Earmuffs Research Articles

Ear-protection cup for ear muffs or head-phones

First Page

Progression of Hearing Loss Caused by Occupational Noise

This review is a compilation of 11 investigations by different authors regarding the progression of hearing deterioration during severe long-term exposure to noise in mines, shipyards, forges, weaving mills, other factories and industries and from field artillery and hunting. With one exception, the reports concern conditions at times when ear protection was virtually unknown or only seldom used. The different investigations are described in a broad outline with their essential measurement and background data. For the first eight studies the results of the hearing deterioration with increasing exposure time are illustrated in figures showing, on the one hand, the original data and, on the other, the progression of hearing loss with increasing age, though reduced by the ISO 1999 (1990) values from database A for the normal threshold of hearing as a function of age. This is followed by a discussion of the results and a compilation of the data from the 11 investigations for, particularly, a noise exposure time of about 5 to 10 years, corresponding to an age of around 30 years, in comparison with an exposure time of 30 to 40 years, i.e. at an age range of about 50 to 60 years. Despite the great diversity in the character and level of the noise, the compilation shows for the higher ages in the range of 3 to 8 kHz a similar median hearing loss from nearly all investigations; however, at 1 kHz and, particularly, at 2 kHz the differences in the character of the noise are apparent in a wide spread of the median hearing loss between the different studies. In addition, it was found that at higher ages and hearing loss levels of more than 45 to 50 dB it is not possible to distinguish between the effect of the noise, on the one hand, and that of ageing, on the other; the ad hoc assumption of their additivity is no longer valid and thus the term "age correction" inadequate. A series of further figures illustrates the progression of the hearing loss with exposure time in the different investigations at particularly 1 kHz, 2 kHz and 4 kHz.(ABSTRACT TRUNCATED AT 400 WORDS)

Concussive Blast-Type Aural Trauma, Eardrum Perforations, and their Effects on Hearing Levels: An Update on Military Experience in Izmir, Turkey

Thirty-two military personnel, exposed to blast injury in the last 15 months, have been investigated according to type of eardrum perforation and hearing loss in this retrospective study. It has been concluded that tympanic membrane perforations and hearing loss due to blast effect have individual patterns. Hearing loss due to trauma is not because of pressure environment alone. Final outcomes have justified the previous recommendations about ear protection in military staff, particularly in those who are working with explosive materials. Ear muffs with ear phones are appropriate, providing ear protection as well as hearing gain.

Grommets, swimming and otorrhoea--a review.

Ever since Armstrong reintroduced the concept of grommet insertion parents have been asking 'may my child swim?', yet there is still no consensus as to the correct answer. This paper reviews the work that has been done on this subject in the last 25 years. A review of the rates of otorrhoea following grommet insertion, irrespective of swimming, shows a variation from 12 to 64 per cent. Evidence suggests that pressures of 12-23 cm H2O are needed to push water through a grommet and that it is unlikely that water will enter the middle ear during surface swimming. Only bath water seems to cause significant inflammatory changes to middle ear mucosa. Not a single paper comparing swimmers with non-swimmers shows an increased rate of otorrhoea in those patients who swam; to the contrary, rates of otorrhoea were repeatedly higher in those patients who did not swim. The evidence suggests that swimming without ear protection can be safely permitted for children with grommets.

Assessment of comfort of various hearing protection devices (HPD).

To evaluate the comfort of hearing protection devices, two models of ear plugs and five models of ear muffs were tested. The psychophysical method of 'single stimuli' was applied on a group of 30 subjects with or without wearing the devices for a short duration of 15 min under noise condition of 100 dBa in the acoustic chamber as also on a group of 10 weavers with the protection devices worn for longer durations of 1 h, 4 h and 8 h under noise exposure of 102-104 dBA in the weaving shed. Each subject performed 8 trials with each type of device on different days. Application force and tightness of spring were also evaluated. The results yielded a comfort grading for hearing protection devices. The comfort grading, however, depended on several factors in addition to application force and tightness of spring, which has been discussed.

