Constant Sound Pressure Level Research Articles

Diffuse sound field synthesis: Ideal source layers

Can uncorrelated surrounding sound sources be used to generate extended diffuse sound fields? By definition, targets are a constant sound pressure level, a vanishing active sound intensity, and uncorrelated sound waves arriving isotropically from all directions. Are there ideal source layouts to synthesize a maximum diffuse sound field within? As methods, we employ numeric simulations and undertake a series of considerations based on uncorrelated source layouts at a finite radius. Statistically expected active sound intensity and sound energy density are insightful and highlight the relation of active sound intensity to potential theory. Correspondingly, both Gauß’ divergence and Newton’s spherical shell theorem apply, and they provide valuable insights. In a circular layout, uncorrelated elementary point-source fields decaying by 1/√r ideally compose an extended sound field of vanishing active sound intensity; in spherical layouts this is the case with a 1/r decay. None of the layouts synthesizes a perfectly constant sound energy density inside. Theory and simulation offer a broad basis for understanding the synthesis of diffuse sound fields with uncorrelated sources in the free sound field.

Speech perception in noise in patients with idiopathic sudden hearing loss

Background Patients with unilateral hearing loss have difficulties perceiving speech in a noisy environment. Unilateral severe to profound hearing loss is most commonly caused by idiopathic sudden sensorineural hearing loss (SSNHL). Objectives To assess speech perception in noise among patients with idiopathic unilateral SSNHL, and examine the factors affecting the results. Material and methods We retrospectively enrolled 93 patients with idiopathic unilateral SSNHL. The speech signal was presented at a constant sound pressure level, while the noise signal varied from +5 dB to −5 dB signal-to-noise ratio (SNR) in units of 5 dB (S0/Nhe). Results As the SNR decreased, the percentage of correct answers also decreased. The correct answer rate decreased with increased hearing level at post-treatment. There was a correlation between age and speech perception, especially when dividing the patients into two groups: <65 years old and ≥65 years old. Conclusions and significance The results showed that speech perception clearly decreased in a noisy environment rather than in a quiet environment, and the correct answer rate of the speech perception test in noise was significantly correlated with hearing level at post-treatment. This study provides important data for future interventions for unilateral hearing loss, including cochlear implants.

Enhancing low frequency sound radiation of electrodynamic loudspeakers with acoustic metamaterials

Since the radiation resistance of a vibrating membrane in the air is proportional to frequency in the subwavelength range, low frequency (&amp;lt;100Hz) sound radiating devices generally require a large vibrating diaphragm and a bulky enclosure to be efficient and loud enough for practical use. The tapped horn topology, where the front radiation of an electrodynamic driver adds up with the back radiation after propagating through the internal volume of a speaker box, has been widely used in custom audio to provide low-frequency enhancement to the bass unit. Recently, people have demonstrated the application of acoustic metamaterials based on multiple Helmholtz resonators (HRs) in sound absorption, sound insulation, directivity control, impedance matching, etc. In this presentation, we show that by branching the sound path of a tapped horn speaker box with multiple Helmholtz resonators and fine-tuning the geometry of each individual element, we can produce high and relatively constant sound pressure levels at sub-wavelength frequencies, making our methodology a good candidate for compact subwoofer design. Genetic algorithm (GA) is used to bring forth optimal performance within the geometric framework. Both transfer matrix method and numerical simulation are employed to derive the sound output of a particular subwoofer.

Pilot studies of noise annoyance in relation to time, amplitude and frequency characteristics of sound

Noise is any unwanted sound that may be disruptive or harmful to health or increase the risk of an accident at work. Noise as a stressor can contribute to the development of various types of diseases, cause distraction, make work difficult and reduce its efficiency. Aim of the pilot studies was to asses noise annoyance in relation to time, amplitude and frequency characteristics of sound in typical office environment. The Vienna Test System was used for this purpose. Virtual office acoustic environments were developed with different psychoacoustic parameters, but with a constant A-weighted sound pressure level of 55 dB - environment with conversations, environment with office equipment (computers, printers, telephones), environment D with all office noise sources together. The reference environment was a quiet office room with no additional noise sources. Recorded real noise sources were transferred to a virtual 3D sound environment and converted into binaural sound, which was then played back on headphones. During the exposure to each of the acoustic environments, the subjects performed the ALS test (work performance series) and then assessed the given environment using a questionnaire. The tested acoustic environments were assessed in the range from not at all annoying to very annoying. On average, environments with office noise were rated as moderately annoying. However, subjective feelings of the respondents were not reflected in the results of psychological tests.

