Low Sound Levels Research Articles

The behavioural response of Australian fur seals to motor boat noise.

Australian fur seals breed on thirteen islands located in the Bass Strait, Australia. Land access to these islands is restricted, minimising human presence but boat access is still permissible with limitations on approach distances. Thirty-two controlled noise exposure experiments were conducted on breeding Australian fur seals to determine their behavioural response to controlled in-air motor boat noise on Kanowna Island (39°10′S, 146°18′E). Our results show there were significant differences in the seals' behaviour at low (64–70 dB) versus high (75–85 dB) sound levels, with seals orientating themselves towards or physically moving away from the louder boat noise at three different sound levels. Furthermore, seals responded more aggressively with one another and were more alert when they heard louder boat noise. Australian fur seals demonstrated plasticity in their vocal responses to boat noise with calls being significantly different between the various sound intensities and barks tending to get faster as the boat noise got louder. These results suggest that Australian fur seals on Kanowna Island show behavioural disturbance to high level boat noise. Consequently, it is recommended that an appropriate level of received boat sound emissions at breeding fur seal colonies be below 74 dB and that these findings be taken into account when evaluating appropriate approach distances and speed limits for boats.

Optimization of Programming Parameters in Children with the Advanced Bionics Cochlear Implant

Cochlear implants provide access to soft intensity sounds and therefore improved audibility for children with severe-to-profound hearing loss. Speech processor programming parameters, such as threshold (or T-level), input dynamic range (IDR), and microphone sensitivity, contribute to the recipient's program and influence audibility. When soundfield thresholds obtained through the speech processor are elevated, programming parameters can be modified to improve soft sound detection. Adult recipients show improved detection for low-level sounds when T-levels are set at raised levels and show better speech understanding in quiet when wider IDRs are used. Little is known about the effects of parameter settings on detection and speech recognition in children using today's cochlear implant technology. The overall study aim was to assess optimal T-level, IDR, and sensitivity settings in pediatric recipients of the Advanced Bionics cochlear implant. Two experiments were conducted. Experiment 1 examined the effects of two T-level settings on soundfield thresholds and detection of the Ling 6 sounds. One program set T-levels at 10% of most comfortable levels (M-levels) and another at 10 current units (CUs) below the level judged as "soft." Experiment 2 examined the effects of IDR and sensitivity settings on speech recognition in quiet and noise. Participants were 11 children 7-17 yr of age (mean 11.3) implanted with the Advanced Bionics High Resolution 90K or CII cochlear implant system who had speech recognition scores of 20% or greater on a monosyllabic word test. Two T-level programs were compared for detection of the Ling sounds and frequency modulated (FM) tones. Differing IDR/sensitivity programs (50/0, 50/10, 70/0, 70/10) were compared using Ling and FM tone detection thresholds, CNC (consonant-vowel nucleus-consonant) words at 50 dB SPL, and Hearing in Noise Test for Children (HINT-C) sentences at 65 dB SPL in the presence of four-talker babble (+8 signal-to-noise ratio). Outcomes were analyzed using a paired t-test and a mixed-model repeated measures analysis of variance (ANOVA). T-levels set 10 CUs below "soft" resulted in significantly lower detection thresholds for all six Ling sounds and FM tones at 250, 1000, 3000, 4000, and 6000 Hz. When comparing programs differing by IDR and sensitivity, a 50 dB IDR with a 0 sensitivity setting showed significantly poorer thresholds for low frequency FM tones and voiced Ling sounds. Analysis of group mean scores for CNC words in quiet or HINT-C sentences in noise indicated no significant differences across IDR/sensitivity settings. Individual data, however, showed significant differences between IDR/sensitivity programs in noise; the optimal program differed across participants. In pediatric recipients of the Advanced Bionics cochlear implant device, manually setting T-levels with ascending loudness judgments should be considered when possible or when low-level sounds are inaudible. Study findings confirm the need to determine program settings on an individual basis as well as the importance of speech recognition verification measures in both quiet and noise. Clinical guidelines are suggested for selection of programming parameters in both young and older children.