Auditory Perception with Level-Dependent Hearing ProtectorsThe Effects of Age and Hearing Loss

Auditory perception with hearing protectors was assessed in three groups of subjects, two with normal hearing, but differing in age, and one with moderate bilateral sensorineural hearing loss. Individuals were tested with the ears unoccluded, and fitted with each of two level-dependent ear muffs and their conventional level-independent counterparts. One of the former devices provided limited amplification. In each of these five ear conditions, the threshold of audibility for one-third octave noise bands centered at 500, 1,000, 2,000 and 4,000 Hz, consonant discrimination, and word recognition were measured in quiet and in a continuous impulse noise background. The results showed that the attenuation of sounds (i.e. the difference between protected and unoccluded thresholds) in quiet did not vary as a function of age or hearing loss for any of the four protectors. In noise, the difference between protected and unoccluded listening was close to zero, as long as hearing was normal. With hearing loss as a factor, there was a significant increment in the protected threshold, the amount determined by the device. Word recognition in quiet was adversely affected in normal-hearing listeners by the three attenuating devices but improved in noise relative to unoccluded listening. Amplification had a deleterious effect for both consonant discrimination and word recognition in noise. In hearing-impaired listeners, speech perception was impeded by all four muffs but less so in quiet with limited amplification.

PT/OT FORUM

Full-thickness burns to the external ear can produce loss of skin and cartilage and can result in severe cosmetic deformity. Even partial-thickness burns render the ear vulnerable to tissue loss if the helix is subjected to pressure from pillows, dressings, or straps that are used to secure endotracheal tubes. Because of the incidence of burned ear deformities and the difficulty in reconstructing the external ear, an ear protection device has been designed. The bilateral ear protection device, referred to as "headgear", is fitted to all patients in the burn center who require intubation for an inhalation injury; it is worn continuously until extubation. During a 15-month period 39 consecutive critically burned patients were fitted with the headgear because of the need for ventilator support and/or for protection of the burned ear(s). Pressure necrosis of ear tissue was prevented in all 33 survivors.

Analysis of the coil generated impulse noise in extracranial magnetic stimulation

An intense impulse noise artifact is generated by the coil used in extracranial magnetic stimulation (EMS) of the brain and cranial nerves. In this study we measured and analyzed the sound pressure level (SPL), spectral content, wave form, and time course of the magnetic coil acoustic artifact (MCAA) impulse noise in the sound field and in the ear canal of life-size models of the human cranium. Two different clinical magnetic stimulators and coils were used. Sound field measurements from both coils showed the MCAA to be a transient impulse noise with a rapid rise-time, brief duration, broad acoustic spectrum, and high intensity. Measurements made on models of the human head with the magnetic coils positioned at selected standard clinical positions for EMS, particularly the peripheral facial nerve, auricle and mastoid areas, indicated that the MCAA may reach sound pressure levels that exceed noise damage-risk criteria limits for sensorineural hearing loss. The maximum peak energy in the acoustic spectrum of the MCAA measured in the ear canal of the model heads was from 2 to 5 kHz, the range of highest sensitivity in human ears. Ear protectors were found to attenuate the SPL of the MCAA, reaching the ear canal of the model heads by 15–22 dB SPL, and were recommended for use by patients and subjecte exposed to EMS.

Noise-induced hearing loss in children and adolescents.

