultrasonic vibration on the formation of porosity is carried out based on narrow-gap laser welding. The peak sound pressure of narrow gap welding increases when the ultrasonic current amplitude changes from 24A to 32A. Under different ultrasonic vibration conditions, the number of welds without applied ultrasound was as high as 95, while the number of porosities gradually decreased to 48 with the increase of applied ultrasound amplitude from 12% to 37%. Furthermore, as the ultrasonic amplitude increased, the residual height decreased by 0.45 ml. In addition, at fixed ultrasonic amplitude, with the increase of laser power, the porosity increased from 0.89% to 2.21%, and the average diameter of the porosity increased from 0.29 mm to 0.43 mm. The porosity for the porosity diameter of less than 200 μm was reduced to 0.020%. The percentage of stomata with a diameter greater than or equal to 200μm increased to 2.098%. This study analyzes the inhibition effect of ultrasonic vibration on porosity to a certain extent. Moreover, the inhibition effect of ultrasonic vibration in narrow gap laser welding is significant and the smaller the laser power under the same amplitude, the better the inhibition effect, which provides a valuable reference for the research of the narrow gap laser welding process.

Maximum Fast time-weighted levels - When can a transient be seen as a Dirac impulse?

It is common practice to use maximum FAST time-weighted sound pressure levels to assess transient impact noise, as these levels correlate well with human perception of impact noise. Maximum FAST time-weighted levels are known to be dependent on the reverberation time of the receiving room. In previous studies, an analytical correction term was developed using a Dirac impulse. The correction term is used to calculate the maximum FAST time-weighted levels from peak sound pressure levels. Peak levels are independent of the reverberation time of the room. Applying the correction term makes it possible to compare measurement results from different rooms. The correction term has been validated in several studies for the standard rubber impact ball. In this paper, the influence of the source signal (Dirac impulse) on the correction term is studied. Analytical and numerical models are employed to investigate the consequences of stretching the impulse in time and of changing its shape. The results are compared with empirical solutions developed in other studies.

Underwater Noise Characteristics of the Tidal Inlet of Zhanjiang Bay

The coupling mechanism between natural and anthropogenic noise in shallow marine areas is of great significance for maintaining the ecological safety of these regions. In this study, a section of Zhanjiang Bay’s entrance was selected as a typical research area, and environmental noise data at different depths were collected during the spring and autumn seasons. The spectral characteristics, sound pressure levels, and underwater noise frequency correlation matrices of environmental noise were analyzed to reveal the underwater noise characteristics of tidal channels in Zhanjiang Bay and their main influencing factors. The results show that underwater noise in this study area had a stable frequency band distribution. In the low-frequency range of 20–50 Hz, the main source of noise was the flow noise influenced by tides and topography, with a peak sound pressure level of approximately 97 dB. In the frequency range of 50 Hz to 500 Hz, the main noise sources were ships at sea, followed by wind-generated noise. At frequencies above 500 Hz, the noise intensity decreased. In addition, it was found that the sound pressure level in the low-frequency range had a significant correlation with the tidal level, increasing with the rise of the tide and decreasing during low tides. This study provides a research case on the impact that human noise activity has on environmental noise in shallow marine bays. These research findings can support the selection of sites and reduce construction noise from offshore wind farms, as well as ensure the acoustic ecological environment in the vicinity of marine ranches.

Underwater soundscape observations and associated demersal fish movement during a seismic airgun survey in coastal Oregon

Sound is a crucial aspect of the underwater environment for fishes—various species use sound to communicate, identify predators, navigate, and many other activities needed for survival in their habitat. In the summer of 2021, a seismic survey passed nearby Southern Oregon to map the Cascadia Subduction Zone using an array of airguns. To evaluate the effect of the seismic survey on the behavior of demersal fish, acoustic pressure and particle motion measurements were collected within a marine protected area, accompanied by tagging of two rockfish species, Black Rockfish (Sebastes melanops) and China Rockfish (S. nebulosus). Acoustic measurements were obtained using a vector sensor array, deployed in 25 m deep water. It was found that while cumulative sound exposure levels were dominated by wind noise, other metrics such as peak sound pressure, kurtosis, acoustic complexity index, crest factor and acoustic entropy showed clear signals associated with the seismic survey. Animal behavior and spatial use by the two rockfish species were also evaluated. Overall, results indicate that there are slight differences in movement and spatial use during times of seismic survey noise presence, but observed differences are reduced after only a few days.

