Proceedings of 20th International Congress on Acoustics, ICA 201023-27 August 2010, Sydney, Australia

Discrepancies between actual-ear and artificial-ear
responses
Tatsuya Hirahara
Faculty of Engineering, Toyama Prefectural University, Imizu, Japan

PACS: 43.38.Si; 43.66.Yw

ABSTRACTThis paper aims at clarifying the discrepancies between actual-ear and artificial-ear responses. The actual- and artificial-ear responses
from five models of insert earphones, three models of intra-concha earphones, and two models of headphones were measured andcompared. The actual-ear responses were measured for one driver of each earphone/headphone with sixteen ears of eight subjects
using a probe-tube microphone ER-7C (Etymotic Research). The artificial-ear responses are measured for four drivers of each earphone/headphone using a head and torso simulator (Brüel and Kjær, type 4128C) with a built-in ear-simulator (type 4158C) and apinna simulator (DZ9763). The results indicate that the actual-ear responses of intra-concha earphones and headphones below 4–5
kHz coincide with the artificial-ear responses and that the actual-ear responses of all earphones and headphones between 6 to 10 kHz
are lower by at least 6 dB than the artificial-ear responses. The actual-ear responses of insert earphones below 300 Hz were lower byat least 6 dB than the artificial-ear responses due to acoustic leaks. We highly recommend that earphones and headphones be calibrated before acoustical experiments are conducted, keeping in mind the discrepancies between actual-ear and artificial-ear responses.

INTRODUCTION
Frequency response is one of the most important acousticalcharacteristics of earphones, which transduce electrical signals to sound. Measuring the frequency responses of a loudspeaker is not too difficult, as it produces sound pressure in
an open space. In contrast, measuring the frequency responses of an earphone is not as easy as one might think.
This is because an earphone produces sound pressure in asmall closed space, which is formed by the outer ear canaland the earphone plug or housing. The physical dimensions
as well as acoustical characteristics of this closed space haveto be taken into account in measuring earphone responses.
The shapes and sizes of the outer ear canal, however, varyfrom one individual to another. The conditions under which
an earphone is worn can also differ from one individual toanother.
Devices used for measuring earphone responses are an artificial ears that are designed to have an overall acoustic impedance similar to that of the average human ear over a given
frequency range. There are three types of artificial ears specified in IEC Publications.

Hz to 8 kHz. The sound pressure measured by the Type 2
artificial ear is referred to the ear-drum reference point (DRP).
The Type 3 artificial ear consists of the IEC 60711 occludedear simulator and a concha simulator or a pinna simulator.
The intended frequency range of the Type 3 artificial ear is
100 Hz to 8 kHz. The Type 3.1 artificial ear has a concha
bottom simulator. The Type 3.2 artificial ear has a simplified
pinna simulator. It is used for measurements on supra-auraland supra-concha earphones. The sound pressure measured
by the Type 3.2 artificial ear is referred to the ERP. The Type
3.3 artificial ear has the pinna simulator described in IEC
Publication 60959. The Type 3.3 artificial ear can be used formeasurements on supra-aural, supra-concha, intra-concha,
and insert earphones. The sound pressure measured by theType 3.3 artificial ear is referred to the DRP. The Type 3.4
artificial ear has a simplified (e.g. geometrically describable)
pinna simulator. The Type 3.4 artificial ear can be applied to
all types of earphones.

The Type 1 artificial ear specified in IEC Publication 60318
is used for measurements on supra-aural and supra-concha
earphones. The intended frequency range of the Type 1 artificial ear is that of the telephone bandwidth (100 Hz to 4 kHz).
The sound pressure measured by the Type 1 artificial ear isreferred to the ear reference point (ERP).

There are currently various types of earphones for portable
solid-state audio players, as typified by iPod available on themarket. Type 3 artificial ears, or IEC 60711 couplers, havebeen widely used to calibrate earphones. Even though its
intended frequency range is 100 Hz to 8 kHz, frequency responses of up to 20 kHz or more are measured with artificial
ears. I have also been using artificial ears to calibrate theearphones I have used in my psychoacoustical experiments,
but have been a little anxious about their frequency-range
limitations [2, 3].

The Type 2 artificial ear specified in IEC Publication 60711
is an occluded-ear simulator for testing insert earphones. The
intended frequency range of the Type 2 artificial ear is 100

This paper aims at clarifying the discrepancies between actual-ear and Type 3.3 artificial-ear responses by comparing
these in various types of earphones.