Occupational noise exposure remains the most commonly identified cause of noise-induced hearing loss (NIHL) in the general population. The issue of NIHL in children has received scant attention. Parents and public policy makers have expressed increasing concern about hearing risks to children and adolescents posed by noise sources such as: rock music, ‘‘boom’’ cars, loud toys, recreational vehicles, and personal cassette players. This report focuses on 114 children and adolescents (ages 19 and under; 90.3% males) who were diagnosed as having probable NIHL on the basis of clinical history and audiometric configuration. Forty-two children had unilateral losses, while 72 had sensorineural losses of varying degree in the contralateral ear. The mean age of referral for evaluation was 12.7 yr (range 1.2 to 19.8 yr, s.d. 4.21 yr), although 26% of the children were age 10 or younger at the time of referral. Inherent weaknesses of currently available clinical studies of NIHL in nonoccupational settings include imprecision in diagnosis and lack of quantification in characterizing the nature and duration of exposure. The occurrence of irreversible but potentially preventable hearing loss among a preschool and school-age sample should prompt improved observational and interventional, prospective longitudinal studies of NIHL in children and adolescents. Advances in molecular medicine as related to hearing loss, incorporated into such studies, could enhance understanding of individual variation in susceptibility to hearing damage from noise associated with age, gender, racial or ethnic status, and genetic make-up. Psychosocial measures should address the issue of improving compliance in the utilization of ear protectors among the younger age group.

Ia expression in keratinocytes following ultraviolet radiation.

Injections of murine gamma interferon (IFN-gamma) into BALB/c nude mice induced Ia expression by keratinocytes. The aim of the present study was to use this murine model to determine the effect of ultraviolet radiation (UV) or cyclosporine A (CyA) on Ia expression by keratinocytes. Two sets of experiments were performed. In the first, mice were injected intraperitoneally with IFN-gamma for 6 days. The mice were divided into three groups. One group, with one ear protected by electrical tape, was exposed to UVB radiation for 15 days starting 4 days before the injection. The second group received subcutaneous injections of CyA simultaneously with the IFN-gamma and during the 10 days following the IFN-gamma injection. The third group received only IFN-gamma injections. Fifteen days after the IFN-gamma injection all mice were killed and evaluations of Ia positive cells were performed. In the second set of experiments the nude mice were treated with CyA or UVB only 10 days after the last IFN-gamma injections. In both experiments UVB inhibited and down-regulated Ia expression by keratinocytes. This effect on keratinocytes was not observed in the protected ears. Thus it appears that the effect of UVB on keratinocytes is local and not systemic. CyA failed to inhibit or down-regulate Ia expression. This study may shed some light on understanding the mechanism effect of UV radiation in a variety of skin diseases.

Speech recognition in noise when wearing amplitude-sensitive ear-muffs.

Speech recognition in background noise when wearing amplitude sensitive (non-linear) ear muffs was studied in the laboratory in 15 young normal-hearing test subjects. Low-redundancy sentences were presented from a loudspeaker in a background noise level of 70 dB (A) and the speech-to-noise (S/N) ratio yielding 50% correctly recognized words was determined. Three background noise spectra were tested: white noise, low-pass filtered noise (-12 dB/octave) and high-pass filtered noise (12 dB/octave). Five listening conditions were used: no protectors, a pair of normal ear-muffs, a passive amplitude-sensitive ear-muff and two types of electronic amplitude-sensitive ear-muffs. An ANOVA shows that speech recognition is significantly influenced by type of hearing protector and by noise spectrum. The interaction between these factors was not statistically significant. In general, the test subjects obtained somewhat better speech recognition thresholds in noise when wearing electronic amplitude-sensitive ear muffs than without muffs, whereas the opposite was true for the passive amplitude-sensitive and the normal ear muffs.

The role of the physical factors involved in sound-attenuation characteristics of ear muffs

This paper deals with the assessment of the factors involved in sound-attenuation characteristics of ear muffs. To this end, the most common methods (subjective, objective on people, and objective on a test fixture), under free and pseudo-diffuse field conditions have been used. The relative importance of these factors in the different measuring methods, their variation with frequency, and the influence of field conditions and the type of head (human or artificial) are studied. Empirical equations are derived that specify the contribution of the individual factors in the different paradigms. In the light of our results, the apparently discrepant behaviour of ear protectors under different conditions can be explained and correlated.

