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Патент USA US2121941

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June 28, 1938. ‘
<5. WURDEL '
‘
2,121,941’
sounn 'rmmsmmme APPARATUS
Filed June 12, 1935
..
.
2,121,941
Patented June 28, 1938
/
.
UNITED STATES PATENT OFFICE
2,121,941
SOUND TRANSMITTING APPARATUS
‘
Giinther Wurdel, Berlin, Germany, assignor to
Apparatebau Gesellschaft Neumann & Borm
Kommanditgesellschaft, Berlin, Germany
imman- June 12, 1935, Serial No. 26,271
In Germany August 25, 1934 I
10 Claims. (01. ria-ms)
This invention relates to a sound-transmitting
apparatus for telephone systems.
The primary object- of the invention is to pro
vide a telephone for vuse under conditions ‘where
6 by a telephone of the oridnary kind will not give
satisfactory results owing to interfering noises, as
for instance in the engine rooms of ships, in air
‘.craft, or in numerous other instances in which
prevailing noises will completely drown the voice
, 10 of the person speaking.
A further ‘object of the invention is to provide
a microphone free from chattering effect and hav
' ing a practically straight characteristic which is
devoid of resonance in the audible range.
15
By chattering effect is meant the reverberatory
' effect or non-linear distortion which arises in the
case of ordinary telephone microphones due to
the fact that, owing to the mechanical natureand
v
disposal of the diaphragm, the movement of the.
i0 diaphragm is not equal on both sides.
A still further object is to provide a telephone
in which the effective surface of the microphone,
whilst in other sounds an exaggerated emphasis
on the initial part of the sound causesa com
plete distortion of the tone.
~
To avoid the disadvantages associated with .
laryngeal microphones attempts have been made‘ 5 t'
to employ microphones which are excited by
sound in the air, and in which there are provided
special auxiliary means, for example screening
or damping means, which have the object of
withholding interfering noises from the micro-. 10
phone. Screening and damping means of this
kind certainly cause a decrease of the interfering
noises at the effective microphone surface, but at , '
the same time they also nullify a part of the voice
energy to a similar extent.. Moreover when using 15 '
the microphones hitherto .usual for telephonic
purposes it is impossible to hold the same as close
to the mouth as would be desirable, as owing to
the greatly increased voice energy impinging on
the surface of the microphone the distortion of 20 ‘ ‘
the speech would in this case be so considerable
as to render intelligibility impossible. These dis
when the telephone is in use, is situated in a tortions are caused by the fact that the micro
plane passing through the corner of the mouth ' phones, when a certain volume of sound is ex
ceeded, are overmodulated. A distortion of‘ the 25
.. of the speaker.
A further object is to make provision‘ for exci
‘ speech also occurs when the microphone is ap
tation of ‘ the effective surface of the microphone proached too closely towards the mouth because -
‘in immediate fashion by the spoken words.
These and other objects and advantages of the
invention will become apparent as the description
proceeds.
_
. It has already been proposed to employ in
rooms in which there is a considerable volume of
noise laryngeal microphones, which receive the
'' speech vibrations by'being placed against the
larynx or the lower jaw of the speaker.
Even
with microphones of this kind, however, it is
mereyl possible to a limited extent to preclude the
effect of interfering noises. The articulation is
also unsatisfactory, because the higher speech os
cillations, which are particularly important for
proper intelligibility, are, despite the location of
the microphone against the larynx or the jaw,
in1 the case of the carbon microphones hitherto
used for telephonic purposes the particles of car
bon do not, as 'a result of the very high exciting 30
intensity, oscillate properly about a ?xed position
of‘equilibrium‘, but are thrown out of their origi
nal position and do not again return to the same.
There then occurs .what I have termed a chatter
ing effect.
