Foam Earplugs Research Articles

Laboratory Attenuation of Earmuffs and Earplugs Both Singly and in Combination

For very high-level noise exposures, especially when 8-hour, time-weighted averages are greater than 105 dBA, the attenuation of a single hearing protection device may be inadequate. For such exposures, double hearing protection, i.e. muffs plus plugs, may be called for. It is well recognized that double hearing protection does not simply yield overall attenuation equal to the sum of the individual attenuation of each device due to the bone-conduction flanking paths and the acoustical-mechanical interaction between two such closely spaced devices. The incremental performance to be gained by double protection was investigated experimentally by measuring the real-ear attenuation at threshold for a number of combinations, according to ANSI S3.19-1974. All tests were conducted on 10 subjects, three replications per subject. Devices included foam plugs (partial, standard and deep insertion), fiberglass down, V-51R earplugs, medium and large volume commercially available earmuffs, and an experimental large-volume lead earmuff. All devices were examined singly and in combination. In all cases, plugs-plus-muffs outperformed either device individually, except at 1 kHz for one combination. Although the two pairs of commercially available earmuffs offered significantly different low frequency attenuation (125–1000 Hz), when either earmuff was combined with the V-51R or deeply inserted foam earplug, the improvements were similar. However, when the situation was reversed and the different inserts were examined in combination with a single earmuff, the choice of insert was important below 2 kHz. At and above 2 kHz all plug-plus-muff combinations that were studied provided attenuation approximately equal to the bone-conduction limits of the skull. Based on these laboratory results, it is clear that double hearing protection may provide the additional noise reduction needed in very high noise level environments.

Laboratory Attenuation of Earmuffs and Earplugs Both Singly and in Combination

For very high-level noise exposures, especially when 8-hour, time-weighted averages are greater than 105 dBA, the attenuation of a single hearing protection device may be inadequate. For such exposures, double hearing protection, i.e. muffs plus plugs, may be called for. It is well recognized that double hearing protection does not simply yield overall attenuation equal to the sum of the individual attenuation of each device due to the bone-conduction flanking paths and the acoustical-mechanical interaction between two such closely spaced devices. The incremental performance to be gained by double protection was investigated experimentally by measuring the real-ear attenuation at threshold for a number of combinations, according to ANSI S3.19-1974. All tests were conducted on 10 subjects, three replications per subject. Devices included foam plugs (partial, standard and deep insertion), fiberglass down, V-51R earplugs, medium and large volume commercially available earmuffs, and an experimental large-volume lead earmuff. All devices were examined singly and in combination. In all cases, plugs-plus-muffs outperformed either device individually, except at 1 kHz for one combination. Although the two pairs of commercially available earmuffs offered significantly different low frequency attenuation (125–1000 Hz), when either earmuff was combined with the V-51R or deeply inserted foam earplug, the improvements were similar. However, when the situation was reversed and the different inserts were examined in combination with a single earmuff, the choice of insert was important below 2 kHz. At and above 2 kHz all plug-plus-muff combinations that were studied provided attenuation approximately equal to the bone-conduction limits of the skull. Based on these laboratory results, it is clear that double hearing protection may provide the additional noise reduction needed in very high noise level environments.

In-flight measures of stress reduction due to wearing expandable foam earplugs : Wichman, H., McIntyre, M., and Accomazzo, E.Aviation, Space and Environmental Medicine, Sep 1979, 50.9, 898–900

Ten low-time pilots (less than 150 h) who did not normally use earplugs flew three flights each in Cessna-152 training planes. The flight routines were all the same, lasting about 45 minutes. Each pilot flew one flight while adapting to earplugs, another flight with earplugs, and a third flight without earplugs. Pilot's breathing rate was the measure of autonomic arousal. A baseline rate was measured before each flight and in-flight scores were expressed as changes from baseline. Half the pilots flew their flights in the order, with-with-without earplugs and half flew in the order without-with-with. Results showed a mean increase in breathing rate above preflight baseline of 30% without earplugs and an increase of only 21% with earplugs (data taken from second flight with earplugs) for a significant savings of 9% (p less than 0.025, Wilcoxsen matched-pairs signed-ranks test, one tailed).

Physical characteristics and attenuation of foam earplugs

The purpose of this investigation was twofold: (1) to determine the physical characteristics of five types of foam earplugs; and (2) to relate their physical characteristics to attenuation of noise. The results indicate that: (1) all commercial polymer foam earplugs have similar physical properties, (2) frequency (Hz) is the single most important variable in determining attenuation of commercial foam earplugs, (3) all earplugs evaluated provided essentially the same attenuation at frequencies > 500 Hz. One non-commercial earplug provided significantly more attenuation at 125 Hz than the other earplugs. This non-commercial experimental plug has significantly different physical and chemical properties. No other consistent effects of physical properties on attenuation were found.

