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Патент USA US2127110

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Aug. 16, y 1938.
2,127,110
c. |_. FARRAND
ACOUSTIC DEVICE
Filed Aug. 3, 1956
2 SheeJts-Sheet 1
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Aug. 16, 1938.4
2,127,110
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ACOUSTIC DEVICE
Filed Aug. 3, 1956
ZISheets-Sheet 2
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INVENTOR.
CLA/z2 L. “F.'AQQA/va
BY4
ATTORNEY.
Patented Aug. 16, 1938
2,127,110:
UNITED STATES PATENT CFFICE
2,127,110
ACOUSTIC DEVICE
Clair L. Farrand, Beverly Hills, Calif., assigner to
United Research Corporation, Burbank, Calif.,
a corporation of Delaware
Application August 3, 1936, Serial No. 94,072
10 Claims.
This invention relates to loud speakers.
It is well known in the art to allocate a part of
the acoustic range of a sound reproducing apparatus toy one type of loud speaker and another
5 part or parts to another type (or other types) of
loud speaker.
_
. This invention relates to the type of loud
(Cl. 181-31)
is provided around the core 3, and receives a
Supply of direct current so as to produce a con
stant magnetic flux between the two separated
pole pieces 4 and 6.
As will be noted in Fig. 2, the adjacent outer 511
and inner edges of the pole pieces, 4 and 6, ref
spectively, are undercut as at I0, leaving only a
speaker useful in a so-called two-way system,
wherein the acoustic range is handled by only
l0 two types of loud speakers, the type of loud
speaker of the present invention being particu-
short length of parallel, closely adjacent,`pole
faces at I|. The space thus provided between
the parallel faces II of the pole pieces 4v and 6, l‘òïï l
larly adapted to reproduce acoustic frequencies
from about three hundred cycles to the upper
limit, i. e., eight thousand cycles or higher.
l5
The objects of the present invention comprise
an `efficient reproduction of sound waves over a
wide frequency range, with large power, and
annular diaphragm I3. The diaphragm I3 is
supported below its inner and outer edges by
means of inner and outer concentric supporting
rings I4 and |41, respectively. Upper concentric 1%?
clamping rings l5 and I6 Clamp the edges 0f tho’
diaphragm upon the supporting rings I4 and I41
while attaining a substantially uniform distribu_ tion of the soundwaves, particularly of the higher
20 frequencies which have a tendency to remain in
a narrow beam.
The novel features of one embodiment of rthe
invention will be described in the accompanying
speciñcation, and particularized in the appended
25 claims in connection with the .accompanying
by means of bolts I'I.
A frusto-conical member I8, with a co-exten
sive conical member I9, secured together and to 20
the upper surface of the inner clamping ring I5
by means o-f bolts 20 and the central bolt 5, and
a casing member 2|, all concentric with the dia
phragm I3, form an annular sound passage 22
leading to the central portion of the annular 25
drawings, wherein;
Fig. 1 is a sectional elevational View of a loud
speaker embodying the present invention.
Fig. 2 is an enlarged fragmentary sectional
30 View of the annular diaphragm and the accompanying sound chamber forming parts.
Fig. 3 is a front view looking toward the mouth
portions of the nested horn assembly.
Fig. 4 isl a plan sectional y View through the
35 throat block and is taken along the line 4-4 of
Fig, 1_
Fig. 5 is 'a sectional plan view through the
lower set of diaphragm clamping rings and is
taken along the line 5_5 of Fig. 1.
40
Fig. 6 is a. bottom plan View of a portion of the
annular diaphragm showing the connection of
accommodates the voice or driving coil I2- of an
diaphragm I3.
The annular sound passage 22, at the tip of the
conical member I9, communicates with a tubular
passage 23 formed in an adapter 24. This pas
Sage 23 iS CO-EXÈGDSNB With a Similar passage 25 30
formed in a throat block 26.