Investigation of noise levels generated by otologic drills

Drilling during temporal bone surgery may result in temporary or permanent noise-induced hearing loss or tinnitus. This has practical implications for both the patient and the surgeon. Different surgical drill devices, routinely used in temporal bone surgery, are examined referring to their emitted sound levels and sound transport. Two surgical drills were used on a brass tubing and a steel wire to simulate sound generation during temporal bone surgery. Overview measurements were performed on human cadaver in a medical laboratory. A set-up in a silent chamber was chosen to exclude external sound sources. The noise emissions and the vibration generated by a silver diamond bur and a cutting drill (Rose bur) were registered when used on a brass tubing and a solid steel wire with sound level meter and a non-contact laser vibrometer. The highest sound rate generated by the diamond burr did not exceed 63 dB(A) when used on a solid steel wire, whereas the cutting burr emitted 76 dB(A). Both drills produced lower sound levels on the brass tubing. Again the cutting burr topped the diamond burr with 68 dB(A) against 56 dB(A). The sound emission did not exceed 76 dB(A) outside a radius 4 cm around the drill location. In conclusion, sound emission generated by different surgical burs routinely used in temporal bone surgery is lower than expected. Still, within a small radius around those burs high sound pressure levels may be induced into surrounding structures such as ossicles, labyrinth, and cochlear. Still damage is feasible when using surgical drills for a longer time period close to sensitive structures.

The Group Delay and Suppression Pattern of the Cochlear Microphonic Potential Recorded at the Round Window

BackgroundIt is commonly assumed that the cochlear microphonic potential (CM) recorded from the round window (RW) is generated at the cochlear base. Based on this assumption, the low-frequency RW CM has been measured for evaluating the integrity of mechanoelectrical transduction of outer hair cells at the cochlear base and for studying sound propagation inside the cochlea. However, the group delay and the origin of the low-frequency RW CM have not been demonstrated experimentally.Methodology/Principal FindingsThis study quantified the intra-cochlear group delay of the RW CM by measuring RW CM and vibrations at the stapes and basilar membrane in gerbils. At low sound levels, the RW CM showed a significant group delay and a nonlinear growth at frequencies below 2 kHz. However, at high sound levels or at frequencies above 2 kHz, the RW CM magnitude increased proportionally with sound pressure, and the CM phase in respect to the stapes showed no significant group delay. After the local application of tetrodotoxin the RW CM below 2 kHz became linear and showed a negligible group delay. In contrast to RW CM phase, the BM vibration measured at location ∼2.5 mm from the base showed high sensitivity, sharp tuning, and nonlinearity with a frequency-dependent group delay. At low or intermediate sound levels, low-frequency RW CMs were suppressed by an additional tone near the probe-tone frequency while, at high sound levels, they were partially suppressed only at high frequencies.Conclusions/SignificanceWe conclude that the group delay of the RW CM provides no temporal information on the wave propagation inside the cochlea, and that significant group delay of low-frequency CMs results from the auditory nerve neurophonic potential. Suppression data demonstrate that the generation site of the low-frequency RW CM shifts from apex to base as the probe-tone level increases.

THE MUD ADDITIVES AND THEIR EFFECT ON THERMAL CONDUCTIVITY OF ADOBE BRICKS

Adobe is one of the oldest building materials in use and abundantly found everywhere with affordable and reasonable cost. It is basically just dirt that has been moistened with water, sometimes with chopped straw or other fibers added for strength, and then allowed to dry in the desired shape. In addition to being simple and economic, adobe bricks are fireproof, durable, non-toxic, possess low sound transmission levels through walls and provide sufficient thermal mass to buildings. Adobe brick walls are load bearing structures, which can be used to build up to several stories high. Also, adobe bricks have ability to build vaults and domes. In addition to this, adobe bricks afford great flexibility in the design and construction process. They can be simply cut, reshaped and can easily be subjected to opening to be use for building’s services. Besides having, these advantages; they have some disadvantages too which can be summarized as follows; moderately low compressive strength, low tensile strength, low scratch resistance and low water resistance. To overcome these defects, additives should be added to the soil to improve its quality and increase its capability to stand against these defects. This paper provides an overview of the mud’s additives that are used in different regions of the world, and their enhancement to improve the soil stability, including mineral, Synthetic, vegetable and animal additives. The paper also includes an experimental study that examines the thermal conductivity of mud brick mixed with some additives (plant oil, ash, soap, and cow dung).