Anthropometric contribution to standardising manikins for artificial-head microphones and to measuring headphones and ear protectors

True-to-size head—torso manikins are required for research in the field of artificial-head stereophony as well as for testing and measuring headphones, soundproof helmets, ear protectors and other headgear. Attempts to design a manikin according to the available anthropometric data available proved to be difficult. By testing 77 men with technical jobs, 15 new quantities have been measured, some of them for comparison and some to complete existing measurements. The tests showed that it is absolutely essential to differentiate manikins of the desired qualities from an ethnic point of view. Manikins of different model dimensions should not be standardised according to percentiles but should represent typical head shapes. To this end, thorough measurements have to be made.

A critical analysis of attenuation effects of different types of ear protective devices

The present study was undertaken to evaluate the noise attenuation characteristics of different types of Ear protective Devices which are commonly used. 20 healthy normal subjects’ open and closed hearing thresholds (with the usage of ear protective device) were recorded in an anechoic chamber and the attenuation charactaristics at 8 discrete frequencies were analysed and compared. Though the attenuation given by different types of ear protective devices are variable and not the ideal, still the present generation of devices have shown satisfactory attenuation characteristics, It is important that proper selection, fitment and usage of these devices should he carefully thought of prior to its usage.

Hearing loss from gun and railroad noise—Relations with ISO Standard 1999

Pure-tone hearing thresholds and anamnestic data pertaining to nosocusis and exposure to gun noise were analyzed for 9778 male railroad train-crew workers. A major portion of losses in hearing sensitivity due to railroad noise are obscured in comparisons of hearing levels of trainmen with the hearing levels of the unscreened samples of United States males given in Annex B, ISO 1999 [ISO 1999 (1990), "Acoustics--Determination of occupational noise exposure and estimation of noise-induced hearing impairment" (International Organization for Standardization, Geneva)]. Comparisons of the hearing levels, adjusted for nosocusis, of trainmen who had used no guns, with the hearing levels of otologically and noise screened males (Annex A, ISO 1999) reveal significant losses due to railroad noise. Additional losses were found at high frequencies in trainmen who had used guns. It appears that the effective Leq8h exposure level of trainmen to railroad noise is about 92 dBA, and 87-89 dBA to gun noise. These results are in general agreement with those of study of railway workers by Prosser et al. [Br. J. Audiol. 22, 85-91 (1988)]. Asymmetries in losses between the two ears, effects of ear protection, losses from nosocusis, and losses from sport, as compared to military, gun noise exposures, are examined.

Schutz vor Lärmschwerhörigkeit durch aktive Gehörschutzsysteme

Though noise induced hearing loss is no longer the most frequent occupational disease in the Federal Republic of Germany, the environmental pollution by the product "noise" in our technical and industrialized world has not been reduced. On the contrary, the situation is worsened by the rising influence of leisure noise. To avoid occupational hearing loss, the "Noise Injury Prevention Code" issued by the insurers would demand wearing personal ear protection, e.g. ear plugs, if ambient noise levels are above 85 dB(A). But there are working places in which such equipment would have precisely the adverse effect, because one of the reasons for possible damage to hearing is radio communication. In military aircraft cockpits for example noise exposure measurements showed ambient noise levels above 90 dB(A) during regular flight service nearly all the time. To be able to understand radio traffic in spite of the noisy environment, the headphone volume must be raised above the noise of the engines. The use of ear plugs can only be of limited value. Whereas pilots with normal hearing show only little impairment of speech intelligibility, those with noise-induced hearing losses show substantial impairment that varies in proportion to their hearing loss. Communication abilities may be drastically reduced which may compromise the reliability of radio traffic. To avoid compromising air security one has to demand a noise protection system which allows to reduce ambient noise levels without disturbing speech intelligibility in the inevitable radio communication. Nowadays active noise cancelling (ANC) systems by electronic compensation in different ways provide effective protection against noise induced hearing loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Ear-mic headset/eardefender

