Low Sound Levels Research Articles

Noise and well-being in urban residential environments: The potential role of perceived availability to nearby green areas

A growing body of literature indicates that contact with nature influence people's health and psychological well-being both directly and by moderating processes. A questionnaire study was conducted in urban residential settings with high road-traffic noise exposure ( L Aeq, 24 h = 60–68 dB). Out of 500 residents, 367 lived in dwellings with access to a quiet side ( L Aeq, 24 h ≤ 45 dB free field value; “noise/quiet”-condition) and 133 had no access to a quiet side (“noise/noise”-condition). The present paper examines whether perceived availability to nearby green areas affects various aspects of well-being in these two noise-condition groups. For both those with and without access to a quiet side, the results show that “better” availability to nearby green areas is important for their well-being and daily behavior by reducing long-term noise annoyances and prevalence of stress-related psychosocial symptoms, and by increasing the use of spaces outdoors. In the process of planning health-promoting urban environments, it is essential to provide easy access to nearby green areas that can offer relief from environmental stress and opportunities for rest and relaxation, to strive for lower sound levels from road traffic, as well as to design “noise-free” sections indoors and outdoors.

Females whisper briefly during sex: context- and sex-specific differences in sounds made by croaking gouramis

Croaking gouramis, Trichopsis vittata (family Osphronemidae), possess enhanced pectoral fin muscles and tendons, enabling the fish to generate series of short or long broadband bursts while beating the fins. Agonistic disputes over territories result in lateral displays during which both sexes produce croaking sounds. During mating, a female approaches a male's nest at the water surface and emits purring sounds in a vertical, head-up position. This behaviour is followed by spawning bouts. I investigated whether aggressive and prespawning sounds differ in acoustic characteristics and whether they might convey different information. Agonistic sounds of both sexes lasted longer than the females' prespawning sounds, consisting of four or five bursts/sound compared to 2.4 bursts in purring sounds, and included a smaller percentage of short bursts. Sound pressure levels were higher in agonistic than in prespawning sounds. The dominant frequency of male agonistic signals was lower than that of female prespawning sounds. Both sexes produced long, high-intensity croaking sounds during agonistic disputes; these probably help them assess the fighting ability of opponents. On the other hand, only females emitted short, low-intensity purring sounds, which probably initiate and coordinate spawning behaviour. The low sound level and short duration of prespawning sounds indicate that they function as mating displays at very short distances; this probably reduces the chance of attracting competitors or predators. The croaking gourami is the only fish species in which females are known to initiate spawning acoustically.

In vivo imaging and low-coherence interferometry of organ of Corti vibration

An optical coherence tomography (OCT) system is built to acquire in vivo both images and vibration measurements of the organ of Corti of the guinea pig. The organ of Corti is viewed through a approximately 300-microm-diam hole in the bony wall of the cochlea at the scala tympani of the first cochlear turn. In imaging mode, the image is acquired as reflectance R(x,z). In vibration mode, the basilar membrane (BM) or reticular lamina (RL) are selected by the investigator interactively from the R(x,z) image. Under software control, the system moves the scanning mirrors to bring the sensing volume of the measurement to the desired membrane location. In vivo images of the organ of Corti are presented, indicating reflectance signals from the BM, RL, tectorial membrane, and Reissner's membrane. The tunnel of Corti and the inner sulcus are also visible in the images. Vibrations of +/-2 and +/-22 nm are recorded in the BM in response to low and high sound levels at 14 kHz above a noise floor of 0.2 nm.

Guided underwater object

A guided underwater object (GUO) ( 100 ) comprises steering means, an on-board guidance system ( 200 ) for controlling the steering means, and a hydrophone unit or units ( 104 A, 104 B, 104 C, 104 D, 104 E, 104 F, 104 G, 104 H) arranged to pass signals induced therein by an acoustic guiding beam to the on-board guidance system to effect directional control of the self-propelled underwater object. The GUO is guided by a remote guidance system characterised by a plurality of transmitter arrays ( 402 A, 402 B, 402 C, 402 D; 412 A, 412 B, 412 C, 412 D; 422 P, 422 Q, 422 R) arranged to transmit a plurality of contiguous acoustic beams ( 302 A, 302 B, 302 C, 302 D) each having a different frequency or frequency chirp (or other acoustic signal coding) and enclosing a guidance corridor of lower sound level (‘null’) ( 304 ) extending approximately in the direction of propagation of the acoustic beams and defining a flight path of the object. The GUO requires no on-board search sensors, no communications link with the guidance system and is of low cost.