HEARING AID WITH SUDDEN SOUND ALERT

A multichannel hearing aid ( 20 ) comprises at least one frequency channel having a compressor ( 38 ) with a compression threshold at an output level below the hearing threshold and an attack time above 0.5 seconds whereby hearing of a sudden sound in a stationary sound environment is facilitated. With this compressor, the amplification of low signal levels may be increased compared to the prior art, as the compressor kicks in to generally suppress steady noises. The gain may generally be increased as high as feasible in view of the microphone baseline noise, which should preferably be kept below the hearing threshold. Thus the user of the hearing aid will generally have the option of a higher gain of low level sounds than generally feasible with prior art hearing aids.

Reply to “On Cochlear Impedances and the Miscomputation of Power Gain” by Shera et al. J. Assoc. Re. Otolaryngol.

Using a scanning laser interferometer, we recently measured the volume velocity of the basilar membrane vibration in the sensitive gerbil cochlea and estimated that the cochlear power gain is ~100 at low sound pressure levels (Ren et al., Nat Commun 2:216-223, 2011a). We thank Shera et al. for recognizing the technical challenges of our experiments and appreciating the beauty of our data in their comment (Shera et al., J Assoc Res Otolaryngol (in press), 2011). These authors argue that our analysis is inappropriate, invalidating our conclusion; moreover, they suggest that our finding of a power gain of >1 could arise from a passive structure or cochlea. While our analysis and interpretation remain to be verified, they are justified according to commonly accepted assumptions and theories in cochlear mechanics. Here, we also show that the mathematical demonstration of a power gain of >1 in a passive cochlea by Shera et al. is inconsistent with our data, which show that the volume velocity and power gain decrease and become <1 as the sound level increases.

Low cost sound level meters for education and outreach

It used to be that when you wanted a low cost sound level meter for teaching and outreach, you could purchase a Radio Shack 33-2050 analog sound level meter. These meters were fairly accurate as well as rugged and could be used as a microphone with preamp in a pinch. Now that the Radio Shack meter is no longer for sale what other options are available? In recent years a plethora of meters and software apps have become readily available at a low cost. In this presentation, the authors will discuss some of the qualities one should look for in a low cost meter to be used for outreach and education and suggest some equipment that meets these needs.

Examination of valued attributes of low sound level environments

The introduction of new noise sources into rural environments presents a number of unique community response challenges not typically encountered in urban and suburban environments. Low ambient sound levels combined with intermittently (rather than continuously) audible anthropogenic ambient contributors create unique soundscapes. Residents appear to value many attributes of these soundscapes and wish to preserve and protect them. Application of existing standards and guidelines (quantitative or nuisance-based) often does not meet resident expectations of protection. This paper examines a number of the valued attributes. It then asks questions about noise policy, resident expectations, adequacy of existing standards, source and ambient noise quantification, and the masking of valued attributes by a new noise source. It concludes with a list of issues that bear close examination in order to set future noise impact guidelines for low-ambient environments.

