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Патент USA US3082308

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March 19, 1963
Filed Feb. 24, 1960
3 Sheets-Sheet 1
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H6 2
0” 45" 90’ 150" I55”
March 19, 1963
Filed Feb. 24, 1960
3 Sheets-Sheet 2
H6. 10
H6. 15
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March 19, 1963
Filed Feb. 24. 1960
3 Sheets-Sheet 3
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H6‘ 75
3000 H2
7000 Hz
5000 Hz
100 Hz
10000 Hz
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@ZOl-F 66!!!!‘
BY QM.“ fog-ma;
Patented Mar. 19, 1963
FIG. 2 shows frequency response curves of the conven
tional condenser microphone for various angles of sound
Rudolf Giirike, Vienna, Austria, assignor to Akustlsche
u. Kino-Gerate Gesellschaft m.b.H., Vienna, Austria,
21 ?rm
Filed Feb. 24, 1960, Ser. No. 10,718
Claims priority, application Austria Mar. 4, 1959
13 Claims. ((11. 179-111)
FIG. 3 is an exploded view showing an illustrative
embodiment of the invention having a unidirectional
FIG. 4 shows the microphone formed from the parts
of FIG. 3 in assembled condition,
FIG. 5 shows an illustrative embodiment of the present
invention having two diaphragms,
The known directional condenser microphones have 10
FIG. 6 shows a microphone according to the invention
having a bidirectional pattern,
only a small self-capacitance (about 30400 picofarads).
To obtain an adequate output voltage it is necessary, there
FIG. 7 shows a microphone according to the invention
having a prearranged diaphragm for protection against
fore, to combine such microphones in a unit with the ?rst
ampli?er stage or to connect them only by very short leads
with the associated ampli?er. This results in one case in a 15
FIG. 8 shows a microphone embodying the invention
relatively large microphone casing and in the other case
which can be changed over from a unidirectional pattern
in a reduction of the output voltage if the cable capacitance
to an omnidirectional pattern,
approaches the self-capacitance of the microphone. An
FIG. 9' shows a microphone according to the invention
increase of the dimensions of such a microphone button for
for stereophonic recording,
a directional condenser microphone with the aim of in
FIG. 10 shows the directional pattern of the micro
creasing the self-capacitance has been opposed by the fact
phone illustrated by FIG. 9,
that the diameter of the button must be approximately of
the order of magnitude of the Wavelength of the highest
frequency to be transmitted in order to obtain a directional
in FIG. 9,
FIG. 12 shows the directional pattern of the micro—
pattern which is largely independent of frequency because
only in this case is the pressure gradient at the diaphragm
linear up to the highest frequency to be transmitted. In ac~
FIG. 11 shows a modi?cation of the microphone shown
phone of FIG. 11,
FIGS. 13 and 14 show frequency response curves in
rectangular coordinates for microphones in accordance
with this invention,
cordance therewith the usual directional condenser micro_
phones have a button about 1.5-3 centimeters in diameter
FIG. 15 is a showing of the frequency response curves
and consequently only a low microphone capacitance.
in polar coordinates,
On the other hand, condenser microphones have been
FIG. 16 shows a microphone in accordance with this
disclosed which have a diaphragm area of about 40 square
invention having an elongated, narrow diaphragm.
centimeters and a capacity of up to about 1000‘ picofarads.
FIG. 17 shows the associated directional pattern for
Iowever, these microphones designed as pressure trans
higher frequencies, and
mitters do not have a frequency-independent directional 35
FIG. 18 shows a microphone embodying the invention
pattern. Owing to their high self-capacitance they may
in the form of a hexagonal pencil.
be arranged at a distance from the ampli?er and may be
The subject matter of the invention will be explained
connected to the latter by a long cable (up to 10 meters
more fully with reference to the above-mentioned ?gures.
and more).
As has already been stated initially hereinbefore, con
As contrasted therewith the invention relates to a direc 40 denser microphones constituting pressure transmitters
tional condenser microphone which has a frequency
having a large diaphragm are already known. FIG. 1
independent directional pattern as well as a high self
shows in polar coordinates, for different frequencies, the
capacitance and which for this reason is particularly suit
directional pattern of a microphone having a diaphragm
able for use with portable tape recorders because, as in
size of 4.5 X 9 centimeters. It is apparent that the direc
the case of a dynamic microphone, it may be connected
tional effect increases with an increase in frequency.
to the recording apparatus by a long cable whereas, com
FIG. 2 shows the frequency curves of the same micro
pared with the dynamic microphone, it has the advantage
that sound phenomena taking place at high speed (tran
sients) are transduced more accurately.
