An Introduction to Microphones

1,298 views

Published on

An Introduction to Microphones

Published in: Technology
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,298
On SlideShare
0
From Embeds
0
Number of Embeds
53
Actions
Shares
0
Downloads
0
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide
  • Microphones are the beginning of the recording chain. They pickup audio sources and vibrate just like the human ear drum
  • String and tin can idea

    An extension of the string and tin can idea was used in Thomas Edisons early phonograph recordings. Edison shouted the words ‘Mary had a little lamb’ into a cone shaped horn which caused a needle at the narrow end to vibrate and cut a groove into a rotating tin foil cylinder. When the process was reversed, the rotating cylinder caused the needle in the groove to vibrate and the horn reproduced the stored vibrations of his voice as a sound output in the horn
  • the invention of the microphone is general attributed to A G B. It was a very impractical invention involving liquid acid.
  • The so called carbon microphone was invented by Emile Berliner and virtually simultaneously by Thomas Edison in 1876.
    The carbon microphone was used in early telephone designs.
    It relied upon the change in resistance caused by sound pressure and consequent change in current between a metal diaphragm and two metal electrodes separated by a layer of carbon particles. Later designs used what we call a moving coil principle.
  • A microphone wouldn’t have any purpose without the existence of a device such as a loud speaker.
    Passive transducers*) convert acoustical energy directly into electrical energy (and vice-versa) without the need for any external power feed. This group includes dynamic, magnetic and piezoelectric microphones, as well as condenser microphones using dc polarization.
    Active transducers*) convert electrical energy from an external source synchronously with the sound vibrations they receive. Carbon microphones and RF-condenser microphones make use of this principle.
  • Input transducers - magnetic pick ups, tape heads, phonograph pick up, laser pick ups, air pressure or velocity microphones
    Output transducers - loudspeakers, headphones
  • Most microphones have a ‘diaphragm’ of some kind.
    The diaphragm is often made of a lightweight plastic coated with metal particles.
    This vibrates in sympathy with sound vibrations (variations in sound pressure level).
    These vibrations are converted into an electrical current which becomes the audio signal.
    This is known as Electromagnetic Transduction.
  • There are basically three types of microphone in common use: piezoelectric, dynamic and capacitor. The piezoelectric mic, it has to be said, has evolved into a very specialized animal, but it is still commonly found under the bridge of an electro-acoustic guitar so it is worth knowing about.
  • The theory of electromagnetic induction states that whenever an electrically conductive metal cuts across the flux lines of a magnetic field, a current of a specific magnitude and direction will be generated within that metal.
    in other words..
    A coil of wire within a magnetic field is attached to the microphone diaphragm
    The coil moves with the diaphragm as sound makes the diaphragm vibrate
    The movement of the coil produces a small alternating electrical current
    = Sound is converted to an electrical signal In this way, sound energy reaching the microphone is turned into electrical energy which can be amplified and turned back into sound energy by the loudspeaker (a speaker effectively being a microphone in reverse).
  • The moving coil process is reversible and we use it for the modern loudspeaker.
  • The condenser mic relies on the change of capacitance between a diaphragm and a fixed electrode. The sound source causes the diaphragm to vibrate so changing the capacitance.
  • they use to be very fragile with valve and tubes but modern solid state designs are much more robust and even suitable for live work.
  • Shows how is a large diaphragm condenser made

    What she calls ventilation holes are actual for the polar pattern pick up
  • The condenser mic relies on the change of capacitance between a diaphragm and a fixed electrode. The sound source causes the diaphragm to vibrate so changing the capacitance.
  • This is a standardised system which passes the power supply current along the conductors of a balanced microphone cable. The standard phantom power supply voltage is 48V and is generated within the mixing console; provided a proper balanced microphone cable is used, it is necessary only to plug in the mic and turn on the phantom power supply.

