1. Rick Pitchford, CSRTE Guest Lecture, COM 494 February 2, 2015
Microphone Basics
Rick Pitchford, CSRTE
Guest Lecture, COM 494
February 2, 2015

2. Microphone Types: BODY STYLES: hand held lavalier body shotgun headset
microphones.ppt
4/14/2017
Microphone Types:
BODY STYLES:
hand held
lavalier
body
shotgun
headset
boom
parabolic
desk/stand
boundary
images from RCA, Shure Brothers, Inc., Electrovoice, Audio Technica, Gibson and AKG
C353 R.A.Pitchford

3. A Microphone is a Transducer:
A transducer is a device, usually electrical or electronic, that converts one type of energy to another for the purpose of measurement or information transfer. Most transducers are either sensors or actuators. In a broader sense, a transducer is sometimes defined as any device that converts energy from one form to another.
Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antennas.
In a microphone, the diaphragm moves in response to changing air pressure (sound), creating an electrical current.
Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.
definitions from wikipedia.org and whatis.com

4. Moving Coil (Dynamic) Transducer:
durable; resists humidity and temperature extremes
no power supply needed
a good quality dynamic is expensive
low output level; closer to noise floor
hard to physically overdrive the mic element with loud sounds
hard to electrically overdrive amp input with loud sounds
identical mechanism as loudspeaker
image from “First Class Radiotelephone License Handbook”, fourth edition, ©1974, Howard W. Sams Co., Inc.

5. Condenser Transducer:
delicate; can be damaged by physical shock, high humidity and temperature extremes
requires battery or external “phantom” power supply for the internal amplifier
brighter sounding than a dynamic mic
more sensitive than dynamic mic of same diaphragm size
higher output level than dynamic; can provide better signal-to-noise ratio
image from “First Class Radiotelephone License Handbook”, fourth edition, ©1974, Howard W. Sams Co., Inc.

6. Ribbon (Dynamic) Transducer:
delicate; easily damaged by shock, humidity and high sound levels
desk mount, boom or handheld body styles
no power supply needed
warm, rich sound
very sensitive
low output level
expensive; difficult to find
image from “electronic communication”, third edition, ©1975, McGraw Hill Inc.

7. Microphone Polar Patterns:
The sensitivity of a microphone varies depending on the design of the mic, orientation of the sound to the mic and the frequencies considered. This is displayed graphically as a polar pattern.
Microphones fit somewhere on a continuum from
omni-directional through unidirectional, to
bi-directional. In general, mics vary more from their “advertised” patterns as frequency increases.
omni
uni bi
images from “ksm44_en.pdf”, Shure Brothers, Inc.

8. Omnidirectional Mics:
Housing
Diaphragm
sensitive
sensitive
sensitive
sensitive
sensitive from all directions
has a sealed housing behind the diaphragm
positive pressure from any direction pushes the diaphragm in
most natural sounding mic pattern due to uniform frequency response
Sound Waves
Sound Waves

9. Unidirectional Mics: The Cardioid:
Housing
sensitive
sensitive
Diaphragm
null
sensitive
Port
sensitive
more sensitive to the front
has a ported housing behind the
diaphragm
positive pressure from front pushes the diaphragm in
positive pressure from rear enters ports, equalizes on both sides of the diaphragm, producing no motion
frequency response not uniform off axis
usually exhibit “proximity effect”
Sound Waves
Sound Waves

10. More Unidirectional Mics:
As the housing ports become larger, the front sensitivity narrows. A rear sensitivity node forms as nulls move to the sides of the mic, producing the supercardioid and then the hypercardioid. Positive pressure to the rear lobe produces an inverted waveform compared to the front lobe, indicated by the negative sign.
Housing
Diaphragm
Port
supercardioid
sensitive
null
sensitive
inverted
sensitive
null
Housing
Diaphragm
Port
hypercardioid
sensitive
null
sensitive
inverted
sensitive
null

11. Ribbon Bidirectional Mics:
null
Diaphragm
sensitive
sensitive
inverted
null
Sound Waves
sensitive front and rear only
no housing used around the diaphragm
rear entering sounds are naturally inverted relative to the front
frequency response not uniform for sounds entering off axis
Sound Waves