Method of processing a sound signal in a hearing aid

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.

HVAD GØR LYD TIL STØJ?

Sounds are found everywhere, including the working environment. When sounds are
 unwanted and annoying they are perceived as noise. An increasing number of people in
 Denmark are reporting that they are exposed to loud noise in their working environment.
 It is noteworthy that the reported incidence of noise exposure comes from non-industrial
 trades, for example, from day-care institutions, and from schoolrooms. In order to reduce
 annoyance due to work-related noise exposure, it is necessary to identify the circumstances
 and factors that are important when sound is perceived as noise. The results of
 our research demonstrate that noise of even low sound levels can cause considerable
 annoyance. Moreover, a number of other factors are important in making sounds being
 perceived as noise. They are, among others, the information content of the sounds, the
 predictability and the possibility to control the sound, the characteristics of the work
 tasks, prevention of the noise, and various individual factors, such as noise sensitivity
 and hearing. Finally, not only is annoyance the effect of exposure to noise in the working
 environment; our research points to the conclusion that sustained exposure to noise
 can result in stress.

Olivocochlear Efferents: Anatomy, Physiology, Function, and the Measurement of Efferent Effects in Humans

This review covers the basic anatomy and physiology of the olivocochlear reflexes and the use of otoacoustic emissions (OAEs) in humans to monitor the effects of one group, the medial olivocochlear (MOC) efferents. MOC fibers synapse on outer hair cells (OHCs), and activation of these fibers inhibits basilar membrane responses to low-level sounds. This MOC-induced decrease in the gain of the cochlear amplifier is reflected in changes in OAEs. Any OAE can be used to monitor MOC effects on the cochlear amplifier. Each OAE type has its own advantages and disadvantages. The most straightforward technique for monitoring MOC effects is to elicit MOC activity with an elicitor sound contralateral to the OAE test ear. MOC effects can also be monitored using an ipsilateral elicitor of MOC activity, but the ipsilateral elicitor brings additional problems caused by suppression and cochlear slow intrinsic effects. To measure MOC effects accurately, one must ensure that there are no middle-ear-muscle contractions. Although standard clinical middle-ear-muscle tests are not adequate for this, adequate tests can usually be done with OAE-measuring instruments. An additional complication is that most probe sounds also elicit MOC activity, although this does not prevent the probe from showing MOC effects elicited by contralateral sound. A variety of data indicate that MOC efferents help to reduce acoustic trauma and lessen the masking of transients by background noise; for instance, they aid in speech comprehension in noise. However, much remains to be learned about the role of efferents in auditory function. Monitoring MOC effects in humans using OAEs should continue to provide valuable insights into the role of MOC efferents and may also provide clinical benefits.

Acoustics measurements in a lean premixed combustor operated on hydrogen/hydrocarbon fuel mixtures

In this study, acoustics and emissions measurements in hydrocarbon flames enriched with hydrogen were obtained for a range of operating conditions. Methane and propane fuels enriched with up to 40% hydrogen (by volume) were used. Fully premixed reactants were burnt in an atmospheric pressure, swirl-stabilized combustor replicating typical geometric features of land-based gas turbines. Acoustics data indicated an increase in the total sound power with an increase in the adiabatic flame temperature. Hydrogen enrichment of methane produced higher sound levels as compared to non-enriched methane with a single frequency band around 450 Hz. Hydrogen-enriched propane flames had lower sound levels, with multiple frequency bands appearing on an intermittent basis. Results suggest that the changes in the combustor dynamics should be considered together with the known benefits of hydrogen addition, i.e., the extended lean blow off limit and lower nitric oxide and carbon monoxide emissions.

