[0001] The present invention generally relates to the field of electro-acoustical devices,
and more particularly, is directed to an apparatus and method for producing high fidelity
sound.
[0002] Electro-acoustical devices, or loudspeakers, emit variable acoustic pressures as
a function of variations in the electrical signals that are fed into them. Such devices
are formed of two main parts. The first is a transducer having electrical input terminals
for the feeding of electrical signals and a movable output component whose displacements
are linked to variations in the electrical signals. The second part is a movable component
in the shape of a plate or diaphragm connected mechanically to the movable transducer
component which ensures the emission of acoustic radiation corresponding to the electrical
signals fed into the device.
[0003] Devices of this type have been widely distributed but normally exhibit a serious
problem arising from the output obtained from the conversion of the energy applied
to produce displacement of the movable diaphragm. Indeed, the acoustic coupling associating
the direct-projection diaphragm and the air produces a low-level output since the
respective acoustic impedances of the diaphragm (high impedance) and the air (low
impedance) are very different.
[0004] For this reason, loudspeakers have been built utilizing an acoustic impedance converter,
i.e., a hollow funnel or horn in the general shape of a cone having a curved generator.
This curve will, most advantageously, be exponential. The conversion of acoustic impedance
takes place in the area located between the small section of the horn, or "throat,"
which corresponds to high impedance levels and where the movable diaphragm is installed,
and the main portion of the horn, or "mouth," which corresponds to low impedance levels
and which leads directly to the outside.
[0005] However, for a given mouth surface, the search for a high conversion ratio dictates
a very small throat area. Consequently, this also leads to a small surface-area of
the loudspeaker diaphragm, and thus, to severe limits to the power obtained from the
loudspeaker.
[0006] To overcome these limits, it has been suggested that a cavity, or intermediate chamber,
be placed between the movable diaphragm and the entrance to the throat. In this way,
the surface-area of the diaphragm could be greater than that of the throat. Transmission
of acoustical energy between the diaphragm and the throat would occur by means of
the compression of air confined in the chamber.
[0007] This type of compression-chamber loudspeaker possesses, however, a serious disadvantage.
The transmission of acoustical energy between the diaphragm and the throat, and therefore,
the proper functioning of the loudspeaker, takes place only within a limited frequency
range or band toward the treble frequencies. The compression chamber produces real
attenuation in this zone.
[0008] Reducing the distance between the diaphragm and the throat permits raising of the
cutoff frequency but introduces the risk of accidental contact of the diaphragm and
the mouth during high-amplitude displacements in the bass range. Thus limiting, here
again, the power that may be obtained from the loudspeaker. Furthermore, it should
be noted that acoustical emission from this type of loudspeaker is severely directional,
and occurs in the axis of the horn. In order to provide for a sizable angle of emission,
typically on the order of 40°, multiple horns, juxtaposed one to the others, or multi-cellular
horns, must be used.
[0009] Figure 1 illustrates a horn-equipped loudspeaker according to conventional technology.
It is comprised of an electro-acoustic transducer and a device for acoustic coupling
with the air. The transducer contains, first, a coil of conducting wire 1 with two
terminals 2 and 3. The coil is immersed in a magnetic field created by a magnet 4.
The transducer contains, second, a movable diaphragm 5 to which the coil is attached.
The air-coupling device contains a cavity or chamber 6 connected to a hollow horn
7 and having a small input opening 8, or "throat," and a large output opening 9, or
"mouth."
[0010] A loudspeaker of this type operates in the following way. The feeding of A.C. electric
voltage into the input terminal 2, 3 causes displacement of the moving coil 1 acted
upon by the magnetic field created by the magnet 4, and, as a result, displacement
of the transducer diaphragm 5. The acoustical energy thus created is propagated across
the chamber 6 toward the output throat 8 of the horn from which it is finally emitted
to the outside through the mouth 9.