The directional
phone for various angles of sound incidence in polar
condenser microphone according to the invention belongs 50 . With such a transmitter the sound character of the
sound recording will depend on the distance of the sound
to the type in which the diaphragm is exposed to the sound
source from the microphone because the ratio of direct to
field on both sides and at least one phase shifting member
sound becomes dependent on distance. Besides,
is provided to provide for directional effect. The micro
the sound recordings made with such microphone are un
phone according to the invention is characterized in that
the diaphragm has an area of at least 10‘ square centi 55 natural owing to an exaggerated reverberation. For this
reason it has become generally accepted that the trans
meters and that the maximum dimension of the diaphragm,
mitter must be small relative to the wavelength of the
that is, the largest side of the diaphragm, in the case of a
highest frequency to be transmitted in order to obtain a
rectangular diaphragm, or the diameter of the diaphragm,
in the case of a circular diaphragm, is much larger than
frequency-independent directional pattern.
the wavelength of the highest frequency of the transmitted 60 The invention discards this opinion because the meas
ures according to the invention, which will be described
range and that the upper limiting frequency of the phase
hereinafter, enable even a condenser microphone having
shifting element approximates the frequency at which the
a relatively very large diaphragm to be designed for a
pressure gradient reaches its highest value.
frequency-independent directional pattern. The inven
If a bidirectional eifect is desired, frictional acoustic
resistance is provided between the diaphragm and electrode 65 tion relates to a-microphone the diaphragm of which is
either alone or in combination with frictional acoustic
resistance disposed directly on the rear of the cathode.
In the drawings which partly illustrate the state of the
exposed to the sound ?eld on both sides and which has a
su?‘iciently frequency-independent directional pattern in
spite of the large area of the diaphragm. For this reason
a perfect sound recording can be made even in rooms hav
art and partly illustrate embodiments of the invention,
FIG. 1 shows the directional pattern of a condenser 70 ing poor acoustic characteristics. It has also been found
microphone which is designed as a pressure transmitter
that cables having a length of up to 20 meters resulted
and has a large diaphragm in accordance with the prior art,
in a loss of only about 4 decibels. This does not involve a
modi?cation of the frequency response, as is known, be
cause only a voltage division occurs between the micro
the sealing frame 4. The diaphragm 7 is placed on the
electrode 5 and stressed by being adhesively connected at
its rim. On the side facing away from the electrode the
diaphragm is vapor-coated with a metal. The front cover
phone capacitance and the cable capacitance.
The invention provides further the use of a second dia
phragm, which may be electrically effective or ineffective.
In the former case different directional patterns can be
adjusted in a manner known per se by a change of the
polarizing voltage.
By the provision of two diaphragms the microphone
8 of the housing with the protective grid 80 or with open
ings forms the closure. The cable 9, which may be plas
ticeinsulated and have a shielded core and a length of
about 1.5 meter or more leads to the ampli?er.
In FIG. 4 the microphone of FIG. 3 is diagrammati
may be converted to a stereophonic microphone operat 10 cally shown in assembled condition. The diaphragm 7 is
supported by the threads 6 and by the rim of the electrode
ing on two separate channels.
5. The cavity 13 and the frictional acoustic resistance 2
Besides, the microphone may also be used as a speaker,
form the phase-shifting member, which according to the
e.g., for dictating apparatus. Owing to the high capacit
invention is effective at frequencies below 2000 cycles per
ance of the microphone a transformer may be connected
second and provides for a unidirectional pattern in this
thereto or a transistor ampli?er may be used which is as
sembled with the microphone to form a unit and which
FIG. 5 shows a microphone having two diaphragms 7a
may also generate the polarizing voltage and which gen
and 7b. One or both of said diaphragms may be elec
erates such a high audiofrequency output voltage that the
trically effective. It is known that different directional
alternating voltage can be transmitted on unshielded lines.
