Sound Pressure Level Research Articles

An investigation into the audio-visual characteristics of restorative spaces using VR

The beneficial effect of nature on stress recovery is a topic of general importance, given that population growth, urbanization and thus noise-induced health impacts are likely to increase in the future. But what makes a recreational space 'restorative'? In this contribution, we present findings from a laboratory experiment using VR environments, on the contributions of different audio-visual characteristics of restorative spaces. Self-reported restorative potential and acoustic quality were assessed in a repeated measures design, varying visual setting (forest, lake, urban built space), soundscape (natural, anthropogenic), and sound pressure level (low, medium, high). First results indicate an additive effect of "naturalness": Restorative potential of spaces with both, natural visuals and natural sounds, was highest, but decreased significantly, when (a) moderate road traffic noise (LAeq ≤ 52 dB) was present, or (b) the visual environment was a non-green urban space. Urban spaces with anthropogenic soundscapes were rated with the lowest restorative potential. While increasing sound pressure levels within an anthropogenic soundscape decreased restorative potential, no such association was found for natural soundscapes. These results simultaneously highlight the beneficial effects of nature and the detrimental impact of road traffic noise on restoration.

Psychoacoustic assessment of automotive fan-systems

In the automotive industry, electrification trends worldwide are inducing an increase of noise sources emergences. This reinforces the acoustic assessment metrics and thresholds set by stakeholders to ensure acoustic comfort of car passengers and passersby. The main acoustic indicator, the overall Sound Pressure Level, is not relevant enough to depict pedestrian annoyance during exposure to fan-system noises. Currently, psychoacoustic assessment of these products is not systematic as the psychoacoustic metrics taken separately are not sufficient for sound quality ranking. In order to address this weakness, studies were performed by Valeo based on fan-system noise jury evaluations. It aims at providing a preference model consisting of an equation which combines several psychoacoustic metrics to assess fan-system noise annoyance; keeping in mind that Loudness -or overall SPL- high levels could mask underlying annoyances biasing its assessment. In a first step, the correlation between Overall SPL, Loudness and aeraulic power is highlighted based on standard benchmark test database. In a second step, since tonal noises affect the perceived annoyance, additional tonal metrics are analyzed versus Loudness, or acoustic classes. Tonality especially is then compared to other tonal criteria, before potential assessment of a preference model equation.

Which acoustic dimensions could act as mediators between urban greenspace and human health?

The beneficial effects of urban greenspace on human health and well-being are widely recognized, but the underlying mechanisms are incompletely understood. The acoustic environment (AE) is often proposed as a detrimental factor and emerging evidence suggests that it may also represent a beneficial resource. If different dimensions of the AE were to represent a mediator between greenspace and human health, they would need to be associated with both. We present results investigating the first prerequisite: the associations between acoustic dimensions and urban greenspace. We use audio recordings from SALVE, randomly sampled at 730 locations four times per year (n=2,746) in Bochum, Germany. The AE is quantified by 122 eco- and psychoacoustic indices, sound pressure levels and complex network measures. Greenspace is defined as the percentage of green area in a 300 m-buffer around each recording location, grouped into quintiles. We apply dimensionality reduction and present descriptive statistics to analyze the associations between identified acoustic dimensions and urban green area. In addition to the "sound volume", we find that biophonic sounds, the Acoustic Richness, the Impulsiveness, the Roughness, and the "acoustic dominance" show a consistently decreasing/increasing trend across the five quintiles of urban green area.

Interplay of perception, behavior, and sound: analyzing music activities in urban open spaces

This study conducted an exploratory investigation into the impacts of music activities in urban open spaces, focusing on the interrelations between perception, behavior, and A-weighted sound pressure levels (LAeq) associated with these activities. Utilizing observational and questionnaire methods, the research categorized music activities into dynamic (e.g., dancing) and static (e.g., singing) types. It revealed significant differences in participant numbers, age demographics, and LAeq between the two categories. Results indicated that dynamic music activities typically attracted an older participant and had lower LAeq than static activities. However, participants in dynamic activities reported lower levels of sound comfort and spatial satisfaction. Within dynamic music activities, a negative correlation was found between LAeq and sound comfort, whereas no significant correlation was observed in static music activities. Additionally, participant numbers in dynamic activities showed no relation to sound pressure levels, which increased with the activity area. Conversely, in static activities, both participant numbers and activity area were found to positively influence LAeq. The study also discovered that for both dynamic and static music activities, the lower the LAeq were when the people's formation approached a circular shape. This research offers valuable insights into understanding the acoustic environment and participant experience in urban open spaces.

