Low-frequency Sound Pressure Level Research Articles

Temporal patterns in the soundscape of the port area in an urban estuary

Soundscape ecology, facilitated by the collection of environmental sounds, enables the determination of the area used by specific species, estimation of population abundance, verification of habitat health, and assistance in management and monitoring processes. Estuaries are key environments in the life cycle of many species. As coastal ecosystems, they face potential impacts by human activities. This study aims to characterize the soundscape of the Patos Lagoon estuary (PLE), Brazil, examining its temporal and seasonal variations. Additionally, it seeks to investigate the influence of temperature and salinity on sound pressure levels (SPL) across three different frequency bands throughout the year. For data collection, two autonomous devices - a SoundTrap digital recorder and an F-POD sampler - were used. The data collection spanned from September 2020 to August 2021 and covered one consecutive week per season. The analysis of audio files was performed manually using Raven software. Sound emissions by Lahille's bottlenose dolphin (Tursiops truncatus gephyreus) and fish were observed throughout the sampling period, with peak detections occurring during the summer and spring, respectively. Boat noise was detected throughout the year but more intensely in the summer. Generalized linear models (GLMs) revealed that, for the three SPL frequency bands, the season significantly influenced the composition of the PLE soundscape, with positive fluctuations in the warmer seasons (summer > spring > autumn > winter). Salinity, in turn, showed a slightly negative relationship with the SPL values in the three models, suggesting a decrease in frequencies with increasing salinity. Our results also indicate that the low-frequency SPL, originating mostly from various sources of anthropogenic noise, constitutes the main component of the PLE soundscape. In conclusion, our study provides novel insights into the temporal patterns of the soundscape in an urban estuary, including biotic and anthropogenic sounds, and their relationships with selected environmental variables.

Design and analysis of two-way microspeaker to enhance mid-frequency sound pressure level

This study presents a novel two-way microspeaker design (SPK) aimed at improving the mid-frequency sound pressure level (SPL) without compromising the overall dimensions. This innovative approach includes a new magnetic circuit design, new diaphragm structures, and electromagnetic-mechanical-acoustic (E-M-A) coupling analysis of two microspeakers (SPKs). First, the E-M-A coupling method is validated on the prototype SPK, which forms the basis for subsequent design iterations. Four types of SPKs, with strategically reduced magnet numbers, are introduced and enhance the force factor of microspeakers. A new diaphragm structure that uses two side diaphragms with varying hardness levels effectively controls the resonance frequencies for each SPK. The SPL results demonstrate that Type 4 with new diaphragm structure exhibits a significant 0.94 dB increase in the mid-frequency SPL compared with the prototype, with minor reduction in the low-frequency SPL. The conclusion turns out the two-way SPKs can be uses as a good approach to improve the mid- frequency SPL.

Towards a practical methodology for assessment of the objective occlusion effect induced by earplugs.

The occlusion effect (OE) occurs when the earcanal becomes occluded by an in-ear device, sometimes leading to discomforts experienced by the users due to the augmented perception of physiological noises, or to a distorted perception of one's own voice. The OE can be assessed objectively by measuring the amplification of the low-frequency sound pressure level (SPL) in the earcanal using in-ear microphones. However, as revealed by methodological discrepancies found in past studies, the measurement of this objective occlusion effect (OEobj) is not standardized. With the goal of proposing a robust yet simple methodology adapted for field assessment, three experimental aspects are investigated: (i) stimulation source and the stimulus's characteristics to induce the phenomenon, (ii) measurement method of the SPL in earcanal, (iii) indicator to quantify the OEobj. To do so, OEobj is measured on human participants in laboratory conditions. Results obtained with a specific insert device suggest using the participant's own voice combined with simultaneous measurements of the SPLs based on the noise reduction method and using a single value indicator leads to a simple yet robust methodology to assess OEobj. Further research is necessary to validate the results with other devices and to generalize the methodology for field assessment.

Design and analysis of watch speaker to enhance waterproof performance by using liquid silicone rubber side diaphragm

Smartwatches provide many useful functions to users, such as texting messages, receiving social media updates, and playing music. The microspeaker used in a smartwatch needs to be smaller than that used in a smartphone, and it also requires high-quality acoustic and good waterproof performance. This study proposes a watch speaker with improved low-frequency acoustic performance by using the electromagnetic-mechanical-acoustic (E-M-A) coupling analysis method. Experimental results obtained using a prototype were used to validate the analysis method. Based on the same method, a novel type of watch speaker with smaller airgaps demonstrated an improved sound pressure level (SPL) at low frequencies when using a 60 A shore-hardness liquid silicone rubber (LSR) side diaphragm (SDP). The novel type using 60 A hardness SDP is named novel type #1. At the same time, novel type #2 and novel type #3 were analyzed for comparison with novel type #1. The analysis SPL results show that the novel type #2 shows a better low-frequency SPL and a minor drop in the mid-frequency. The watch-speaker samples were manufactured and subjected to SPL measurements. Furthermore, the novel type #2 with LSR has lower von Mises stress on the SDP, excellent waterproof performance that can withstand 10 ATM, and similar total harmonic distortion (THD) to prototype.