Soundscape study methods of band rehearsal room

Soundscape study methods were applied to a band rehearsal room to understand the acoustical issues involved in this situation. A taxonomy of sound sources, direct observation to identify the specific sonic events and the multiple source and receiver paths involved in the complex listening and performing tasks that occur during band rehearsals were identified. It was found that students spend almost 1/2 of their rehearsal time involved with verbal instruction and discussion. Interviews with conductors and questionnaires administered to music students in three different band rooms were used to determine what musicians are listening for during rehearsals. Source and receiver combinations for physical acoustical measurements were located to study the multiple listening tasks identified in the questionnaires. Musicians were constantly trying to “hear each other” for intonation, rhythm, dynamics, articulation, and tone quality during rehearsals. Statistical models linking the qualitative results of the questionnaires with the acoustical measurements and architectural features of the rooms show that the ceiling height, room volume, area of sound diffusing surfaces, low frequency sound level, early reflected sound energy, and reverberation were related to the ability of musicians to hear each other and the detailed attributes of music.

The Study on Influence of High Frequency Noise on Sound Quality for Generator

As cars become quieter the sound quality of components becomes more critical in the customer perception of car quality. This requires a need of new evaluation method for the specification of component sounds. Considering that high frequency noise plays an important roll for internal noise, the noise signals in the range from 7000Hz to 8000Hz are specially emphasized. Then the acoustic evaluation parameters, such as Sound Pressure Level, Sharpness and Steadiness have been evaluated. Judged from experiences and measuring results, an abnormal noise comes from Generator, through the exchange of Generator, Sound Pressure Level and sharpness were greatly improved. At the same time, subjective evaluation also indicated that there was no complaint any more in passenger compartment. Low Sound Pressure Level, sharpness can lead to perceived high product quality.

Localization of the Cochlear Amplifier in Living Sensitive Ears

BackgroundTo detect soft sounds, the mammalian cochlea increases its sensitivity by amplifying incoming sounds up to one thousand times. Although the cochlear amplifier is thought to be a local cellular process at an area basal to the response peak on the spiral basilar membrane, its location has not been demonstrated experimentally.Methodology and Principal FindingsUsing a sensitive laser interferometer to measure sub-nanometer vibrations at two locations along the basilar membrane in sensitive gerbil cochleae, here we show that the cochlea can boost soft sound-induced vibrations as much as 50 dB/mm at an area proximal to the response peak on the basilar membrane. The observed amplification works maximally at low sound levels and at frequencies immediately below the peak-response frequency of the measured apical location. The amplification decreases more than 65 dB/mm as sound levels increases.Conclusions and SignificanceWe conclude that the cochlea amplifier resides at a small longitudinal region basal to the response peak in the sensitive cochlea. These data provides critical information for advancing our knowledge on cochlear mechanisms responsible for the remarkable hearing sensitivity, frequency selectivity and dynamic range.

Persistent effects of early augmented acoustic environment on the auditory brainstem

Acoustic experiences significantly shape the functional organization of the auditory cortex during postnatal "critical periods." Here, we investigate the effects of a non-traumatic augmented acoustic environment (AAE) on the central nucleus of the inferior colliculus (ICC) and lower brainstem nuclei in rat during the critical period. Our results show that an AAE during P9-P28 had a persistent effect on the evoked auditory brainstem responses leading to a decreased latency and an increased amplitude of the response at and above the frequency of the stimulus used for the AAE. These findings are correlated with increased numbers of sites in the ICC that responded to the AAE frequency and show higher thresholds. There also were persistent effects in neurons with a best frequency higher than the AAE stimulus. These neurons showed decreased activity at low sound levels in the low frequency tail of the frequency response area. This was at, below and above the AAE stimulus frequency. Less often, increased activity at higher sound levels also was seen. Together, these findings suggest multifaceted interactions between activity-dependent plasticity, homeostasis, and development in the brainstem during the initial stages of hearing. A neonate exposed to an altered auditory environment may experience long-lasting change over the entire network of the auditory system.

