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THE IMPACT OF HEADPHONES AND EARPHONES ON HEARING OF USERS
P. Obdržálek, [email protected], M. Rod, [email protected], Praha
INTRODUCTION
OBJECTIVE MEASUREMENT
By inserting the earphones into the human ear canal
the excitation conditions are changed (change of
impedance). Consecutively, the transfer function of the
ear canal changes too: its resonance peaks are shifted
and highly emphasized, which can lead to hearing losses
at these frequencies.
For objective measurements we were using
frequency response type Sweep (sampling rate: 96.000
kHz, recording time: 1.4 s, frequency weighting – white)
in program EASERA (http://easera.afmg.eu/).
Measurements were performed on a mannequin,
respectively on the artificial ear. At the end of ear canal
was placed a microphone. We can´t use our own head
because in our ears, we haven’t got a place to put a
microphone and of course we don’t want to get hearing
loss, ´cause if we want accurate results, we must use
high level of acoustic pressure (90-110 dB).
Fig. 1. Acoustic horn - closed x opened
SUBJECTIVE MEASUREMENT
To verify the simulation we used subjective
measurements – audiograms. We used Békésy’s
measuring method [1] another methods you can find in
Measurement of Hearing Protector Attenuation [2].
Measurements were carried on the person, who records
if he/she heard or didn’t hear a sound. If we interconnect
these points and unzig – zag this line, we obtain the
resultant graph. In our audiogram hearing threshold was
measured at earphones and headphones, at each type at
least 3 representatives. In fig. 2, you can notice the area
around 6 kHz, where the headphones (Philips) don’t
playing. This is probably caused by inverter in the
headphones.
Fig. 2. Audiogram of headphones
Fig. 3. Frequency response – Earphones Koss
MEASURED DEVICES
For measuring we use our headphones or earphones,
also we use headphones (earphones) from CVUT. We
measured 6 headphones and 4 earphones, further details
are at Table 1.
TAB. 1. Table of measured devices
Audiogram
Frequency
analyse



Model
Type
Bayer
k.55
Koss
Koss
(Lenka)
Philips
Sennheiser
Koss
Creative
MX
Nokia
noname
Headphones
Headphones
Headphones



Headphones


Headphones
Headphones
Earphones






Earphones


Earphones
Earphones




CONCLUSIONS
Fig. 4. Headphones vs. earphones
COMPARISON OF SUBJECTIVE AND
OBJECTIVE MEASUREMENT
For the purpose of the comparison we set the Koss
headphones as reference. In Fig. 5. is comparison
between MX (earphones) and Phillips (headphones)
with both kinds of measurements. Red thick line
(frequency response) should correlate with a thin red
line (audiogram), the same goes for the blue lines.
The artificial ear is not suitable for measuring
earphones. Thus the measured values achieve the
distortion in values of tens of decibels (maximum is 23
dB). Given that the most companies test their earphones
on artificial models, we can conclude that the
misunderstanding or using these measured results to
optimize the headphones can lead to ill-configured
earphones and thus damage hearing of their users. To
build proper artificial model we would need to use
living tissue, or substance that has similar properties, the
existing models are sufficient for the measurement of
headphones, not for earphones.
ACKNOWLEDGEMENTS
We are very grateful for the cooperation and interest
of Ing. František Rund, Ph.D., who was our advisor. It
wouldn´t have been possible without his help. This
project was created in cooperation with the Department
of Radioelectronics, Faculty of Electrical Engineering,
Czech Technical University in Prague with the support
of the project Cesta k vědě.
REFERENCES
1. Nováček, J.: Application of the Signal Processor for
Analysis of Sound Signals Perception (In Poster
2007 – Prague).
2. T. Baráth: Measurement of Hearing Protector
Attenuation (Bc. Thesis, in Slovak CTU FEL 2011)
3. http://www.itu.int/ITUT/worksem/qos/200606/presentations/s3paperrasmussen.pdf
4. Ing. F. Rund: Modeling of Sound Transfer into Inner
Ear
Fig. 5. Comparison of measurement: MX vs. Phillips
(audiogram vs. frequency response)
As you can see, the premise for the red line has been
confirmed - audiogram correlates with frequency
response. However, the blue lines correlate only in
certain parts of the graph. In the 500 Hz to 3000 Hz,
which is crucial for the perception of human speech, the
lines don´t resemble - function trend is opposite. You
can also notice that in this area, a thin blue line
correlates with red ones. This effect is caused by
impedance change of, which will also move the
resonance peaks and their amplification. The human ear
reflects these changes so you can hear the sound, while
the artificial ear can´t satisfactorily mimic the
characteristics of the human ear, and this is reflected in
the frequency response as a low noise level for stretch
500 Hz - 3000 Hz.
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