Design and Analysis of a Novel Microspeaker with Enhanced Low-Frequency SPL and Size Reduction

In the era of multimedia devices, smartphones have become the primary device for consuming multimedia content. As technological developments have facilitated a more immersive multimedia experience, enlarged displays and the use of several sensors have limited the allowable size of microspeakers. Although sound plays an important role when consuming multimedia content, the limited space for microspeakers in modern devices leads to poor acoustic performance, especially at low frequencies. To address this issue, this paper proposes a novel microspeaker structure that enhances the low-frequency sound pressure level (SPL), while also featuring reduced exterior dimensions. The structure was designed and analyzed using 3D finite element analysis. Through coupling analysis, the simulation results were verified on the basis of the experimental results. The novel microspeaker has one outer magnet surrounding the entire coil, unlike in prototype microspeakers, which have two outer magnets. The gap between the top plates and coil is reduced, and a new type of coil is introduced for the purpose of increasing electromagnetic force. The samples were manufactured, and their SPLs were tested in an anechoic chamber. The experimental results prove that the proposed microspeaker offers an improved SPL at low frequencies compared with prototype microspeakers.

On the design of piezoelectric MEMS microspeaker for the sound pressure level enhancement

This study aims to design and realize MEMS microspeakers with high sound pressure level (SPL) for in-ear applications. On the basis of high piezoelectric coefficient PZT thin film, the proposed suspension-spring and dual-electrode designs enhance the out-of-plane displacement of central diaphragm to improve low-frequency SPL. The preliminary tests show that both proposed single-curve and dual-curve spring designs have higher low-frequency SPL than that of the reference clamped diaphragm microspeaker. Measured in the standard ear simulator systems with 2 Vpp driving voltage, the proposed dual-curve spring design demonstrates good performance at low frequencies. At the resonant frequency of 1.85 kHz, the dual-curve spring design is 28 dB SPL higher than the clamped diaphragm. In addition, from 100 Hz to 3 kHz, more than 10 dB SPL enhancement is achieved. Furthermore, the total harmonic distortion (THD) of dual-curve spring design is less than 2% in most of the audio range. Compared with the published literature of piezoelectric MEMS microspeakers, this study shows a reasonable SPL with the smallest diaphragm area of 1 mm2.

The influence of axial-flow fan trailing edge structure on internal flow

Axial-flow fan with advantages such as large air volume, high head pressure, and low noise is commonly used in the work of air-conditioner outdoor unit. In order to investigate the internal flow mechanism of the axial-flow fan with different trailing edge structures of impellers, four kinds of impellers were designed, and numerical simulation and experiment were deployed in this article. The pressure distribution on the blades surface and distribution of vorticity in impellers were obtained using numerical simulation. Distribution of blade loading and velocity at the circumference are discussed. The relationship between the wideband noise and the trailing edge was established based on the experiment results. The results show that after the optimization of the trailing edge structure, the distribution of vorticity near the trailing edge of the blade is more uniform, especially at the trailing edge of 80% of the chord length of the suction surface. From the blade height position of 70% to the impeller tip, the pressure on the surface rapidly increases due to the tip vortex and the vortex shedding on the blade edge occurred in the top region of impeller. The pressure fluctuation amplitude at the trailing edge structure of the tail-edge optimization structure is smaller. In the distribution of blade loading, the three tail-edge optimization structures have smaller pressure fluctuations and pressure differences at the trailing edge structure. It is extremely important to control the fluctuation amplitude at the trailing edge. The amplitude of low-frequency sound pressure level of optimizing the trailing edge structure decreases obviously in the range of 50–125 Hz, and the optimization structure of trailing edge has an obvious effect on low-frequency wideband noise.