_ '
‘
'
35
Assuming an attempt is made so to construct
the damping means above referred to that the
overmodulation or the chattering effect of the
microphone is eliminated,_this will also not lead a
to the desired result, as the frequency character- 40
istic of the microphone is not disposed in a ~
straight line but possesses powerful resonance
points at numerous points-of the audible range.
absorbed by the intermediately disposed skin,‘ Generally speaking, interfering noises are not
‘5 which/acts as a cushion, and in consequence do
not ‘wholly reach the microphone. Moreover in
numerous spokensounds there is no appreciable
. vibration on the part of the jaw or the larynx,
Any attempt to overcome the strong drop in
the alternating potentials delivered by the laryn
geal microphone in the range of the higher speech
oscillations by the‘ inclusion of rectifying ele
ments between the microphone and the sound re
producing means does also ‘not lead to the de
55 sired'resvult, as the drop in the directiontowards
the higher speechoscillations'does not take place
evenly, i. e., in a straight line, but is disturbed by
the fact that in'the case of numerous spoken
sounds, particularly sibilant sounds, there is no
.0 conduction of the sound on the part of the body,
con?ned to a narrow section of the entire sound 45
range. Accordingly, at resonance points of the
microphone affected by corresponding interfering
‘ frequencies, the alternating potentials delivered
by the microphone increase to such extent that
the interfering noise occurs in a much more pow- 50
erful form at the reproducing apparatus than is
represented by the ratio between interfering I
noise and voice energy at the microphone. It is, '
therefore, impossible to obtain a proper reproduc
tion of speech in noisy rooms with the micro- 55
phones of poor frequency characteristic hereto~
fore employed for telephonic purposes.
.
Microphones are known, which possess a good ,7
frequency characteristic, that is to say-which do
not reveal any or any appreciable resonance o0
2
2,121,941
points within the entire audible range. These
microphones accordingly reproduce the voice en
ergy passed to the same without any appreciable
distortion. Their frequency characteristic, there
fore, is disposed practically in a straight line, i. e.,
is devoid of resonance points.
These micro
,
Figs. 3 and 4 are front and side views of the,
form of embodiment of the telephone according
to Fig. 2, Fig. 4 being partly in section. .
‘Figs. 5 and 6 are front and side views of a
modi?ed form of embodiment of the telephone.
In the diagram according to Fig. 1_ the curve ’
phones, which may be constructed as contact I a-b shows in millivolts the alternating poten
or also condenser or electro-dynamic sound
tial delivered by a. microphone approached more
transmitters have heretofore been employed for and more towards the source of sound, 1. e.,
10 radio transmitters, the making of talking ma
chine records and for sound-film purposes, as
in these cases it is necessary to attain a very
natural reproduction of speech and music, which
would be impossible with the carbon micro
15 phones employed in the telephonic. art. Micro
phones having a good frequency characteristic
have heretofore not been employed at all for
telephonic purposes, primarily on account of
their small sensitivity, which renders necessary
20 an ampli?cation of the alternating potentials
of the microphone.
-
a
It is shown by this diagram that the sound
energy in the range of the usual spacing of the
effective surface of the microphone from the
source of sound, 1. e., in the range of approxi
supplied by them. It is quite readily possible,
mately 40 to '70 mm., is completely covered by
without detriment to the good properties of the
same, to construct these microphones in a small
size suitable for the purposes of the present in
vention. 0f the microphones of good frequency
characteristic above referred to the contact
sound is greatly approached towards the micro
phone, i. e., to within approximately 6 mm., the
the interfering energyie-d). ‘ If the source of
alternating potential delivered by the micro
transmitter possesses a comparatively good sen
phone increases in the case of the example shown
in the diagram to more than ten times the value
sitivity.
of the interfering potential.
.
Now it has been ascertained that microphones
30 of good frequency characteristic also have no
chattering effect even if-in departure from the
mode of use hitherto usual-the effective sur
face of the microphone is approached as close
as possible towards the mouth, where the sound
85 output of the speech possesses its maximum
value.
This necessitates that the microphone,
also in contradistinction to the sound transmit
ters previously employed for telephonic purposes,
does not have a mouthpiece or the like. Hereto
40 fore it has been the general impression that a
mouthpiece of the elongated or trumpet variety
could not be dispensed with as this served to
withhold at least in part the interfering noises
and to exert a favorable effect on the frequency,
45 characteristic of the microphone.
If, however,
in the case of the microphone of straight fre
quency characteristic employed according to the
invention a trumpet or similar mouthpiece ‘were
employed, the column of air enclosed within the
50 mouthpiece and acting as resonator would also
be caused to oscillate by some frequency of the
interfering noise. The interfering noise audible
in the receiver would accordingly assume a dif
ferent character in tone, and would be ‘much
55 stronger than would correspond with the in
tensity of the sound at the sound inlet aperture.