The Influence of Different Genres of Music on the Performance of Medical Students on Standardized Laparoscopic Exercises

Whether and how music influences the performance of surgical procedures such as laparoscopy is unclear and can be feasibly determined using laparoscopic box training tools under standardized conditions. The aim of this prospective study is to evaluate the effect of different genres of music on the performance of laparoscopic novices. Between May 2018 and December 2018, n = 82 students (38 male, 44 female) from Heidelberg University Medical School performed 3 different laparoscopic exercises (A, B, C) from the "Luebecker Toolbox" with 2 repetitions each under standardized conditions. Time was recorded for each exercise. The students were assigned either to one of four groups, each of which was exposed to a compilation of music from 1 genre (hip hop, classical, rock, or mixed radio music), or to a fifth, control group, without exposure to music. The music was played at a constant sound pressure level of 70 decibels . Each group was compared with the others using a t-test for independent samples. Exposure to music generally led to better performance compared with the control group. Compared with exposure to mixed radio music or to rock, significantly better performance could be demonstrated for exposure to classical music in Exercise B, with an average exposure time of 127 s needed (± 21.4; p < 0.05). No significant differences could be demonstrated for Exercise A, though for classical music, best performance was possible with 120 s (±17.3) of exposure. In Exercise C, hip hop triggered significantly better performance than rock or radio music (p < 0.05). At an sound pressure level of 70 decibels, exposure to classical music or hip hop appears to have beneficial effects on training performance for surgical novices under standardized conditions.

Combustion noise analysis of a turbulent spray flame using a hybrid DNS/APE-RF approach

Combustion generated noise of a turbulent spray flame has been investigated using a hybrid Computational Fluid Dynamics/Computational Aero-Acoustics (CFD/CAA) framework. In this two-step framework, the reacting flow-field of a flame is simulated using Direct Numerical Simulations (DNS) in the first step, while the acoustic wave propagation in a non-uniform mean flow is captured by solving the Acoustic Perturbation Equations extended to Reacting Flows (APE-RF) in the second step. The numerical approach used in this study is therefore, termed as the hybrid DNS/APE-RF approach. First, this hybrid DNS/APE-RF approach is used to simulate a benchmark experimental open turbulent non-premixed flame, and the results obtained for the non-premixed flame’s flow-field statistical quantities, as well as radiated sound intensities are extensively validated against experimental data. Next, the hybrid DNS/APE-RF approach is applied to an experimental open turbulent spray flame, for simulating its two-phase reacting flow-field along with its combustion generated acoustic field, to predict and analyze the noise radiation behavior. The DNS results of the spray flame are compared with measurements, in terms of droplet velocity statistics and gas-phase temperatures, and favorable agreement is observed. The computed acoustic power spectra of the spray flame exhibit a power law dependence of the form f−2.4 (where f is the frequency) in the frequency range 300 Hz < f < 1000 Hz. And, the computed noise spectra of the spray flame contain a nearly constant sound pressure level plateau, for frequencies greater than 1000 Hz and up to 3000 Hz. Acoustic refraction effects induced by sound speed variations in the flame, resulting in the attenuation of high-frequency noise radiated in the flame downstream direction, are also captured in the simulation. Noise radiation characteristics of the turbulent spray flame are found to resemble those of turbulent premixed and non-premixed flames.

Modeling of acoustic lined duct with and without grazing air flow by an analytical method

An analytical method is proposed to characterize the sound acoustic transmission in a rectangular lined duct with and without grazing air flow. The acoustic wave number in the duct is determined using Taylor series expansion. The proposed method is validated by comparison with a finite element method in grazing air flow environment and experimental measurements at grazing sound incidence for the case with no flow. Excellent agreement is found in both configurations. The proposed method is used for sensitivity analysis of acoustic duct lined with micro perforated panel absorber in order to evaluate the impacts of the inputs parameters on the transmission loss of the duct. It is shown for a constant sound pressure level that the transmission loss of the duct is very sensitive to the cavity depth of the absorber while the resonance of the transmission at high sound pressure level is controlled by the perforation ratio of the panel. The effects of the perforation diameter and the plate thickness are negligible for higher pressure excitation and the impact of the sound pressure level on the transmission is preponderant.