Active and Passive Helicopter Noise Reduction Using the AVINOR/HELINOIR Code Suite

A suite of computational tools capable of predicting in-plane low-frequency rotorcraft noise and its control using blade-tip geometry modifications is developed. The combined code, consisting of AVINOR, a comprehensive rotorcraft analysis code, and an acoustic code called HELINOIR, is first validated against wind-tunnel tests and subsequently verified by comparing with computational results. Three rotor configurations resembling the Messerschmitt-Bölkow-Blohm BO105 with a tip sweep, dihedral, and anhedral were simulated for level flight at a moderate advance ratio. The impact of passive blade geometry modification on in-plane noise and vibration is studied and compared to the in-plane noise reduction obtained using a single 20% chord active plain trailing-edge flap with a feedback microphone on the left boom. Active control, which is implemented using an adaptive higher harmonic control algorithm, reduces in-plane low-frequency sound pressure levels below the horizon by up to 6 dB, but there is an increase in vibratory loads. The tip dihedral reduces low-frequency sound pressure level by up to 2 dB without a vibratory load penalty, but there is an increase in the midfrequency sound pressure levels. The tip sweep and tip anhedral increase in-plane low-frequency sound pressure level below the horizon. There is a general tradeoff associated with in-plane low-frequency sound pressure level reduction, vibration performance, and midfrequency sound pressure level.

A large-diaphragm piezoelectric panel loudspeaker and its acoustic frequency response simulation method

The authors applied the Finite Element Method (FEM) to analyze the electro-mechanical transformation and micro dynamical characteristics of a piezoelectric panel loudspeaker with triple layered piezoelectric ceramic slices in 2×2 rectangular arrangements. According to the simulated micro-vibration data, the authors built an acoustic analysis model combined with a linear superposition method to rapidly obtain the Sound Pressure Level (SPL) frequency response. FEM calculations of resonant modes, resonant frequencies, and the amplitude at the center of the diaphragm were in good agreement with measured values. The measured SPL frequency response agreed with the simulation, supporting the FEM model and the SPL frequency response calculation method proposed in this paper. In addition, an improved structure by addition of an elastic mat was illustrated and demonstrated to provide a smoother low-frequency SPL frequency response verified by both measurement and simulation methods.

Use of passive acoustic monitoring to characterize fish spawning behavior and habitat use within a complex mosaic of estuarine habitats

Structurally complex estuarine habitats, such as seagrass beds, salt marshes, and oyster reefs, are used by fish for foraging, avoiding predators, and spawning. Here, we used passive acoustics to characterize spatiotemporal patterns in the soundscape of an estuarine reserve that contained a mosaic of habitat types, and focused on relating characteristics of the soundscape [e.g., low-frequency (150–1500 Hz) sound pressure levels (SPLs), amount of fish chorusing] to patterns in the seascape (percent cover of estuarine habitats surrounding the recording sites). Over a 3-mo period, 2-min duration underwater sound recordings were made every 20 min at eight sites within Middle Marsh in Back Sound, North Carolina, USA. While habitat composition was not related to spatial patterns in low-frequency SPLs, there was a positive and statistically significant relationship between the percent recordings with fish chorusing, and percent cover of seagrass for silver perch [Bairdiella chrysoura (Lacepede, 1802)], spotted seatrout [Cynoscion nebulosus (Cuvier, 1830)], and other fish, irrespective of spatial scale (10 vs 25 m). Moreover, silver perch and spotted seatrout, soniferous species that share similar spawning locations, exhibited temporal partitioning in the soundscape with seatrout calls occurring just before sunset and peaking several hours after sunset, and declining sharply as perch chorusing increased after sunset with a peak at midnight. Overall, local habitat composition and the soundscape at these sites were not highly correlated; where major sound producing fish species are transient, other seascape characteristics, such as proximity to channels, likely have a larger influence on the resulting soundscape.

Measuring the Marine Soundscape of the Indian Ocean with Southern Elephant Seals Used as Acoustic Gliders of Opportunity

AbstractThe underwater ambient sound field contains quantifiable information about the physical and biological marine environment. The development of operational systems for monitoring in an autonomous way the underwater acoustic signal is necessary for many applications, such as meteorology and biodiversity protection. This paper develops a proof-of-concept study on performing marine soundscape analysis from acoustic passive recordings of free-ranging biologged southern elephant seals (SES). A multivariate multiple linear regression (MMLR) framework is used to predict the measured ambient noise, modeled as a multivariate acoustic response, from SES (depth, speed, and acceleration) and environmental (wind) variables. Results show that the acoustic contributions of SES variables affect mainly low-frequency sound pressure levels (SPLs), while frequency bands above 3 kHz are less corrupted by SES displacement and allow a good measure of the Indian Ocean soundscape. Also, preliminary results toward the development of a mobile embedded weather sensor are presented. In particular, wind speed estimation can be performed from the passive acoustic recordings with an accuracy of 2 m s−1, using a rather simple multiple linear model.

