Absolute Sound Pressure Level Research Articles

Relationships between loudness and preference judgments for fan sounds as a function of the reference sound pressure level

In a prior study, the level of fan test sounds was adjusted in a listening test using an adaptive procedure, until they became equally loud or equally preferred as a reference sound at a fixed level. Depending on the test sound, level reductions of up to 15 dB compared to the 60 dB(A) reference level were necessary to reach equal loudness or preference compared to the reference sound. It turned out that the preference-equivalent levels were highly correlated with the loudness-equivalent levels, indicating that the preference decision and the loudness judgment were closely related to each other. In a follow-up study, the measurements were extended towards a higher reference level of 75 dB(A) and a lower reference level of 45 dB(A). The preference-equivalent levels obtained at 75 dB(A) were again closely related to the loudness-equivalent levels. For the lower reference level of 45 dB(A), the preference-equivalent levels deviate from the loudness-equivalent levels by 3.5 dB on average and also the inter-individual variability increased. This result suggests an increasing effect of additional fan-noise characteristics to play a role for the preference decisions on top of the perceived loudness especially at low absolute sound pressure levels.

Piezoelectric bimorph MEMS speakers

One of the key requirements for MEMS speakers is to increase the sound pressure level (SPL) while keeping the size as small as possible. In this paper we present a MEMS speaker based on piezoelectric bimorph cantilevers that produces a higher SPL than conventional unimorph cantilever speakers. The active diaphragm size is 1.4 × 1.4 mm2. The bimorph cantilevers are connected in parallel to make full use of the actuation voltage. At 1 kHz, the measured SPL reached 73 dB and the peak SPL reached 102 dB at the resonance frequency of 10 kHz in a 711 ear simulator under a driving voltage of 10 Vrms. The total harmonic distortion of the MEMS speaker was less than 3% in the range from 100 Hz to 20 kHz. Although the absolute SPL was not the highest, this work provides a better SPL for all piezoelectric MEMS speakers.

Realization of Noise Dosimeter Calibration Based on Percentage of Noise Dose Exposure using Absolute Method

The application of noise dosimeter in an industrial and construction area has shown an increase in the last decade in Indonesia significantly. The benefit of using this acoustical instrument is having a parameter known as a percentage of noise dose exposure that appropriate for the workers located in a loudness area. Moreover, the industrial necessity related to this instrument calibration quantity tends to increase in recent years. However, the calibration service related to this parameter is not available in Indonesia yet. Therefore, the aim of this work is to realize the calibration of noise dosimeters based on the percentage of noise dose exposure using an absolute method. In this method, it is necessary to apply the insert voltage technique to determine an absolute sound pressure level (SPL), where a whole measurement process is performed in a free field condition. The determined parameter is the percentage of noise dose (D), and time-weighted average (TWA) with SPL of 104 dB and 114 dB. From the result, the deviation value of D between the two devices under test and the reference tends to increase and has maximum values at the frequency of 8000 Hz that the values are 2.2% and 3.7% respectively. Meanwhile for the TWA parameter, the maximum deviation for the first DUT is found at the of 4000 Hz that has the value is 2.4 dB(A), while for the other device is about 4.1 dB(A) at the frequency of 8000 Hz. Besides, these methods are necessary to be implemented for validating the calibration of noise dosimeter using acoustic comparison coupler as a prototype research that still under development.

Listening in the bog: II. Neural correlates for acoustic interactions and spacing between Sphagniana sphagnorum males

Males of the katydid Sphagniana sphagnorum maintain inter-male distances from one another using agonistic song interactions with a frequency-modulated song that consists of alternating audio and ultrasonic parts. We studied the neuronal representation of this song in auditory receptors and interneurons of receivers, using playbacks of songs that mimicked the absolute and relative sound pressure levels of the two song modes varying with distance. The tuning and sensitivity of both receptors and interneurons strongly determine their responses to the two song modes at different distances. Low-frequency interneurons respond preferentially to the audio mode of the song at larger distances. High-frequency (HF) interneurons respond preferentially to the HF component of the song at close range. ‘Switch interneurons’ are sensitive to both spectral song components, but exhibit a typical activity switch towards the high-frequency mode at distances nearer than 3–6 m. The activity of the latter two groups of interneurons correlates with the distance in the field at which males begin to interact acoustically with their neighbours. Important information about the rate of changes in the song mode is represented by the afferent activity despite the influence of the masking song produced by a sympatric katydid species.