First Page

Acoustic trauma in extracranial magnetic brain stimulation

The effects of the magnetic coil acoustic artifact (MCAA) associated with extracranial magnetic field stimulation (EMFS) of the brain were studied in normal hearing rabbits. Spectral and intensity analyses showed that the MCAA is a high intensity transient signal with peak energy between 2 and 5 kHz, and peak amplitudes in the first 100–200 μsec. At EMFS levels of 50–100% of maximum output (2.0 Tesla), the corresponding MCAA levels were 131–142 dB sound pressure level (peak hold) at the outer ear and amplified by the external meatus to reach 145–157 dB sound pressure level (SPL) at the position of the tympanic membrane in rabbits. Measurements of the acoustic middle ear muscle reflex (AMR) in non-anesthetized rabbits indicated that exposure to EMFS levels of 50–100% resulted in correspondingly increasing compound threshold shifts (CTS) and permanent threshold shifts (PTS) in the unprotected ears of the experimental animals. Auditory brain-stem responses (ABR) measures on the same and additional animals corroborated these findings. Morphological studies showed evidence of substantial cochlear trauma at EMFS levels as low as 50%, with increasing severity up to 100% EMFS. Morphological examination of inner ear structures following exposure to the MCAA in the acute preparation (fixed within hours after exposure) showed ruptures between pillar cells and a detached organ of Corti. Preparations examined 3 or more weeks after exposure showed damaged pillar cells, a widespread loss of outer hair cells, fused and fractured inner hair cell stereocilia, and kinocilium outgrowth on inner hair cells. Although this extremely short impulse contains approximately 2 orders of magnitude less acoustic energy than a continuous noise exposure of 131 dB for 15 min, it is substantially more injurious to the cochlea. The present findings suggest that the acoustic artifact produced by the EMFS coil in some clinical instruments may pose a potential risk for temporary and permanent hearing loss in patients and clinicians when held in close proximity to the unprotected ear. Initial studies suggest that the magnetic field alone did not appear to cause permanent hearing impairment. We recommend the use of ear protectors for the patient and clinician during EMFS as a precautionary measure to prevent possible hearing loss from the MCAA.

The Effectiveness of an Educational Hearing Conservation Program for Elementary School Children

An educational hearing conservation (HCP) program was designed and presented to 45 normal hearing third- and fourth-grade children enrolled in regular education programs. Questionnaires assessing knowledge of hearing, noise-induced hearing loss, and hearing conservation practices were administered prior to and following a HCP which consisted of a lecture, film, hearing screening demonstration, question and answer and discovery learning periods, and distribution of earplugs and a handout. Most children reported that they did not participate in noisy activities; however, of those who did participate an average of only 5.5% (2.5) reported use of ear protection. Knowledge about noise and noise-induced hearing loss increased an average of 23% following the HCP and 91.1% reported that they "learned something" from the HCP. Post-HCP responses revealed that 96.7% of the children intended to use ear protection when engaged in the depicted noisy activities. Although students indicated their intentions to pursue hearing conservation practices, follow-up studies are needed to determine whether hearing conservation programs are effective in establishing positive, long-term hearing health habits. School hearing conservation programs must be comprehensive in scope, including educational programming aimed at prevention and reduction of the prevalence of hearing loss, as well as identification and management of hearing loss.

Acoustic ear muff

An acoustic ear muff includes a pad or cup (2) which is made of rigid material and incorporates an opening for receiving one ear of the wearer, and a resilient sealing annulus (10) intended for abutment with the head of the wearer, and also resilient pressure-exerting means (5) connected to the shell of a protective helmet (1), a head strap or like head gear. The ear muff provides good acoustic damping and a high degree of comfort, owing to the fact that the resilient pressure-exerting means is configured to produce a low pressing force substantially independently of head sizes which vary within given limits. The pressure-exerting means includes, to this end, a spring element in the form of a combined torsion and bending spring.