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Microphones (PowerPoint)

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									   Microphones
Dynamic and Condenser
         Polar patterns
   Frequency response
              Wireless
How a microphone functions
   Dynamic microphones
       Based on a moving coil of
        wire
         Think of the reverse of a
           loudspeaker
       Sound waves push on a
        diaphragm which in turn
        moves a coil of very fine wire
        through a magnetic field
         Produces current
           proportional to the sound
           waves
Dynamic microphones
   Usually very robust and durable
       Very often used on stage where rough handling or
        dropping is common
       Damage is most often caused by breaking
        suspension wires
           Two wires which hold the diaphragm and coil in place
   Often do not produce a flat frequency
    response and not very sensitive to low SPL
       The relatively massive coil of wire takes a great
        deal of power to make move
Condenser microphones
   Creates a capacitor using the
    diaphragm as one plate.
       Capacitor is used to store an
        electric charge. Changing the
        distance between plates changes
        it’s ability to do that.
       Requires the plates to be charged
        by an external source
         Battery, phantom power…
       As the diaphragm moves, it causes
        a ripple in the current from the
        phantom power. This ripple is
        proportional to the sound waves
Condenser microphone
   Due to the lightweight diaphragm, only small
    pressure changes are required to produce an
    audio signal.
       Very sensitive to small SPL
       Much flatter frequency response than dynamic
   Much more susceptible to damage
   Requires external power supply to function
Frequency Response
   A graph showing how a specific microphone
    responds to different frequencies.
       No microphone is perfectly flat
         Usually not desirable anyway

         Microphones are designed for specific purposes and
          frequency responses are tailored for each use
   Proximity effect
       Usually only seen on dynamic microphones
       As you move the mic closer to the sound source, you get
        an increase in the low frequency response.
       Trained vocalists will make good use of this effect, the
        untrained will make themselves unintelligible.
Frequency Response
        Dynamic Vocal Mic      Condenser Vocal Mic




        Live Instrument Mic   Studio Instrument Mic
Directional properties
   Every microphone will have a polar pattern
       Description of the sensitivity of the microphone
        related to the direction the sound is coming
        from
       Omni-directional
           Sensitive from all directions
           Used for ambient noise recording or where the
            sound source is moving and the mic cannot
               Often on lavaliere mics
           Sound is often general and unfocused.
                                                            Omni-directional
           Feedback more likely
                                                            polar pattern
Directional properties
    Uni-directional
      Mostly sensitive from one direction and less
       from all others
      Cardioid pattern
            Sound is mostly picked up from the front, but
             some from the sides as well to allow for some        Cardioid polar
             movement of the mic off axis                         pattern
            Most common pattern, good for general use
            Most common on hand held mics
        Super and Hyper Cardioid pattern
            Less sensitive to the sides, more sensitive to the
             rear
            Sometimes called a “shotgun” mic
            Very directional
                                                                    Super cardioid
                                                                    polar pattern
Directional properties
    Bi-directional
      Sensitive from the front and back and
        much less to the sides
      Not much use on stage

    Variable directionality
      Polar pattern is adjustable to different
        patterns                                  Bi-directional pattern
      Seems like a good idea, but rarely works
        perfectly well
Specialty Microphones
   PCC and PZM microphones
       Collectively known as Boundary microphones
       Trade names of Crown International
         http://www.crownaudio.com/mic_web/pcc.htm
               http://www.crownaudio.com/pdf/mics/101062.pdf
         http://www.crownaudio.com/mic_web/pzm.htm
       Often used as a floor mic to reinforce a large group of
        people who are moving
         Musical chorus for example

   Choir microphones
       Small sensitive condenser mics usually hung overhead
           http://www.shure.com/microphones/models/mxoverhead.asp
RF (wireless) microphones
   A microphone which transmits it’s audio signal using
    radio frequencies rather than a cable
       The mic has a radio transmitter built into it which transmits
        to a receiver off-stage. The receiver then sends the audio
        signal to a mixer
   Most often in the form of a wireless
       Vocal mic – transmitter is built into the body of the mic
       Lavaliere – small mic capsule is clipped onto clothing or
        taped to the head (preferred). The mic capsule is wired to
        a small pack with the transmitter and batteries.
RF (wireless) microphones
   The frequency that the packs transmit on are
    very important
       Usually transmit in the VHF or UHF range and are
        susceptible to interference from other radio
        sources
       Diversity receivers
           MUCH more interference resistant than non-diversity
           Involves two separate receivers spaced apart from
            each other
               The system will select the strongest signal
RF (wireless) microphones
   Lavaliere mic mounting
     Usually mounted on the center of the forehead or over the ear
           Toupee clips, bobby pins, high quality surgical tape.
           Spirit gum only if ALL else fails
       Occasionally mounted on clothing
           Traditional use. TV interviews for example
           Poor sound quality
               Low frequency boost from being near the chest
               Wind or clothing noise likely
               Sound level changes as performer moves their head
       Boom mounting – a.k.a. “Madonna Mic”
           Mounted on a rig over the ear which puts mic very close to the mouth.
           Best sound. Poor aesthetics.
Additional Readings
   http://electronics.howstuffworks.com/framed.
    htm?parent=question309.htm&url=http://hom
    e1.pacific.net.sg/~firehzrd/audio/mics.html
   http://www.mediacollege.com/audio/
   Interesting discussion on mic techniques
       http://www.informatik.uni-
        bremen.de/~dace/guitar/recording/

								
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