Hearing in renal failure

The incidence of sensorineural hearing loss among patients with chronic renal failure (CRF) is considerably higher than in the general population. Bazzi et al. [1] found an incidence of 77% including patients with mild and very mild hearing loss. Ozturan and Lam [2] found a moderate to severe hearing loss in 46% of the tested patients. The general consensus in audiometric findings among patients with CRF claims a high frequency hearing loss [3,4] with a notch at 6 kHz [2]. Presence of hearing loss and estimation of type and degree constitute one of the most common methods used to investigate the effects of renal disease on the auditory system. Degree of hearing loss may give an indication of the extent of damage to auditory function, whereas the type of hearing loss may distinguish between lesions in the outer and middle ear (conductive hearing loss) or the cochlea and the neural pathways (sensorineural hearing loss). In addition to these indicators, the reports to be reviewed in the following sections have also described auditory function in CRF with methods such as otoacoustic emissions (OAEs) (namely transient evoked OAEs, TEOAEs and distorion product OAEs, DPOAEs), and auditory evoked potentials (AEPs). OAEs are low level sounds emitted by the cochlea in the process of receiving the sound vibrations and transforming them to cellular and neural stimulation. Recording of OAEs implies a functioning cochlea and healthy middle ear mechanism. TEOAEs are produced by the action of the hair cells, and they reflect special characteristics of the stimulus. DPOAEs are produced when the ear is stimulated with a combination of pure tones that are close in frequency (the primary tones). DPOAEs reflect non-linear processes of hair cell motion. Both TEOAEs and DPOAEs are generated by the active cochlear mechanisms responsible for enhancing basilar membrane vibration; this is known as the ‘cochlear amplifier’ [5]. AEPs represent neural activity related to auditory stimulation. They show summated neural energy at the various synaptic levels of the auditory pathway; this activity is generated by specific stimuli and extracted from the ongoing EEG activity by specialized technical manipulation. AEPs are recorded from the scalp representing activity in the cochlea and brainstem, thalamus and cortical areas. They are distinguished in early, middle and late evoked potentials, respectively. AEPs recorded from the cochlea include the cochlear microphonic (CM), the summating potential (SP) and the auditory nerve action potential (AP). The CM originates in the outer hair cells and mirrors the incoming signal. The SP also reflects hair cell function. The auditory nerve AP represents the sum of synchronous responses of auditory nerve fibers at the level of the cochlea. The largest component of the AP is the N1, a characteristic wave that constitutes also the first identifiable component of the auditory brainstem response (ABR). The ABR is also an ‘early’ evoked response, as it reflects neural function along the ascending auditory pathway, from the cochlea to the inferior colliculus. The five distinct waves of the normal ABR waveform are mainly generated by successive nuclei in the ascending auditory pathway: waves I and II originate from the distal and proximal portions of the auditory nerve, respectively, wave III originates from the cochlear nucleus, wave IV originates from the superior olivary complex and wave V originates from the lateral lemniscus/inferior colliculus. Each higher level order wave receives contributions from lower levels of the pathway [6]. The AEP reflecting function from auditory cortical areas is the Auditory Late Response (ALR). Major identifiable waves of the ALR are the N1 and P2 waves. ALR measurements reflect higher-level auditory function [7]. In general, latency of AEP waves indicates speed of neural function, whereas amplitude is a variable indicator of response robustness. The cochlea and kidney have similar physiological mechanisms, namely the active transport of fluid Correspondence and offprint requests to: Dr Chryssoula ThodiPetrou Cyprus, Audiology Center, Kallipoleos and 1Damaskinos Str, 1070, P.O. Box 20739, 1663 Nicosia, Cyprus. Email: DrC@cyprusaudiologycenter.com Nephrol Dial Transplant (2006) 21: 3023–3030

Effect of Probe Tube Insertion Depth on Spectral Measures of Speech

This study investigated how depth variations in the tip of the probe tube affected spectral measures of speech recorded in the external ear canal. Consonant-vowel nonsense syllables were recorded with a probe tube microphone system in 10 adult participants with normal middle ear function. Recordings were made with the probe tube tip placed 1 mm, 5 mm, and 10 mm beyond the medial tip of a custom earmold. The effect of probe depth was evaluated on spectral levels (one-third octave and one- twelfth octave band). Extending the probe tube 10 mm past the medial tip of the earmold gave the most accurate results, with relatively lower sound levels for either the 1-mm or 5-mm insertion depth. In general, the effect of insertion depth was minimal at frequencies below 3 to 4 kHz, although this varied with the specific phoneme and the width of the analysis bands. The authors found no significant difference between 1- and 5-mm insertion depths, suggesting that as long as the tip of the probe tube is sufficiently close to the tympanic membrane to capture the highest frequency of interest, it makes little difference if it is less than 5 mm beyond the earmold tip.

