Figures for Chapter 14

Binaural and bilateral issues

Dillon (2001)

Hearing Aids

Figure 14.1 Variation of the source direction in the horizontal plane.

Near earFar ear

Source: Dillon (2001): Hearing Aids

Horizontal localization

Inter-aural time differences

-0.8-0.6-0.4-0.2

00.20.40.60.8

-180 -120 -60 0 60 120 180

Horizontal angle of incidence (deg)

Inte

raur

al ti

me

diff

(ms)

Sounds from rightSounds from left

Figure 14.2 Interaural time difference for low-frequency sounds as a function of direction measured from directly in front. Data are the average of measurements on people and on a manikin (Kuhn, 1982).

Source: Dillon (2001): Hearing Aids

0

5

10

15

20

25

0.1 1 10Frequency (kHz)

Inte

rau

ral l

eve

l d

iffe

ren

ce (

dB

)45o

30o

90o

Figure 14.3 Interaural level difference for three source directions in the horizontal plane. Data are calculated from Shaw (1974). Interaural level differences are zero for frontally incident sound.

Source: Dillon (2001): Hearing Aids

Inter-aural level differences

Figure 14.4 Variation of the source direction in the vertical plane.

Source: Dillon (2001): Hearing Aids

Vertical localization

-20

-10

0

10

20

30

100 1000 10000Frequency (kHz)

Hea

d di

ffrac

tion

(dB

)30o

-120o -60o

60

-30o

120o

Figure 14.5 Head diffraction effects from the undisturbed field to the eardrum for five source directions in the horizontal plane, with positive angles representing sound arriving from the side of the ear in question. Data are from Shaw (1974).

Source: Dillon (2001): Hearing Aids

Head diffraction

SN

30o

60o

SNR increased by 11 dB at 3 kHz, and by 9 dB averaged across frequency

SNR decreased by 9 dB at 3 kHz, and by 8 dB averaged across frequency

Figure 14.6 Effect of head diffraction on the SNR at each ear, relative to the SNR in the undisturbed field. The SNR at the right ear is thus 20 dB better than at the left ear at 3 kHz, and 17 dB better when averaged across frequency.

Source: Dillon (2001): Hearing Aids

Effect of head diffraction on SNR

Signal

Noise

++

Figure 14.7 Waveforms at the left and right ears when noise arrives from directly in front and a signal (in this case a pure tone) arrives from one side.

Left Right

Source: Dillon (2001): Hearing Aids

Inter-aural time differences

S

N

Bilateral Fitting

Unilateral Fitting

S N

Figure 14.8 Test arrangement for demonstrating bilateral advantage, showing the location of the speech (S) and noise (N) loudspeakers. Speakers should be 0.5 m or more from the patient. For unilateral fittings to the left ear, the S and N sources should be reversed for both the bilateral and unilateral tests.

Source: Dillon (2001): Hearing Aids

Demonstrating binaural advantage

Bilateral Fitting

Unilateral Fitting

Figure 14.9 Test arrangement for detecting negative binaural interactions. Speech and noise both come from the same loudspeaker.

Source: Dillon (2001): Hearing Aids

Detecting negative binaural interactions

Figure 14.10 An audiogram for a person who is likely to benefit from the hearing aid cross-over effect if a bilateral fitting is provided.

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

Hea

ring

thre

shol

d (d

B H

L)

Source: Dillon (2001): Hearing Aids

Binaural cross-over effect

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

Hea

ring

thre

shol

d (d

B H

L)

Figure 14.11 An audiogram where the poorer ear should be aided if the person chooses to have a unilateral fitting.

Source: Dillon (2001): Hearing Aids

Poorer ear fitting

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

Hea

ring

thre

shol

d (d

B H

L)

Figure 14.12 An audiogram where the better ear should be aided if the person chooses to have a unilateral fitting.

Source: Dillon (2001): Hearing Aids

Better ear fitting