Final

Question 1

High Viscosity

Answer 1

Thick and provides resistance during flow, stretches the aperture for a snug fit. Condensation-cured silicone

Question 2

Medium Viscosity

Answer 2

Provides some stretch to aperture-methyl-methacrylate

Question 3

Low Viscosity

Answer 3

Loose, flows with little resistance, suitable for devices requiring deep insertion

Question 4

Shore Value

Answer 4

After cure hardness; low values are likely to be damaged during shipment. Silicone has a high value.

Question 5

Contraction Ratio

Answer 5

Shrinkage over a 7 day period
Silicone shrinks 0.1-0.7%
Methyl-methacrylate shrinks 3%

Question 6

Stress-Relaxation

Answer 6

Materials ability to return to shape after removal.
Silicone is superior, MM can distort after removal

Question 7

Shock Damage

Answer 7

Vibration of dislodged receiver radiates back to the microphone adding extra frequencies (distortion) to input signal.

Question 8

In-Phase Signal at Diaphragm

Answer 8

acoustic signals arrive at the same time and produce an analog electric signal

Question 9

Out of Phase Signal at Diaphragm

Answer 9

Arrive at different times which stops movement and electric signal is not produced

Question 10

Impact of Standing Waves in sound bore

Answer 10

1. 2 waves with the same frequency and phase will combine to create a single sound of greater amplitude.
2. 2 identical waves 180 degrees out of phase will cancel each other out.

Question 11

Directivity Index

Answer 11

The amount of attenuation provided by different polar patterns.
Hypercartiod: 6 dB
Supercartiod: 5.7
Cartiod: 4.8
Omni: 0
Real-world DI: 2-3 dB

Question 12

Low Frequency Roll-off

Answer 12

Low frequency sine waves are wide and more likely to arrive out of phase so low frequency is reduced.

Question 13

Solution to Low frequency roll-off

Answer 13

Equalization filters-add low frequency energy to replace attenuated signal

Question 14

Internal Noise

Answer 14

Caused by random motion of gas molecules creating small pressure changes of the diaphragm and electrical noise from circuits cause diaphragm to move.
Acceptable noise: 25 dB SPL

Question 15

Purpose of a Damper

Answer 15

provide acoustic resistance in order to smooth peaks of the frequency response. Higher ohms= higher resistance.
Most practical place is the tip of the BTE earhook

Question 16

Head Shadow impact on various frequencies

Answer 16

Head shadow effect refers to the phenomenon where the head obstructs sound waves that causes a reduction in intensity at the ear further from sound source. High frequencies are most affected.