An Acoustical Analysis of the Frequency-Attenuation Response of Musician Earplugs Page: 2
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Citation: Chesky K, Amlani AM (2015) An Acoustical Analysis of the Frequency-Attenuation Response of Musician Earplugs. Commun Disord
Deaf Stud Hearing Aids 3: 127. doi:10.4172/2375-4427.1000127
Page 2 of 5
REAT testing adequately quantifies whether a hearing protector
preserves the tonal balance of music, reduces sounds equally across the
frequency range associated with music, and reproduces musical
sounds for the user as heard in an unoccluded condition. The evidence
is based on the fact that the REAT procedure includes neither music
stimuli nor musicians as test subjects. Music is characterized by
complex spectral characteristics, most of which are concentrated in the
low frequencies (i.e., <100 Hz). Research has shown that the REAT
procedure has known limitations for accurately assessing occluded
perception of frequencies below 500 Hz, due to masking by
physiological noise .
Together, these shortcomings warrant the assessment of additional
methods for understanding how an MEP processes the full frequency
and complex spectral nuances of musical sounds. This is the goal of
the present study. Specifically, our goal is to assess the influences of
earplugs on the spectral characteristics of musical stimuli using an
acoustic test fixture (i.e., KEMAR; Knowles Electronics Manikin for
Acoustic Research) . Using this approach, we are able to
characterize objectively the influence of custom- and non-custom-fit
MEPs on both the attenuation levels and the spectral characteristics of
music in and over a wide range of intensity levels in a simulated
human ear canal. Findings from the present study will be used to
direct future studies related to the influences of acoustic alterations of
MEPs on perception.
A custom-fit MEP was ordered from Westone Laboratories from
earmold impressions taken on the right ear of KEMAR, along with
three attenuating filters (ER-9, ER-15, ER-25). For the non-custom-fit
earplug, we used a single ER-20 earplug obtained from Etymotic
The stimuli used in this study were digital music recordings of
ensemble-based activities at the College of Music, University of North
Texas (UNT). The recorded music represented a cross section of
genre, ensemble size, and performance venue. Ten musical segments,
each between 20 and 25 seconds in duration, were placed in a single
way file (16-bit, 44100 Hz sampling rate) with a two-second silent
interval inserted between each musical segment (Figure 1). The
inclusion of the silent interval allowed us to analyze the implications of
each recording in additional detail.
We recorded and analyzed the musical stimuli presented to
KEMAR without and with the four MEPs (ER-9, ER-15, ER20, ER-25).
KEMAR-based recordings of the musical stimuli took place in a multi-
use music studio housed within the UNT College of Music. The studio
measured 5.9 m (1) x 4.2 m (w) x/3.0 m (h), had a carpeted floor,
concrete-block walls with acoustic damping material covering one
third of each wall area, and a suspended ceiling with standard 2 feet
x/2 feet acoustical panels. This multi-use music studio contained a
table, 2 chairs, audio-visual equipment, and a measured reverberation
time of 1.246 seconds for the frequencies of 500, 1000, 2000, and 4000
During testing, the musical stimuli were presented simultaneously
from eight loudspeakers positioned in 45-degree increments relative to
0-degrees azimuth. The loudspeakers (Tannoy 800A) were positioned
at an equal distance of 1 meter relative to the center-head position of
KEMAR and at a height of 1.5 meters. We recorded the influence of
the MEP only in the right ear of KEMAR. Separate recordings of the
musical stimuli were made for five conditions that included the
unoccluded condition and four occluded conditions (ER-9, ER-15,
ER-20, ER-25). Each condition was retested at nine presentation levels,
between 85 dB and 109 dB in 3-dB intervals. The presentation levels
were determined by presenting pink noise through the loudspeaker
array and measuring the sound pressure levels (+1 dB) at 1000 Hz
using a sound level meter (Larson-Davis 800B). All five conditions
were recorded, as illustrated in Figure 2, before proceeding to the next
presentation level, in order to control for influences of presentation
level across conditions. Because the experimental procedure required
removal and reinsertion of earplugs prior to recording each condition,
all artifacts associated with insertion anomalies or custom-fit MEP
filter-to-body connections would be noted during the acoustical
analysis. Photographs were taken of each condition to verify fit.
During the recording process, the amplified output from KEMAR
(Etymotic Research microphone preamplifier model ER-11) was
routed to a personal computer and saved as a monaural way file (16-
bit resolution, 44100 Hz sampling rate).
Commun Disord Deaf Stud Hearing Aids
ISSN:2375-4427 JCDSHA, an open access journal
Volume 3 . Issue 1 . 1000127
Figure 1: Waveform depicting the 10 short musical segments used
as stimuli for this study.
Figure 2: Wave files of the musical stimuli recorded through each of
the ear plugs placed on KEMAR at 91 dB SPL. Panels
A=unplugged; B=ER-9; C=ER-15; D=ER-20; and E=ER-25.
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Chesky, Kris S. & Amlani, Amyn M. An Acoustical Analysis of the Frequency-Attenuation Response of Musician Earplugs, article, January 16, 2015; Los Angeles, California. (https://digital.library.unt.edu/ark:/67531/metadc1042574/m1/2/: accessed June 14, 2021), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Music.