Psychoacoustic analysis of noise and the application of earplugs in an ICU: A randomised controlled clinical trial.

Patients and medical staff are exposed to high noise levels in ICUs, which may have a negative impact on their health. Due to the diversity of noise sources present, including the operating noise of medical devices, staff conversations and the unwrapping of disposables, noise profiles are varied. Psychoacoustics deals with the analysis of sound, focusing on its effects on physiological perception and stress. The aim of our study was to examine and to classify noise and its psychoacoustic properties in different locations in our ICU at different times. The impact of noise on subjective parameters and stress-related physiological data was also assessed with and without interventional methods. A randomised, controlled, single-blinded clinical trial. University Hospital, from November 2010 to May 2011. One hundred and forty-four patients in the ICU. In the first part, multidisciplinary psychoacoustic measurement was performed on the patients in our ICU. In the subsequent clinical trial, patients were equipped with effective earplugs, less effective earplugs and no earplugs. Thereafter, active noise cancellation headphones with or without sound masking were employed on a third patient population. Cortisol and α-amylase in saliva, skin conductance measures, vital signs, psychoacoustic analyses and two standardised questionnaires [State-Trait Anxiety Inventory (STAI) and Hospital Anxiety and Depression Scale (HADS)] were assessed. In the first part, the mean ± standard deviation (SD) subjective loudness was 9.2 ± 4.0 sone. Although absolute sound pressure level and loudness were lower during the night, the number of loud events increased significantly. Skin conductance in the earplug groups was significantly reduced in comparison to that in the control population but not the active noise reduction groups. Nevertheless, noise reduction was found to be comfortable for most patients. Noise in the ICU is of high clinical relevance. Diverse noise reduction methods, such as earplugs and active noise cancellation, are available. The avoidance of unnecessary noise, however, should be the primary focus. German Clinical Trials Register (DRKS00000534).

Can auditory brainstem and midbrain processing of interaural level difference cues really explain perceptual performance?

Neurons in the lateral superior olive (LSO) are believed to be involved in processing of interaural level difference (ILD) cues for sound localization. However, the ILD-tuning of LSO neurons varies with the absolute sound pressure levels (SPLs) at the two ears, in contrast to the relatively robust perceptual processing of ILD cues at different absolute SPLs. Tsai et al. (J. Neurophysiol. 2010) proposed that if some inferior colliculus (IC) neurons compute the difference between the contralateral and ipsilateral LSO outputs, the dependencies on absolute SPLs could be canceled out. However, they only considered pure-tone stimulation of single neurons at their characteristic frequencies and at relatively low SPLs. In this study, we evaluated the hypothesis of Tsai and colleagues using computational models of populations of auditory nerve, LSO and IC neurons consistent with Tsai and colleagues’ proposal. Predictions from two different neural decoder algorithms applied to LSO and IC model outputs indicate that discharge-rate saturation and spread of excitation in the auditory nerve lead to even greater SPL-dependence of ILD coding across a population of LSO neurons than is apparent in single neurons, and the IC differencing operation proposed by Tsai and colleagues does relatively little to ameliorate this problem.