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Proceedings of 20th International Congress on Acoustics, ICA 2010

METHOD

artificial-ear response
audio analyzer
Brüel and Kjær3560C/3100

Earphones

HATS
Brüel and Kjær4128C

amplifierAccuphase
E-308

Five models of insert earphones, three models of intra-concha
earphones, and two models of "headphones" were tested. The
specifications for the earphones are listed in Table 1.

ear simulator
4158C
with
pinna simulator
DZ9763The insert earphones tested were the E4C (Shure), ER4B
(Etymotic Research), MDR-EX90SL (SONY), ATH-CK32(Audio Technica) and SR-001MK2 (STAX). The E4C andER4B use a balanced armature type sub-miniature speaker asa driver. The MDR-EX90SL and ATH-CK32 use a small
dynamic speaker as a driver. The SR-001MK2 uses an electro-static driver. This earphone is mounted on a headband andits ear tip is pushed to the outer ear canal, resulting the outerear canal being almost completely sealed. Thus, the SR001MK2 is classified as an insert earphone in this article.
These insert earphones are designed for consumer use.

actual-ear response
100 Hz ～ 20 kHz
1/12 oct. step tone

probe microphone
Etymotic Research
ER7C

Figure 1. System for measuring earphone responses
10
Relative response in dB

The intra-concha earphones tested were the MX500 (Sennheiser), DNC2007 (manufacturing company is undisclosed)
and TriPort IE (Bose). The DNC2007 is the earphone used
for the English-listening-comprehension test held by the National Center Test for University Admissions in 2007 in Japan. All of these earphones use a small dynamic speaker as adriver. The MX500 and DNC207 are typical intra-concha
earphones. The TriPort IE, however, is an intermediate between the insert and the intra-concha types. This is because
the ear piece of the TriPort IE is partially inserted into the ear
canal but it dose not seal the ear canal. Thus, the TriPort IE isclassified as an intra-concha earphone in this article. The
MX500 and TriPort IE are designed for consumer use.

0
-10
-20
-30
-40

75mm

-50
100

1k
Frequency in Hz

10k

20k

Figure 2. Free-field response of ER7C with probe tube

The circum-aural earphone tested was the HDA200 (Sennheiser), which is a closed-type dynamic headphone foraudiometric use. Another earphone tested was the K-1000(AKG), which is an open-type dynamic headphone for consumer use. The K-1000 might be better classified as an "earspeaker" rather than supra-aural type. This is because small
loudspeakers are placed very close to the ears.

tympanic membrane. The exact position of the probe-tube tip
in the outer-ear canal for each subject, however, was unknown. The mean insertion length of the probe tube from theentrance of the outer-ear canal for the eight subjects was 22.1mm with a standard deviation of 4.4 mm. The frequency
response of the ER7C with the probe tube was calibrated in afree field. The response of the ER7C in Figure 2 was subtracted when calculating the actual-ear response of each earphone.

Measurement system and procedure
The artificial-ear responses were measured for the four drivers of each earphone using a head and torso simulator (Brüel
and Kjær, type 4128C) with a built-in IEC60711 earsimulator (type 4158C) and a pinna simulator (DZ9763).

A PULSE audio analyzer (Brüel & Kjær, type 3560C) with awideband frontend module (type 3110) was used for signal
generation, acquisition and data analysis. Frequency responses were measured from 100 Hz to 20 kHz in 1/12 octave steps using the steady state response (SSR) mode of theaudio analyzer. The audio amplifier E-308 (Accuphase) wasused as the driver amplifier for the earphones. The output
sound pressure level of each earphone was set at 80 dB SPL
for a 1- kHz tone by adjusting the amplifier gain. The measurements were carried out in a sound attenuated room.