USING A BILINGUAL GAPS AND HAND-WASHING DVD TO TRAIN FRESH PRODUCE FIELD AND PACKINGHOUSE WORKERS

The Southeastern Fresh Produce Food Safety Training Program has been training extension agents across the southeastern U.S. since 2000. This program has utilized a variety of methods including group case study to enhance learning and promote team work. Multistate trainings have fostered collaboration between states and institutions. One goal of the program was to produce a method for agents to provide training that was repeatable and easy to implement. As a result, two videos were produced for use in training field and packinghouse workers. These videos were an English language good agricultural practices (GAPs) video entitled Bridging the GAPs: From the Farm to the Table and a Spanish language hand-washing video entitled ¡Lave sus Manos: Por Los Niños! This program has been very effective, but has faced challenges due to language barriers. Many field and packinghouse crews were mixed in terms of language with some crew members speaking only English while others spoke only Spanish. As a result, Spanish speakers were unable to access the information in the good agricultural practices video while English speakers were unable to access information in the hand-washing video. The solution was to produce a bilingual training aid that included both sets of information and has been compiled into a DVD containing the footage of both of the original videos in both languages. For the Spanish version of the GAPs video and the English of the hand-washing video, the audio of the video's original language was left at a low sound level and the audio of the alternate language was added. These DVDs are currently being distributed to extension programs in all of the cooperating states with the aim of reaching growers who want to start a food safety plan.

A Biophysical Model of the Inner Hair Cell: The Contribution of Potassium Currents to Peripheral Auditory Compression

The term peripheral auditory compression refers to the fact that the whole range of audible sound pressure levels is mapped into a narrower range of auditory nerve responses. Peripheral compression is the by-product of independent compressive processes occurring at the level of the basilar membrane, the inner hair cell (IHC), and the auditory nerve synapse. Here, an electrical-circuit equivalent of an IHC is used to look into the compression contributed by the IHC. The model includes a mechanically driven transducer potassium (K(+)) conductance and two time- and voltage-dependent basolateral K(+) conductances: one with fast and one with slow kinetics. Special attention is paid to faithfully implement the activation kinetics of these basolateral conductances. Optimum model parameters are provided to account for previously reported in vitro observations that demonstrate the compression associated with the gating of the transducer and of the basolateral channels. Without having to readjust its parameters, the model also accounts for the in vivo nonlinear IHC transfer characteristics. Model simulations are then used to investigate the relative contribution of the transducer and basolateral K(+) currents to the nonlinear IHC input/output functions in vivo. The simulations suggest that the voltage-dependent activation of the basolateral currents compresses the DC potential for stereocilia displacements above approximately 5 nm. The degree of compression exceeds 2-to-1 and is similar for all stimulation frequencies. The AC potential is compressed in a similar way, but only for frequencies below 800 Hz. The simulations further suggest that the nonlinear gating of the transducer current is responsible for the expansive growth of the DC potential with increasing sound level (slope of 2 dB/dB) at low sound pressure levels.

Cochlear transducer operating point adaptation

The operating point (OP) of outer hair cell (OHC) mechanotransduction can be defined as any shift away from the center position on the transduction function. It is a dc offset that can be described by percentage of the maximum transduction current or as an equivalent dc pressure in the ear canal. The change of OP can be determined from the changes of the second and third harmonics of the cochlear microphonic (CM) following a calibration of its initial value. We found that the initial OP was dependent on sound level and cochlear sensitivity. From CM generated by a lower sound level at 74 dB SPL to avoid saturation and suppression of basal turn cochlear amplification, the OHC OP was at constant 57% of the maximum transduction current (an ear canal pressure of -0.1 Pa). To perturb the OP, a constant force was applied to the bony shell of the cochlea at the 18 kHz best frequency location using a blunt probe. The force applied over the scala tympani induced an OP change as if the organ of Corti moved toward the scala vestibuli (SV) direction. During an application of the constant force, the second harmonic of the CM partially recovered toward the initial level, which could be described by two time constants. Removing the force induced recovery of the second harmonic to its normal level described by a single time constant. The force applied over the SV caused an opposite result. These data indicate an active mechanism for OHC transduction OP.