[0011] The surface-area of the throat 8 must be small, to ensure effective coupling, i.e.,
adaptation of acoustic impedance, with the large surface-area of the mouth 9. However,
the surface-area of the diaphragm 5 must be large, in order to produce a high level
of acoustic power. These contradictory requirements are reconciled by the presence
of a chamber or cavity 6, whose internal air volume transmits acoustical energy as
a result of the elevated compressions and depressions which take place there, thus
obtaining acoustical impedance adaptation between the diaphragm 5 and the throat
8.
[0012] However, the use of a compression chamber 6 constitutes a serious disadvantage, mentioned
previously, consisting of the limitation of the transmission of treble frequencies
and leading to an elevated "cutoff frequency" beyond which acoustical energy is no
longer transmitted.
[0013] The loudspeaker of the present invention overcomes the above mentioned disadvantages
of prior art speakers.
[0014] One of the objectives of the present invention is to provide a horn-equipped loudspeaker
containing a movable diaphragm whose dimensions are significantly greater than those
of the throat of its horn without requiring recourse to a compression chamber.
[0015] Another objective of the present invention is the creation of a horn-equipped loudspeaker
permitting sizable displacements of the moving coil without risking accidental contact
of the diaphragm and the mouth.
[0016] A still further objective of the present invention is to provide a horn-equipped
loudspeaker ensuring acoustic emission in an angle extending up to 360°.
[0017] In the horn-equipped loudspeaker of the present invention, a portion of the horn
wall, which is located in the area of the throat and which is made up of the diaphragm
responsible for the emission of acoustic radiation, is made movable. More particularly,
the loud-speaker of the present invention is formed of an electro-acoustic transducer
which converts electrical signals into acoustic signals, a coil equipped with input
terminals for the application of the electrical signals and at least one movable
diaphragm for the emission of the acoustic signals. A hollow horn with conically-shaped
walls forming a small input area or throat and a large output area or mouth is also
provided. The speaker diaphragm is formed of a portion of the walls of the input area
of the horn.
[0018] The invention may be better understood using the following description based on the
attached drawings, in which:
Figure 1 illustrates a horn-equipped loudspeaker as known in the prior art.
Figure 2 illustrates a first embodiment of a loudspeaker according to the present
invention.
Figure 3 illustrates a second embodiment of a loudspeaker according to the present
invention.
Figure 4 illustrates a variation of the second embodiment of the horn-equipped loudspeaker
according to the present invention.
[0019] Figure 2 illustrates a first embodiment of the horn-equipped loudspeaker according
to the present invention. It contains an electro-acoustic transducer and a device
ensuring acoustical coupling with the air. The electro-acoustic transducer contains
a conducting coil 1 with two terminals 2, 3 and is immersed in the magnetic field
created by a magnet 4. It also contains a movable diaphragm 20, whose edges are supported
by a flexible spring suspension, such as 21, to which the coil is fastened.
[0020] The air-coupling device is formed of a hollow horn 22, with a throat, an input area
23, and an output area 24, or mouth. The movable diaphragm of the electro-acoustic
transducer is formed of a portion of the walls of the input area of the horn.
[0021] A loudspeaker in accordance with the above described construction produces a progressive
conversion of the acoustic impedance between the diaphragm and the horn without requiring
an intermediate compression chamber. As a result, it has no limits to the transmission
of treble frequencies between the diaphragm and the horn. There is no elevated "cutoff
frequency."
[0022] According to the invention, operation of the conversion of acoustical impedance between
the transducer and the horn of the loudspeaker depends on the progressively-increasing
distance separating the two walls of the horn located in the input area. Within the
horn, one of the walls 25 is stationary, and the other 27 is partially made up of
the movable diaphragm 20.
[0023] In the first portion of input area 23, displacements of the diaphragm involves a
small volume of air and as a result of the short distance to the wall, causes substantial
variations in pressure. In the final output area 26, on the other hand, the displacements
of the diaphragm involves large volumes of air and creates slight variations in pressure
as a result of the substantial distance between the diaphragm and the walls arranged
opposite to each other.