It is known that the directional pattern of a pressure 20 patterns can be set by electrical remote control where two
electrically conducting diaphragms are provided. A fric
transmitter is spherical as long as the wavelength of the
tional resistance 1:’) may be arranged between the elec
sound is small relative to the dimensions of the trans
trodes 5a and 51').
mitter. Beyond this range the pressure builds up to pro
A microphone having a bidirectional pattern is shown
vide a directional effect which increases with the fre
in FIG. 6. The diaphragm 17 of this microphone con~
quency. It is also known that the pressure gradient as a
tains only a perforated electrode 18 as an acoustically
driving force in a diaphragm exposed to the sound ?eld
effective element. The frictional resistance is formed
on both sides rises linearly until half the wavelength of the
between the diaphragm and the perforated electrode. An
sound approximately equals the sound detour around the
additional frictional resistance 19 may be provided. For
microphone, i.e. the sound path from the center of the
front side of the diaphragm to the center of the rear side 30 protection against moisture, a microphone as shown in
FIG. 4 may be provided with a slack, thin resilient dia~
of the diaphragm. The two effects described are obtained
phragm 20 (FIG. 7). To vary the directional pattern it is
almost at the same frequency so that the microphone be
possible in accordance with the invention to provide a
gins to show a directional effect due to a build-up of pres
mechanically actuable slide 21 (FIG. 8). When the
sure where the pressure gradient reaches its highest value.
openings of the housing 22 are closed the undirectional
As the limits are not de?nite, the transition is not strictly
pattern is changed to an omnidirectional pattern. The
de?ned so that it appears to be more suitable to consider
latter pattern, however, has the above-described disad
the phenomena which occur considerably above and be
vantages of being dependent on frequency, although this
low the critical frequency and then to draw conclusions
may the desirable for achieving certain acoustic effects.
regarding the behavior at the limiting frequency.
The mechanism may also serve to obtain the highest
At a frequency at which the sound detour corresponds
approximately to the wavelength the driving force effec
The microphone according to FIG. 5 may also be used
tive at the diaphragm due to the pressure gradient is
for stereophonic recording if the two diaphragms are con
theoretically zero. At the same frequency, however, the
nected to separate transmission channels I and II, as is
build-up of pressure on the front side of the diaphragm
is already effective so that the resultant driving force at 45 shown in FIG. 9. En this case the microphone is oriented
so that the diaphragm surfaces face the sound source.
the diaphragm is larger than zero. Practical experiments
The directional pattern is shown in FIG. 10. For stereo
have shown that disturbing effects are virtually absent.
With a diaphragm having an area of about 40 square
phonic recording two individual microphones according
to the invention may also be used which are disposed
50 close to each other for intensity recording and for A—B
stercophonic recording are ‘spaced from each other and
As is apparent from FIGS. 1 and 2 a unidirectional
arranged at an angle of 90° relative to each other.
effect is already obtained above 2000 cycles per second.
The diaphragms may be inclined relative to each other.
For this reason measures must be taken to provide for a
This is an arrangement which has already been provided
unidirectional effect below 2000 cycles per second. If
the diaphragm has a bidirectional pattern the directional 55 in small microphones (FIG. 11). The patterns will ob
viously also be inclined, as is shown in FIG. 12. In FIG.
effects are obtained above approximately 2000 cycles
13 the frequency response curves are shown which are
per second on both sides of the diaphragm.
obtained with the microphones according to the invention
In connection with small microphones, it is known to
for a sound incidence at 0°, 45°, 90°, 135° and 180°,
provide an unidirectional pattern by an RC member and
to provide a bidirectional effect by an R member disposed 60 whereas FIG. 14 shows the frequency response curves for
a microphone according to the invention having a bidirec
in back of the diaphragm. This is also utilized according
' tional pattern for 0°, 90° and 180°. FIG. 15 shows in
to the invention but these measures are effective accord
polar coordinates the characteristics of a unidirectional
ing to the invention only in the frequency range below
centimeters the critical frequency is about 2000 cycles per
approximately 2000 cycles per second.
microphone according to the invention. Without depart
trode 5 with parallel spacing threads 6 consisting, e.g.,
denser microphone in the form of, a hexagonal pencil. A
In FIG. 3 a ?rst illustrative embodiment of the inven 65 ing from the invention the diaphragm may have any de
sired proportions. For instance, a circular or oval form
tion is shown. The ?gure shows the components of
may be chosen provided that in accordance with the in
a condenser microphone having a unidirectional pattern.
