Viscoelastic foam earplugs are commonly used for personal hearing protection to help reduce the incidence of hearing loss;however, many work environments exist where the protection from currently available earplugs is insufficient. In addition, the ability of existing foam earplugs to attenuate low frequency energy is relatively poor. Pilot experiments were able to produce viscoelastic foam constructions of substantially higher controlled structure than believed to be found in currently available viscoelastic foam earplugs. Even with minimal optimization, this structure contributed to substantially higher overall attenuation >3 dB and some very significant low frequency (250-1000 Hz) attenuation improvements;>4 dB. Thus, an opportunity exists to improve the attenuation resulting from the commercial production of viscoelastic foam earplugs. An increase of 3dB attenuation allows the user to double their exposure time in the sound field for which the hearing protector is rated. This Phase I project will be divided into three stages: 1. Verifying the results from the pilot samples. The results of our pilot experiments will be verified through collaboration with acoustic experts. The comparative attenuation of the samples will be measured using an impedance tube measurement system. 2. Characterizing and comparing the foam structures of these new foams and existing commercial foam earplugs. The foam structures will be measured using mercury intrusion porosimetry, x-ray micro CT scanning, and microscopy. 3. Optimizing the foam structure by comparing attenuation of varied 'controlled structure foams'. The structures of the new foams will be varied using known techniques and the resulting effects on attenuation will be measured.
Daily many tens of millions of Americans have their hearing exposed to potentially damaging noise. Foam earplugs are inexpensive, comfortable and widely used;however, they do not always provide enough protection, especially in high-noise industrial and military work environments or in low frequency noise. Success with this research to improve foam attenuation at all frequencies will result in a more effective foam earplug, reducing incidence of hearing loss - the most common industrial injury.