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Патент USA US2119272

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- May 31, 1938'.'
Filed July 5, 1934
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Patented May 31, 1938
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Bernard A. Engholm, Shaker Heights, Ohio, as
signor to The Bola Company, Cleveland, Ohio,
a‘ corporation of Ohio
Application July 5, 1934, Serial No. ‘733,757
2 Claims. (01. 179-4155)
This invention relates to loud speakers, such opening 13 into which the tip of the inner pole
for exampleas those, which utilize a moving coil piece extends, whereby an‘ annular air gap is
that operates in an air gap across a magnetic
?eld. Speakers, which have a magnetic ?eld that
is produced by a permanent magnet usually comprise a strip which is rectangular in cross section, and which has a width that is severaltimes
the thickness. The strip is generally arranged in
the form of a U and supports an inner pole piece
10 on the intermediate portion, and an outer pole
piece at the ends of the arms of the U.
The inner pole piece, heretofore, so far as I
am aware, has been a solid cylinder, the diameter of which has been considerably smaller than
it the width of the magnet. I have found however,
that such construction is objectionable in that
it restricts the extent to which the magnet can
be charged at the time of excitation. I believe
that the restriction is due to the fact that the
20 pole piece, because of its small size becomes saturated before the magnet, and thereby prohibits
the introduction of su?icient flux at the time of
excitation to saturate the magnet. As a result,
_ the flux distribution in the magnet does not have
s the desired degree of uniformity, and the density
is greatly impaired.
provided between the two pieces. A voice coil M
is removably mounted on a support !5, within
the air gap, and the support in turn is attached
to a diaphragm l6, which is illustrated as being
substantially conical in form. The interconnected
support and diaphragm are shown as being at
tached to a centering member I‘! which is rigidly
fastened at its inner periphery to the neck of 10
the diaphragm and at its outer periphery to the
clamping rings '9- The clamping rings in turn
may be attached to astationary diaphragm hous
ing 20, as by securing members 72 I.
I have found that if the inner pole piece is 15
made solid and of uniform diameter throughout
its length,‘and that if the diameter is less than
the width of the permanent magnet, that the
magnet can be charged, but that the extent of
it will be materially less than if the inner pole 20
piece were made in accordance with my inven
tion. The invention therefore, comprises a
structure in which the pole tip is circular in cross
section, within the region 0f the air gap but is
?ared outwardly from such region until it is sub- 25
stantially equal to the width of the _magnet.
An object of my invention therefore, is to make
a low reluctance pole structure, which when ap-
This is particularly ShOWn in Fig- 3- ‘ F01‘ @6011
omy of manufacture, I make the inner pole piece
plied to a permanent magnet enables it to be
of laminations and fasten'them rigidly together,
39 charged to a much greater degree than any con-
as by rivets.
struction heretofore designed, and of which I
The permanent magnetic ?eld structure, which
am aware. Furthermore, my invention is directed to a construction which, when the magnet
is in use will result in a ?eld of greater inten-
is produced by my invention, as described, great
1y increases the charge that can be imparted to
the magnet at the time of excitation, and pro
duces a structure that has more uniform flux 35
distribution over any type of pole structure here
tofore used.
sity and of more uniform ?ux distribution, for
a magnet of a given Size, and Which can be made
economically and readily assembled.
Referring now to the drawing, Fig. l'is a side
I c1aim:-— ’
elevation, partly in section, of a loud speaker hav40 mg 1'1 Permenent ?eld magnet; Fig- 2 is a real"
View Of the Speaker shown in Fig. 1, but on a
reduced Scale, with part Of the magnet broken
away to show the interior construction, and Fig.
3 is a sectional view taken through the magnet
45 to show the inner pole piece in side elevation.
The loud speaker with which I have illustrated my invention has a permanent magnetic
1_ In a loud speaker having a permanent mag
netic structure comprising a one-piece U-shaped 40
strip- having substantially uniform width through
out its length, and having an inner pole piece fas
tened thereto, the inner pole piece comprising a
plurality of ?at plates which extend parallel to
each other and in the same direction as the arms 45
of the U, and having an outer pole piece at
tached to the ends of the arms and having an
?eld structure, which comprises a U-shaped
magnetic strip iii, to- which an inner pole piece
mi N is rigidly connected, adjacent the midportion
thereof, and to which an outer pole piece I2 is
connected at the ends thereof. Pole pieces are
opening that cooperates with the inner pole piece
to provide an annular air gap, one end portion
of the plates forming a cylinder and the inter- 50
mediate portion of the plates being ?ared in
all planes which transversely cut the midportion
preferably attached to the strip 58 by welding,
although other forms of connection may be uti55 lized, if desired. The outer pole piece has an
of the U-shaped strip.
2. A magnetic structure for a loud speaker
comprising a permanent magnetic one piece 55
strip, an outer pole piece attached to the strip
nection thereto, the plates terminating at the
and having an opening therein, an inner pole
opposite end in a reduced cylindrical tip which
piece comprising a plurality of plates, means for
holding the plates in abutting face to face rela
tionship, each of said plates having a width equal
to that of said strip adjacent its point of con
projects into the opening in the outer pole piece
to provide an annular air gap.
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