08 - Transducers Flashcards
Name 2 types of transducers
Microphones
Loudspeakers
Headphones
Bone oscillators
Name 2 types of transduction parameters
Sensitivity
Frequency response
Dynamic range
Directional characteristics (microphones)
Polarization type & voltage (microphones)
What is microphone sensitivity?
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
What does a microphone’s dynamic range refer to?
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)
Why do we want a flat response for our microphone’s frequency response curve?
We want the input at any frequency to give the same output at any frequency
-tolerance is usually + or - 3 dB
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
True
Sound waves can propagate freely in a ______ (near/diffuse/free) field
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
The “critical distance” is the point in the far field where the direct sound is ____ () to the reflected sounds
Where the direct sound is = to the reflected sounds
The reverberant field is also known as the ____ field
Diffuse
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
False - this is the diffuse field, which is only in environments where there is reverberation
In the ____ field, the sound level will drop by 6 dB for every doubling of the distance
Free field
True or False: When we use a microphone to make a measurement, it acts as a reflective surface, and its effect is frequency dependent
True - low frequencies will bend around it, and high frequencies will bounce off it
What is it called when we correct for the effect that the presence of the microphone has on our sound readings?
Equalization of the microphone response
The effect of the microphone is related to the __________ of the microphone to the sound source
Angle of orientation
0 degrees = mic facing sound source, 90 degrees = source is directly to the right of the mic
What type of microphone is meant for making measurements in the reverberant field?
Diffuse field microphones
What type of microphone is meant for making measurements in small, enclosed environments?
Pressure field microphones
What type of microphones need to be pointed directly at the source?
Free field microphones
A pressure-field is characterized by a sound pressure which has the same _____ and _____ at any position within the field
Magnitude and Phase
A polar plot it used for _______ microphones to give a visual representation of the microphone ______ in different directions
Directional microphones
Sensitivity
Do measurement microphones need to be calibrated to ensure proper use?
Yes
A typical loudspeaker is base on what principle?
The electromagnetic principle
A typical frequency response in all transducers should be ____dB from ____ Hz to ____ Hz
+ or - 3 dB from 1000 to 18000 Hz
How is sensitivity in a loudspeaker specified?
x dB SPL at 1 meter per 1 Watt of electrical power
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
3%
10%
1 m
Which headphone cushions fit over and around the pinna: circum-aural or supra-aural?
Circum-aural
True or False: headphones work based on the moving-coil principle?
True
How is the sensitivity for headphones written?
dB SPL/1mW
Insert earphones are based on the ________ principle of transduction
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
Which insert phones have a flatter frequency response: ER2’s or ER3’s?
ER2’s (more expensive, mainly used in research)
What does a bone vibrator consist of?
An electromagnetic transducer that converts electrical energy into mechanical energy
True or False: ANSI does not require documentation on non-standard transducers to be provided in the audiometer manual
False
Name 2 transducer specifications
Sensitivity, Dynamic range, Frequency response, Distortion and directionality