Proposed Criteria for Assessing Low Frequency Noise Annoyance in Occupational Settings

The aim of the study was to recommend methods for assessing low frequency noise (LFN) in the occupational environment to prevent annoyance and its effects on work performance. Three different evaluating methods and corresponding admissible values were proposed: (i) method I--frequency analysis in 1/3-octave bands within the range of 10-250 Hz, (ii) method II--consisting in 1/3-octave band measurements and determination of low frequency equivalent-continuous A-weighted sound pressure level (SPL) in the frequency range of 10-250 Hz, and (iii) method III--based on equivalent-continuous A-weighted SPL corrected due to the presence of low frequencies and tonal character of LFN. Separate noise limits were recommended for workplaces in control rooms and office-like areas. The proposed criteria were verified in laboratory and field studies. The laboratory study included 55 volunteers, aged 21.8 +/- 2.1 years, with normal hearing (< 25 dB HL). The subjects listened to different noises at A-weighted SPL of 45-65 dB, and evaluated annoyance using a 100-score graphical rating scale. In the field study, 35 male workers, aged 40.1 +/- 7.2 years, exposed to LFN at A-weighted SPL of 48-61 dB, were asked to rate noise annoyance at their workplaces using a similar graphical scale. The subjective ratings of LFNs were compared to objective results from various assessing methods. The relations between annoyance and excesses of proposed limits were analyzed using Pearson's correlation coefficient (r). Linear relationships between the subjective ratings and results from all proposed exposure criteria were observed (0.550 < or = r < or = 0.673; p < 0.001). In the field conditions, however, the highest correlation coefficient was found for method II (r = 0.673), while during the laboratory study for method I (r = 0.612) and criterion curves based on hearing threshold level (HTL). All proposed criteria, especially the evaluation method based on the low frequency equivalent-continuous A-weighted sound SPL (method II) as well as the frequency analysis in 1/3-octave bands 10(20)-250 Hz (method I) and criterion curves based on HTL or A-weighting characteristics, seem to be able to quite well predict annoyance experienced from LFN at workplaces.

Medial-olivocochlear-efferent inhibition of the first peak of auditory-nerve responses: evidence for a new motion within the cochlea.

Despite the insights obtained from click responses, the effects of medial-olivocochlear (MOC) efferents on click responses from single-auditory-nerve (AN) fibers have not been reported. We recorded responses of cat single AN fibers to randomized click level series with and without electrical stimulation of MOC efferents. MOC stimulation inhibited (1) the whole response at low sound levels, (2) the decaying part of the response at all sound levels, and (3) the first peak of the response at moderate to high sound levels. The first two effects were expected from previous reports using tones and are consistent with a MOC-induced reduction of cochlear amplification. The inhibition of the AN first peak, which was strongest in the apex and middle of the cochlea, was unexpected because the first peak of the classic basilar-membrane (BM) traveling wave receives little or no amplification. In the cochlear base, the click data were ambiguous, but tone data showed particularly short group delays in the tail-frequency region that is strongly inhibited by MOC efferents. Overall, the data support the hypothesis that there is a motion that bends inner-hair-cell stereocilia and can be inhibited by MOC efferents, a motion that is present through most, or all, of the cochlea and for which there is no counterpart in the classic BM traveling wave.

Comments on draft ANSI S12.2, American National standard on criteria for evaluating room noise

In 1995, American National Standard S12.2‐1995 on room noise criteria was issued. Two methods for specifying and evaluating room noise were presented, the NCB noise‐criterion curves [J. Acoust. Soc. Am. 86, 650–664 (1989)] and the RC curves [Noise Control Eng. J. 45, 243–250 (1997)]. The NCB curves were derived from the characteristics of hearing with emphasis on speech interference level and loudness level, while the RC curves were derived from experimental studies in offices where the HVAC noise was low enough that there were no complaints from room occupants. The NCB curves were applicable to rooms ranging from concert halls to factory spaces, while the RC curves were largely restricted to office, hospital, and residential spaces. The two sets were incompatible at low frequencies and low sound levels. The NCB curves assumed that the HVAC noise was free of surging and strong turbulence. The RC curves demanded lower levels at low frequencies, thus permitting some degree of surging and turbulence. The new draft standard specifies two methods for evaluating room noise, the NC [Noise Control 3, 19–27 (1957)] and the RNC methods [Noise Control Eng. J. 48, 85–96 (2000)]. The former (NC) have found widespread use and the latter (RNC) bridges the differences between the NC (and NCB) and the RC criteria curves. This paper comments on the promise of the new RNC method and compares measured data were available.

