Lectures 6 - 10 Flashcards
What are the four types of microphones?
Dynamic microphone
Simple condenser microphone
Electret microphone
Silicon microphone
Sound wavelength equation
A sound wave is a typical wave, with wavelength λ and frequency f related to the velocity of the wave c
c = λ f
Properties of a sound wave
A sound wave in air is an example of a Longitudinal wave, where the molecules vibrate in the direction of the wave travel
What are microphones?
Microphones are a type of transducer - a device which converts energy from one form to another. Microphones convert acoustical energy (sound waves) into electrical energy (the audio signal).
What are Dynamic Microphones?
These use a wire coil attached to the moving diaphragm.
When the diaphragm vibrates in response to incoming sound waves, the coil moves backwards and forwards past the magnet. This creates a current in the coil which is fed to an external amplifier. They do not require batteries or external power.
What are Ribbon Microphones?
The ribbon microphone uses a conducting metal foil, which vibrates when a sound wave hits it. It is usually folded, as in the diagram, to give it a bit of rigidity. As it is in a magnetic field from a magnet, a current is generated directly in the foil (there is no separate membrane and coil). The current is then amplified, and changed into a voltage as the signal.
What are Condenser Microphones?
A voltage is applied between the diaphragm and back plate (supplied usually by a battery).
As the diaphragm vibrates, the distance between them changes, as does the capacitance.
Dynamic VS Condenser Microphones
Dynamic microphones are thus generally used for:
•Vocals;
•Instruments that have a high acoustic output - so sensitivity isn’t an issue - (e.g. electric guitar amps, drums, brass);
•Situations where the microphone could be dropped or otherwise damaged.
Condenser microphones, on the other hand, are good for:
•Quieter instruments (e.g. acoustic guitars);
•Instruments needing more high-frequency detail (e.g. acoustic guitars, fiddles, cymbals etc).
Microphones – Directional Properties
Every microphone has a property known as directionality - the sensitivity to sound from various directions. There are different types of directionality, but the two main ones are:
OMNIDIRECTIONAL: Picks up sound evenly from all directions (omni means “all” or “every”).
CARDIOID: Picks up sound predominantly from one direction.
Omnidirectional
Used in mobile phones, and where sound may be coming from many directions
Cardioid
Cardioid means “heart-shaped”. Emphasises sound from the direction in which the microphone is pointed.
Handheld (stage) microphones are usually cardioid.
This is controlled by the physical construction of the microphone.
“Super-cardioid” is a slightly more directional version of this shape.
How does a guitar single coil work?
The string oscillates, and distorts the magnetic field from the magnetic pole piece one per string).
The changing magnetic flux causes a current to be generated in a coil which is wrapped round the pole pieces as shown.
The signal from each pole piece adds its own component to the sound.
How does a guitar Humbucker coil work?
A humbucker consists of two single-coil pickups wired in series. However, both the direction of the magnetic field and the direction in which the coil is wound is opposite in each case. Hence the signals from the two due to a vibrating string are the same, and hence they can be added together to give a larger signal.
However, noise picked up by each coil (e.g. from the mains, lights etc) will be out of phase with respect to each other, and will cancel when added together, i.e. the hum is “bucked”
Guitar Single coil VS Humbucker
Single coil pickups have a wide frequency response, a clean sound with lots of “attack”.
Humbucker’s are warmer. They tend to loose high frequencies, as the slightly different positions on the string of the two sets of pole pieces lead to some cancellation of high frequencies (as they may be slightly different in phase). This is less of a problem at low frequencies.
What are the three main filters?
Low Pass Filter
High Pass Filter
Band Pass Filter