Dolphin auditory brainstem responses to frequency-modulated “chirps.”

Previous studies have demonstrated that increasing-frequency chirp (up-chirp) stimuli can enhance auditory brainstem response (ABR) amplitudes by compensating for temporal dispersion occurring along the cochlear partition. In this study, ABRs were measured in two bottlenose dolphins in response to 5-µs, spectrally “white” clicks, up-chirps, and decreasing-frequency chirps (down-chirps). For all stimuli, bandwidth was constant (10 to 180 kHz) and peak-equivalent sound pressure levels (peSPLs) were 115, 125, or 135 dB re 1 μPa. Chirp durations varied from 125 to 2000 μs. Up-chirps with durations less than ~1000 μs generally increased ABR peak amplitudes compared to clicks with the same peSPL or energy flux spectral density level, while down-chirps with durations above ~250 to 500 μs decreased ABR amplitudes relative to clicks. Increases in ABR amplitude occurred with up-chirps having a broad range of durations. The findings parallel those from human studies and suggest that the use of chirp stimuli may be an effective way to enhance broadband ABR amplitudes in larger marine mammals. [Work supported by US Navy Living Marine Resources Program.]

Frequency characteristics of neuromagnetic auditory steady-state responses to sinusoidally amplitude-modulated sweep tones

ObjectiveThis study aimed to capture the neuronal frequency characteristics, as indexed by the auditory steady-state response (ASSR), relative to physical characteristics of constant sound pressure levels (SPLs). Relationship with perceptual characteristics (loudness model) was also examined. MethodsNeuromagnetic 40-Hz ASSR was recorded in response to sinusoidally amplitude-modulated sweep tones with carrier frequency covering the frequency range of 0.1–12.5kHz. Sound intensity was equalized at 50-, 60-, and 70-dB SPL with an accuracy of ±0.5-dB SPL at the phasic peak of the modulation frequency. Corresponding loudness characteristics were modeled by substituting the detected individual hearing thresholds into a standard formula (ISO226:2003(E)). ResultsThe strength of the ASSR component was maximum at 0.5kHz, and it decreased linearly on logarithmic scale toward lower and higher frequencies. Loudness model was plateaued between 0.5 and 4kHz. ConclusionsFrequency characteristics of the ASSR were not equivalent to those of SPL and loudness model. Factors other than physical and perceptual frequency characteristics may contribute to characterizing the ASSR. SignificanceThe results contribute to the discussion of the most efficient signal summation for the generation of the ASSR at 0.5kHz and efficient neuronal processing at higher frequencies, which require less energy to retain equal perception.

Distortion-product otoacoustic emission suppression tuning curves in hearing-impaired humans

Distortion-product otoacoustic emission (DPOAE) suppression tuning curves (STCs) were measured in 65 hearing-impaired (HI) subjects at f(2) frequencies of 2.0, 2.8, 4.0, and 5.6 kHz and L(2) levels relative to sensation level (SL) from 10 dB to as much as 50 dB. Best frequency, cochlear-amplifier gain (tip-to-tail difference, T-T), and tuning (Q(ERB)) were estimated from STCs. As with normal-hearing (NH) subjects, T-T differences and Q(ERB) decreased as L(2) increased. T-T differences and Q(ERB) were reduced in HI ears (compared to normal) for conditions in which L(2) was fixed relative to behavioral threshold (dB SL). When STCs were compared with L(2) at constant sound pressure levels (dB SPL), differences between NH and HI subjects were reduced. The large effect of level and small effect of hearing loss were both confirmed by statistical analyses. Therefore, the magnitude of the differences in DPOAE STCs between NH and HI subjects is mainly dependent on the manner in which level (L(2)) is specified. Although this conclusion may appear to be at odds with previous, invasive measures of cochlear-response gain and tuning, the apparent inconsistency may be resolved when the manner of specifying stimulus level is taken into account.