12. Condenser Bidirectional Mics:
Diaphragms
Ports
null
sensitive
sensitive
inverted
null
formed by two identical unidirectional mic capsules mounted back-to-back
capsules are connected together electrically out of phase so that positive pressure entering the rear produces inverted waveform compared to positive pressure entering the front, mimicking a ribbon bidirectional
Sound Waves
Sound Waves

13. Hemispherical Mics: omnidirectional mic mounted near a boundary
microphones.ppt
Hemispherical Mics:
4/14/2017
Housing
Diaphragm
sensitive
sensitive
Boundary
null
omnidirectional mic mounted near a boundary
sensitive only on one side of the boundary
boundary size determines how closely the mic pattern emulates the “ideal”
natural sounding due to uniform frequency response
C353 R.A.Pitchford

14. Interference Tube Mics:
Housing
null
sensitive
Slotted Tube
null
sensitive
sensitive
null
null
sensitive
Diaphragm
primarily sensitive to the front
a slotted tube is fitted to the front of a non-ported housing
sound pressure waves from the front travel down the tube to the diaphragm
sound pressure waves from the side enter the tube through slots and travel down the tube by varying-length paths
off axis sounds cancel at the end of the tube – a process called comb filtering
polar pattern varies with frequency

15. mic techniques.ppt
4/14/2017
Comb Filtering:
the effect of mixing two identical signals, one delayed in time from the other
all frequencies in the delayed signal are delayed by the same amount of time
different phase delays are created for different frequencies because every frequency has a unique wavelength
the sum of the two signals exhibits a frequency response of alternating peaks and nulls
level
frequency
C353 - R.A.Pitchford

16. For Example,
level
time
1 msec.
1000 Hz.
time
1 msec.
level
500 Hz.
the same time delay has the exact opposite affect on these two frequencies
at 1 msec. all even multiples of 500 Hz., (1000 Hz., 2000 Hz., 3000 Hz., etc.) will fully reinforce; all odd multiples (500 Hz., 1500 Hz., 2500 Hz., etc.) will fully cancel
at frequencies in between, the interaction will vary from reinforcement to cancellation
1msec = 1 foot additional acoustic path length + = + =
level
level

17. Non-Acoustic Comb Filtering:
mic techniques.ppt
4/14/2017
Non-Acoustic Comb Filtering:
First 5-6 weeks of ABC’s Spring, 2009 season live broadcast of Dancing With the Stars demonstrated severe comb filtering. Commercial breaks were not affected. The problem may have been caused by mis-timed, redundant signal paths being summed.
Frequency response of
commercial break
Frequency response of
live program
C353 - R.A.Pitchford

18. Taming Acoustic Comb Filtering:
mic techniques.ppt
4/14/2017
Taming Acoustic Comb Filtering:
place the mic in such a position that reflections are delayed only slightly; smaller delays push the first null point to higher frequencies
place the mic closer to the sound source and further from the reflectors so the Inverse Square law helps the direct sound overwhelm the reflected sounds
level
frequency
C353 - R.A.Pitchford

19. Obey the Inverse Square Law!
Mic Placement:
Obey the Inverse Square Law!
Doubling the distance from source to transducer quarters the sound pressure level on the diaphragm.
Halving the distance from source to transducer quadruples the sound pressure level on the diaphragm.

20. Proximity Effect:
DIRECTIONAL MICS respond to the Inverse Square law differently than omnidirectional microphones. Low frequencies are enhanced more than mid and high frequencies as the source-to-mic spacing decreases. This is the reason many performers and announcers work directional microphones closely, giving their voice more low end. Be aware varying source-to-mic spacing during a performance can drastically change the timbre of the voice.
Many directional mics include a bass-rolloff switch to equalize this effect for close-micing situations. Some mics are carefully designed to minimize it.
~17dB change at 100Hz, from 1/8 inch to 24 inches
image from “us_pro_beta57a_ug.pdf”, Shure Brothers Inc., 2004

21. mic techniques.ppt
4/14/2017
Selecting a Mic:
Using a mic for a particular situation requires these decisions be made about:
the appropriate body style
the appropriate transducer type
the best polar pattern to use
the proximity of the mic to the source
handling sound reflections
C353 - R.A.Pitchford

22. Body Style Selection: Hand held: Lavalier: Body: Shotgun: Headset:
“universal”
Lavalier:
spoken voice
some instruments
Body:
stage or screen
Shotgun:
high-noise situations
Headset:
hands-free uses
sports commentators
performers
Boom:
instrument
studio voice
Parabolic:
sports sidelines
surveillance
Desk:
interview
Boundary:
complete room coverage
conferences