    In theory, it is quite safe (though pointless) to apply phantom power to a Dynamic microphone, so long as it is wired for balanced operation, as the same voltage will appear at both ends of the voice coil -- which means no current flows through it. The reason I mention this is that some budget mixing consoles have a global phantom power switch, so if you intend to use both Dynamic and Capacitor mics on the same session with such a console, you will have to ensure that all cables are balanced and that the mics are internally wired for balanced operation. As a rule, if the mic body is fitted with a three-pin XLR socket, then it is balanced
  • Cardioid

    Good for minimising feedback on stage.
    Can be used to minimise unwanted room acoustic / ambience
    Often used as ‘spot’ mics
    Also ‘hyper-cardioid’ or ‘super-cardioid’ patterns

    Bi Directional
    Figure-of-eight pattern.
    Can be used in similar applications to cardioid, but with a more ‘ambient’ sound.
    Sounds appearing at the sides of the mic are effectively cancelled out.
  • Most professional microphones are low impedance, 200 Ω, and are designed to work into a load of 2000 Ω. High-impedance microphones are 50,000 Ω and are designed to work into an impedance of 1–10MΩ. The low-impedance micro- phone has the following advantages:
    ● Less susceptible to noise. A noise source of relatively high impedance can- not “drive” into a source of relatively low impedance (i.e., the microphone cable).
  • As the source is moved closer to the diaphragm, the low-frequency response increases due to the proximity effect. The proximity effect is created because at close source-to-microphone distance, the magnitude of the sound pressure on the front is appreciably greater than the sound pressure on the rear.

    Designers often try to compensate for the P.E. in their designs although sometimes this very intimate effect is exactly what we want.
    Movie trailer voice for example.
  • An Introduction to Microphones