It is known in itself in the acoustical art that
the sound output increases approximately ac
cording to a quadratic function with approach
towards the sound source. It has, however, not
been appreciated heretofore that the'sound out-'
put assumes in the immediate vicinity of the
mouth, 1. e., at the point of the sound generation,
enormous values which are incapable of being
65 measured even with the apparatus available at
the present time.
70
dependent on the distance, measured in milli
metres,,of a source of sound with constant sound
energy from the microphone. The broken line
0-0‘. indicates the intensity of an interfering
noise in the same room, this intensity remaining
the same at the point of the effective surface 16
-
-
The steep ascent
of the curve a-b in the case of small spacial
disposal provides a certain indication of the un- '
usual extent to which the potential delivered by
the microphone will rise when the microphone is
approached even more towards the sound source,
1. e., is moved immediately up to the latter.
It will accordingly be obvious from the above
that the approach of the effective surface of the
microphone of good, i. e., straightfrequency char
acteristic employed according to the invention
immediately up to the mouth of the person
speaking is of decisive importance. Since the
ratio between voice energy and interfering energy
at the effective surface of a microphone situated
immediately against the source of sound is ex
ceptionally favorable. particular precautions do
not require to be taken to withhold the interfer
ing noise from the microphone. Practical ex
periments have shown that with the apparatus
according to the invention proper and faultless
intelligibility is capable of being obtained even if
the unprotected ear is acted upon even to the
extent of a sensation of pain.
.
It has also been found thatv particular ad
vantage is obtained if the current of air pro
duced upon speaking is not allowed to impinge
vertically on the surface of the microphone situ
ated immediately in front of the mouth and
thus exert a detrimental effect on the vibrations.
According to the invention, therefore, the effec
tive surface of the microphone arranged in the
immediate vicinity of the source of sound is dis
posed approximately parallel to the direction of
speech, 1. e., to the direction of movement of the
current of air formed upon speaking. With this
arrangement the current of air is more or less
able to sweep past the surface of the microphone,
so that it is then unable appreciably to distort
The invention will be described more fully
with reference to the accompanying drawing, in
the alternating potentials delivered by the micro
phone. Preferably the holding member for the
which
on the distance of the latter from the source of
microphone is so constructed that the effective
surface of the microphone when the receiver is 70
placed against the ear is situated at the corner
of the mouth.
sound.
Fig. 2 is a perspective view showing the tele
microphone surface 2, which is located in a pro
‘
Fig. 1 is a diagram showing the alternating
potential delivered by a microphone dependent
75 phone according to the invention in actual use.
As shown, for, example, by Fig. 2, the effective
tective casing I,‘is situated, when the holding
3
9,121,941
' member 3 with the receiver 4 is lifted to the ear,~ ' at the corner of the mouth'of-the user and’in a
' ,very' close ‘to the comer of the mouth of the plane parallel to the breath currents of the user. '
‘speaker.
The microphone, therefore, as shown .
in Fig. 4, is not furnished with the usual trumpet
like or similarly shaped mouthpiece. vAs stated
above, there is‘ employed a. microphone with good,
5. In a telephone transmitting and receiving
set, a non-mouthpiece microphone casing and a
microphone free of chattering e?z‘ect and having
a‘ practically straight-line frequency character
istic in the audible range, the said microphone
being mounted forwardly in the said casing, and
In the forms ‘of embodiment, shown in the the construction and arrangement being ‘such
that the. effective surface of the microphone is
10 drawing the holding member 3 has af?xed there
movably disposed in the immediate vicinity of
‘ torboth the transmitter l, 2 as well as they re
ceiver 4. Naturally, as» regards the invention, the speaker's mouth to positions substantially
' it'is quite immaterial whether the ‘microphone parallel to, the direction of speech‘when the tele
i. e., approximately straight frequency‘ charac
teristic not revealing a chattering effect.
and the receiver are united in one holder, or
whether the holder,- which may be placed for ex
phone-is in use.