Recommended noise criteria for siting industrial facilities near residential communities with extremely low ambient sound levels

Noise limits or criteria in many residential communities are based on an allowable increase in level above the prevailing ambient sound level, usually on the order of 3 to 5 dBA. The theory is that such a small increase results in masking of the new or existing intruding facility noise by the environmental ambient sound. However, many facilities are planned for installation or already exist in remote and very quiet ambient environments with residual levels as low as 25 dBA during the day or nighttime. This paper summarizes a study conducted to determine appropriate criteria in such remote and quiet areas where little or no noise masking will occur from ambient sources. The paper discusses both audible noise measured by the A-weighted level, low frequency noise characterized by the C-weighted level and tonal noise.

Speech Recognition With the Advanced Combination Encoder and Transient Emphasis Spectral Maxima Strategies in Nucleus 24 Recipients

One of the difficulties faced by cochlear implant (CI) recipients is perception of low-intensity speech cues. A. E. Vandali (2001) has developed the transient emphasis spectral maxima (TESM) strategy to amplify short-duration, low-level sounds. The aim of the present study was to determine whether speech scores would be significantly higher with TESM than with the advanced combination encoder (ACE) strategy fitted using procedures that optimize perception of soft speech and other sounds. Eight adult recipients of the Nucleus 24 CI system participated in this study. No significant differences in scores were seen between ACE and TESM for consonant-vowel nucleus-consonant (CNC) words presented at 55 and 65 dB SPL, for sentences in noise presented at 65 dB SPL at 2 different signal-to-noise ratios, or for closed-set vowels and consonants presented at 60 dB SPL. However, perception of stop consonants within CNC words presented at the lower level (55 dB SPL) was significantly higher with TESM than ACE. In addition, percentage of information transmitted for words at 55 dB SPL was significantly higher with TESM than with ACE for manner and voicing features for consonants in the initial word position. Analysis of closed-set consonants presented at 60 dB SPL revealed percentage of information transmitted for manner was significantly higher with TESM than with ACE. These improvements with TESM were small compared with those reported by Vandali for recipients of the Nucleus 22 CI system. It appears that mapping techniques used to program speech processors and improved processing capabilities of the Nucleus 24 system contributed to soft sounds being understood almost as well with ACE as with TESM. However, half of the participants preferred TESM to ACE for use in everyday life, and all but 1 used TESM in specific listening situations. Clinically, TESM may be useful to ensure the audibility of low-intensity, short-duration acoustic cues that are important for understanding speech, for recipients who are difficult to map, or if insufficient time precludes the use of mapping techniques to increase audibility of soft sound.

Evaluation of Drum Sound with ISO Tapping Machine

A branch norm, EPLF NORM 021029-3,1 has been established for measuring drum sound on laminate floor coverings. ‘Drum sound’ refers to the sound occurring when an object, e.g. a foot, strikes the flooring in the room in which the receiving ear is located. The norm evaluates the subjective perception of the drum sound's loudness using the ISO tapping machine. A round-robin study of the norm is reported along with the results of a paired comparison listening test using the same floor coverings. The article discusses general aspects of evaluation measures, tapping machines, test environments, etc., that need to be considered when measuring drum sound on various floor coverings, such as linoleum, wood parquet and laminate. It is concluded that loudness as measured according to ISO 532B correlates the best with the subjective perception of the drum sound's loudness. The tapping machine can be used to excite hard floor coverings to produce the drum sound, but should be used with caution in studying low-level drum sounds due to the tapping machine's inherent mechanical noise.

Simplified nonlinear outer hair cell models

We present a consistent second-order expansion of nonlinear constitutive theories for outer hair cells. For a particular theory, we will test the validity of such a model for small variations in voltage and strain about the resting state of outer hair cells. An analysis of the various terms in the simplified nonlinear model and their relevance to outer hair cell mechanics are presented. Results show that the second-order expansion is adequate for modeling outer hair cell mechanics in a global model of the cochlea. Model predictions agree with the notion that voltage nonlinearities are the dominant ones at low sound levels in vivo.