Adapter 24 is fitted in a Counter-bored portion
on the topi of the casing member 2|, and has an'
annular shoulder portion 241, which is engaged by
a locking nut 21 threadably secured to the cas- 35
ing member 2|. 'I‘he throat block 26 is thread-r
ably scoured at 261 to thoupper portion of
adapter 24. The upper portion of the throat
block 26 is formed in a funnelfshape having
divergíïlg flanges 28, S0 aS t0 I‘eCeíVo the thI‘OaÈ 40
DOI'ÈÍOHS Of a plurality `0f 110m SSCÈÍOHS 29`t0 44,
the Voice coil thereto.
Referring now to Figs. 1 and 5, the driving unit
I of the loud speaker comprises a U shaped mag45 netic frame 2, having a central core 3 of magnetic material secured thereto. A circular plate
4, comprising an inner pole piece, is provided on
the upper surface of the core 3, and this assembly, including the frame 2, core 3, and pole
50 piece 4, is secured together by means of a bolt 5.
inclusive. A suitable cement 54 is provided to
secure the throat portions of the various horns
together between the flanges 28 of the throat
block 26. These various‘horns‘are all identical 45
in Shape and SiZey having their IODgïtudinal aXeS`
diverging from each other away from their throat
portions. This arrangement of nested horn sec
tions eliminates the well known directional or
beam effect of the higher'frequencies by means 50
An annular plate 6, comprising an outer pole
piece, is secured to the magnetic frame 2 by
means of bolts '|, with its inner edge concentric
with and closely adjacent to the outer edge of the
55 inner pole piece 4. An electro-magnetic coil 9
of the approximate spherical surface formed by
the combined mouth opening 45 thereof. That is,
in the case of a spherical source of sound, suchl
as a diaphragm in the shape of a sphere, the sur
face of which vibrates radially in accordance 55
2
2,127,110
with the frequency and amplitude at every point
thereon, sound would be radiated through the
entire frequency range, including the higher fre
quencies, in all directions. In case, however, the
source from which the sound is radiated consti
tutes only a segmental portion of a sphere, this
uniform sound radiation would still prevail
through the solid angle subtending the segmental
surfaces and the center of curvature thereof.
10 This condition is approximated by the nested
horn assembly 29 to 44, inclusive, by angularly
disposing the longitudinal axes thereof so as to
form at their combined mouth opening a spheri
cal segment from which the sound is radiated
15 into the atmosphere. It will thus be seen that
the individual sound waves propagated in the
various horns will have exactly the same charac
teristics and will be so timed that they will unite
at the combined mouth opening to form a spheri
20 cal wave front. The combined throat opening 46
of the various horns 29 to 44, inclusive, is also
in the shape of a spherical segment. Preferably,
the height of the segmental surface thus formed,
as indicated by the dimension “A”. between the
single throat opening of the center horn 43 and
the chordal line passing through the throat por
tions of the outer horns 29 and 35 (Fig. l) is of
the order of one-quarter wave-length of the high
est frequency sound to be reproduced so as to
3.01 prevent distortion and/ or cancellation of a nearly
`planar wave front on entering the combined
throat opening 46 and emerging from the com
bined mouth opening 45. It will be seen, there
fore, that since all of the horns are of the same
3.5'. length, intersection “B” of the longitudinal axes
of the horns also forms the center of curvature
for both the combined throat openings 46 and
the combined mouth openings 45.
As will be seen in Fig. 3, the combined throat
portion as indicated by the dotted line 461 is
rectangular in shape and opens into the sound
passage 25 of the throat block 26, which is of the
same rectangular shape and size in cross-section
at its upper end (Fig. 4). The passage 25 and
45.. the co-extensive passage 23 in the adapter 24
gradually change in cross-sectional shape until
they assume a substantially circular cross-sec
ticular auditorium or theatre in which the loud
speaker is to be placed. The length and rate of
taper of the various horns is determined by the
lowest frequency sound to be reproduced and are
preferably such that the smallest dimension of
the combined mouth opening of the various horns
is on the order of one-half of the wavelength of
the lowest frequency to be radiated.