수음실 잔향시간 변화에 따른 중량 충격음 레벨 특성 - 실험실 환경을 중심으로 -

Floor impact sound in high-rise apartment building became one of social problems. A lot of civil complaints on floor impact sound occur continuously and the number of disputes between neighbors in small and aged apartment buildings is increasing. Interests on heavy-weight impact sound pressure level measurement and evaluation method is increased. Previous study reported that heavy-weight impact sound level was changed by the sound field condition of receiving reverberation chamber. In this study, heavy-weight impact sound pressure level change by the receiving sound field condition was measured in standard test facility and mock-up test room. These two experimental conditions were designed to simulate averaged living room of common apartment units. By the change of sound absorption power in receiving room, heavy-weight impact sound pressure level in most of frequency bands were changed in standard test facility and mock-up room. Normalized maximum sound pressure level regulated in ISO 16032 showed wider range of heavy/soft impact sound pressure level. Heavy/soft impact sound pressure level change was became smaller by the application of standardized maximum sound pressure level and ISO/CD 10140-3 Amd 2 method. In the case of standardized maximum sound pressure level, absolute sound pressure level changed. From these results, receiving sound field correction method regulated in ISO/CD 10140-3 Amd 2 is needed for the precision measurement and evaluation of heavy-weight impact sound.

Erratum: “Overshoot using very short signal delays” [J. Acoust. Soc. Am. 128, 1915–1921 (2010)

All absolute sound-pressure levels mentioned in McFadden et al. (2010) were, in fact, 8.1 dB weaker than stated because of a malfunction in the true rms voltmeter used to adjust the stimulus levels at the earphones. We regret this error. However, we have no reason to question the basic outcomes; the data simply were collected with weaker stimuli than intended. The overall masker levels in Fig. 1 correspond to spectrum levels of about 17 dB and 7 dB, for the 3.0-kHz [Fig. 1 (top)] and 4.0-kHz data [Fig. 1 (bottom)], respectively, both of which are on the low side of optimal for overshoot according to the data of Bacon (1990).

Acoustic performance of an installed real‐time three‐dimensional audio system—Part II.

The exterior effects room (EER), located at the NASA Langley Research Center, was recently upgraded to allow for simulation of aircraft flyovers in a three‐dimensional (3‐D) audio and visual environment. The 3‐D audio server employs an implementation of the vector base amplitude panning (VBAP) method to position virtual sources at arbitrary azimuth and elevation angles in the EER. Recent work focused on the development of loudspeaker equalization first using high order FIR filters [POMA 9 015004 (2010)], and later using low order IIR filters [J. Acoust. Soc. Am. 128 2482 (2010)]. The latter, in conjunction with full‐path time delay compensation and relative gain compensation, were implemented in real‐time and shown to reproduce the desired sound field to within about ±5 dB over an extended frequency range for stationary and moving sources. In the present work, the performance is further characterized both objectively and subjectively. Addressed are calibration of the system for absolute sound pressure level reproduction and measurement of the spatial uniformity of the generated sound field. Further, localization of sound sources will be subjectively measured to assess the efficacy of the VBAP implementation in the EER.

Verbal communication in MR environments: effect of MR system acoustic noise on speech understanding.

To assess the masking effect of magnetic resonance (MR)-related acoustic noise and the effect of passive hearing protection on speech understanding. Acoustic recordings were made at 1.5 T at patient and operator (interventionalist in the MR suite) locations for relevant pulse sequences. In an audiologic laboratory, speech-to-noise ratios (STNRs) were determined, defined as the difference between the absolute sound pressure levels of MR noise and speech. The recorded noise of the MR sequences was played simultaneously with the recorded sentences at various intensities, and 15 healthy volunteers (seven women, eight men; median age, 27 years) repeated these sentences as accurately as possible. The STNR that corresponded with a 50% correct repetition was used as the measure for speech intelligibility. In addition, the effect of passive hearing protection on speech intelligibility was tested by using an earplug model. Overall, speech understanding was reduced more at operator than at patient location. Most problematic were fast gradient-recalled-echo train and spiral k-space sequences. As the absolute sound pressure level of these sequences was approximately 100 dB at patient location, the vocal effort needed to attain 50% intelligibility was shouting (>77 dB). At operator location, less effort was required because of the lower sound pressure levels of the MR noise. Fast spoiled gradient-recalled-echo and echo-planar imaging sequences showed relatively favorable results with raised voice at operator location and loud speaking at patient location. The use of hearing protection slightly improved STNR. At 1.5 T, the level of MR noise requires that large vocal effort is used, at the operator and especially at the patient location. Depending on the specific MR sequence used, loud speaking or shouting is needed to achieve adequate bidirectional communication with the patient. The wearing of earplugs improves speech intelligibility.