23. Transducer Selection:
Moving Coil:
extremely loud sounds
sports remotes
emergency/backup mic
general purpose
bad weather situations
Condenser:
extremely quiet sounds
high quality recording on a budget
covert/concealed applications
near strong magnetic fields
Ribbon:
predictable sound levels
controlled studio locations
experienced performers
feeding high-gain, low-noise amplifiers

24. Polar Pattern Selection:
Consider both the desired and all UNDESIRED sound sources when choosing a pattern. Use the best pattern to attenuate undesired audio as well as delayed reflections of desired audio.

25. Multiple Mics for Mono and Stereo:
Multiple Mics for Mono work:
large sound source needing coverage
multiple sound sources
Beware comb filter effects!
Micing in Stereo requires a minimum of two discreet signals, Left and Right.
Stereo is a spatial effect stemming from
both intensity and time differences of sounds stimulating left and right ears or the ear’s representatives, the microphones.
Consideration must be given to
mono mixes derived from
stereo signals.

26. Spaced Pair (A-B Pair):
two mics placed in front of and facing sound source (center mic, fed to both channels, is optional)
spacial (stereo) effect due to both time and intensity differences
mic placement must follow "3 to 1" rule to minimize comb filtering effect in mono
recreates a sound field in one dimension; listener movements will change the mix
Sound Source
8 ft.
25 ft.
L (C) R

27. Coincident Pair (X-Y Pair):
crossed or head-to- head unidirectional mics placed in front of and centered on a sound source
spacial (stereo) effect due to intensity differences only
no comb filtering effects in mono - fully mono compatible
recreates an aural sweet-spot
Sound Source
R L

28. Coincident Pair Deviations:
Sound Source
6-7”
Sound Source
L R
L R
ORTF
cardioid microphones at an angle of 110°
spaced about 6.5 inches apart
susceptible to comb filtering
recreates a head-sized sound field
Blumlein Pair
developed in 1931
crossed bi-directional mics placed head-to-head
not susceptible to comb filtering
recreates a sweet spot

29. Mid/Side (M-S): Sound Source L+R L -R
mid mic picks up left plus right (mono/sum) signal
side mic picks up left minus right (difference) signal
adding side to mid gives double left signal (L+R) + (L-R) = 2L
subtracting side from mid gives double right signal (L+R) - (L-R) = (L+R) + (-L+R) = 2R
spacial (stereo) effect due to intensity differences only
no comb filtering effects in mono - fully mono compatible
recreates sweet spot
Sound Source
L+R
L R
MID mic is UNIDIRECTIONAL facing forward
SIDE mic is BIDIRECTIONAL facing left/right

30. Multi-Mic: HORNS DRUMS STRINGS PIANO
combine multiple AB, XY, MS, ORTF and/or Blumlein mic pairs with or without accent mics
spacial (stereo) effect due (hopefully) to intensity differences only
mic placement must still follow "3 to 1" rule to minimize comb filtering effect in summed L and R channels
aspects of both a sound field and multiple sweet spots
HORNS
DRUMS
STRINGS
PIANO

31. Close Mic:
one mic (or direct connection) per source, each recorded separately
high acoustic isolation required between mics to prevent leakage
no natural spacial (stereo) effect - artificially created during the track mixdown
multi-track mono - not true stereo
produces a totally synthetic sound field
DRUMS
HORNS
GUITARS
VOCAL 1
VOCAL 2
KEYBOARDS

32. mic techniques.ppt
4/14/2017
Beyond Stereo:
consumer multi-track “surround sound” systems are everywhere
quadraphonic sound of the 1970s fell flat due to competing incompatible formats, poor results, questionable production practices and music-only implementation
Dolby Surround presentation of major films and the emergence of HiFi home video formats in the 1980s re-awakened consumer interest
“5.1” surround systems consist of left, center, right, left and right surround, and LFE (non-directional, low frequency/effects) channels
surround sound tracks are usually “built” from dry, close-mic, multitrack original material recorded in studio/sound stage
“live” surround recording techniques are emerging based on established stereo practices
C353 - R.A.Pitchford

