1. MEMRO 2009
What does the Acoustic Reflectance tell us about the middle ear? MEMRO 2009
The equivalent volume (in ccm) of the ear canal is estimated
based on the imaginary part of the impedance in the frequency range
from 200 Hz to 400 Hz. The values obtained at each frequency are averaged.
The mean and std are provided in the plots and in the exported file.
The formula is
volumes = abs(1.4179e+5/(2*pi*f*Imag(Impedance))) * 1e6;
It is derived from the low-frequency approximation of the ear-canal
impedance. The number e+5 is derived from the density of air
and the speed of sound at 20 degree Centigrade.
Patricia Jeng, Pierre Parent, Jont Allen, Mimosa Acoustics
Harry Levitt, Advanced Hearing
Mimosa Acoustics, Inc.

2. Mimosa Acoustics, Inc. - MEMRO, 2009
Goals
Acoustic power measurements quantify wide band complex:
Reflectance
Transmittance
Immittance
These measures provide clues to our puzzle:
Resonance frequencies - Stiffness vs. mass dominance
Sites of reflection
Conductive hearing loss: mild, moderate, severe
Air-bone gap & Tympanometry
The acoustic power measurement provides a whole family of quantities that are like pieces of puzzles when put together we know how the a middle ear works. Our goal for this presentation is to show you the pieces of the puzzle and the possible interpretations.
In delivering acoustic energy into the ear canal, some are reflected, some are transmitted into the middle ear structure and onto cochlea, while some are dissipated by the middle ear structure and do not reach cochlea. We would like to know how much acoustic power reaches cochlea, in what frequency region. If the acoustic power is reflected, how much, in what frequency region, and from where.
In this session we would like to look to show the pieces of puzzle by presenting to you the power measurements first in a rigid cavity using that as a reference to the measurements in human ears, which include adult, children, and infant, and for ‘normal’ ear and pathological ears.
We are specifically interested in
relationship of audiometric air-bone gap and the transmittance expressed in log scale;
the sites of reflection as a function of frequency;
how much energy is transmitted to the middle ear structure, how much acoustic energy is dissipated by the middle ear structure, and how much energy is transmitted to the cochlear
Using power measurements, we might be able to answer these questions.
In this presentation we will examine the power measures of a rigid cavity, the B&K 4157 artificial ear coupler, normal, OME, perforated TM and PE-tubed TM in adult, children, and infant.
Following the previous session by Dr. Keefe, we do not need to repeat what the acoustic reflectance is and how it is measured, so we will go straight to the cases.
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