The actual-ear responses were measured for one driver of
each earphone with eight subjects using a probe-tube microphone ER-7C (Etymotic Research). The probe tube of the
ER-7C, which was 72.5-mm long with an outer diameter of
0.95 mm, was carefully inserted into the ear canal and theend of the probe tube was placed very close to the subject's

Table 1. Specifications of the earphones (from the catalogues)
earphone typemodel

manufacturertransducer

bandwidth

sensitivity

impedance

weight

E4C

Shureelectro magnetic―

109 dB

29 Ω

31g

ER4B

insertintra-concha
circum-auralear-speaker
2

Etymotic Research electro magnetic 20 Hz～16 kHz

MDR-EX90SLSONY

ATH-CK32

Audio Technica

98 dB

100 Ω

28 g

5 Hz～25 kHz

106 dB

16 Ω

7g

electro magnetic 18 Hz～22 kHz

101 dB

16 Ω

5g

dynamic

SR-001 MK2

STAXelectro static

20 Hz～20 kHz

111dB

360 kΩ/10 kHz

28 g

MX500

Sennheiser

dynamic

18 Hz～22 kHz

119 dB

32 Ω

6g

DNC2007

not disclosed

dynamic

―

―

―

―

TriPort IE

Bosedynamic

―

―

―

20 g

HDA200Sennheiser

dynamic

20 Hz～20 kHz

100 dB

40 Ω

330 g

K-1000AKG

dynamic

30 Hz～25 kHz

74 dB

120 Ω

270 g
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Proceedings of 20th International Congress on Acoustics, ICA 2010

RESULTSstandard deviation of actual-ear responses indicates intersubject and re-wearing variations. The mean value and standard deviation of measured frequency responses of two setsof each model (one set for K-1000), viz., four drivers (twodrivers for K-1000) for each, for artificial-ear responses areplotted by the red line. Thus, the standard deviation of artificial-ear responses indicates inter-driver variations.

100

100

E4C

80

80

60

60

40

10
5
0

20
100
100

1k

20
100
100

MDR-EX90SL

80

80

60

60

10
5
0

20
100
1k
100
SR-001MK2
Mean Response in dB

40

10k

40

10k

60

40

10

40

20

5
0

20

80

60

60

40

10
5
0

20
100
100
HDA200

1k

10k

80

60

60

20
100

1k
Frequency in Hz

10k

10k

10
5
0
1k

10k

DNC2700

10
5
0

20
100

10
5
0

1k

40

80

40

10
5
0

100
100

80

10
5
0

ATH-CK32

100
100
TriPortIE

60

10k

10k

20

80

1k

1k

40

80

100
100
MX500

ER4B

Standard Deviation in dB

Figure 3 plots the actual-ear and artificial-ear responses foreach earphone. The mean value and standard deviation of
measured frequency responses of one driver of each model
for four discrete measurements with the eight subjects for
actual-ear responses are plotted by the blue line. Thus, the

100

1k

10k

K-1000

40

10
5
0

20
100

1k
Frequency in Hz

10k

Figure 3. Actual-ear response (blue line) and artificial-ear response (red line) of each earphone.
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The MDR-EX80SL and ATH-CK32 also have discrepancies
between the actual-ear and artificial-ear responses. The discrepancies are large above 6 kHz, while those at low frequency are small, in particular for the MDR-EX80SL. The
standard deviation of the actual-ear responses is large above
5 kHz but is small below 2–3 kHz. The standard deviation of
the artificial-ear responses is smaller than 3 dB below 10 kHz.
The SR-001MK2 has small discrepancies between the actualear and the artificial-ear responses below 5 kHz, yet has large
discrepancies at high frequency. The standard deviation of
the actual-ear responses is relatively larger than that of theother insert earphones. The standard deviation of the artificial-ear responses is very small.
The TriportIE also has small discrepancies between the actual-ear and artificial-ear responses below 5 kHz, yet haslarge discrepancies at high frequency. The standard deviationof the actual-ear responses is large in the higher-frequency
region. The standard deviation of artificial-ear responses islarge below 1 kHz.
The MX500 and DNC2007 have very small discrepancies
between the actual-ear and artificial-ear responses below 4
kHz and above 10 kHz. The standard deviation of the actualear and artificial-ear responses is the same below 1 kHz, butthat of the actual-ear responses is larger than that of the artificial-ear responses above 1 kHz.
The HDA200 has small discrepancies between the actual-ear
and artificial-ear responses below 5 kHz. The standard deviation of the actual-ear responses is larger than that of theartificial-ear responses at any frequency.
The K-1000 has very small discrepancies between the actualear and artificial-ear responses below 6 kHz. The standard
deviation of the actual-ear responses is larger than that of theartificial-ear responses at any frequency. The standard deviation of the artificial-ear responses is almost 0 dB up to 10
kHz.
Figure 4 plots the mean discrepancy between the actual-ear
and artificial-ear responses of each earphone type in decibels.
That is, the ratio of actual-ear responses to artificial-ear responses at each frequency was calculated for each earphonemodel, then the means of discrepancy functions were obtained by taking the mean of the ratio function for five insert
earphones (red), three intra-concha earphones (green), andthe other two earphones (blue), i.e. headphones.
The artificial-ear responses were higher at low frequencies
below 600 Hz than the actual-ear responses in the insert earphones. The discrepancies were 6 dB or more below 300 Hz.
In contrast, the artificial-ear responses were about the sameas the actual-ear responses for intra-concha earphones andheadphones below 2.5 kHz. The artificial-ear responses in the
mid-frequency from 6 to 10 kHz were higher by at least 6 dBthan the actual-ear responses for any type of earphone. The
artificial-ear responses at frequencies above 10 kHz werehigher by at least 6 dB than the actual-ear responses for any
type of earphone. In particular, the actual-ear responses ofinsert earphones were much higher than the artificial-ear
responses.
4