A new method for measurement of impulsive peak level attenuation of hearing protectors

ASA/ANSI S12.42-2010 contains the first standardized test method for measuring the performance of hearing protection devices (HPDs) with high-level impulsive noise. This standard defines the impulsive peak insertion loss (IPIL) as a time-domain metric that quantifies the reduction in peak sound pressure level provided by an HPD for impulsive noises. However, IPIL as defined in S12.42-2010 is dependent on the spectrum of the impulsive noise source used for measurements of HPDs. Recent studies of HPDs with impulsive noise have led to the investigation of frequency-domain metrics and calculation methods. Using frequency-domain calculations allows the impulsive peak level attenuation to be computed for a wide range of impulsive noises, not only those used for the measurement. Consequently, significant revisions to S12.42 are under consideration and a new standard, ISO 4869-7, is being developed in parallel with the ANSI revision. This presentation highlights key proposals and substantive changes including: measurement and calculation of the frequency-dependent impulsive insertion loss (IIL), incorporation of frequency-domain aspects such as real-ear attenuation at threshold (REAT) limits to attenuation, and a new impulsive peak level attenuation metric (IPLA) to be calculated from the REAT-bounded IIL.

Sound source direction-of-arrival estimation method for microphone array based on ultra-weak fiber Bragg grating distributed acoustic sensor.

A sound source direction-of-arrival (DOA) estimation method for microphone array based on ultra-weak fiber Bragg grating (UW-FBG) distributed acoustic sensor is proposed. The principle of acoustic signal demodulation is introduced, the sound pressure sensitivity and frequency response range of a single UW-FBG microphone are analyzed, and a series linear array with three UW-FBG microphones is designed. Combined with convolutional recurrent neural networks, the DOA estimation method is developed. Log-Mel spectral features and SCOT/PHAT joint weighting generalized cross correlation features are used for DOA estimation. The corresponding system is established and experimentally verified. Results show that the measured sound pressure sensitivity of the UW-FBG microphone is in the range of 0.1032-3.306 rad/Pa within the frequency range of 1000-3000 Hz, and the peak sound pressure sensitivity is about 3.306 rad/Pa. The estimated mean error of 2D DOA estimation is about 2.85°, and the error of 3D DOA estimation is about 5.465°. This method has good application prospects in distributed sound source localization.

Analysis of the Effect of Circular Ring Baffles in Suppressor on Flow Field and Far Field Noise Levels at 9 mm Semi Automatic Pistol

A firearm generates complex phenomena in muzzle flow and modelling the flow field around the projectile has great importance on high-intensity noise prediction. The negative effects of noise can be reduced using a suppressor which can be internally or externally attached to the barrel of a firearm. The purpose of this paper is to numerically and experimentally investigate the effect of the number and distance of circular ring baffles in the suppressor on the flow field and far field noise levels. Calculations were carried out in two-dimensional, axisymmetric, transient conditions and Ffowcs Williams and Hawkings acoustic analogy (FW-H) equations were solved to predict the far field noise. Nine cases including a gun without a suppressor, a suppressor without baffles, one, three, and five baffles which were placed at 20 mm intervals from the suppressor inlet, and one, three, five, seven, and nine baffles which were placed with equal intervals in the suppressor were simulated and compared; generations of noise during the shooting process were analyzed. The results showed that in the case without a suppressor, the peak sound pressure level was 156.1 dB at a 2.5 m distance, while this value decreased by nearly 7.6% in the case of the suppressor with seven baffles which has an average value of 144.2 dB. The results obtained here may provide a beneficial reference for predicting the muzzle noise and optimizing the number of baffles in the suppressor for small caliber gun systems.

Research on the directional characteristics of wind noise emitted by bionic rods

In this paper, the directional characteristics of wind noise emitted by different bionic rods were studied based on a hybrid computational aeroacoustics method. The noise reduction mechanism of surface grooves, pits, and bumps was analyzed, respectively. The basic principle of noise reduction is to reduce the influence of the vortex shedding on the rod by changing the shape of the rod or passive control technology to reduce the dipole sound source. The unsmooth transverse surface will increase the loss of flow on the leading edge of the rod and reduce the vertical effect of vortex shedding on the rod. The convex leading edge of the rod can help to transfer the vertical noise from low frequency to high frequency and reduce the vertical effect of wake vortex shedding to reduce the peak sound pressure level. The cost of those was the increase in the aerodynamic drag and the increase in noise in the flow direction (the increase in the amplitude of drag fluctuation). In particular, the longitudinal v-groove structure on the surface of the elliptical rod can reduce the circumferential aerodynamic noise while keeping the aerodynamic drag coefficient unchanged.