3. Mimosa Acoustics, Inc. - MEMRO, 2009
Rigid cavity vs. B&K4157
Power reflectance
Transmittance
Reflectance phase
Reflectance group delay (residual length)
Impedance magnitude (Z)
Normalized resistance - real(Z) – frictions of joints / energy dissipation
Normalized reactance – imaginary(Z) – stiffness and masses
Impedance phase = reactance / resistance
+/- 90 degrees
This is the power measurement in a rigid cylindrical cavity, compared against the measurement in an artificial ear coupler, B&K 4157 in this case. Eight quantities are presented here as function of frequency from 0.2 to 6 kHz. The set of 4 in the left column shows power reflectance in percent, transmittance in dB, reflectance phase in radians over two pi, and the reflectance group delay expressed as residual length in mm. The set of 4 subplots in the right column shows the quantities related to the input impedance of the middle ear structure re the characteristic impedance in the ear canal, i.e., impedance magnitude, resistance, reactance, and impedance phase.
In a rigid cavity, the acoustic energy is reflected nearly completely. The power reflectance subplot shows a straight line close to 100 % across all frequency, indicating near complete reflection. The yellow line is the power reflectance measured by Voss & Allen (1994) in an artificial ear coupler (B&K 4157) shows high reflectance at low frequency, decreses to 40% reflectance between 1 to 4 kHz, and increases again above 4 kHz.
The transmittance plot shows the amount of acoustic energy transmitted in the rigid cavity is very small, less than -15 dB below 1 kHz (EXAMPLE of computation converting from reflectance to transmittance in dB) The transmittance of the artificial ear (yellow curve) resembles the middle ear transfer function, sloping down below 1 kHz at about 5 dB per octave.
The reflectance phase tells where the reflectance point is, closer to value 0, closer is the reflection point. A smooth monotonical curve is indicative of a single point reflection. In the rigid cavity, the acoustic energy is the back plan of the cylinder. The artificial ear’s reflectance phase has a shallower slope toward high frequency indicating in this case it is shorter in acoustic length. This concept is further clarified in the reflectance group delay subplot, which the residual length is shown in mm. The plot shows the acoustic length is about 23 mm across complete frequency range (0.2 to 6 kHz) indicataing the acoustic energy is reflected from the same site. This number matches our apriori knowledge of this cavity. The reflectance group delay in the artificial ear shows similar acoustic length below 500 Hz, while the acoustic length is near constant and shorter above 1.5 kHz. Between 0.5 to 1.5 kHz, there is a null at 1 kHz matching the knee frequency of the transmittance of the artificial ear. [IS THIS NULL A RESONANT POINT IN THE MIDDLE EAR SYSTEM? WHAT IS THE PHYSICAL MEANING OF A NULL in residual length?]
The four panels on the right are normalized impedance magnitude, normalized resistance, normalized reactance, and the impedance phase. The measured input impedance is normalized against characteristic impedance of the air in the ear canal. [Get the value from Pierre.]
The impedance of the rigid cavity at low frequency is mainly dominated by the stiffness and by mass at high frequency with almost no resistance. The frequency, 3.7 kHz in this case, where the reactance crosses from stiffness dominance to mass dominance is the same frequency for the null of the impedance magnitude and for the impedance phase where it crosses cross-over the 0 radian line from -90 degree to + 90 degree rapidly. This is also the frequency of the standing wave in this cavity.
Unlike the rigid cavity, the impedance in the artificial ear canal is mostly affected by the resistance and the stiffness. The normalized resistance is about 1 below 2 kHz indicating the impedance of the coupler in this frequency region matches the characteristic impedance of the air allowing maximal transmission of the acoustic power. Above 2 kHz, the coupler’s resistance diminishes toward 0 and hence diminishes its contribution to its impedance. The normalized reactance shows that the artificial ear cavity is mostly dominated by the stiffness below 6 kHz, because the reactance curve remains close to but below 0. The impedance phase remains close to -90 degree indicating the dominance of resistance and stiffness. The impedance magnitude does not have a null, neither does it have an anti-resonance, the null point.
These power measurements in these two cavities serve as a reference point to those measures in the human ears.
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

