Equal Loudness Contours Research Articles

Toward parametric Bayesian adaptive procedures for multi-frequency categorical loudness scaling.

A series of Bayesian adaptive procedures to estimate loudness growth across a wide frequency range from individual listeners was developed, and these procedures were compared. Simulation experiments were conducted based on multinomial psychometric functions for categorical loudness scaling across ten test frequencies estimated from 61 listeners with normal hearing and 87 listeners with sensorineural hearing loss. Adaptive procedures that optimized the stimulus selection based on the interim estimates of two types of category-boundary models were tested. The first type of model was a phenomenological model of category boundaries adopted from previous research studies, while the other type was a data-driven model derived from a previously collected set of categorical loudness scaling data. An adaptive procedure without Bayesian active learning was also implemented. Results showed that all adaptive procedures provided convergent estimates of the loudness category boundaries and equal-loudness contours between 250 and 8000 Hz. Performing post hoc model fitting, using the data-driven model, on the collected data led to satisfactory accuracies, such that all adaptive procedures tested in the current study, independent of modeling approach and stimulus-selection rules, were able to provide estimates of the equal-loudness-level contours between 20 and 100 phons with root-mean-square errors typically under 6 dB after 100 trials.

The influence of the reference level on loudness and preference judgements for spectrally manipulated fan sounds.

Fan sounds are often quantified using A-weighted sound pressure levels, silently acknowledging their limitations to fully capture the perceived unpleasantness. To overcome this limitation, level adjustments are a way to quantify the subjective preference of spectrally different sounds in listening experiments by adjusting the level of a test sound until it is equally preferred to a fixed reference sound. Since equal loudness contours differ, depending on the overall level, level adjustments might vary for different levels of the reference sound. This study aims to quantify the effects of spectral manipulations on level adjustments for loudness and preference judgements at reference sound pressure levels of either 45, 60, or 75 dB(A). Level adjustments of up to 12 dB were measured to make the stimuli equally preferred to the reference, particularly for sounds with prominent high-frequency components. The loudness and preference judgements were closely linked with each other, but an offset of about 3.5 dB at a reference level of 45 dB(A) indicates that equal loudness is not synonymous with equal preference. A linear regression model to predict level adjustments based on the reference level and an index reflecting the ratio of mid- to high-frequency loudness explains 73% of the variance.

A subwavelength ventilated structure for efficient broadband sound insulation

Multifunctional structures such as ventilated sound barriers, have become the focus of recent research on the noise reduction and environmental comfort. However, its large size and complex inner structure hinder its potential applications. Novel structures with side-branch sectorial Helmholtz resonators and double-layered perforated slit plates enlightened by macro-perforated plates to enhance the soundproof performance and facilitate natural ventilation are proposed and experimentally validated. Compared with simple muffler ducts, the combinations with slit plates provide a smoother transmission loss (TL) curve with a broad and continuous TL band. We also study the influences of the independent parts and interactive effects of the assembly on the sound field, including the frequency migration and plate vibration. The proposed sub-wavelength structures with a thickness of 15 mm can obtain TL values up to 25 dB with a broad bandwidth from 930 Hz to 1600 Hz. Moreover, soundproof walls can be fabricated by using these structures with plenty of ventilated slits to freely exchange air and heat. This ventilation sound barrier is suitable for acoustic landscape buildings as it covers the main frequency spectrum of a human equal loudness contour.

Auraltypical acoustics? A critical review of key standards and practices

The concept of aural diversity was born out of awareness that there is a deeply embedded and intertwined, singular model of hearing at the core of the preponderance of acoustic standards and guidance, and hence practice (Drever 2015, 2017). This is exemplified with the prescription of the 'otologically normal' hearer derived equal loudness contours (ISO 226:2003), giving form to ubiquitous A-weighted decibel - the 'otologically normal' characterising the hearing of 18 to 25-year-olds, arguably the healthiest sub-group of society. This paper will critically review this assumption through reviewing the current set of acoustics standards in the UK. Crucially it will probe at some of the methods underpinning historic and foundational studies and concepts that are referenced in current standards, such as the reliance on WEIRD (Western, Educated, Industrialized, Rich, and Democratic societies) samples to stand in for the whole of the human population. (Henrich, Heine, Norenzayan 2010; Cobianchi & Rosas Pérez, 2021). Through interviews with acoustic professionals, the paper will then look at how this is carried through into practice and finally, discuss the consequences of slavishly following these models, which studies have shown (Drever 2017), results in distress, negative impact on health and well-being and societal exclusion for some.