An efficient robust sound classification algorithm for hearing aids.

An efficient robust sound classification algorithm based on hidden Markov models is presented. The system would enable a hearing aid to automatically change its behavior for differing listening environments according to the user's preferences. This work attempts to distinguish between three listening environment categories: speech in traffic noise, speech in babble, and clean speech, regardless of the signal-to-noise ratio. The classifier uses only the modulation characteristics of the signal. The classifier ignores the absolute sound pressure level and the absolute spectrum shape, resulting in an algorithm that is robust against irrelevant acoustic variations. The measured classification hit rate was 96.7%-99.5% when the classifier was tested with sounds representing one of the three environment categories included in the classifier. False-alarm rates were 0.2%-1.7% in these tests. The algorithm is robust and efficient and consumes a small amount of instructions and memory. It is fully possible to implement the classifier in a DSP-based hearing instrument.

Ambiguities in sound-duration selectivity by neurons in the inferior colliculus of the bat Molossus molossus from Cuba.

This study examines duration selectivity in auditory neurons of the inferior colliculus of the bat Molossus molossus (Molossidae, Chiroptera) from Cuba. Three main types of duration selectivity, short-, band-, and long-pass, as previously described in other species, are present in M. molossus. The range of best durations in the inferior colliculus of this species approximates the durations of their echolocation calls, suggesting that, as has been shown in other species of bats and frogs, the filter mechanism that produces duration tuning is selective for species-specific sounds relevant to behavior. Duration coding in M. molossus is not unambiguous because approximately 30% of the short- and band-pass neurons respond best to two different stimulus durations. This bimodal duration selectivity could be explained by time delayed excitatory inputs that coincide with an inhibitory rebound. In addition, the effect of stimulus intensity on duration selectivity was tested. For most of the neurons (78%), duration selectivity was affected by absolute sound pressure level and/or small changes of sound pressure. In this respect, the processing of stimulus duration by collicular neurons seems to be more complex in M. molossus than in other species studied so far.

LOCALISING BITTERNS BOTAURUS STELLARIS WITH AN ARRAY OF NON-LINKED MICROPHONES

ABSTRACT Some animals emit sounds usable for acoustic monitoring of their population size. Such signals should be loud, omni-directional and easy to recognise and localise. Eurasian Bittern Botaurus stellaris mating calls (booms) are known to be loud and probably omni-directional but there is no data on acoustic localisation of this species. We made recordings of bittern booms with a 4-element GPS-linked microphone array, calibrated for absolute sound pressure level measurements. Receiver spacing was 65 to 294 m. The source level was 101 ± 3 dB re 20 μPa @ 1 m. The source level did not vary more than 7 dB for the same boom recorded at two different locations, with angular separations of 3°-27° as seen from the source. The geometric transmission loss was close to spherical, and the excess attenuation was much smaller than what was expected from the prevailing temperature and humidity conditions. The prevailing wind conditions caused sound velocity variations of up to 3%. The source location error was 104 ± 113 m (mean ± 1 s.d.). The prevalence of large location errors was probably caused by problems of discerning the direct path from multipath arrivals of the signal at the receivers and by sound velocity variations.

Intensity control during target approach in echolocating bats; stereotypical sensori-motor behaviour in Daubenton's bats, Myotis daubentonii.