20
Mean discrepancy in dB
artificial-ear resp. / actual-ear resp.

The E4C and ER4B have large discrepancies between theactual-ear and artificial-ear responses below 300 Hz andabove 3 kHz. The actual-ear responses are lower than thosefor the artificial ears in these frequency bands. The standard
deviation of actual-ear responses is large for these earphones,
suggesting large variations in inter-subject and re-wearing. In
contrast, that of the artificial-ear response is almost 0 dB up
to 10 kHz, suggesting inter-driver variations are small.

Proceedings of 20th International Congress on Acoustics, ICA 2010

Insert earphones
100Intra-concha earphones-10

Headphones

-20
100

1k
Frequency in Hz

10k

20k

Figure 4. Mean discrepancy between actual- and artificialear responses for each type of earphone.

DISCUSSION
The Type 3.3 artificial-ear simulated the actual ear fairly wellfor the intra-concha earphones and headphones below 4–5
kHz. However, the discrepancies between the actual-ear andartificial-ear responses were large below 300 Hz for the insert
earphones. The air gaps between the ear tips of the earphones
and the outer-ear canal could be the cause of the lowered
actual-ear responses at low frequency [2, 3]. The probe tube,
whose diameter was 0.95 mm, was sandwiched between theear tip and outer-ear canal wall, creating small air gaps. Suchdiscrepancies were not seen for the MDE-EX80SL. The ear
tip of the MDE-EX80SL was less stiff than that of the E4C,
ER4B or ATH-CK32, sealing off the outer-ear canal more
efficiently even when the probe tube was sandwiched between the earpiece and outer-ear-canal wall. The discrepancies between the actual-ear and artificial-ear responses werelarge between 6 to 10 kHz for all earphone types. The actualear responses were always higher by at least 6 dB than theType 3.3 artificial-ear responses. The cause for this remains
unknown. The discrepancies between the actual-ear and artificial-ear responses were also large above 10 kHz. This frequency range, however, is beyond the intended frequency
range of the Type 3.3 artificial-ear.

CONCLUSION
The artificial-ear responses below 5–6 kHz were about thesame as the actual-ear responses except for the insert earphones. The actual-ear responses of the insert earphones
below 300 Hz were lower by 6 dB or more due to acoustic
leaks. The artificial-ear responses of all type of earphones
between 6 to 10 kHz were higher by at least 6 dB than theactual-ear responses. The discrepancies between the actualear and artificial-ear responses were large above 10 kHz. It ishighly recommended that earphones be calibrated before
acoustical experiments are conducted, keeping in mind thediscrepancies between actual-ear and artificial-ear responses.
ACKNOWLEDGEMENTPart of this work was supported by KAKENHI (22300061).

REFERENCES
1
2
3

IEC268-7 Second edition, Sound system equipment- Part
7: Headphones and earphones, (1996).
T.Hirahara,“Physical characteristics of headphones usedin psychophysical experiments,” Acoustical Science andTechnology 25(4), 276-285 (2004).
T. Hirahara, H. Aoyama, and M. Otani. “Acoustic characteristics of earphones and issues of IEC60711 coupler,”J. Acoust. Soc. Jpn. 66, 45-55 (2010). (in Japanese)
ICA 2010