Bandwidth and Audible Noise Improvement of Sensorless IPMSM Drives Based on Amplitude Modulation Multirandom Frequency Injection

The high-frequency (HF) signal injection method has been widely used in sensorless control for IPMSM drives. However, the audible noise caused by HF injection restricts the sensorless application. Moreover, the control bandwidth of systems based on sinusoidal multifrequency injection or variable-frequency injection for audible noise reduction is limited due to the need for filters. This article proposes a novel amplitude modulation multirandom frequency injection (AMMRI) method to improve control bandwidth and reduce audible noise. First, the detailed message signal modulation, error extraction, position tracking, and position estimation error compensation based on amplitude-modulated voltage signal are derived and analyzed. Because the filters for HF current and error extractions are removed, the control bandwidth is improved. Second, in order to reduce audible noise, the proposed AMMRI is derived by selecting the message signal according to equal-loudness contour. The proposed method improves the control bandwidth compared to conventional multifrequency injection and reduces audible noise compared to conventional square wave injection. Finally, experimental results verify the proposed method on a 1.5-kW IPMSM platform.

Hearing threshold, loudness, and annoyance of infrasonic versus non-infrasonic frequencies

Research related to perception, loudness, and annoyance of infrasound (frequency below 20 Hz) is limited compared to non-infrasound (20–20000 Hz). The purpose was to determine hearing threshold, equal loudness contours, equal annoyance contours, and other sensations apart from hearing. The laboratory experiment involved 19 normal hearing participants. Observed hearing thresholds within 4–8000 Hz agreed with previous findings supporting the adequacy of our methods. Equal-loudness contours for 20, 40, and 60 phon were determined within 4–1000 Hz. They emphasized the non-linear nature of hearing. The dynamic range of hearing is extremely suppressed at infrasonic frequencies: an increment of 5 dB at 4 Hz feels like an increment of 10 dB at 20 Hz and an increment of 20 dB at 1 kHz. Equal-annoyance contours were derived for 20, 40, and 50 phon within 4–1000 Hz. Because individual hearing thresholds varied up to 20 dB, an infrasonic tone still being inaudible for one participant could be loud or annoying for another participant. The finding may explain why some people perceive low frequency sound more annoying than the others. Other sensations apart from hearing (such as pressure in the ear, headache, and vibration sensation) were reported both for infrasound and non-infrasound. Thus, other sensations apart from hearing are not limited to infrasonic frequencies. The study findings emphasize that sound below 20 Hz should be treated similarly as sounds within 20–20000 Hz. Health effect assessment procedures would benefit from standardized hearing threshold below 20 Hz.

Reinforcement of Low-Frequency Sound by Using a Panel Speaker Attached to the Roof Panel of a Passenger Car

<div class="section abstract"><div class="htmlview paragraph">The woofer in a car should be large to cover the low frequencies, so it is heavy and needs an ample space to be installed in a passenger car. The geometry of the woofer should conform to the limited available space and layout in general. In many cases, the passengers feel that the low-frequency contents are not satisfactory although the speaker specification covers the low frequencies. In this work, a thin panel is installed between the roof liner and the roof panel, and it is used as the woofer. The vibration field is controlled by many small actuators to create the speaker and baffle zones to avoid the sound distortion due to the modal interaction. The generation of speaker and baffle zones follows the inverse vibro-acoustic rendering technique. In the actual implementation, a thin acrylic plate of 0.53x0.2 m<sup>2</sup> is used as the radiator panel, and the control actuator array is composed of 16 moving-coil actuators. The shape of the desired speaker zone is an ellipse, and the required amplitude of this piston source is pre-calculated to satisfy the desired sound radiation at the ear position. The gain of the actuator array to properly generate the desired vibration field is obtained by solving an inverse problem constructed by the transfer mobility between each actuator and field point on the plate. For the recruitment of the low-frequency deficiency of human auditory characteristics, the desired sound spectrum is set to follow the equal-loudness contour of 40 phons. It is confirmed that the woofer in a car can be replaced by the developed panel speaker.</div></div>

