TR41.3.3-05-11-004a-Acoustic Impedance of Ear Simulators

1
TR41.3.3-05-11-004a-Acoustic Impedance of Ear
Simulators
2
This contribution consists of a brief PowerPoint
summary of the following complete
documents TR41.3.3-05-11-004b-Acoustic
Impedance Measurements BK 2005.pdf TR41.3.3-05-11
-004c-Acoustic Impedance Measurements BK
2001.pdf TR41.3.3-05-11-004d-Equivalent Volumes
of Ear Simulators BK 2001.pdf
3
Why does the acoustic impedance of an ear
simulator matter?
The fundamental purpose of an ear simulator is
to test a receiver under conditions that most
closely approximate actual use by real persons.
Please see next slide for illustration . . .
IEEE 269-2002
4
Simplified Equivalent Circuit of Receiver Ear
Simulator
Receiver
q?
pS source pressure pE pressure at ear q
acoustic current ZS source impedance ZE ear
impedance
ZS
pS
High impedance source ZS gtgt ZE and q ?
constant, so pE ? ZE
Low impedance source ZS ltlt ZE, so pE ?
constant
5
Volumes of Historical Couplers
Except as noted, equivalent volume of most
couplers is about 6cc
Volume of Type 3.4 is larger mostly due to a
larger concha.
IEEE/STIT BK 2001
6
The Impedance Probe in Use
IEEE/STIT BK 2001
7
Acoustic Impedance of 5 Human Ears at Normal
force, with Parametric Average
Note variation in real ears !!
Notice M2 average about 210dB at about 2.4kHz
IEEE/STIT BK 2001
8
Acoustic Impedance of Type 3.3 vs Human Average
M2 of Type 3.3 is about 212dB at 2.6kHz
IEEE/STIT BK 2001
9
Acoustic Impedance of Type 3.4 vs Human Average
M2 of Type 3.4 is about 206dB at 2.6kHz
IEEE/STIT BK 2001
10
Acoustic Impedance Measurements 2005 - New
Procedures
Research Graph BK 2005
11
Acoustic Impedance of 10 Human Listeners - 2005
Impedance measured with probe in form of cell
phone. Subjects held probe in natural position,
without further instruction, as they would
normally hold a phone. Positions were generally
different from HATS.

• Although the probe was held in positions
  different from HATS,
• The natural position curves are well-grouped,
  considering human variation
• Type 3.3 35pinna in HATS position at 10N
  simulates the group average well

Notice M2 of Type 3.3 about 210dB at about
2.5kHz
Research Graph BK 2005
12
Comparison of Type 3.3, with Shore 35 Pinna, and
Type 3.4

• Conclusions
• Human-like leakage is simulated by Type 3.3 or
  3.4
• Leakage is force and/or position dependent
• Both types generally require more handset force
  than humans use for equivalent leakage
• Acoustic impedance of M1 is similar
• Acoustic impedance of M2 is different
• Type 3.3 M2 is similar to humans
• Type 3.4 M2 is lower, generally resulting in
  underestimate of receiver response around 2.5kHz
  (most receivers)