    1. 1. Microphones stuart.jones3@southwales.ac.u k www.stuartjones.org Microphone Technology and Application
    2. 2. Microphones Agenda History Transducers Microphone Construction Microphone Diaphragms Phantom Power Polar Patterns Impedance Proximity Effect Application Connect 2 Application & Booking Microphones
    3. 3. History
    4. 4. Edison’s Early Phonograph
    5. 5. Alexander Graham Bell
    6. 6. Emile Berliner
    7. 7. Transducers Microphones
    8. 8. A microphone is an acoustic-to-electric transducer which converts sound into electrical signal Microphones Devices that convert mechanical or other measurable energy into an electrical one are called Transducers
    9. 9. Microphone Input Transducer Mixing Console Signal Processing Power Amplifier Loudspeake r Output Transducer Microphones
    10. 10. Other Types of Input Transducers Magnetic pick ups Tape heads Phonograph pick up Laser pick up Microphones Other Types of Output Transducers Headphones Microphones
    11. 11. Microphones Microphone Construction
    12. 12. • Most microphones have a ‘diaphragm’ of some kind. • This vibrates in sympathy with sound vibrations (variations in sound pressure level). • These vibrations are converted into an electrical current which becomes the audio signal. • This is known as Electromagnetic Transduction. Microphones Microphone Construction
    13. 13. Microphones The three types of microphone in common use: • Dynamic (moving coil) • Condenser (capacitor) • Piezoelectric Microphone Construction
    14. 14. Microphone Diaphragms Microphones
    15. 15. Microphones Shure SM57 Moving Coil (Dynamic)
    16. 16. Sound Waves diaphragm Cross Section of a Dynamic mic Coil of wire Cable carrying AC signal Magnet The theory of electromagnetic induction states that whenever an electrically conductive metal cuts across the flux lines of a magnetic field, a current of a specific magnitude and direction will be generated within that metal. In other words.. • A coil of wire within a magnetic field is attached to the microphone diaphragm • The coil moves with the diaphragm as sound makes the diaphragm vibrate • The movement of the coil produces a small alternating electrical current = Sound is converted to an electrical signal Microphones Microphone Diaphragms
    17. 17. Dynamic Microphone Characteristics Microphones •Robust and durable •Inexpensive •They are not sensitive to changes in humidity •They do not need external or internal power to operate • They usually have a resonant peak in the mid-frequency response • Can be weak in the high-frequency response above 10kHz Microphone Diaphragms
    18. 18. Cross Section of a Condenser mic Sound Waves diaphragm Cable carrying AC signal Backplate Condenser mics operate on an electrostatic principle rather that the electromagnetic principles used by dynamic and ribbon mics. The base head, or capsule, of the condenser mic consists of two very thin plates - one moveable and one fixed. When a sound wave is introduce, the distance between the plates vary creating an electrical voltage. Microphones Microphone Diaphragms
    19. 19. Microphones • Capacitance is the ability to store an electrical charge • Condenser mics are sometimes called capacitor mics Condenser (Capacitor)
    20. 20. Microphones Condensers fall into two main types: Polarized - Include Neumann U87 Electret - Developed in the early 1960‘s. Often associated with low cost mics used in modern telephone and communication devices although also used in modern microphone design (Audio Techinca/AKG Condenser (Capacitor)
    21. 21. Condenser Microphone Characteristics Microphones • They have extended low and high-frequency response with low distortion and noise • Produce a higher output level than dynamic mics (better signal to noise ratio) • Can be expensive • Low cost models can suffer from poor or inconsistent frequency response • They require internal or external power • Humidity and temperature affect performance Microphone Diaphragms
    22. 22. Video - How its Made Neumann U87 Microphones
    23. 23. Microphones
    24. 24. Ribbon Mics Microphones Microphone Diaphragms
    25. 25. Phantom Power Microphones
    26. 26. Phantom Power • Normally +48V DC (Direct Current). • Sent to mic via XLR cable. • Phantom power supplies are often built into mixing desks, microphone preamplifiers and similar equipment. • Valve microphones require special power supply units, but the vast majority of Capacitor and Back-Electret mics are designed to work using a system know as phantom powering Microphones
    27. 27. Polar Patterns Microphones
    28. 28. Polar Patterns What are Polar Patterns? Microphones
    29. 29. Microphones
    30. 30. Impedance Microphones
    31. 31. Impedance What is Impedance? Impedance is an electronics term which measures the amount of opposition a device has to an AC current (such as an audio signal). Microphones
    32. 32. There are three general classifications for microphone impedance. These are: 1. Low Impedance (less than 600Ω) 2. Medium Impedance (600Ω - 10,000Ω) 3. High Impedance (greater than 10,000Ω) Ω = Ohms As a general rule low impedance is better than high impedance. D.I. Boxes convert high impedance into low impedance. Typically the output of an electric guitar is high impedance Microphones Impedance
    33. 33. Microphones All professional dynamic mics incorporate a transformer that gives them an output impedance of somewhere around 200 ohms. This is a fairly low output impedance that can drive a cable of 100 meters or perhaps even more with little loss of high frequency signal (the resistance of a cable attenuates all frequencies equally, the capacitance of a cable provides a path between signal conductor and earth conductor through which high frequencies can ‘leak') Impedance of a Moving Coil (Dynamic) Mic
    34. 34. Proximity Effect Microphones
    35. 35. Proximity Effect As the source is moved closer to the diaphragm, the low-frequency response increases due to the proximity effect. The proximity effect is created because at close source-to-microphone distance, the magnitude of the sound pressure on the front is appreciably greater than the sound pressure on the rear. Graph Showing the proximity effect for a Beyer Dynamic M160 hypercardioid ribbon microphone Microphones
    36. 36. Microphones Application The Use of Microphones for Music
    37. 37. Microphones Small Diaphragm Dynamic SM58, SM57, Audix OM5 Possible Application Vocals, snare, toms, guitar amplifiers, percussion
    38. 38. Microphones Large Diaphragm Dynamic AKG D112, Shure SM7b, Sennheiser MD421, Electrovoice RE20 Possible Application Vocals, snare, toms, guitar amplifiers, percussion
    39. 39. Microphones Small Condenser Microphones AKG C300B, AKG430, AKG C1000, Rode NT5 Possible Application snare, drum overheads, brass, guitar amplifiers, acoustics guitars, percussion, piano, brass
    40. 40. Microphones Large Condenser Microphones AKG 414, SE Electronics 2200, Neumann U87 Possible Application Studio vocals, drum overheads, brass, guitar amplifiers, acoustics guitars, percussion, piano, brass, strings
    41. 41. Microphones Connect 2 Equipment & Booking
    42. 42. Microphones References Books Boré, G. Peus, S (1999), Microphones Methods of Operation and Type Examples, Berlin: Druck- Centrum Fürst GmbH. Gibson B (2002), Microphone Techniques, USA: ProAudio Press Web Discovery Channel: How its made; Microphones. Available at http://www.youtube.com/watch?v=2JKXPIyz444 Lynda Tutorials: An Introduction to Mic Types and how they work. Available at: http://blog.lynda.com/2012/10/30/an-introduction-to-mic-types-and-how-they-work/ http://www.record-producer.com/dynamic-microphones
    43. 43. Microphones Microphone Technology and Application stuart.jones3@southwales.ac.u k www.stuartjones.org

    ×