[0024] Furthermore, at distances further from the input area 23, the accumulated impedances
of the preceding sections of volume remains greater than the impedance of the following
section. In addition, the respective volumes and pressure variations vary inversely
between the input 23 and output 26 regions of the horn. This phenomenon effectively
constitutes the desired conversion of acoustic impedance.
[0025] Figure 3 shows a second embodiment of a loudspeaker according to the invention which
incorporates rotational symmetry. This embodiment results from a 360° rotation of
the structure of the horn-equipped loudspeaker shown in Figure 2 around an axis or
symmetry 39.
[0026] All of the loudspeaker components share this axis of symmetry. The electro-acoustic
transducer contains a moving coil 1 which activates a diaphragm 30 held in place
by flexible suspensions, such as 37 and 38. In accordance with this embodiment, the
diaphragm is a component of the input area of hollow horn 32 having conically-shaped
walls such as 34 and 35. Operation is identical to that of the loud-speaker shown
in Figure 2 and produces acoustical energy emitted mainly in the directions shown
in Figure 3 along the axis of symmetry 39. The energy-emitting surface also produces
two lobes 40 and 41.
[0027] Figure 4 shows a variant of the embodiment of the loudspeaker shown in Figure 3.
In this embodiment an energy-emitting surface having one lobe 50 is provided which
insures excellent directivity in the direction of the axis of symmetry 39. This result
is achieved by a reduction in the angle formed by the conical diaphragm 30 and its
axis of symmetry.
[0028] It should be obvious from the above-discussed apparatus embodiment that numerous
other variations and modifications of the apparatus of this invention are possible,
and such will readily occur to those skilled in the art. Accordingly, the scope of
this invention is not to be limited to the embodiment disclosed, but is to include
any such embodiments as may be encompassed within the scope of the claims appended
hereto.
1. In a loudspeaker, having an electro-acoustic transducer which converts electrical
signals into acoustical signals, a coil having input terminals for the feeding of
said electrical signals, at least one movable diaphragm for the emission of said acoustical
signals, a hollow horn with walls placed opposite to each other with progressively-increasing
separation between them, wherein said horn having a small input area and a large output
area, the improvement comprising:
said diaphragm being formed of a portion of one of the walls of said horn in said
input area.
2. A loudspeaker according to Claim 1, wherein said walls of said horn and said diaphragm
are formed of rotational surfaces around a common axis of symmetry.
3. A loudspeaker according to Claim 2, wherein said movable diaphragm is displaced
by the action of said electric coil, said coil being displaced in a magnetic circuit,
said diaphragm, said coil, and said magnetic circuit having the same axis of symmetry.
4. A loudspeaker according to Claim 1, wherein the spacing between the walls of said
horn is in accordance with a linear function.
5. A loudspeaker according to Claim 1, wherein the spacing between the walls of said
horn is in accordance with an exponential function.
6. A sound reproducing device, said device comprising:
a horn having oppositely opposed side walls separated by a progressively increasing
distance;
an electric coil having input terminals for receiving an electrical signal corresponding
to a sound to be reproduced;
magnetic means for producing a magnetic field around said electric coil; and
a movable diaphragm coupled to said coil and adapted to move in accordance with said
electrical signal, said diaphragm being formed as a portion of one of said side walls.
7. A sound reproducing device according to Claim 6, wherein said diaphragm is suspended
along said side wall by spring means for permitting said diaphragm to free move in
response to said electric signal.
8. A sound reproducing device according to Claim 6, wherein said side walls are formed
of rotational surfaces around a common axis of symmetry.
9. A sound reproducing device according to Claim 6, wherein said diaphragm and said
magnetic means have the same axis of symmetry as the side wall opposite said diaphragm.
10. A method of producing high fidelity sound from a loud speaker having oppositely
opposed side walls separated by progressively increasing distances, an electric coil
having an input terminal for receiving an electrical signal corresponding to a sound
to be reproduced, wherein said coil is surrounded by a magnetic field and is coupled
to be a diaphragm which is adapted to move in accordance with said electrical signal,
said method comprising the step of:
forming said diaphragm as a portion of one of said side walls.