Inverse and direct impedance eduction of liners in the MAINE Flow facility

The assessment of acoustic liners typically involves conducting experiments with airflow in a duct under various incident sound pressure levels and flow velocities. Impedance, as the most intrinsic parameter characterizing an acoustic wall (due to its independence from the duct section), is often the primary focus. Experimental techniques for its determination can be categorized into two classes: direct and inverse eduction methods. This paper contrasts these two methodological classes within the context of the MAINE Flow facility-a 150mm x 280mm rectangular duct capable of generating flow Mach numbers up to 0.63 and multimodal sound fields of Sound Pressure Levels up to 150 dB. Direct impedance determination necessitates a substantial degree of attenuation along the liner. However, in the current implementation, inverse impedance determination is constrained by the uniform flow hypothesis, which is invalid for large Mach numbers in such facilities. The findings illustrate that both methods can yield valuable impedance data, enabling the examination of the effects of flow and incident modal content on the measured impedance.

Correction for reverberation time in acoustic measurements from service and equipment - Comparison between different methods

The measured values of the sound pressure level in ordinary rooms in dwellings vary depending on the combined effect of the absorption and the scattering of the furniture, or to the presence of absorbent surfaces on walls and ceilings. Regarding the measurement of noise from building services, ISO 16032 and ISO 10052 methods allow to normalize the sound pressure levels to a reference reverberation time of 0,5s. Several European countries incorporate this reverberation time correction into their regulations. However, Spanish regulations, specifically RD 1367/2007, and the majority of regional decrees and ordinances concerning the evaluation of noise from activities or equipment within buildings, do not incorporate this correction, even when measurements are performed in two scenarios: before the building's occupation when rooms are empty, or when the building is fully furnished, as may occur in the case of complaints. For that reason, this study compares the values of the reverberation time index obtained in 180 residential rooms using various methods while also evaluating the benefits and drawbacks of their application.

Unequal segment areas and corner positions with the enveloping surface method for sound power determination

The standardised methods for the determination of the sound power level according to the enveloping surface methods require a measurement of the sound pressure or sound intensity level on the enveloping surface. While the subdivision of the enveloping surface into unequal segment areas is correctly standardised for the intensity method (ISO 9614, all parts), the sound pressure methods (e.g. ISO 3744) reveal some fuzziness. The reason is the necessary allocation of partial surfaces to measurement points which are normatively located at corners or edges of the parallelepiped measurement surfaces. This effect is especially important with the proposed local increase of the measurement point density in regions of increased sound radiation. The contribution shows which effects unequal areas have and how a correct surface averaging can be implemented in these cases.

Optimizing a small room for critical listening with Treble

This work presents a detailed validation of new software Treble launched in 2023 that hybridizes the discontinuous Galerkin method and pressure-based geometrical acoustics methods. We investigated a small studio for voice productions both through physical measurements and treble's room acoustic simulations. By employing a dense measurement grid with a spacing of 25 cm at the ear level, a comprehensive validation of the room acoustic simulation was conducted in terms of room impulse responses, transfer functions, ISO 3382 acoustic parameters and sound pressure level distribution. Treble's simulation successfully predict the room modes, ISO 3382 acoustic parameters as well as the sound level distribution. The study demonstrates the impact of speaker positions, particularly regarding their interaction with boundary surfaces and how this can be planned with the simulation.

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.

A pilot study: developing acoustic model for immersive environment

In the landscape of higher education in Malaysia, the adoption of immersive technologies still in its infancy, particularly within the field of building science education. This research endeavors to elevate the learning experiences of Indoor Environmental Quality (IEQ) concepts, with a specific focus on lighting and acoustics. The ongoing study seeks to revolutionize current learning methodologies by converting traditional modules into an immersive virtual environment, offering learners an interactive, and sensory-rich experience with the subject matter. To ensure the effectiveness of the acoustic immersive environment, this paper prioritizes the initial step of developing the acoustic simulation model. In an early pilot study, on-site measurements of sound pressure levels were recorded at various points within a basic classroom setting and an acoustic model will be developed subsequently. Consequently, the alignment between the developed acoustic model and real-world physical measurements establishes a solid foundation for the subsequent calibration process, during which the acoustic model will be tailored to meet VR-ready specifications delve into immersive environment model. This finding ensures a seamless transition of real-world acoustic conditions into the virtual realm, amplifying the authenticity and educational impact of the VR learning experience, thereby contributing to the advancement of immersive technologies in higher education.

Sound quality evaluation in special vehicles based on multiple linear regression

The issue of interior sound quality in specialized vehicles has received widespread attention, which could directly affect the riding comfort of the vehicle. This research primarily focuses on the objective quantification of subjective perception of sound qualitySQ in special vehicles. The noise of special vehicles under different working conditions is measured and analyzed, and psychoacoustic parameters and A-weighted sound pressure levels are calculated. The subjective evaluation of interior sound quality was conducted using the grading scale method. A multiple linear regression model is used to establish the correspondence between subjective perceptions and objective parameters. It provides a reference basis for evaluating the sound quality of special vehicles.