Referring to Fig. 2 it will be noted that the
annular diaphragm I3, which in the present case 10
is constructed of Duralumin on the order of .002
inch in thickness, comprises, in radial cross-sec
tion, an annular trough 46, with relatively
smaller annular corrugations 41 and 48 on either
side thereof. These corrugations 41 and 48 in 15
crease the flexibility at the edge to allow the an
nular trough portion 46 to be reciprocated as a
rigid section by the voice coil I2. The sound
chamber or sound box 49, as defined by the upper
surface of the diaphragm I3 and the lower sur 20
faces Aof the ring I6 and member I8, closely fol
lows the contour of the cross-sectional shape of
diaphragm I3. That is,-the under surfaces ofthe
ring I6 and member I8, directly above the active
portion of diaphragm I3, are similar in shape to 25
the cross-sectional form of the annular trough 46
and corrugations 41 and 48. However, the curva
ture of the bottom surfaces of the ring I6 and
member I8, directly opposite the trough portion
46, and which extend thereinto, is slightly less 30
than that of this trough portion.
The distance from the annular throat opening
55 of the annular passage 22 to the inner and
outer edges of the diaphragm sound chamber 49,
or in other words, to the supported edges of the 3,5
diaphragm I3, is of the order of one quarter
wavelength of the highest frequency sound in
tended to be reproduced. In the present case,
the dimension is about 0.4 inch. Thus, there will
be no undue cancellation of a sound wave of 8000
cycles generated in the chamber 49 due to the
difference between the time required for a wave
originating at the extreme inner or outer edge of
the diaphragm I3 to enter the sound opening 55
and the time required for a corresponding wave
generated at the central portion of the trough
46 of diaphragm I3 to enter the same sound
opening 55. If, for example, this distance be
tween the supported edges of diaphragm I3 and
tion adjacent the tip of the plug I6.
Preferably, the annular passage 22, tubular
_passages 23 and 25, and the passages forming
the various individual horns 29 to 44, inclusive,
the opening 55 were as great as one-half the
have an exponential rate of taper or exponential
rate of cross-sectional increase along the lengths
thereof, increasing from the throat to the mouth
tended to be reproduced, a wave originating at
the furthermost point in the chamber 49 would
be 180° out of phase with a wave originating at
55. portions thereof, this rate being the same
throughout. The size of these various passages
a point directly opposite the opening 55 and
therefore the two waves would cancel each other.
Referring to Figs. 2 and 6, the Voice coil I2 is
secured to the central portion of the annular
is determined by the upper and lower frequency
limits. For example, the size of the throat open
ing of the annular passage 22, adjacent the dia:
60 phragm I3, is determined by the amount of air
velocity change between the diaphragm chamber
and the annular passage 22. The limiting factor
in making the throat of passage 22 as small as
possible is the frictional resistance of the air with
65 the walls of passage 22 when moving at the in
creased velocity and `the harmonic distortion
which results when the instantaneous pressures
depart too far from atmospheric pressure. The
4,0
wavelength of the highest frequency sound in
tro-ugh 46, directly below the annular sound pas
sage 22. This construction allows »the driving
force, i. e., the coil I2, to be directly in the center
of the plunger portion, i. e.. the trough 46 of dia
phragm I3, and also directly in line with the exit
of sound through the passage 22. .As will be
noted in Figs. 2 and 6, the drivingl or Voice coil
I2 is secured to the central portion of diaphragm
I3 by means of a cylindrical support 56 of card
board or the like material around which coil I2
number of horns is determined by the solid angle
through which the sound, particularly of the
higher frequencies, is to be distributed. In the
present case (Fig. 3), the horns are arranged in
is wound. One edge of theV support 56 is serrated
with alternate serrations 51 and 58, etc., extend 70
ñve Vertical rows with three horns in each row.
the under surface of the annular trough portion
45.
