Specification Sheet

Volume 1 Issue 2 | February 2005
Honeywell Safety Products
900 Douglas Pike
Smithfield, RI 02917
www.howardleight.com
SoundSource
For an earmuff to block noise effectively, a tight seal between the ear cushion and the head is critical. Gaps provide an easy
path for sound to penetrate the earcup, thus reducing the amount of attenuation provided by the earmuff. Several factors
contribute to the size of those gaps:
EARMUFFS & SAFETY EYEWEAR
In our facility, several noisy work areas require safety eyewear as well as hearing protection. Can earmuffs be worn
over safety eyewear without affecting attenuation?
• Band pressure of the earmuff, head shape and head size
• Compliance of the ear cushion material (stiffer material creates more gaps)
• Thickness of the eyewear frames
• Compliance of the eyewear frames
In a study conducted at the Howard Leight Acoustical Lab, ve models
of safety eyewear were tested in combination with two popular earmuff
models, Howard Leight
®
Thunder
®
T3 and Leightning
®
L3. Hearing tests
were administered to listeners while they wore the earmuffs alone, and
then in combination with the safety eyewear, to determine if there was
any change in earmuff attenuation with the addition of the eyewear
frames.
The results show that for safety eyewear with a thin frame (a width
of 2mm or less at the temples where the earmuff cushion meets the
frame), the eyewear caused no signicant decline in attenuation –
the mean attenuation was nearly equivalent to the earmuff alone, or
within one standard deviation. However, safety eyewear with wider
frames caused noticeable gaps in the cushion seal, resulting in lower
attenuation, particularly in the low frequencies. One pair of safety
eyewear with an unusually wide frame of 6mm at the temples caused a
drop of 9 to 12 dB in the low and high frequencies. A gap in the earmuff
cushion can occasionally even cause some frequencies to be slightly
amplied. The typical reduction in attenuation for each frame style is
shown in Table 1.