Acoustic Characteristics of Hybrid Electric Vehicles and Safety of Blind Pedestrians

Quieter cars, such as electric vehicles and hybrid electric vehicles (HEVs), may reduce auditory cues used by pedestrians to assess the state of nearby traffic and, as a result, their use may have an adverse impact on pedestrian safety. To document differences in the sound levels of HEVs and internal combustion engine (ICE) vehicles, the authors measured the sound pressure levels in one-third octave bands of three HEVs and three corresponding ICE vehicles for the following operating conditions: idle, backing up at 5 mph, approaching at a constant speed (6, 10, 20, 30, and 40 mph), accelerating from stop, and slowing from 20 to 10 mph at 3.28 ft/s2. Sound level results comparing the HEVs with the ICE vehicles are presented. In general, HEVs have lower sound levels than ICE vehicles for operating conditions below 20 mph; but above 20 mph, the sound from road–tire interactions dominates and the sound levels of the two vehicle types converge.

Effects of electrical stimulation on the acoustically evoked auditory-nerve response in guinea pigs with a high-frequency hearing loss

Criteria for cochlear implantation keep expanding and people with substantial residual low-frequency hearing are considered candidates for implantation nowadays. Therefore, electro-acoustical stimulation in the same ear (EAS) is receiving increasing interest. We have investigated the effects of intracochlear electrical stimulation on acoustically evoked auditory-nerve activity, using a forward masking paradigm. The stimulation electrode was placed in the basal turn of the cochlea. Compound action potential (CAP) recordings were performed in guinea pigs with severe high-frequency hearing loss and in normal-hearing control animals. In normal-hearing animals, electrical stimulation generally suppressed CAPs, especially at high acoustic frequencies (8 and 16 kHz) and low sound levels. At low frequencies (0.5 and 1 kHz), suppression was observed only at high sound levels. In animals with a high-frequency hearing loss, suppression of CAPs at low frequencies was substantially less compared to control animals, even at high current levels and temporal overlap of acoustic and electric stimuli. Hence, effects of electrical stimulation substantially differed between normal-hearing animals and animals with a high-frequency hearing loss. These findings stress the need for a proper animal model when investigating EAS. We conclude that in case of high-frequency loss, the basal part of the cochlea can be stimulated electrically with little effect on responses to low-frequency acoustic stimuli.

높은 입사 음압에서의 미세 천공판을 이용한 흡음 기구의 설계

Reduction of acoustic loads of space launch vehicles can be achieved by acoustic absorbers satisfying strict cleanness requirements. This limited the use of general porous materials and requires non-porous sound absorbers. Micro-perforated panel absorbers(MPPA) is one of promising sound absorbers satisfying the cleanness requirement for launch vehicles. However, its applicability was limited to low sound pressure levels according to the acoustic impedance model of micro-perforated panels. In this paper the applicability of micro-perforated panel absorbers at high incident sound pressure was investigated in experimental ways. The absorption characteristics of a micro-perforated panel absorber was simulated according to its design variables, e.g., minute hole diameters and aperture ratios. It was shown that optimal design can be readily done by using proposed design charts. Experiments were conducted to measure acoustic properties of the designed micro-perforated panel absorbers. The results showed that acoustic resistance increases rapidly as incident sound pressure level does but change of acoustic reactance can be neglected in a practical point of view. This caused the decrease of peak value of absorption coefficient at high incident sound pressure level, but the amount of reduction can be accepted in practice. The major advantage of the micro-perforated panel absorber(wide absorption bandwidth) was still kept at high sound pressure level.

Spatial acoustic measurement in rabbits and humans and neural spatial tuning in the midbrain of the rabbit.

There are only a handfull of studies that address the effects of sound source distance on the head‐related transfer function (HRTF). We found in rabbits and humans that (1) the spectral shape of the HRTF changed with sound source location; (2) ILD increased with decreasing distance and increasing frequency. ILDs can be substantial even at low frequencies when distance is close; and (3) ITD decreased with decreasing distance and generally increased with decreasing frequency. These findings refute the common notions that ILD is negligible at low frequencies and that ITD is constant across frequency. Neural coding of using virtual auditory space (VAS) stimuli was investigated in the inferior colliculus of the unanesthesized rabbit. The bulk of our neurons were tuned to azimuths on the contralateral side (re: recording site) with best azimuths ranging from 0 to 90 deg. This tuning tended to broaden with stimulus level, although the degree of level tolerance differed among neurons. At low sound levels, the azi...