Vents 59 (Figs. 2 and 5) in the form of a plu 7.5
This particular arrangement of horns, however,
may be varied to suit the conditions of the par
ing on the same side, horizontally, to form a base
which may be cemented or otherwise secured to
3
2,127,110
rality of holes arranged in a concentric path
about the diaphragm I3 are provided in the inner
l pole piece 4 to communicate the inner back
the inlets of the outside horns, to the inlets of
the center horns, and the distance from the edges
of the annular diaphragm to the sound exit open
chamber 6‘0, formed between the back surface of
diaphragm I3, pole piece 4 and ring I4, with the
outer atmosphere. A second series of vents in the
form of radial slots 6I, provided in the dia
ing of said sound box portion being of the order '
phragm supporting ring M1, communicate the
5. An acoustic device in accordance with claim
4 in which the back of said diaphragm is con
nected with the open air through a plurality of 10
outer back chamber 62, formed by the back sur
face of diaphragm I3, outer pole piece 6 and ring
M1, with the outer atmosphere. These two series
of one-quarter wavelength of the highest fre
quency to be produced, and means for driving
said diaphragm.
vents.
of vents thus >assist the very narrow spaces be
tween the voice coil I2 and the adjacent inner
6. An acoustic device in accordance with claim
4 in which said last mentioned means comprises
and outer edges II of the pole pieces 6 and 4',
respectively, in relieving the damping eiî'ect on
the diaphragm due to the practically enclosed
back chambers 60 and 62.
I claim:
1. An acoustic device comprising an .annular
a voice coil attached to the center of the convex
side of said diaphragm, said attachment compris
ing a serrated medium uniformly distributed on
said diaphragm about the line of attachment to
said coil.
'
.
7. A sound reproducer comprising an annular
diaphragm
having a central annular curved 20
diaphragm
having
a
single
annular
trough
thereY
20
trough body portion, a casing forming a sound
in, a housing forming a sound box for said dia
phragm, said sound box having a sound exit box for said diaphragm, and means for mounting
opening therein at the center of and within the said diaphragm, said body portion being sup
ported by said mounting means by flexible in
trough portion of said diaphragm, and means at
tegral inner and outer circumferential corrugated 25
tached
to
the
convex
side
of
said
trough
for
actu
25
portions concentric with said diaphragm.
ating said diaphragm.
8. A sound reproducer in accordance with claim
2. An acoustic device in accordance with claim
1 in which said last mentioned means comprises "7 wherein the corrugations of said corrugated
portions are small in comparison with said curved
a driving coil connected to said diaphragm di
30 rectly opposite said sound ein't opening in said i
housing.
3. An acoustic device in accordance with claim
1 in which said housing forming said sound box
has a convex portion thereof extending into» said
35 sound box and into the concave trough portion
of said diaphragm and conforming to the outline
of said trough.
l
4. An acoustic device comprising a sound pro
ducing unit having an annular diaphragm, iiex
40 ible corrugations at the edges thereof, a casing
forming a sound box for supporting the edges of
said diaphragm, said sound box having a sound
exit opening therein, a common throat portion
for said sound box, a plurality of horns connected
to said throat portion, the inlets of said horns
45
being arranged .along an arc concentric with the
arc along which the outlets of said horns are
arranged, the distance from the chord connecting
trough body portion.
30
9. A sound reproducer in accordance with claim
7 in which said sound box casing has a convex
portion thereof extending into and conforming
to the curvature of the annular curved trough
body portion of said diaphragm and also con 35
forming to the curvature of said corrugated por
tions.
10. An acoustic device comprising an annular
diaphragm having a central annular curved
trough portion with corrugated flexible inner and 40
outer portions, a casing forming a sound box
surrounding said diaphragm, said casing having
a convex portion thereof extending into and con
forming to the trough body portion of said dia
phragm, and a driving coil mounted along the 45
central portion and on the convex side of the
trough body portion of said diaphragm.
CLAIR L. FARRAND.
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