-
Y
6._In a telephone transmitting and receiving 15
set, a non-mouthpiece. microphone casing‘, a
ample about the head,.carries merely. the trans
mitter I, 2. The essential feature is that the microphone free of chattering eifect‘and having a
surface of the microphone 2 is situated in the ' practically straight-line frequency characteristic
in the audible range, the said microphone being
immediate vicinity of the source of sound.
mounted with its effective surface forwardly in V20
To be able to adapt the requisite small spac
20
the said casing substantially parallel to the direc
ing of ' the effective microphone surface accord
ing to the invention to diiferentsizes of head the tion of speech when the telephone is in use, and
transmitter is secured ‘to the holding member ‘ means for moving the effective surface of the said
3 so as to. be adiustable in the plane of the microphone while maintaining the eifective sur-,
face thereof in the same plane to a position in the
microphone surface 2.
‘
I
_
In the form of embodiment according to Figs. _ immediate vicinity of the speaker's mouth irre
2 to 4 this adjustability is obtained by an arm - spective of the size of the head of the speaker. ‘L'A sound'transmitting device for telephone
5, which is eccentric and mounted to be rotatable
in a corresponding abutment 8 on the holding systems intended for use more particularly under
‘so member. In this way it ‘is a simple matter to noisy conditions, comprising a microphone, free 30
adjust the transmitter in such fashion in relation from chattering effect and having a practically
straight frequency-characteristic, devoid of res
to the holding member in the plane of the micro
phone surface as to ensure the necessary mini-v onance in the audible range, said microphone be
mum spacing of the microphone surface from the ing adjustably mounted in a telephone set, so
that when the receiver is applied to the ear, the
source of sound.
In the form of embodiment ‘according to Figs. effective surface of the said microphone may be
5 and6the casing I of the'transmitter is mounted
tolbe oscillatory on the holding member 1 by
be situated in the immediate vicinity of the
means of an‘arm 1;
speaker’s mouth at one of the'corners thereof.
'
‘
I
‘
It will be understood that the invention is
not limited to the speci?c details of construc
tion illustrated in the drawing, and that nu
merous modifications ‘are quite possible within
.40
the meaning of the above description and the
45 annexed claims without departing from the spirit
of the invention.
What I claim as new and desire to secure by
1. A telephone transmitting and receiving set
comprising a rigid holder, a receiver mounted at
one end thereof and an abutment carried by
the other end of said holder, a microphone cas
‘ing having an arm eccentrically ?xedl'thereto,
said arm being rotatable on said abutment, and
a
microphone
of relatively low sensitivity
mounted in said casing.
f
2. The device as claimed in claim 1, in which
the plane of the effective surface of ‘the micro
phone is always parallel to the effective surface of
the
receiver.
"
,
'
‘
3. The device as claimed in claim 1, wherein
> the ‘microphone casing arm extends angularly
' from the casing.
8. A sound-‘transmitting device according to '
claim 7, in which the effective microphone sur
face arranged in the immediate vicinity of ‘the
source of speech is located‘ in a plane, which is
directed parallel 'or approximately parallel to
the direction of movement of the current of air
resulting upon the formation of the spoken
sounds.
-
‘
9. A receiving ‘and transmitting set for tele
Letters Patent is:
65
moved in a plane of the surface thereof so as to
,
4. A telephone transmitting and receiving set
comprising a holder, a sound receiving apparatus
mounted in said holder, a microphone free of
chattering effect and having a practically
' straight frequency characteristic which is devoid
_-of resonance in the audible range, adjustably
mounted at the other end of the holder, the con
struction and arrangement being such that when
L70, the sound. receiving apparatus is held to the ear.
the e?ective surface of the microphone may lie
phones, intended for use more particularly under
noisy conditions, comprising a stock, a receiver
mounted therein, an arm mounted in said stock,
a microphone free from chattering effect and '
having a practically straight frequency character
istic, devoid of resonance in the audible range,
mounted in said arm the axis of said microphone
being eccentric to the arm's axis of rotation and V
the plane of the'surface of said microphone par
allel to the face of the said receiver.
10. A telephone transmitting and receiving set,
comprising a holder,.a sound receiving apparatus ‘
mounted in said holder, 9. non-mouthpiece micro
phone casing mounted on the holder, a micro
phone free of chattering effect and having a prac
tically straight frequency characteristic which is
devoid of resonance in the audible range mounted 65
forwardly in the said casing, the construction and
arrangement being such that when the sound re
ceiving apparatus is held to the ear the effective
surface of the microphone may be moved to lie
at the corner of the mouth of the user and in a 70
plane parallel to the breath currents of the user.
GiiN'rrmR. 'WURDEL.
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