Reducing the Effects of Background Noise During Auditory Functional Magnetic Resonance Imaging of Speech Processing: Qualitative and Quantitative Comparisons Between Two Image Acquisition Schemes and Noise Cancellation

The intense sound generated during functional magnetic resonance imaging (fMRI) complicates studies of speech and hearing. This experiment evaluated the benefits of using active noise cancellation (ANC), which attenuates the level of the scanner sound at the participant's ear by up to 35 dB around the peak at 600 Hz. Speech and narrowband noise were presented at a low sound level to 8 listeners during fMRI using 2 common scanning protocols: short ("continuous") and long ("sparse") temporal schemes. Three outcome measures were acquired simultaneously during fMRI: ratings of listening quality, discrimination performance, and brain activity. Subjective ratings and discrimination performance were significantly improved by ANC and sparse acquisition. Sparse acquisition was the more robust method for detecting auditory cortical activity. ANC reduced some of the "extra-auditory" activity that might be associated with the effort required for perceptual discrimination in a noisy environment and also offered small improvements for detecting activity within Heschl's gyrus and planum polare. For the scanning protocols evaluated here, the sparse temporal scheme was the more preferable for detecting sound-evoked activity. In addition, ANC ensures that listening difficulty is determined more by the chosen stimulus parameters and less by the adverse testing environment.

A less stressful animal model: A conditioned avoidance behaviour task for guineapigs

In the conventional shuttle box, animals are trained to avoid electric foot-shocks. As a consequence of these stress-inducing foot-shocks the animals become anxious and are difficult to train. The aim of the present study was to avoid the stress-inducing foot-shocks and to develop a fast and reliable conditioned avoidance behaviour task for guineapigs. We examined whether narrowband noises at four different sound levels above hearing threshold could be used as conditioned stimulus (CS). The unconditioned stimulus (UCS) was a stream of air, which was used instead of the conventionally used electric foot-shocks. The animals were initially trained with a CS of 78 dB sound pressure level (SPL). In this initial training, guineapigs learned to detect a narrowband noise of 78 dB SPL. Interestingly, during the first additional training session in which three other sound levels were applied, guineapigs did not immediately generalize the learned response at 78 dB SPL to lower sound levels of 58 and 68 dB SPL. However, in this session a noise level of 88 dB SPL led immediately to a high level of responses. The response latency decreased with increasing sound level, from approximately 7 s at 58 dB SPL to approximately 3 s at 88 dB SPL. The escape latency during the UCS was approximately 0.6 s. The present results demonstrate that after reducing the level of stress guineapigs can acquire a response in only a few sessions and furthermore, although the guineapigs were less anxious, training at sound levels of 78 and 88 dB SPL was influenced by an aversive reaction by the guineapig. The results indicate that this aversive reaction of the guineapig is crucial for the training.

Fast Reverse Propagation of Sound in the Living Cochlea

The auditory sensory organ, the cochlea, not only detects but also generates sounds. Such sounds, otoacoustic emissions, are widely used for diagnosis of hearing disorders and to estimate cochlear nonlinearity. However, the fundamental question of how the otoacoustic emission exits the cochlea remains unanswered. In this study, emissions were provoked by two tones with a constant frequency ratio, and measured as vibrations at the basilar membrane and at the stapes, and as sound pressure in the ear canal. The propagation direction and delay of the emission were determined by measuring the phase difference between basilar membrane and stapes vibrations. These measurements show that cochlea-generated sound arrives at the stapes earlier than at the measured basilar membrane location. Data also show that basilar membrane vibration at the emission frequency is similar to that evoked by external tones. These results conflict with the backward-traveling-wave theory and suggest that at low and intermediate sound levels, the emission exits the cochlea predominantly through the cochlear fluids.