Study of measured indoor low-frequency noise levels resulting from outdoor noise sources, using a simplified physical model as well as empirical and FEM calculations

The paper presents an investigation simulating transformations of an acoustic field at low frequencies indoors, when the sound source is outdoors. The investigation was performed using a simplified and 5-times-smaller physical model. The paper presents measured spatial sound pressure level (SPL) distribution at 1/3 octave bands as well as at discrete frequencies (at various room modes). Measurements inside the physical model (at a total of 2,565 points) confirm that when exposed to outdoor broadband noise, low-frequency sound pressure levels at 1/3 octave bands inside the room can differ by more than 30 dB, while at discrete frequencies measured SPL can vary by 50 dB or more. Below the calculated lowest room mode, due to resonant vibrations of physical model walls, large differences in sound pressure levels inside the model (up to 20.7 dB at 100 Hz 1/3 octave band and up to 32.4 dB at discrete Hz frequencies) were found. The investigation also includes analysis of levels in the corners of physical models compared to average sound pressure levels in the whole model space or some cross-sections, which shows that sound pressure levels in corners can be up to 10 dB lower. Calculation of the indoor average sound pressure level at low frequencies according to empirical formulas specified in standard ISO 12354-3 showed conformity between measurement and calculation results only in a part of the investigated range of frequency bands. Calculations using FEM at discrete frequencies gave more adequate results of sound pressure levels and their spatial distribution. FEM calculations proved that calculation of the average sound pressure level from measurements at points every 25 cm (every 5 cm in the physical model) can produce results close to the average of the sound pressure level of the room if it were measured at every possible position.

Slat Noise Suppression with Mass Injection

The efficiency and mechanism of slat noise suppression with upstream mass injection was investigated through validated numerical simulations. Delayed detached-eddy simulation was used to describe the noise sources and Ffowcs Williams–Hawkings integration was carried out to obtain the far-field noise characteristics. Outward mass injection from the suction side of the slat near the cusp uplifted the free shear layer, and the corresponding impingement of free shear layer with slat pressure surface was alleviated. The tonal component of the far-field noise was diminished, and the suppression of the broadband noise was also observed. The inward injection of mass at the pressure side of the slat near the cusp facilitated the three-dimensional flow and the breakup of large-scale spanwise vortices, weakening the strength of the free shear layer, especially at the vicinity of the reattachment point. However, the introduction of strong turbulence at the downstream of the injection slot offset the benefits gained from the suppression of unsteadiness at the reattachment area. Although the low-frequency sound pressure level was lowered, two new strong peaks arose at higher frequencies, which contributed to a higher overall sound pressure level at the upstream direction below the airfoil.

Amplitude modulation of audible sounds by non-audible sounds: Understanding the effects of wind turbine noise

Our research has suggested a number of mechanisms by which low-frequency noise could bother individuals living near wind turbines: causing endolymphatic hydrops, exciting subconscious pathways, and amplitude modulation of audible sounds. Here we focus on the latter mechanism, amplitude modulation. We measured single-auditory-nerve fiber responses to probe tones at their characteristic frequency in cats. A 50 Hz tone, which did not cause an increase in spontaneous firing rate (i.e., was not audible to the fiber when presented alone) was used to amplitude modulate responses to the probe tone. We found that as probe frequency decreased, a lower level of the low-frequency non-audible tone was needed to achieve criterion amplitude modulation. In other words, low-frequencies that are coded in the cochlear apex require less low-frequency sound pressure level to be amplitude modulated as compared to higher-frequencies that are coded in the cochlear base. This finding was validated, and extended to lower frequencies, by amplitude modulating gross measures of onset-synchronous (compound action potentials) and phase-synchronous (auditory nerve overlapped waveforms) in guinea pigs. Our results suggest that that infrasound generated by wind turbines may cause amplitude modulation of audible sounds, which is often the basis for complaints from those living near wind turbines.

On the Threshold Level of Rattling Fittings Due to Low Frequency Sound Pressure Level

On the Threshold Level of Rattling Fittings Due to Low Frequency Sound Pressure Level

Managing an "Own Voice" Problem That Has an Amplifier Origin

The complaint from hearing aid wearers of hollowness in the sound of their voice is typically associated with excessive low-frequency sound pressure level (SPL) in the ear canal. Increasing the vent diameter and/or reducing the gain in the low frequency would typically minimize this complaint. This paper reports on a case where the origin of hollowness was insufficient low-frequency gain compared to a previous hearing aid fitting. It describes the systematic process that was followed in uncovering the origin of the patient's hollowness complaint. Clinicians might follow a similar objective approach in their fine-tuning process to resolve wearer complaints.