Vibro-acoustics based sound pressure minimization in a cam-follower system using micro-geometric modifications on minimizing the noise

The systems with inherent combined rolling-sliding contacts, such as cam-followers, gearboxes, and clutches, generate undesirable noise. It affects operator well-being, environmental acoustics, and component wear during operation. The sound produced due to interaction between the cam and the follower can be reduced by micro-geometric changes, i.e., profile modification of the cam surface while maintaining the macroscopic geometry of the system. This study aims to identify an optimal profile modification to the cam, using a vibro-acoustic relationship between the contact forces, sound pressure to minimize the sound pressure. The methodology utilizes a mathematical model of a cam-follower system to estimate the contact forces for different parametric values, and an equivalent finite element model to obtain vibro-acoustic transfer functions for various profile modifications. Sound pressure is predicted for each profile based on the obtained transfer functions, and contact forces. The optimal profile is then selected based on a comparative evaluation of the predicted sound pressure levels. The outcome of this study would lead to the development of quieter systems with combined rolling-sliding contact.

Large aperture microphone array measurement at operating airport for sound source model creation of J-FRAIN

In 2022, authors conducted microphone array measurements at an operating airport to create sound source models for commercial aircraft based on the noise prediction framework J-FRAIN. A similar measurement was also performed by our colleagues in 2019, but it was a trial to establish the concept of the framework and was done using a microphone array in which the number of microphones was reduced to about half. In order to improve the accuracy of the sound source models, the microphone array with a 30-meter diameter consisting of 195 microphones mounted on the ground was used in 2022. Recording-based simultaneous noise measurement using sound level meters was also performed around the airport to validate prediction results in terms of time histories of 1/3 octave band sound pressure levels. This paper describes an overview of the microphone array measurements conducted in 2022 and a case study of noise prediction around the airport using sound source models created from the data of microphone array measurements conducted in 2022. Predicted results are compared with 1/3 octave band data measured using sound level meters mounted at a height of 4 m above the ground at sites of noise monitoring stations around the airport.

Non-auditory effects of noise at work: an overview and perspective

It is widely known that noise at high sound pressure levels may have adverse effects on the auditory system, which can end up in noise-induced hearing loss. In addition to these auditory effects, non-auditory effects of noise, which can already appear at moderate levels, should be thoroughly considered in an occupational context in order to ensure safety and health at work. An overview of non-auditory effects will be given, along the questions: Which effects are typically summarised under the term "non-auditory effects"? What approaches are frequently used to uncover these effects? With regard to cognitive performance: Which other factors can influence the effects of noise? Why is it often challenging to verify detrimental effects caused by noise, although most people feel disturbed? Along the legal regulations in Germany, it will be explained what the term "rating level" means and for which categories of professional activities what rating levels must not be exceeded in order to avoid or minimise non-auditory effects. Finally, by means of results from own studies carried out at BAuA, it will be shown that also sounds at moderate levels can lead to detrimental effects, and what issues may occur when trying to reveal effects on cognitive performance.

Recent investigation on VHF sound exposure sources around us

We have reported recent investigation of sound exposure sources in very-high frequency (VHF) region as the activities for research project of VHF sounds in Japan. Recently, the devices which utilize or generate VHF sounds as like rodent repelling devices, ultrasonic cleaning machines, IH cookers and corner sensors of automobile continue to increase in public space or our living environment. The VHF sounds in high level have physical or/and psychological effects for young people who can hear such sounds. So, in environment around us, we identified VHF sound sources using acoustic camera and measured the sound pressure level for such sources. In this paper, we introduce newly-discovered several VHF sounds: for example, ultrasounds from corner sensors of automobile car, VHF sounds from photovoltaic installation and VHF sounds of interior train, and so on. From both the results measured by acoustic camera and microphones show source positions and frequency characteristics of VHF sounds. However these play important role in our life environment, we need to note that these contain potential hazard for young people who can hear such VHF sounds.

