Theatre Design & Technology - Winter 1981 - 14

it were the basic workhorses of radio, recording, and movies.
Many are still in use today, although none has been manufactured since the 1950's.
As noted, in the 1950's there was a great move away from the
large, heavy, fragile ribbons to the smaller, lighter, tougher
moving coil microphones. One of the discoveries that made this
change possible was an easy way to make a cardioid microphone with only one element instead of two. It is said to have
happened by accident. At the RCA labs a developmental model
omnidirectional microphone was checked for polar response
and was found to have a cardioid pattern. The puzzled engineers took it apart and found that a technician had done a
careless job of soldering. He had left a small hole in the rear
pressure chamber thus accidentally creating the first acoustical
(rather than electrical) cardioid.
Figure 6 shows that paths P1 and P2 from the rear are equal
in length, so sound pressure from the rear arrives at both sides
of the diaphragm at the same instant, thus tending to hold the
diaphragm in place-very similar to side sound in the bidirectional microphone. Paths P3 and P4 from the front differ in
length, hence no cancellation occurs for front-originating
sounds.
This microphone type has some problems which are found in
all acoustical cardioids-moving coil, ribbon or condenser. They
are less rugged and are much more susceptible to wind noise
and breath pops than are similar omnidirectionals. A microphone intended for hand-held work needs a blast filter to control
breath noises. The more expensive models have excellent builtin filters. Never assume a microphone will work well up close
until you have tested it for breath pops.
The acoustical cardioid has a frequency response both onand off-axis that is poorer than an omnidirectional. On-axis the
cardioid has less deep bass and less upper highs than a similar
omni. It is very difficult (hence, expensive) to manufacture a
cardioid microphone that has the same cardioid pattern at all
frequencies. This uneven off-axis response results in a great
deal of coloration. Even expensive cardioids should be used
with care to avoid noticeable coloration.
The on-axis response of a cardioid changes in the mid-bass
region depending on how close the sound source is to the
microphone. This is called proximity effect. The difference in
bass sounds produced can be enormous as the distance to the
microphone varies from V4' to 24". Vocalists often love the effect
and many singers use it well. On the other hand, careless
movements of the microphone while singing up close can also
spoil the act. Some cardioids have a switch to roll off the bass
response for close work. While this bass rolloff restores a more
natural sound for close work, the bass still changes with
distance-a point often forgotten by users. Proximity effect can
be used to good advantage by the pros, but for many users it is a
real problem.

Super-Cardioid
Several improvements have been made on the basic cardioid
by adding tubes and more holes to the rear chamber. The major
contributions of these various acoustical labyrinths are a tighter
cardioid pattern with greater back rejection, a reduction in offaxis coloration, and a reduction in the proximity effect. The
reduction in the proximity effect is accomplished at the cost of
reduced response in the whole bass region. This bass rolloff
condition is of very little concern for voice work, but it would be a
poor idea to use such a microphone for an organ or a string
bass. (An omnidirectional should always be used for deep bass
pickup.) In terms of overall sound coloration, the super-cardioid
is an improvement on the simple cardioid. It also represents a
good increase in cost. (It should be noted that a few supercardioid models have been engineered to maintain the proximity
effect. Read the product literature carefully.)
Various manufacturers have developed other cardioid-family
microphones with increasingly tight patterns. These are mostly
12

Theatre Design & Technology

used for boom applications in TV and film. Most of these hypercardioids and "shotguns" have severe off-axis coloration and
are often best used only for speech pickup.

Presence
The last decade has seen the introduction of a large number
of cardioid microphones that have been engineered to have a
non-flat frequency response. Most of these tailored response
units have been intended for vocalists. About twenty years ago it
was discovered that a boost in the 2,500 to 4,000 Hertz range
would make a vocalist (male or female) seem louder and stand
out from the backup music without actually being much louder in
electrical output to the record or broadcast. This high-frequency
boost has come to be called a presence boost.
The presence boost can also be accomplished by proper
equalization in the control board. However, not all mixer boards
have equalization available and not all live acts have an
operator to run the mixer. So there is a very sizable market for
microphones with proximity and presence boost. The great
problem with these microphones is that they are made for a very
limited application. If you try to use them for any1hing except
vocals, you are very likely to have a poor result.
The majority of U.S. manufactured microphone models on the
market today have these proximity and presence boosts. Because these microphones are so common, so widely advertised
and so well loved by many musicians, conditions are ripe for a
folklore to grow up by which the unwary may be misled. Some
typical examples of response and polar patterns are reproduced
in these pages. By learning to identify the typical response and
polar curves associated with different microphone types, you
can quickly separate the obviously undesirable from the potentially useful microphones by examination of the product literature.