vention the area of the diaphragm is suf?cient to ensure a
One or more layers of a sheetlike acoustic frictional
capacitance of approximately 1500 picofarads or more.
resistance 2, e.g., ?lter paper, are inserted in a sheet metal
casing 1 having a perforated bottom. A trough 3 consist 70 If the shape according to FIG. 16 is chosen a directional
pattern as ‘shown in FIG. 17 is obtained for the higher
ing, e.g., of plastic and having also a perforated bottom
sound frequencies. This may be desirable for certain
is placed on this resistance. An elastic sealing frame 4
applications. FIG. 18 is an enlarged view showing a con
of plastic is inserted in the trough. The perforated elec
of beads having a thickness of about 20 microns, rests on 75 hexagonal sleeve 21 is perforated on all side faces and
serves as an electrode. It is wound with spacing threads
22 and the diaphragm 23- is stretched on the outside over
these threads on three adjacent side surfaces. The three
side faces opposite to the diaphragm 23 are lined inside
the sleeve with ?lter paper 24, a textile insert or the like
forming an acoustic resistance. The ends of the sleeve
are closed by plugs, not shown.
I claim:
‘1. A directional condenser microphone for transmitting
7. A directional condenser microphone as in claim 3;
wherein said sheet material is textile fabric.
8. A directional condenser microphone as in claim 3;
wherein said perforated electrode is in the form of a hol
low sleeve having said spacing threads wound thereon,
said diaphragm covering a portion of the outer surface of
said perforated sleeve, and said sheet material covering
another portion of the surface of said sleeve.
9. A directional condenser microphone as in claim 8;
a predetermined frequency range; comprising at least one 10 wherein said sleeve is of hexagonal cross-section and has
diaphragm having front and rear faces with a minimum
six ?at outer surface areas, said diaphragm covering three
area of 10 square centimeters and a maximum dimension
of said surface areas and said sheet material covering the
substantially larger than the wavelength of the highest
remaining three of said surface areas.
frequency of said range, both of said faces- being exposed
10. A directional condenser microphone as in claim 2;
to the action of the sound ?eld; support means carrying 15 wherein said spacing threads are of silk.
said diaphragm; means constituting a frictional acoustic
11. A directional condenser microphone as in claim 2;
resistance; said support means, said rear face of the dia
wherein said spacing threads are of plastic.
phragm and said means constituting a frictional acoustic
12. A directional condenser microphone as in claim 1;
resistance de?ning a cavity; and said cavity and said fric
further comprising an additional diaphragm disposed at
tional acoustic resistance being operative as a phase-shift 20 the side of said phase-shifting element remote from the
ing element only up to a predetermined frequency in said
?rst mentioned diaphragm.
range at which one-half of the wavelength of sound is
13. A directional condenser microphone as in claim 12;
less than the effective length of the sound path from the
wherein said additional diaphragm is electrically inef
center of said front face of the diaphragm around the
microphone to the center of said rear face of the dia 25
References Cited in the ?le of this patent
2. A directional condenser microphone as in claim 1;
wherein said support means includes a perforated elec
Seibt _________________ __ Apr. 1, 1930
trode disposed at the rear face of the diaphragm and hav
Edelman ____________ __ Sept. 16, 1930
ing spacing threads on the surface of the electrode facing 30 1,776,112
toward said diaphragm, said diaphragm being secured, at
the periphery thereof, to said electrode.
Harry ________________ __ Oct. 30, 1945
Aamodt ______________ __ Aug. 17, 1954
3. A directional condenser microphone as in claim 2;
wherein said means constituting a frictional acoustic resist
ance includes porous sheet material disposed at the side 35
Grosskopf et al _________ __ Apr. 2, 1957
Schoeps et al. ________ __ Sept. 16, 1958
Morgan _______________ __ Jan. 5, 1960
‘Great Britain _________ __ Sept. 12, 1945
Germany _____________ __ July 27, 1953
Germany ____________ __ Nov. 18, 1954
of said electrode facing away from said diaphragm.
4. A directional condenser microphone as in claim 3;
wherein said support means further includes means spac~
ing said sheet material from said electrode.
5. A directional condenser microphone as in claim 3; 40
wherein said sheet material is against said side of the
electrode facing away from the diaphragm.
6. A directional condenser microphone as in claim 3;
wherein said sheet material is ?lter paper.
Acoustics, Beranek, 1954, pp. 149-1150‘.
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