Using auditory reaction time to measure loudness growth in rats

Previous studies have demonstrated that auditory reaction time (RT) is a reliable surrogate of loudness perception in humans. Reaction time-intensity (RT-I) functions faithfully recapitulate equal loudness contours in humans while being easier to obtain than equal loudness judgments, especially in animals. In humans, loudness estimation not only depends on sound intensity, but on a variety of other acoustic factors. Stimulus duration and bandwidth are known to impact loudness perception. In addition, the presence of background noise mimics loudness recruitment; loudness growth is rapid near threshold, but growth becomes normal at suprathreshold levels. Therefore, to evaluate whether RT-I functions are a reliable measure of loudness growth in rats, we obtained auditory RTs across a range of stimulus intensities, durations, and bandwidths, in both quiet and in the presence of background/masking noise. We found that reaction time patterns across stimulus parameters were repeatable over several months in rats and generally consistent with human loudness perceptual data. Our results provide important building blocks for future animal model studies of loudness perception and loudness perceptual disorders.

Fast estimation of equal-loudness contours using Bayesian active learning and direct scaling

Fast estimation of equal-loudness contours using Bayesian active learning and direct scaling

Combined Effect of Noise and Smoking on the Cognitive Performance of Automotive Industry Workers.

Introduction:Noise is an environmental stressor and can cause or exacerbate mental disorders, and affect the individual performance in certain conditions. This study aimed to evaluate the combined effects of noise and smoking on the cognitive performance of the workers in the automotive industry.Methods:This research is a descriptive-analytical study with a cross-sectional design conducted on 300 workers randomly assigned into two groups of noise-exposed and nonexposed. They were examined using computerized tests, including the Tower of London test (TOL), Continuous Performance test (CPT), and Stroop test. The sound pressure levels were measured based on an 8-hour equal-loudness contour in each group according to ISO 9612 standard, using the Testo CEL-815 sound level meter.Results:The study of combined effects of noise and smoking on 12 CPT indicators using the 2-way Analysis of Variance (ANOVA) indicate that noise and smoking factors had a significant impact on the mean number of errors and correct responses in the third 50-stimuli stage, the mean number of errors and correct responses in the second 50-stimuli stage with P<0.001, P<0.001, P=0.012 and P<0.001 for smoking respectively, but only noise affected the other 7 indicators (P<0.001).Conclusion:Smoking and noise have negative impacts on concentration, attention, and cognitive processing speed, which can lead to an individual’s mistakes and delayed decision making at the workplace.

Feasibility of interleaved Bayesian adaptive procedures in estimating the equal-loudness contour.

A Bayesian adaptive procedure, the interleaved-equal-loudness contour (IELC) procedure, was developed to improve the efficiency in estimating the equal-loudness contour. Experiment 1 evaluated the test-retest reliability of the IELC procedure using six naive normal-hearing listeners. Two IELC runs of 200 trials were conducted and excellent test-retest reliability was found at both the group and individual levels. Using the same group of listeners, Experiment 2 compared the IELC procedure to two other procedures that required frequency-by-frequency testing. One of these procedures was the commonly adopted interleaved staircase (ISC) procedure from Jesteadt [(1980). Atten. Percept. Psychophys. 28, 85-88]. The other procedure, the interleaved maximum-likelihood (IML) procedure, was a modification of the updated maximum-likelihood procedure [Shen and Richards (2012). J. Acoust. Soc. Am. 132, 957-967]. For each of the ISC and IML procedures, two runs of approximately 500 trials were conducted, followed by one additional IELC run. The test-retest reliability of the IELC procedure was comparable to that of the ISC and IML procedure. The accuracies of all three procedures measured in Experiment 2 were similar, which was superior to the accuracies of the IELC runs from Experiment 1, indicating a potential training effect.