33. Spaced Surround: Sound Field
mics are suspended above audience space in trapezoid arrangement
front spaced omnis for left and right
rear spaced omnis for left/right surround
single unidirectional for center channel and LFE placed somewhere in front of or within trapezoid
spacial effect due to both time and intensity differences
recreates the sound field in two dimensions; listener can move around to change aural perspective
Sound Field
L, R, Ls, Rs C

34. Coincident Surround: Sound Field
mics are either suspended above or located in audience space
left, center, right, left and right surround unidirectionals are mounted crossed or within a “dummy head”
down-facing omni for LFE pickup
spacial effect due to intensity differences only
re-creates specific aural sweet-spot to locate listener; movement within the sound field doesn’t change perspective greatly
stereo and mono compatible; no comb filtering
Sound Field
L, C, R, Ls, Rs LFE

35. MSM Surround Array: Sound Field LF+RF L -R LR+RR
three mics pick up front, rear and side audio
adding and subtracting side signal from front and rear produce Left front, Right front, Left rear and Right rear
LFE and Center channels derived or from additional dedicated mics
recreates a sweet-spot
stereo and mono compatible; no comb filtering
LF+RF
L R
LR+RR
MID mics are UNIDIRECTIONAL facing forward and rearward
SIDE mic is BIDIRECTIONAL facing left/right

36. “Sports Event Capture Array-2”
designed for 2-goal sporting events
first used for 2003 NCAA TV broadcasts on CBS
mic arrays mount on backboard, goal stands, etc., provide front and rear L/R audio
two supercardioid mics spaced 11” apart, face forward, down and slightly in
mid-side pair centered between and facing back toward seating area
center channel is feed from the announcers; LFE is derived from the array via low-pass filters
L, R Ls, Rs

37. ESPN Monday Night Football:
coincident (XY) pair of shotguns on 50 yd line to pick up crowd on opposite side for L, R
coincident (XY) pair at top of stadium for Ls, Rs
stereo wireless on umpire for field ambience; L, R
6 wireless parabolic mics for field effects; L, R
umpire and player wireless, synthesized to stereo, for field perspective; L, R
music to L, R
all cameras have mounted mics for shot perspective
announcers mics to Center only
L, R, Ls, Rs
image from

38. Fox Football:
coincident (XY) pairs on opposite 25 yd. lines to pick up crowd; L, R
spaced (AB) pair hung from press box for crowd surround; Ls, Rs
umpire and player wireless, synthesized to stereo, for field perspective; L, R
4 wireless parabolics plus camera mounted mics on field for shot perspective; L, R as needed
music to L, R; sound effects produced in 5.1
announcers mics to Center only
L, R, Ls, Rs
image from

39. World Series on Fox:
parabolic mics high behind home plate, down first and third base lines, focused on home plate, to L & R
AB pair at high first and high third pointed across field to farthest crowd to L, R
omnis mounted in bases, pointed toward outfield, to L, L & R, R
three or four manned parabolic mics in the outfield, to L, R
XY configured shotguns in centerfield, to Ls, Rs
“a bunch” of hemispherical mics and lavs on “anything that makes noise”
music to L, R; sound effects produced in 5.1
announcers mics to Center only
image from

40. NBA:
five short shotguns on the table aimed at each basket, center court, and to either side of the center
12 boundary mics on the court
one boundary mic below each basket
music to L, R; sound effects produced in 5.1
announcers mics to Center only
image from

41. Other Sporting Events:
Golf:
a stereo mic on a stake at the tee
two stereo shotguns on the greens
stereo mics for the crowd in the
long shotguns with operators on the fairway
“bird mics” in the trees
Mixed Martial Arts:
a cluster of five shotguns: one picking up the center of the ring, the other four splayed to capture the rest of the circular cage
shotguns on boom poles
lavs placed under the pad around the ring
mics on the 9 handheld cameras

42. “The Two Towers” percussion brass high strings low strings woodwinds
captured near-100 piece orchestra in a 135’ X 75’ auditorium
three omnidirectional mics on a Decca Tree over conductor’s head; L, C, R
two omnidirectional mics wide and outside of strings; L, R
two omnidirectional mics very high and rear facing for Ls, Rs
various omnidirectional mics for spot pickup
percussion brass
high
strings
low
strings
woodwinds
woodwinds
4.5’ Decca
6’ Tree
all mics

43. end