4. Adult: “Normal” (le) vs. OME (re)
MEMRO 2009
Adult: “Normal” (le) vs. OME (re)
Stiffness dominates
R - OME (blue)
AC:
10, 20, 30, 25, .25, .5, 1, 2, 4 kHz
BC:
-10,5, -10, 10, 15
ABG:
20, 15, 40, 15, 35
Tymp:
NP daPa
1.1 cc
NP mmho
L – normal (red)
5, 5, -10, 0, -5
0, 5, -10, 5, 0
5, 0, 0, -5, -5
-20 daPa,
1.2 cc,
1.6 mmho
This slide shows the power measurements of an adult’s two ears, whose right ear (re) has otitis media with effusion (OME) and the left ear (le) is normal according to the audiometric measurements. The audiometric measurements show that the OME ear has mild conductive hearing loss with air-bone gap (ABG) and an equivalent volume of 1.1 cc, but no observable static acoustic admittance [Y_0 from TYMP]. The “normal ear” has a normal ABG and TYMP. The power reflectance shows a very stiff OME right ear having a stiffness below 0.8 kHz of about 1.5 that of an average-normal adult ear.
Because the patient was an audiologist, we presume the measurements may have been more precisly measured, than in a typical clinical measurement.
* The acoustic power measurements show the OME ear behaves like a rigid cavity: with high reflectance, reduced transmittance, monotonic sloping of the reflectance phase, less variations in the reflectance group delay, higher impedance with a sharp null at ~3.6 kHz, increased resistance below 0.4 kHz and nearly 0 resistance above, increased stiffness, and a sharp switching of the impedance phase from -90 to +90 degree.
* The audiometric air-bone gaps (ABG) of this OME ear are 20, 15, 40, 15, and 35 dB at .25, .5, 1, 2, and 4 kHz. Using the transmittance of the artificial ear (B&K 4157) as a reference, the amount of the transmittance reduction in the OME ear is the largest between .6 and 1 kHz and at 4 kHz and is less in other frequency regions. This pattern seems to agree with the amount of the ABGs having the larger gaps, 40 dB and 35 dB at 1 kHz and 4 kHz respectively, and smaller gaps in other frequencies. The air conduction thresholds also seem to follow the same pattern. It is not a dB-to-dB match, but a qualitative one.
* Comparing the power measurement of the normal ear (left ear in red lines) with those of the OME ear and of the artificial ear coupler, the normal ear behaves more like the artificial ear with variations.
The reflectance slope in the range of 0.7 to 1 kHz is shallower (higher reflectance), due to the reduction of the resistance in this region, causing the stiffness to dominate the impedance. However the resistance in this region is close to 1 meaning a match between input impedance and the characteristic impedance allowing good transmission of the acoustic energy.
* In the frequency region between 2 to 5 kHz, the reflectance is lower due to lower impedance magnitude. Does it mean more acoustic power is transmitted to the middle ear structure? If so, are all extra acoustic power transmission passed to the cochlea or consumed by the middle ear structure? In this region, the impedance phase show slow progressive change from stiffness dominance at 2 kHz to resistance dominance at 4 kHz (crossing 0 angle), then to mass dominance at 6 kHz. This is typical in most of the normal adults’ ears and in normal children’s ears.
In the same frequency region, this normal ear’s reflectance group delay has large numbers of peaks and dips comparing to the OME and artificial ears. The envelope of the reflectance group delay (RGD) in the normal ear matches the reflectance group delay of the OME ear seem to indicate the similarity due to the same middle ear structure, from where the reflection comes, while the condition of the OME ear causes this structure to be rigid, and the condition of the normal ear allows this structure to be mobile. The maximal point of the RGD in OME ear is at ~ 3.5 kHz, the same as the anti-resonant frequency where the impedance phase crosses 0 angle switching from stiffness to mass dominance. The estimated acoustic length is ~32.5 mm. The large number of peaks and dips with two large dips in the RGD of the normal ear might indicate the mobility and interactions of the ossicles. This is typical in the normal ears, except the frequency range is shifted from .7 to 2 kHz (see Voss & Allen, 1994) to 2 to 4 kHz. This shift might due to the effect of middle ear infection in a much lesser degree comparing to the right ear (OME ear).
Comparing to the acoustic lengths in this frequency region, those in the region below 400 Hz are about 15 and 25 mm for the OME and normal ears respectively. Can these lengths be used to identify the sites of reflections? The equivalent volumes computed from the power measurements are 0.8 and 1.1 cc (tip A) respectively indicating small volumes between the probe tip and the TM. Based on the rigid cavity example, the acoustic length of the OME ear at the low frequency region indicates the ear drum is a reasonable site of reflection, while the acoustic length of the normal ear at this frequency region indicates the site of reflection to be further down the ossicular path.
Below 500 Hz, the reflectance group delay in OME ear is about 15 mm comparing to 25 mm for the normal ear. We suspect the site of reflection in the frequency region is from the TM in the OME ear and from annular-ligament for the normal ear. This speculation needs further examination.
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

5. Mimosa Acoustics, Inc. - MEMRO, 2009
Child – OM-no fluid
Stiffness dominate
Site of reflection
ABG
66L & 66 R – both OME
Age: 7 year old
L ear
Tymp type: B
AC: 45, 45, 50, 40, 50 dB .25, .5, 1, 2, 4 kHz
BC: 5, 5, 5, 20, 25 dB HL
ABG: 40, 40, 45, 20, 25 dB
No fluid with retracted TM
R ear
AC: 45, 45, 50, 35, 50 dB .25, .5, 1, 2, 4 kHz
BC: 10, 0, 0, 20, 0 dB HL
ABG: 35, 45, 50, 15, 50 dB
Fluid - unacertain, with Rretracted TM
44 normal children ears
This slide compares the power measures of two OME ears in a 7-year-old child to the normative data from a group of 44 children. The audiometric measurements of this child show type B tympanograms with retracted TM, and ABGs in both ears, however with no fluid in left ear and uncertain in the right.
We expect this data from the routine clinical measurement leave more room for variations.
The power measurements show raised reflectance with transmittance gap between the mean of the norm to the OME measures varying between 2 to 7 dB. The impedance magnitude has not-so-sharp dips at resonant frequencies and the impedance phase shows the stiffness dominance below 2.5 kHz and has sharper stiffness to mass transition comparing to the norm, but less sharp transition to the rigid cavity.
The reflectance group delays expressed in the residual lengths in the two ears are relatively quiet with no large spikes and dips, closer to the previous adult OME case but not as straight. The acoustic lengths at the low frequency are ~22 and ~26 mm corresponding to the equivalent volumes of .62 and .73 cc (tip B) for the left and right ears respectively. Comparing these values to those in adult OME ear, the equivalent volumes are slightly smaller, but the lengths are longer. Perhaps the lack of the fluid in these OME ears allows the site of reflection to be further down the conductive path from the TM.
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