Automatic assessment of blood pressure for Korotkoff sounds on the basis of human hearing threshold.

In this study, to measure blood pressure (BP) on the basis of human hearing threshold, we proposed a method that detects the audible or inaudible Korotkoff sounds (K-sounds) using the equal loudness contour and automatically assesses the BP. In this study, we detected the systolic period of K-sounds using cuff pressure oscillation and then converted the K-sounds corresponding to the systolic interval into sound pressure levels (SPLs). Next, the systolic blood pressure (SBP) and diastolic blood pressure (DBP) were assessed by mapping the K-sounds, which were converted into SPLs on an equal loudness contour. To validate the accuracy of our proposed method, we compared it with the auscultatory method. The mean differences (mean±SD) in the SBP and DBP were 0.31±1.95 and 1.20±2.17 mmHg, respectively. For the SBP, the linear regression equation was y=0.98x+1.56 mmHg (where x and y represent the auscultatory and the proposed method, respectively), with a SE of estimate of 1.93 mmHg and a correlation coefficient of 0.99. For the DBP, the linear regression equation was y=1.01x-1.94 mmHg, with an SE of estimate of 2.18 mmHg and a correlation coefficient of 0.98. All P values were less than 0.0001 for both regressions. The auscultatory method of BP monitoring is sensitive to the observer's condition or environmental noise. To overcome these disadvantages, we used the human hearing threshold for objective SBP and DBP automatic assessment, and this method can be applicable to an automatic auscultatory method.

An evaluation and comparison of two psychoacoustic loudness models used in low-noise ventilation fan testing

The usage of loudness in standards and rating programs promoted by ASHRAE, HVI, and Energy Star is supported by the fact that occupants in buildings are exposed to noise from ventilating fans that are in close operational proximity to people. The current loudness calculation procedure, which is based on ANSI S3.4-1980 following a model by Stevens, is widely considered to be outdated because of its limited accuracy on equal-loudness contours, loudness-level-to-loudness conversions, and tonal components. Therefore, the study presented herein utilizes an extensive database consisting of 394 fan testing results to perform a detailed comparative analysis of this conventional Stevens loudness model and a revised loudness model developed by Moore et al. Although loudness results from each model were close to each other, a majority of fans under 2 sone show an overall larger loudness when the revised model is used for the noise calculation while there was no clear trend of noise differences for fans over 3 sone. These loudness differences between the two models are significant and would result in more fans failing certification if a revised loudness model is integrated into ventilation rating and certification programs. This effect on certification is more easily understood if one notes that less than a 0.5 sone difference in the certification limit would result in the same number of certified ventilating products presently conforming to Energy Star V4.0, at least for the large database evaluated in this study.

A history of loudness before 1950

Loudness is a perceptual correlate of the physical intensity of a sound, but the relationship between loudness and intensity is not simple. The derivation from loudness-matching data of equal-loudness contours for tones across frequency was described as early as 1927. However, the most influential work on loudness prior to 1950 was the formulation by Fletcher and Munson (1933) of a method for calculating the loudness of any steady sound from the intensities of its frequency components. In a subsequent publication, Fletcher and Munson (1937) described how the loudness of a tone changes in the presence of another tone, which is a phenomenon known as masking. Stevens (1936) made extensive contributions to the theory of loudness scaling and methods for loudness measurement. Miller (1947) discovered that “just detectable increments in intensity” were of the same order of magnitude for noise as for pure tones.” Dix et al. (1948) suggested a clinical use in differential diagnosis of hearing loss for the phenomenon known as loudness recruitment, which is defined as an abnormally-rapid loudness growth. In part because of its relevance to the remediation of hearing loss, the measurement, quantification, and prediction of loudness continue to be active areas of psychophysical research.