The influence of preconceptions on perceived sound reduction by environmental noise barriers

The paper presents research that answers three main questions: (1) Do preconceptions held about the constituent materials of an environmental noise barrier affect how people perceive the barrier will perform at attenuating noise? (2) Does aesthetic preference influence the perception of how a barrier will perform? (3) Are barriers, which are deemed more aesthetically pleasing, more likely to be perceived as better noise attenuators? In a virtual reality setting with film to improve the contextual realism of the intersensory interaction test, participants were required to compare the perceived effectiveness of five standard ‘in-situ’ noise barriers, including concrete, timber, metal, transparent acrylic and a vegetative screen. The audio stimulus was held at a constant sound pressure level (SPL), whilst the visual stimulus changed, as the influential factor. As the noise levels projected during the study were held constant, it was possible to attribute the participants’ perception of noise attenuation by the barriers, to preconceptions of how the varying barrier material would attenuate noise. There was also an inverse correlation between aesthetics and perception of how a noise barrier would perform. The transparent and deciduous vegetation barriers, judged most aesthetically pleasing, were judged as the least effective at attenuating noise.

Soundscape measurement and analysis

Soundscapes typically include a variety of sources, with individual and collective attributes (level, spectral structure, time structure, and perceived characteristics such as loudness, sharpness, fluctuation, and roughness). Relevant sound sources impinge on listeners from multiple directions and distances. Examples will be given of large differences between conventional and psychoacoustic values as a function of distance, and of multi‐source summations. As an example, the subjective loudness difference for sound incidence over a small versus large solid angle for a constant sound pressure level and spectrum is known. Individual‐source‐relevant information, important in context, may be unrecognized unless spatial hearing is included in soundscape assessment. A demonstration of binaural versus monaural soundscape data acquisition, and subsequent analysis by both conventional and psychoacoustic measures considering human perception including time dependency, will be given. Evidence will be presented for considering human hearing not only in the analysis, but also in the acquisition.

Method for producing a constant sound pressure level in hearing aids and corresponding hearing aid

The invention relates to a hearing aid comprising a microphone (1), a loudspeaker (13) and a signal processing unit (2), with a switching unit (16) for producing a constant sound pressure level. Said switching unit (16) has an envelope generator (6) for generating an envelope value of a signal value to be processed and a divider (8) for establishing the quotient of the signal value and the envelope value as a signal to be output or reprocessed. The invention also relates to a method for operating a hearing aid of this type.

DURATION SENSATION WHEN LISTENING TO BANDPASS NOISES

The duration sensation of bandpass noise was examined while changing the factors (τ1, φ1and τe) extracted from the autocorrelation function. The white noise and bandpass noises with six center frequencies (125, 250, 500, 1000, 2000 and 4000 Hz) with different bandwidths were used as stimuli. A paired-comparison test comparing the white-noise duration with bandpass-noise duration was conducted under the conditions of constant sound pressure level (SPL; 80 dB(A)) and rise and fall times (1 ms). Results indicate that the duration of bandpass noise is judged to be longer than that of the white noise. The duration sensation of the bandpass stimuli with longer τ1is significantly longer than that of the stimuli with shorterτ1 (p<0·01).

Effect of healed tympanic membrane perforations on umbo velocity in the rat.

Heterodyne laser interferometry was used to measure tympanic membrane (TM) velocity at the umbo during acoustic stimulation in 2 groups of rats. The control group had a normal TM, while in the other group the TM was perforated and then allowed to heal for at least 28 days. Umbo velocity functions for constant sound pressure level stimuli were obtained for test tones between 0.3 and 40.0 kHz in each animal. The results revealed that velocity was the same in the control and healed TMs below 3.0 kHz. Above 5.0 kHz, the velocity response in the healed ear was between 3 and 12 dB smaller than in the control ears. Histologic evaluation of the healed perforation revealed a thick fibrous reaction between the epidermal and lamina propria layers. The results indicated that the added mass of the scar tissue changed the middle- and high-frequency TM responses.

The effect of frequency-modulation systems on the communication skills of deaf–blind children

Classrooms and other public places provide a poor acoustical environment for individuals who have a hearing loss, and it is often difficult for them to discriminate between the speaker and background noise with a hearing aid. The use of a frequency-modulation (FM) system can often reduce this problem by providing a constant sound pressure level of the speaker’s voice. The effect of FM systems on communication skills of deaf–blind children was investigated using a single-subject alternating treatment design. There was a marked improvement for a number of the subjects in the FM condition. The results will be discussed along with individual case studies. FM technology has exploded. A relatively new type of FM receiver is now available which combines the hearing aid and FM in a single behind-the-ear unit (BTE/FM). The most recent development is a ‘‘boot’’ attachment which changes a standard over-the-ear hearing aid into a FM system. An overview of these FM systems will be presented. [Work supported by OSERS.]

