Microphone theory Flashcards
What are the 3 most important characteristics of microphones for live sound?
operating principle, frequency response and directionality
What are the secondary charateristics most important of microphones in live sound?
Their electrical output and actual physical design
What is meant by a microphones operating principle?
The type of transducer inside the microphone, that is, how the microphone picks up sound and converts it into an electrical signal.
What is a transducer?
a device that changes energy from one form into another, in this case, acoustic energy into electrical energy.
What are the two most common types of transducer?
Dynamic and Condenser
What components make up a dynamic microphone
diapragm, voicecoil and magnet which forms a miniature sound-driven electrical generator.
Describe how a dynamic microphone works
Sound waves strike a thin plastic membrane (diaphragm) which vibrates in response.
A small coil of wire (voice coil) is attached to the rear of the diaphragm and vibrates with it.
The voice coil itself is surrounded by a magnetic field created by a small permanent magnet.
It is the motion of the voice coil in this magnetic field which generates the electrical signal corresponding to the sound picked up by a dynamic microphone.
Which type of microphone requires phantom power?
Condenser micriophones
What is another name for a condenser microphone
Capacitor microphone
What is another name for a dynamic microphone?
Moving coil microphone
What is transient response?
Transient response refers to the ability of a microphone to respond to a rapidly changing soundwave.
What is the major factor in a microphones transient response?
Diaphragm weight. For instance, the diaphragm and voicecoil assembly of a dynamic microphone may weigh up to 1000 times more than the diaphragm of a condenser microphone.
What is a polar plot/polar pattern graph used for?
polar plots shows the variation in sensitivity as you move 360 degrees around the microphone. aka the pick up pattern
Describe the polar response pattern of a cardio microphone.
Cardioid (kar-dee-oid) has the highest sensitivity to sound coming in from directly in front of the microphone capsule (0º), practically no sensitivity to sound coming directly from behind (180º), and a reduced sensitivity to sound coming in from the sides (90º/270º)
Describe the polar response pattern of a omni-directional microphone.
An omnidirectional polar pattern picks up sound in a 360-degree radius – it is equally sensitive to sound at all angles. Imagine its pattern as a perfect sphere in three directions.
Describe the polar response pattern of a figure of eight microphone.
Figure-8. The figure-8 pattern has the same sensitivity at 0° and 180°; it is the least sensitive at 90° and 270°. It is often used for various stereo recording techniques
What is the proximety effect?
The proximity effect is an increase in bass or low frequency response when a sound source is close to a directional or cardioid microphone
What do we mean by ‘undesired’ sound – example?
“Undesired”sound may mean the direct or ambient sound from othernearby instruments or just stage and background noise.
What do we mean by ‘suitable’ – example?
“Suitable”sound from the desired instrument may mean either thenatural sound of the instrument or some particular soundquality which is appropriate for the application.
What do we mean by ‘sufficient gain’?
Sufficient” gain-before-feedback means that the desired instrument is reinforced at the required level without ringing or feedback in the sound system.
What is meant when you talk about microphone techniques?
The selection and placement of microphones
What are the 4 main objectives of microphone techniques?
to maximize pick-up of “suitable” sound from the desired instrument,
to minimize pick-up of “undesired” sound from instruments or other sound sources.
to provide sufficient gain-before-feedback.
Using Directional Patterns to Reject Unwanted Sources
What is another name for speakers?
Output transducers
What is High Frequency Beaming
Direct radiators exhibit a feature whereby the high frequencies emitted by the driver tend to be strong on axis of the driver, but fall off rapidly once we move off axis. This is called high frequency beaming.
What is a band pass filter?
A band-pass filter “passes” a band of frequencies (a defined range above a low cutoff and below a high cutoff) while progressively attenuating frequencies below the low cutoff and above the high cutoff.
What is a high-pass filter?
A high-pass filter is the opposite of a low-pass filter, in that it allows frequencies higher than the cutoff frequency to pass. Similar terminology applies. High-pass filters are also called low cut filters. High-pass filters drive the high frequency drivers in the speaker system.