Physiological motivated transmission-lines as front end for loudness models.

The perception of loudness is strongly influenced by peripheral auditory processing, which calls for a physiologically correct peripheral auditory processing stage when constructing advanced loudness models. Most loudness models, however, rather follow a functional approach: a parallel auditory filter bank combined with a compression stage, followed by spectral and temporal integration. Such classical loudness models do not allow to directly link physiological measurements like otoacoustic emissions to properties of their auditory filterbank. However, this can be achieved with physiologically motivated transmission-line models (TLMs) of the cochlea. Here two active and nonlinear TLMs were tested as the peripheral front end of a loudness model. The TLMs are followed by a simple generic back end which performs integration of basilar-membrane "excitation" across place and time to yield a loudness estimate. The proposed model approach reaches similar performance as other state-of-the-art loudness models regarding the prediction of loudness in sones, equal-loudness contours (including spectral fine structure), and loudness as a function of bandwidth. The suggested model provides a powerful tool to directly connect objective measures of basilar membrane compression, such as distortion product otoacoustic emissions, and loudness in future studies.

Using Reaction Time and Equal Latency Contours to Derive Auditory Weighting Functions in Sea Lions and Dolphins.

Subjective loudness measurements are used to create equal-loudness contours and auditory weighting functions for human noise-mitigation criteria; however, comparable direct measurements of subjective loudness with animal subjects are difficult to conduct. In this study, simple reaction time to pure tones was measured as a proxy for subjective loudness in a Tursiops truncatus and Zalophus californianus. Contours fit to equal reaction-time curves were then used to estimate the shapes of auditory weighting functions.

Abnormal Auditory Gain in Hyperacusis: Investigation with a Computational Model.

Hyperacusis is a frequent auditory disorder that is characterized by abnormal loudness perception where sounds of relatively normal volume are perceived as too loud or even painfully loud. As hyperacusis patients show decreased loudness discomfort levels (LDLs) and steeper loudness growth functions, it has been hypothesized that hyperacusis might be caused by an increase in neuronal response gain in the auditory system. Moreover, since about 85% of hyperacusis patients also experience tinnitus, the conditions might be caused by a common mechanism. However, the mechanisms that give rise to hyperacusis have remained unclear. Here, we have used a computational model of the auditory system to investigate candidate mechanisms for hyperacusis. Assuming that perceived loudness is proportional to the summed activity of all auditory nerve (AN) fibers, the model was tuned to reproduce normal loudness perception. We then evaluated a variety of potential hyperacusis gain mechanisms by determining their effects on model equal-loudness contours and comparing the results to the LDLs of hyperacusis patients with normal hearing thresholds. Hyperacusis was best accounted for by an increase in non-linear gain in the central auditory system. Good fits to the average patient LDLs were obtained for a general increase in gain that affected all frequency channels to the same degree, and also for a frequency-specific gain increase in the high-frequency range. Moreover, the gain needed to be applied after subtraction of spontaneous activity of the AN, which is in contrast to current theories of tinnitus generation based on amplification of spontaneous activity. Hyperacusis and tinnitus might therefore be caused by different changes in neuronal processing in the central auditory system.

Categorical loudness scaling and equal-loudness contours in listeners with normal hearing and hearing loss.

This study describes procedures for constructing equal-loudness contours (ELCs) in units of phons from categorical loudness scaling (CLS) data and characterizes the impact of hearing loss on these estimates of loudness. Additionally, this study developed a metric, level-dependent loudness loss, which uses CLS data to specify the deviation from normal loudness perception at various loudness levels and as function of frequency for an individual listener with hearing loss. CLS measurements were made in 87 participants with hearing loss and 61 participants with normal hearing. An assessment of the reliability of CLS measurements was conducted on a subset of the data. CLS measurements were reliable. There was a systematic increase in the slope of the low-level segment of the CLS functions with increase in the degree of hearing loss. ELCs derived from CLS measurements were similar to standardized ELCs (International Organization for Standardization, ISO 226:2003). The presence of hearing loss decreased the vertical spacing of the ELCs, reflecting loudness recruitment and reduced cochlear compression. Representing CLS data in phons may lead to wider acceptance of CLS measurements. Like the audiogram that specifies hearing loss at threshold, level-dependent loudness loss describes deficit for suprathreshold sounds. Such information may have implications for the fitting of hearing aids.