THE INTERACTION OF WELL-CHARACTERIZED, LONGITUDINAL ACOUSTIC WAVES WITH A NONREACTING SPRAY

The effect of a variable acoustic field on the evaporation characteristics of a nonreacting ethanol spray has been investigated in a long, vertical tube using a phase Doppler particle analyzer. The parametric effect of the first, second, and third acoustic modes were studied fora constant sound pressure level, using the steady flow condition as a reference. Axial and radial profiles of Sauter mean and arithmetic mean droplet diameters, and time-resolved droplet velocities, were measured and compared for the four experimental conditions while holding the spray location fixed inside the tube. Spectral analysis of the droplet axial velocity component revealed dominant frequencies equal to the frequencies of the acoustic waves in the tube. Average droplet velocities under all four experimental conditions remained the same. Droplet diameters decreased between 13% and 31%, 15% on average, in the presence of the first and third modes, compared to steady values. The second mode had little effect on the droplet diameters because the location of the nozzle corresponded to a velocity node of the stationary acoustic field for the second harmonic. A simple mathematical model describing the evaporation of a droplet in a pulsating flow field yielded results that agreed qualitatively well with the experimental results obtained.

An experimental and theoretical investigation on the effects of acoustics on spray combustion

Spray characteristics in an ethanol-fired, Rijke-tube combustor were studied experimentally by measuring Sauter-mean diameter axial and radial profiles with a phase-Doppler instrument. Predictions of axial Sauter-mean diameter profiles were also obtained by use of a simplified model describing the spray burning in an acoustic field. The effect of flame locations (L/2, L/3, L/4, and L/6) and acoustic modes (first [118 Hz], second [259 Hz], and third [393 Hz]) were studied parametrically at a constant sound pressure level of 150 dB. Both theoretical and experimental results showed that oscillations enhanced the combustion process and resulted in a smaller burnout distance and higher slopes in the Sauter-mean diameter axial profiles when the spray was positioned at locations of high acoustic-velocity fluctuations. Comparisons of these experimental results and model predictions showed very good qualitative agreement. Flame lift also played a significant role delaying the spray ignition at locations of high acoustic-velocity fluctuations. The mean axial droplet velocity component along the axial and radial directions were not affected significantly by the acoustic oscillations. Finally, the theoretical Rayleight integrals showed that the particular spray used here had very little acoustic-driving capability, a result that has been also supported by experimental observations.

Controlled Excitation of a Cold Turbulent Swirling Free Jet

Experimental results from acoustic excitation of a cold free turbulent jet with and without swirl are presented. A flow with a swirl number of 0.35 (i.e., moderate swirl) is excited internally by plane acoustic waves at a constant sound pressure level and at various frequencies. It is observed that the cold swirling jet is excitable by plane waves, and that the instability waves grow about 50 percent less in peak r.m.s. amplitude, and saturate further upstream compared to corresponding waves in a jet without swirl having the same axial mass flux. The preferred Strouhal number based on the mass-averaged axial velocity and nozzle exit diameter for both swirling and nonswirling flows is 0.4. So far no change in the mean velocity components of the swirling jet is observed as a result of excitation.

The role of pars flaccida in human middle ear sound transmission.

The role of the pars flaccida in middle ear sound transmission was studied with the use of twelve otoscopically normal, fresh, human temporal bones. Peak-to-peak umbo displacement in response to a constant sound pressure level at the tympanic membrane was measured with a noncontacting video measuring system capable of repeatable measurements down to 0.2 micron. Measurements were made before and after pars flaccida modifications at 18 frequencies between 100 and 4000 Hz. Four pars flaccida modifications were studied: (1) acoustic insulation of the pars flaccida to the ear canal with a silicone rubber baffle, (2) stiffening the pars flaccida with cyanoacrylate cement, (3) decreasing the tension of the pars flaccida with a nonperforating incision, and (4) perforation of the pars flaccida. All of the modifications (except the perforation) had a minimal effect on umbo displacement; this seems to imply that the pars flaccida has a minor acoustic role in human beings.