08 - Transducers

Question 1

Name 2 types of transducers

Answer 1

Microphones
Loudspeakers
Headphones
Bone oscillators

Question 2

Name 2 types of transduction parameters

Answer 2

Sensitivity
Frequency response
Dynamic range
Directional characteristics (microphones)
Polarization type & voltage (microphones)

Question 3

What is microphone sensitivity?

Answer 3

The amount of voltage generated for a given sound pressure level

• called “open circuit” sensitivity
• denoted in mV/Pa or dB re 1 V/Pa

Question 4

What does a microphone’s dynamic range refer to?

Answer 4

The levels that the microphone can measure accurately

• lower limit = noise level of the microphone (electrical noise or thermal noise)
• upper limit (the 3% distortion level OR the 10% distortion level OR the damage level)

Question 5

Why do we want a flat response for our microphone’s frequency response curve?

Answer 5

We want the input at any frequency to give the same output at any frequency
-tolerance is usually + or - 3 dB

Question 6

True or False: the type of microphone you use will depend on the location (type of room, proximity to sound source, etc) of the measurement

Answer 6

True

Question 7

Sound waves can propagate freely in a ______ (near/diffuse/free) field

Answer 7

Free field - the distance between the source and the measurement site should be at least five to ten times the largest dimension of the source and the microphone

Question 8

The “critical distance” is the point in the far field where the direct sound is ____ () to the reflected sounds

Answer 8

Where the direct sound is = to the reflected sounds

Question 9

The reverberant field is also known as the ____ field

Answer 9

Diffuse

Question 10

True or False: The free field exists at a location if the field is created by sound waves arriving more or less simultaneously from all directions with equal probability and level

Answer 10

False - this is the diffuse field, which is only in environments where there is reverberation

Question 11

In the ____ field, the sound level will drop by 6 dB for every doubling of the distance

Answer 11

Free field

Question 12

True or False: When we use a microphone to make a measurement, it acts as a reflective surface, and its effect is frequency dependent

Answer 12

True - low frequencies will bend around it, and high frequencies will bounce off it

Question 13

What is it called when we correct for the effect that the presence of the microphone has on our sound readings?

Answer 13

Equalization of the microphone response

Question 14

The effect of the microphone is related to the __________ of the microphone to the sound source

Answer 14

Angle of orientation

0 degrees = mic facing sound source, 90 degrees = source is directly to the right of the mic

Question 15

What type of microphone is meant for making measurements in the reverberant field?

Answer 15

Diffuse field microphones

Question 16

What type of microphone is meant for making measurements in small, enclosed environments?

Answer 16

Pressure field microphones

Question 17

What type of microphones need to be pointed directly at the source?

Answer 17

Free field microphones

Question 18

A pressure-field is characterized by a sound pressure which has the same _____ and _____ at any position within the field

Answer 18

Magnitude and Phase

Question 19

A polar plot it used for _______ microphones to give a visual representation of the microphone ______ in different directions

Answer 19

Directional microphones

Sensitivity

Question 20

Do measurement microphones need to be calibrated to ensure proper use?

Answer 20

Yes

Question 21

A typical loudspeaker is base on what principle?

Answer 21

The electromagnetic principle

Question 22

A typical frequency response in all transducers should be ____dB from ____ Hz to ____ Hz

Answer 22

+ or - 3 dB from 1000 to 18000 Hz

Question 23

How is sensitivity in a loudspeaker specified?

Answer 23

x dB SPL at 1 meter per 1 Watt of electrical power

Question 24

The ANSI requirement for a loudspeaker are:
THD < ___% to at least 80 dB SPL
THD < ___% to at least 100 dB SPL
Flat response from 250-4000 Hz (+/- 3 dB)
Head level heigh, ___m distance
Minimal changes near the subject’s head

Answer 24

3%
10%
1 m

Question 25

Which headphone cushions fit over and around the pinna: circum-aural or supra-aural?

Answer 25

Circum-aural

Question 26

True or False: headphones work based on the moving-coil principle?

Answer 26

True

Question 27

How is the sensitivity for headphones written?

Answer 27

dB SPL/1mW

Question 28

Insert earphones are based on the ________ principle of transduction

Answer 28

Balanced armature - the transducer is contained in the casing, and the basic underlying mechanism is still 1 permanent magnetic field and 1 moveable magnetic field

Question 29

Which insert phones have a flatter frequency response: ER2’s or ER3’s?

Answer 29

ER2’s (more expensive, mainly used in research)

Question 30

What does a bone vibrator consist of?

Answer 30

An electromagnetic transducer that converts electrical energy into mechanical energy

Question 31

True or False: ANSI does not require documentation on non-standard transducers to be provided in the audiometer manual

Answer 31

False

Question 32

Name 2 transducer specifications

Answer 32

Sensitivity, Dynamic range, Frequency response, Distortion and directionality