Equal-latency curves and auditory weighting functions for bottlenose dolphins (Tursiops truncatus) and California sea lions (Zalophus californianus)

Reaction time (RT) data obtained from simple tonal detection tasks have been used to estimate frequency-specific equal-loudness contours in non-human animals. In order to guide the design of auditory weighting functions for marine mammals, equal-latency contours were generated using RT data from a simple tonal detection including two bottlenose dolphins (under water) and three California sea lions (in air). Median RT increased exponentially with decreased SPL in all cases. Equal-latency contours for near-threshold RTs were similar to audiograms in both species. Data for the sea lions showed some compression of equal-latency contours with increases in SPL; however, large inter-subject differences in the data for dolphins made results for that species more difficult to interpret. The equal-latency contours for all subjects progressively diverged from predicted equal-loudness contours at higher SPLs, likely a result of very small changes in RT with relatively large increases in SPL. As a result, the contours of most interest for designing weighting functions for high-level noise exposures were also the least reliable. The general similarity of most of the contours to species-typical audiograms suggests that more easily obtained auditory thresholds may provide useful approximations for weighting. [Funded by U.S. Navy Living Marine Resources Program.]

Loudness as a cue for acceptable noise levels.

The acceptable noise level (ANL) test is the only test that is known to predict success with hearing aids with a high degree of accuracy. A person's ANL is the maximal amount of background noise that he or she is "willing to put up with" while listening to running speech. It is defined as the speech level minus the noise level, in decibels (dB). People who are willing to put up with high levels of background noise are generally successful hearing-aid wearers, whereas people who are not willing to put up with high levels of background noise are generally unsuccessful hearing-aid wearers. If it were known what cues that listeners are using to decide how much background noise they are willing to tolerate, then it might be possible to create technology that reduces these cues and improves listeners' chances of success with hearing aids. As a first step toward this goal, this study investigated whether listeners are using loudness as a cue to determine their ANLs. Research Design and Study Sample: Twenty-one individuals with normal hearing and 21 individuals with sensorineural hearing loss participated in this study. In each group of 21 participants, 7 had a low ANL (<7 dB), 7 had a mid ANL (7-13 dB), and 7 had a high ANL (>13 dB). Participants performed a modified version of the ANL in which the speech was fixed at four different levels (50, 63, 75 and 88 dBA), and participants adjusted the background noise (multitalker babble) to the maximal level at which they were willing to listen while following the speech. These results were compared with participants' equal-loudness contours for the multitalker babble in the presence of speech. Equal-loudness contours were measured by having the participants perform a loudness-matching task in which they matched the level of the background noise (multitalker babble), played concurrently with speech, to a reference condition (also multitalker babble). During the test condition, the speech played at 50, 63, 75, or 88 dBA. All testing was performed in a sound booth with the speech and the noise presented from a loudspeaker at a 0° azimuth, 3 feet in front of the participant. Each condition was presented multiple times, and the results were averaged. Presentation order was randomized. Participants were tested unaided. Participants' ANLs were compared with their equal-loudness contours for the background noise. ANLs that ran parallel to the equal-loudness contours were considered consistent with a loudness-based listening strategy. This pattern was observed for only two participants - both hearing-impaired. The majority of listeners showed no consistent trend between their ANLs and their loudness-matched data, suggesting that they are using cues other than loudness to determine their ANLs. ANLs were consistent with loudness-matched data for a small subset of listeners, suggesting that they may be using loudness as a cue for determining their ANLs.