6. Infant – passed OAE screen
MEMRO 2009
Infant – passed OAE screen
Floppiness of the canal wall
Small volume
UU_395L_normal_day2
Age: Day 2
Moderate occlusion
Vernix / cerumen
Normal TM mobility
Effusion: uncertain
44 normal
children ears
Equivalent Vol: 0.7 cc using 05 tip.
This slide show the measurements in a 2-days-old infant’s ear that has passed OAE screening with moderate occlusion from vernix and cerumen, but normal TM mobility.
All power measures point to small size of the canal and the floppiness of the canal wall in a new-born infant’s ear.
Note that the imaginary part of the impedance has a minimum around kHz, where the reactance goes from a resistance below and a stiffness above this frequency. A reasonable interpretation of this minimum is that it is the resonance of the floppy canal wall, where the wal goes from a stiffness to a resistance. In older ears the canal would stiffen-up, and this resonance would disappear (go to zero).
Comparing against the normative data of children in yellow patch, the power reflectance and transmittance have different shape below 0.5 and above 2 kHz. The reflectance phase shows immediate reflection from the canal wall
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

7. Infant – failed OAE / obstructed canal
MEMRO 2009
Infant – failed OAE / obstructed canal
UU_395R_occluded
Age: Day 2
Vernix / cerumen
Moderate occlusion
Normal TM mobility
Effusion: uncertain
Failed OAE screening on day 1, passed on day 2.
E. V. = 0.4 cc, tip=5
The angle of the impedance is close to pi/4 (45 degrees), that is like a “lossy spring or compliance” having an impedance of 1/sqrt(j\omega) – probpability due to the viscosity of the vernix and cerumen in the canal.
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

8. Adult - Perforated TM & OM
MEMRO 2009
Adult - Perforated TM & OM
R ear - normal – blue
AC: 0, 10, 0, 0, 15, 5
BC: -5, -10, -5, 15, 5
ABG: 5, 10, -, 5, 0, 0
Tymp: 5, 1.5, 0.5
SRT/WR: 5, 100
L ear – acute otitis with drum rupture - red & pink
AC: 15, 10, 10, 15, 35, 45
BC: 0, -5, -5, 5, 40, 30
ABG: 15, 15, 15, 10, -5, 15
Tymp: -85, 0.2, 0.2
SRT/WR: 10, 100
EV= 11.3 cc, 8.8, 20.8 tip: A
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

9. Mimosa Acoustics, Inc. - MEMRO, 2009
Summary
The intention of this presentation is to show that all the measures obtained by the power measurements provide informative clues to the middle ear transmission status by identifying
the interrelations of the three impedance components (resistance, stiffness and mass);
the sites of reflections;
how much energy is transmitted to the middle ear structure;
how much acoustic energy is dissipated by the middle ear structure;
how much energy is transmitted to the cochlear; and
the relationship of audiometric air-bone gap and the transmittance expressed in log scale.
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

10. Mimosa Acoustics, Inc. - MEMRO, 2009
Summary
The residual distance as computed from the reflectance group delay might be used to indicate the sites of reflections at low frequency. From the examples shown, the sites of reflections in the OME ear is at or close to the ear drum depending on the severity of the infection. In the normal ears, the sites of reflection are beyond TM.
In the OME ear, the middle ear structure is much simpler in its mechanical property giving much less complex reflectance group delay than in the normal.
Transmittance might provide as an objective and qualitative prediction of the audiometric air-bone gaps in screening and better identifying young children with OME who need follow up assistance.
in normal middle ears might come from the annular-ligament around the stapes footplates, while
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

11. Data come from several projects
MEMRO 2009
Data come from several projects
SBIR 6554 at Mimosa Acoustics
Patrick Feeney, University of Washington
Lisa Hunter, University of Utah
Gravelino Study –
Andrea Bohnert, Mainz, DE
Mimosa Acoustics
Kyle Rust
Elizabeth Allen
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

