TABLE I.
Summary of subjective attenuation measurements in this study and previous reports using similar earmuffs and earplugs. Attenuations are specified in dB (mean±1 standard deviation). Attenuations for this study are based on data in N ears; the datum for each ear is the average of 1–3 measurements. The previous studies of earmuff attenuation used Bilson UF-1 earmuffs,a presented mean results for several types of earmuffs,b or did not specify the type used.c The previous studies of earplug attenuation used E.A.R® Classic® foam earplugsa or did not specify the type used.c
| Subjective attenuation of various sound stimuli (dB) |
||||||||
|---|---|---|---|---|---|---|---|---|
| Stimuli | ||||||||
| Imager noise | Tone bursts | |||||||
| Isolation device This study |
Number of ears N |
1.5-T (1 kHz) |
3.0-T (1.4 kHz) |
500 Hz | 1 kHz | 1.4 kHz | 2 kHz | 2.8 kHz |
| Earmuffs | 5 | 30±6.0 | 37±3.9 | … | 32±6.9 | 37±4.7 | 34±7.9 | 35±3.8 |
| Earplugs | 3 | 26±6.1 | 25±0.8 | … | 28±4.2 | 27±6.8 | 35±2.4 | 41±1.0 |
| Earmuff/earplug combination | 8 | 41±68 | 39±4.0 | 41±8.6 | 41±6.5 | 39±6.5 | 47±7.1 | 48±5.8 |
| Helmet/earmuff combination | 3 | 47±2.7 | 52±1.7 | … | 50±0 | 58±6.9 | 56±10.4 | 64±6.4 |
| Helmet/earmuff/earplug combination | 5 | 57±9.7 | 63±9.9 | 58±5.5 | 55±7.3 | 63±9.7 | 66±5.8 | 82±2.1 |
| Stimuli: 1/3-octave bandwidth noise bursts except as noted | ||||||||
| Other studies | 125 Hz | 250 Hz | 500 Hz | 1 kHz | 1.4 kHz | 2 kHz | 3.15 kHz | |
| Earmuffs, “Subject fit”a | 7.4±3.6 | 14.0±3.4 | 20.7±3.3 | 29.2±3.8 | … | 31.7±4.2 | … | |
| Earmuffs, mean of several studiesa | 9±3.6 | 12±4.0 | 19±4.7 | 27±4.9 | … | 28±5.2 | … | |
| Earmuffsb Stimuli: pure tones | 13±4.5 | 19±5.5 | 26±5.5 | 34±7.0 | … | 32±6.5 | 33±8.0 | |
| Earplugs, “Subject fit”a | 21.4±7.8 | 22.0±7.8 | 24.2±7.8 | 25.2±6.9 | … | 31.0±4.7 | … | |
| Earplugs, mean of several studiesa | 17±9.0 | 17±8.7 | 20±9.2 | 22±8.5 | … | 29±8.3 | … | |
| Earmuff/earplug combinationc | 37.5±4.6 | 41.8±5.1 | 51.3±6.7 | 47.8±4.2 | … | 37.3±3.5 | 46.8±4.5 | |
a
Compiled by Berger et al., 1998.
c
Berger, 1983, for “small-volume” earmuffs and earplugs inserted to “standard depth” (50%–60% of earplug in ear canal).