Indiscernible noise determination of a military system equipped with an internal combustion engine

The main objective of this paper is to explore the non-detectability criteria of military systems and to determine the indiscernible noise of military systems equipped with internal combustion engines. Non-detectability is one of the critical requirements evaluated for military defense systems and it is defined strictly in MIL-STD-1474E standard. Furthermore, this standard specifies the limits of sound pressure levels conservatively for 1/3 octave bands. Though, the standard does not define indiscernible or inaudible noise levels for events in the presence of background noise. It is also not explicitly well-defined in the existing literature. This study presents a comparison of non-detectability distance defined in MIL-STD-1474E standard and indiscernible noise of a military system extracted from the measured octave band sound levels, which are processed based on sound propagation theory. In this study, several parameters such as atmospheric absorption, geometric spreading, ground effect, terrain type, obstacle existence are included to determine the indiscernible noise level of the military system of interest. The results are compared with the non-detectability distance limits given in the MIL-STD-1474E standard, and it is observed that the proposed method of indiscernible noise, which is defined as extracted sound level should be lower than the background noise, is well-correlated.

Effect of sound absorption on noise reduction in the automotive industry

Industrial noise is one of the most common physical factors that cause annoyance and damage workers' health in the long term. Precautions should be taken to reduce noise and improve acoustic performance in industrial working environments. This paper aims to analyze the acoustic performance of the automotive industry and contribute to the global outcomes of sustainability and the development of strategies to improve the quality of the working environment through improvement scenarios. For this purpose, the automotive industry in Türkiye was examined as a case study. In-situ acoustic measurements were made in the seat manufacturing unit of an automotive factory and the current situation was transferred to the simulation program. The effects of acoustic improvements on A-weighted sound pressure level and reverberation time at mid-frequencies (500, 1000, 2000 Hz) were investigated through three different scenarios. In the investigations, noise distributions were carried out through noise mapping. The A-weighted sound pressure levels in the automotive industry were reduced by approximately 15 dB. As a result of the study, suggestions for noise control precautions and their effects on the automotive industry seat manufacturing unit are presented.

Partial equivalent sound pressure level as an approach to manage irrelevant sounds in environmental noise measurements

Residual sound and unwanted events are known factors affecting the accuracy of environmental noise measurements. ISO 1996-2 provides methods to manage these irrelevant sounds, for example by applying correction factors, but the methods require a degree of knowledge of the irrelevant sounds that is not always practical or possible to obtain when performing long-term measurements with unattended monitoring stations in complex urban soundscapes. While automatic detection of irrelevant sounds provides the required information, it also allows for new approaches not described in ISO 1996-2. In this paper, we discuss a metric called partial equivalent sound pressure level (Partial Leq), calculated after data samples with residual sound and unwanted events are identified automatically and replaced by project-specific values. Our hypothesis is that better estimates of equivalent sound pressure levels (Leq) can be achieved with this metric, compared with the general methods given in ISO 1996-2. Comparisons of results are presented, together with a discussion of applicability of the Partial Leq metric and experiences gathered from its use.

A comparison of results with different logging rates using ISO/PAS 1996-3:2022

Noise with prominent impulsive sound is more annoying than continuous types of noise (without impulses) with the same equivalent sound pressure level. Therefore, an adjustment is added to the measured LAeq if prominent impulsive sound is present. In ISO 1996, three categories of impulsive sound are defined, with adjustments for each. The list of sources of impulsive sound for each category is incomplete. ISO/PAS 1996-3 defines an objective method to measure the prominence of impulsive sound relative to residual sound. This can be used to categorize the impulsive sources, complementing the ISO 1996-2 environmental noise assessment method. The method is based on logging LpAF with 10-25 ms time intervals. Short-term LAeq (e.g. 10 ms), although not preferred, can be used to compute these values. 100 ms sampling is permitted for surveys and screening. Annex A of ISO/PAS 1996-3 PAS encourages further research to support the development of a full ISO standard. This includes the application of real-world sources assessed at receiver locations including typical signal to residual noise ratios. This paper describes such a study under these conditions that investigates the impact of the time intervals on results.

Measured and predicted sound transmission through a laboratory concrete floor

The direct sound transmission through a simple, massive, homogeneous building element with and without lining is investigated experimentally and compared with analytical and empirical models from the literature. A 150 mm thick concrete floor and a 100 mm thick floating floor were measured in the floor transmission facility of the National Research Council Canada, i.e. without flanking sound transmission. In addition to the sound reduction index and the normalized impact sound pressure level, loss factors, radiation efficiencies, and mean squared velocities were recorded in the laboratory. The measured data is compared to established models of sound transmission. A focus is placed on the calculation model of ISO 12354-1 (Appendix B), which uses calculated radiation efficiencies and loss factors to predict the sound reduction index of heavy, homogeneous building elements. Some difficulties with the calculation model and the examples in the standard are discussed. In principle, the results in this study show that the calculation model of ISO 12354-1 gives good estimates when the correct input parameters are used. However, deviations between the calculated and the measured loss factors and radiation efficiencies have large effects on the accuracy of the estimates, particularly in the region around the coincidence frequency.