Physical characteristics and attenuation of foam earplugs

The purpose of this investigation was twofold: (1) to determine the physical characteristics of five types of foam earplugs; and (2) to relate their physical characteristics to attenuation of noise. The results indicate that: (1) all commercial polymer foam earplugs have similar physical properties, (2) frequency (Hz) is the single most important variable in determining attenuation of commercial foam earplugs, (3) all earplugs evaluated provided essentially the same attenuation at frequencies > 500 Hz. One non-commercial earplug provided significantly more attenuation at 125 Hz than the other earplugs. This non-commercial experimental plug has significantly different physical and chemical properties. No other consistent effects of physical properties on attenuation were found.

Relation of physical characteristics of foam earplugs to insertion loss

The relation between the physical characteristics of foam earplugs (i.e., weight, length, width, density, expansion pressure, and expansion force) and attenuation in high noise levels (105 dB SPL) was investigated using KEMAR. The results indicated that all commercial polymer foam earplugs have similar physical properties; frequency (Hz) is the single most important variable in determining attenuation of foam earplugs; and chlorination seems to have a pronounced effect on attenuation. The measured attenuation does not change in a consistent manner with changes in physical properties which may reflect an incomplete understanding of cause‐effect relationships between the variables studied.

Effects of relative humidity on attenuation of foam earplugs

The effects of relative humidity (RH) on attenuation of foam earplugs is important because many people work in high noise levels that have controlled RH conditions. Five types of foam earplugs were tested for attenuation in 100 dB SPL white noise under three conditions of RH; <5%, 50%, and 80%. Attenuation measurements were made utilizing KEMAR. A Fast Fourier Transform (FFT) was used to manipulate, store, and output the collected data. In general, there is not a significant difference in attenuation between the various foam earplugs measured under different RH conditions. However, one type of foam earplug would not stay compressed long enough to get them inserted into either KEMAR'S or our ear canal at 80% Rh.

Estimating hearing protector attenuation for the second percentile using parametric statistics

One method for reducing hearing protector attenuation data for multiple frequencies is a single number method such as the Noise Reduction Rating (NRR). Averaged data from ten subjects, three replications per subject, are combined with a subtractive two standard deviation (σ) correction in order to predict the 98% protection rate (second percentile). This study examined the errors incurred by assuming that the distribution of attenuation data is sufficiently normal to equate a −2σ correction to the protection achieved by the second percentile. Attenuation for a foam earplug was measured on 92 subjects of varying experience, according to ASA STD 1‐1975, with one replication per subject for both a “subject” and “experimenter” fit. The second percentile single number attenuation was calculated from the actual distribution, and estimated by using a −2σ correction, as in the NRR. For the subject fit, the NRR underpredicted the second percentile attenuation by 1.6 dB. For the experimenter fit, it overpredicted p...

A modified polymer foam earplug for the hearing aid evaluation.

Functional gain was compared with 12 subjects using three earmold conditions: an E-A-R polymer foam earplug modified for use with a hearing aid, a personal custom earmold, and a best-fit receiver-type stock earmold. Functional gain was equivalent between the modified E-A-R earplug and the custom earmold conditions. The stock earmold condition resulted in a significant shunting of low-frequency amplification. The gain control of the personal hearing aids could be adjusted to the user comfort level gain setting without resulting in acoustic feedback in only the modified E-A-R earplug and custom earmold conditions. These findings are discussed relative to the hearing aid evaluation.

Aspects on personal noise protection.

Two groups of noise-exposed workers were compared with respect to their use of ear protectors. One group had a severe, noise-induced hearing loss; the other group had normal hearing. Both groups were composed of workers of similar age and total duration noise-exposure. It was found that those with normal hearing had used ear protectors considerably more than those with severe hearing loss. Interestingly, quite a few workers had normal hearing in spite of working in noise for many years without ear protectors. Also, quite a few workers had a severe hearing loss in spite of frequent use of ear protectors. The reasons for not using ear protectors were analysed as also was the condition of the protectors and frequency with which they were replaced. Plastic ear plugs were preferred by 44%, vinyl foam ear plugs by 26%, fibreglass down by 18%, and ear muffs by 11% of the workers. In general, the condition of the ear protectors was good. Surprisingly, one-third of the workers did not use ear protectors, many of them because they had not realized that the environment they worked in had a noise intensity level above the injury risk level.