12. The middle ear is the gateway to the auditory system
MEMRO 2009
The middle ear is the gateway to the auditory system
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

13. Case: B&K4157 – Artificial Ear
MEMRO 2009
Case: B&K4157 – Artificial Ear
Normalized impedance magnitude (Z)
Normalized resistance - real(Z)
Normalized reactance – imaginary(Z)
Impedance phase
Power reflectance
Transmittance
Reflectance phase
Reflectance group delay (residual length)
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

14. Mimosa Acoustics, Inc. - MEMRO, 2009
Case: Normal - Child
Age:
Mean +/- 1 std
Tymp type: A
AC:
BC:
ABG:
ME is a crucial components for us to understand because it is the gateway of the paths of most of the audiometric measurements. All these measurements depends on the acoustic stimulus coming through ME to reach higher order components of the auditory system. A good understanding of the ME function allows us better diagnosis of the other auditory function and pathology.
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

15. Mimosa Acoustics, Inc. - MEMRO, 2009
Case: Normal - Infant
393R
Age: new born
Vernix / cerumen
Moderate occlusion
No effusion (or unlikely)
Normal TM mobility
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

16. Case: Normal – Adult – update fig
MEMRO 2009
Case: Normal – Adult – update fig
WH13L – L ear, 37 year old
Tymp:
0 daPa
1.6 cc
1.1 mmho
Freq
250
500
1000
2000
4000 AC 15 10 20 BC 5
ABG
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

17. Mimosa Acoustics, Inc. - MEMRO, 2009
Child: PE Tube & OME
52R with PE & 52L with OME)
Age: 6.7
R ear – PE tube (t type)
AC (sound field): 30, 30, 25, 30, 30 dB .25, .5, 1, 2, 4 kHz
Tymp: ng
No fluid
No retracted TM
L ear – OME
AC / BC: nb
Tymp: nb
Fluid
TM - nb
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

18. Mimosa Acoustics, Inc. - MEMRO, 2009
Child - Normal
26L
Age: 8.1
Tymp type: A
AC: 10, 10, 5, 10, 5 dB .25, .5, 1, 2, 4 kHz
BC: 0, 0, 5, 0, 5 dB HL
ABG: 10, 10, 0, 10, 0 dB
No fluid
No retracted TM
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

19. What is Power Reflectance?
MEMRO 2009
What is Power Reflectance?
Reflectance =
Reflected Power
Incident Power
Transmittance =
Absorbed Power
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

20. Acoustic Parameters - Set of 8
MEMRO 2009
Acoustic Parameters - Set of 8
Power reflectance
Transmittance
Reflectance phase
Reflectance group delay in terms of residual distance (MM)
Normalized (N) impedance magnitude
N-impedance phase
N-resistance (Real part of N-impedance)
N-reactance (Imag part of N-impedance)
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

21. Mimosa Acoustics, Inc. - MEMRO, 2009
Examples
Hard-wall cavity
Artificial ear (B&K 4157)
Normal adult ear
Normal child ear
Normal infant ear
Otitis media with effusion (OME)
Child
Adult
PE tube / TM perforation
What we would like to present to you today are divided in the following areas:
1, Basic principles for measurement – introduce to you the function of ME, and clarify few terms.
2. Then we will show how to measurement reflectance
3. We will show you available clinical data and discuss the measurements.
Applications –
measurements and interpretations of physical properties
Emphasizing power reflectance
Introduce other properties – power absorption, transmittance, impedance magnitude, resistance, and reactance
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.

22. Mimosa Acoustics, Inc. - MEMRO, 2009
Questions of Interest
Resonance frequencies - Stiffness vs. mass dominance
Sites of reflection in time domain
Air-bone gap
Tympanometric type:
A, B, C, AS, AD
Conductive hearing loss:
mild, moderate, severe
What we would like to present to you today are divided in the following areas:
1, Basic principles for measurement – introduce to you the function of ME, and clarify few terms.
2. Then we will show how to measurement reflectance
3. We will show you available clinical data and discuss the measurements.
Applications –
measurements and interpretations of physical properties
Emphasizing power reflectance
Introduce other properties – power absorption, transmittance, impedance magnitude, resistance, and reactance
Mimosa Acoustics, Inc. - MEMRO, 2009
Mimosa Acoustics, Inc.