When approaching a prey target, bats have been found to decrease the intensity of their emitted echolocation pulses, called intensity compensation. In this paper we examine whether intensity compensation in the echolocation of bats is flexible or stereotyped. We recorded the echolocation calls of Daubenton's bats (Myotis daubentonii) while the animals attacked targets of different dimensions. Myotis daubentonii reduced the peak sound pressure level emitted by about 4dB for each halving of distance, irrespective of the target presented (mealworms and two different sizes of spheres). The absolute sound pressure level emitted by the bat is not or only a little affected by target strength. Furthermore, the decrease in emitted intensity over distance shows less scatter than the same intensity over time for the last 20 cm of target approach. The bats matched the emitted intensity to target distance equally well for the spheres (aspect-invariant target strength) as for the mealworms (aspect-dependent echo strength). We therefore conclude that intensity compensation does not rely on feedback information from received intensity, but instead follows a stereotyped pattern.

Mechanisms underlying the sensitivity of neurons in the lateral superior olive to interaural intensity differences.

The initial processing of interaural intensity differences (IIDs), the major cue to the azimuthal location of high-frequency sounds in mammals, is carried out by neurons in the lateral superior olivary nucleus (LSO) that receive excitatory input from the ipsilateral ear and inhibitory input from the contralateral ear (IE neurons). The "latency" hypothesis asserts that it is the effects of intensity differences on the latency, and hence the relative timing, of the synaptic inputs to these neurons that is the basis of their sensitivity to IIDs, while other models assign the major role to changes in the relative amplitude of the inputs. To test the latency hypothesis and to determine the contributions of changes in the relative timing and amplitude of synaptic inputs to the IID sensitivity of LSO neurons, a method was developed of generating sets of stimuli that produced either the same changes in the relative timing of inputs without any change in their amplitude (equivalent interaural time difference stimuli) or the same differences in amplitude without any difference in timing (delay-cancelled IID stimuli) as a given range of IIDs. Data were obtained from a sample of IE neurons in the LSO of anesthetized rats using these stimulus paradigms and click and tone-burst stimuli. For click stimuli, the IID sensitivity of a small proportion of neurons was explained entirely by sensitivity to differences in input timing, but the sensitivity of most neurons reflected either sensitivity to the relative amplitude of inputs or to the joint operation of both factors. In neurons whose sensitivity was tested at a number of different absolute sound pressure levels (SPLs), the relative contributions of the two factors tended to differ at different SPLs. The IID sensitivity of onset responses to tone stimuli could be classified into the same three categories but was explained for a larger proportion of neurons by sensitivity to differences in input timing. The IID sensitivity of the late response component of neurons with sustained responses to tones in all cases reflected sensitivity to the relative amplitude of the inputs. The results confirm the contribution of changes in latency produced by intensity changes to the IID sensitivity of the onset responses of many IE neurons in LSO but require rejection of the strong form of the latency hypothesis, which asserts that this factor alone accounts for such sensitivity.

A Quantitative Analysis of the Courtship Acoustic Behaviour and Sound Patterning in Male Sand Goby, Pomatoschistus minutus

Many animal groups use sounds in reproduction in order to court mates or repel rivals. We describe the sounds and behavioural context of courtship sound production in male sand gobies, Pomatoschistus minutus, and examine the variability of acoustic parameters and the fine temporal patterning of sound units. Male sand gobies excavate a nest under a suitable solid substrate and attract females to mate, attaching the eggs to the ceiling of the nest. Before mating a female may repeatedly enter and leave a male's nest. Sounds were not detected during the courtship phase outside the nest, but were recorded when females were in the nest before spawning. Sounds were produced in 44–100% of such nest visits, varying with individual males. The sand goby sound consists of a train of pulses repeated at a rate of 23–29 pulses per second. The frequency spectrum of single pulses was continuous from 20–30 Hz to 500 Hz and reached a peak around 100 Hz. The absolute sound pressure level ranged from 118 to 138 dB re 1 µPa at 1–3 cm. The sand goby emits sound in distinct sound groups (bursts). Sound temporal features (duration, pulse repetition rate) vary systematically over the course of the burst. Within- and between-male variation of acoustic parameters was examined from sounds emitted by the male. Sound amplitude (peak-to-peak, mV) and pulse rate varied significantly among males, despite low individual stereotypy. Furthermore, sound pressure level correlated with body size. The potential informative content of acoustic parameters is discussed in the light of a possible role of the sand goby sound in mate choice.