Combinations
The first cardioid microphone was an electrical combination of
an omni and a bi-directional. It is also possible to use two
cardioid elements with which both omni and bi-directional patterns can be created electrically. Today both of these techniques are used in some very high-quality condenser microphones. These combinations can be switched from an omni to a
figure-eight and on to a variety of cardioid forms. Some of these
units can even be changed while in use from a control box
located in the control room. Combination microphones are
commonly, but not exclusively, used in coincident stereo recording techniques.
The combinations based upon an omni and a bi-directional
element are generally blessed with a smooth frequency response and very little off-axis coloration. However, those units
that rely upon cardioids for pattern structure will have typical
cardioid colorations in all combinations.
There is another family of polydirectional microphones which
operate by opening or closing a hole in the rear pressure
chamber. Completely closed makes an omni; completely open
gives a bi-directional; intermittent settings yield various cardioid
patterns. This was the system employed in the famous RCA
770, introduced in 1941 (~ig. 8).

Pressure Zone Microphones
Our last acoustical type is the Pressure Zone Microphone' , or
PZM&.* The PZM is a new concept only three years old. It is
probably the first really new microphone principle since the
discovery of the acoustical cardioid in 1936. The PZM doesn't
even look like a microphone. It is a small metal plate upon which
is mounted a small block with an XLR connector in one end. The
microphone element (a condenser) is less than V4' in diameter
and is mounted facing the metal plate with only a few thousandths of an inch space between them. With the element so
mounted, there is no such thing as on-axis; all the sounds
reaching the microphone will come in scooting along the mount-

* PZM'

and Pressure Zone Microphone' are trademarks of Crown Inc.



Table of Contents for the Digital Edition of Theatre Design & Technology - Winter 1981

Contents
Theatre Design & Technology - Winter 1981 - 1
Theatre Design & Technology - Winter 1981 - 2
Theatre Design & Technology - Winter 1981 - 3
Theatre Design & Technology - Winter 1981 - Contents
Theatre Design & Technology - Winter 1981 - 5
Theatre Design & Technology - Winter 1981 - 6
Theatre Design & Technology - Winter 1981 - 7
Theatre Design & Technology - Winter 1981 - 8
Theatre Design & Technology - Winter 1981 - 9
Theatre Design & Technology - Winter 1981 - 10
Theatre Design & Technology - Winter 1981 - 11
Theatre Design & Technology - Winter 1981 - 12
Theatre Design & Technology - Winter 1981 - 13
Theatre Design & Technology - Winter 1981 - 14
Theatre Design & Technology - Winter 1981 - 15
Theatre Design & Technology - Winter 1981 - 16
Theatre Design & Technology - Winter 1981 - 17
Theatre Design & Technology - Winter 1981 - 18
Theatre Design & Technology - Winter 1981 - 19
Theatre Design & Technology - Winter 1981 - 20
Theatre Design & Technology - Winter 1981 - 21
Theatre Design & Technology - Winter 1981 - 22
Theatre Design & Technology - Winter 1981 - 23
Theatre Design & Technology - Winter 1981 - 24
Theatre Design & Technology - Winter 1981 - 25
Theatre Design & Technology - Winter 1981 - 26
Theatre Design & Technology - Winter 1981 - 27
Theatre Design & Technology - Winter 1981 - 28
Theatre Design & Technology - Winter 1981 - 29
Theatre Design & Technology - Winter 1981 - 30
Theatre Design & Technology - Winter 1981 - 31
Theatre Design & Technology - Winter 1981 - 32
Theatre Design & Technology - Winter 1981 - 33
Theatre Design & Technology - Winter 1981 - 34
Theatre Design & Technology - Winter 1981 - 35
Theatre Design & Technology - Winter 1981 - 36
Theatre Design & Technology - Winter 1981 - 37
Theatre Design & Technology - Winter 1981 - 38
Theatre Design & Technology - Winter 1981 - 39
Theatre Design & Technology - Winter 1981 - 40
Theatre Design & Technology - Winter 1981 - 41
Theatre Design & Technology - Winter 1981 - 42
Theatre Design & Technology - Winter 1981 - 43
Theatre Design & Technology - Winter 1981 - 44
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http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1971Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1971May
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http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1970Dec
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http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1970Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965May
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