Apparatus for and method of performing high frequency audiometry

An apparatus for and method of applying a selected range of high frequency acoustic energy to the apical end of the eardrum of an ear canal at a predetermined, substantially absolute sound pressure level at any frequency in the range of interest. The selected range of frequencies is generated at a location remote from the ear canal and the sound pressure level of each frequency is varied at the time of generation in accordance with a calibration function to ensure the frequencies reaching the apical end of the eardrum are at the predetermined sound pressure level. The calibration function is calculated by transmitting an acoustic pulse of broad frequency spectrum into the ear canal, measuring the sound pressure of the transmitted acoustic pulse and reflection thereof adjacent the entrance of the ear canal, and removing from the spectrum of the measured sound pressure the destructive interference effects between the transmitted and reflected acoustic pulses. The resultant sound pressure level contains nonuniformities having information regarding the sound transmission characteristics of the ear canal and the acoustic pulse generation and transmission system from which the calibration function is calculated.

The emission pattern of vocalizations and directionality of the sonar system in the echolocating bat, Pteronotus parnelli

The radiation patterns of the first three harmonics (approx. 30, 60, 90 kHz) of the mustached bat biosonar signal were measured from vocalizations elicited by cortical microstimulation. The primary foci of the acoustic beam patterns were in front of the mouth but somewhat below the horizontal plane. The prominent second and third harmonics showed sharp cutoffs between 20 degrees and 30 degrees lateral to the midline. Sidelobes were found, suggesting the influence of some vocal tract interference. When compared with previously measured estimates of the directionality of the auditory system, the vocal emission patterns are roughly complementary: Regions of maximum auditory sensitivity are found in areas of submaximal power for the sonar pulse beam pattern. The result is that, for the two most important harmonics, the "biosonar system" (i.e., vocal beam pattern plus receiver directionality) has a broader and more uniform directionality than either component alone. Therefore, within a limited region of space, echo amplitude will vary less as a function of angular displacement. This reduces the confounding influences of absolute sound pressure level on interaural intensity differences.

Auditory Frequency Resolution in Human Infancy

Frequency resolution is a fundamental capacity of the auditory system that underlies the perception of all complex sounds. The development of this capacity has not been well characterized in humans. This investigation used a nonsimultaneous pulsation threshold technique to examine the development of infant frequency resolution. Psychophysical tuning curves were obtained for 3- and 6-month-olds and for adults at either 500, 1,000, or 4,000 Hz. Both the sensation level and the sound pressure level of the stimulus were varied for adults to determine the contribution of stimulus intensity to age differences in frequency resolution. At 500 and 1,000 Hz, 3- and 6-month-olds' tuning curve widths were equivalent to adults'. At 4,000 Hz, the 3-month-olds' tuning curves were broader than those of 6-month-olds and adults, even when absolute sound pressure level was equivalent. The maturation of psychophysical frequency resolution in infants is discussed in terms of the general development of the auditory system and of nonsensory factors that might contribute to age differences in performance.

A neural map of interaural intensity differences in the brain stem of the barn owl

The nucleus ventralis lemnisci lateralis pars posterior (VLVp) is the first binaural station in the intensity-processing pathway of the barn owl. Contralateral stimulation excites and ipsilateral stimulation inhibits VLVp cells. The strength of the inhibition declines systematically from dorsal to ventral within the nucleus. Cells selective for different intensity disparities occur in an orderly sequence from dorsal to ventral within each isofrequency lamina. Cells at intermediate depths in the nucleus are selective for a particular narrow range of interaural intensity differences independently of the absolute sound-pressure level. A simple model of the interaction between inhibition and excitation can explain most of the response properties of VLVp neurons. The map of selectivity for intensity disparity is mainly based on the gradient of inhibition.