JP3084281B2 - Panel type speaker - Google Patents

Abstract

A panel-form loudspeaker has a resonant multi-mode radiator panel which is excited at frequencies above the fundamental frequency and the coincidence frequency of the panel to provide high radiation efficiency through multi-medal motions within the panel, in contrast to the pistonic motions required of conventional loudspeakers. The radiator panel is a skinned composite with a honeycomb or similar core and must be such that it has a ratio of bending stiffness to the third power of panel mass per unit area (in mks units) of at least 10 and preferably at least 100. An aluminium skinned, aluminium honeycomb cored composite can meet this more severe criterion easily. <IMAGE>

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonant multi-mode radiator suitable for applications requiring a thin loudspeaker section, such as in the case of loudspeakers.
iator). The loudspeaker exhibits a conversion efficiency close to 1, and is therefore suitable for applications requiring a high acoustic power output from the loudspeaker.

[0002]

2. Description of the Prior Art Conventional loudspeakers use a diaphragm or similar element that is substantially entirely reciprocated to produce an acoustic output. The movement of the diaphragm must be in phase over its entire surface so that the diaphragm moves forward and backward in response to the drive of the diaphragm drive, especially when the loudspeaker is This is achieved by the nature and size of the diaphragm relative to the frequency band required to operate over that band. Such speakers can operate at a frequency higher than the first resonance frequency of the diaphragm by appropriately attenuating the resonance mode of the diaphragm.
The diaphragm operates primarily at a lower frequency than the frequency at which the diaphragm exhibits a resonant mode, which places undesirable spatial and / or frequency restrictions on the speaker. Small diaphragms are used to increase the resonance frequency threshold, but these small diaphragms are not sufficient radiators at low frequencies.

There are two main types of speakers currently in use, both of which use a reciprocatingly driven diaphragm. A first type of loudspeaker is an electrostatic loudspeaker, in which the diaphragm has a charge generated between the diaphragm and a fixed back plate slightly spaced behind the diaphragm. Driven by the difference.
Electrostatic speakers are capable of producing high fidelity output over a wide frequency band and have a relatively flat shape suitable for loudspeaker applications. However, such electrostatic speakers are expensive and have very low conversion efficiencies that reduce the benefits of such speakers. Another established type of piston-like diaphragm speaker is a conventional dynamic speaker that includes an edge-mounted diaphragm driven by an electromechanical drive. Although such dynamic speakers have a relatively narrow band and are more efficient radiators than electrostatic speakers, they still have low conversion efficiency.
In this type of loudspeaker, it is necessary to prevent harmful interference between the forward output and the backward output of the diaphragm. This generally requires that the diaphragm be mounted on the front face of a rigid box housing, thus making a flat panel configuration impossible.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high conversion efficiency flat panel speaker having a frequency band at least suitable for loudspeaker applications. This goal is achieved by using the possibilities offered by some modern composite panels to make speakers that work in a novel way. For example, composite panels comprising a thin structural skin with a lightweight spacing core sandwiched therebetween are commonly used for aerospace structures, and some of these composite panels are It can be used in the speakers described in the range. Some sandwich-like panel materials are described, for example, in German Patent Specification GB 2010637A, G
B 2031691A, GB 2023375A, as previously disclosed for diaphragm structures in conventional dynamic speakers, to the best of the applicant's knowledge, such panel materials can be used in the method of the present invention in resonant multimode It has never been used as a radiator.

[0005]

SUMMARY OF THE INVENTION The claimed invention is directed to a transverse cellular construct.
a single sandwich panel formed of two material skins with a spacing core of (ruction) and said panel has at least 10 "bending stiffness (B)" versus "per unit surface area" in all directions. Panel mass
a resonant multi-mode radiator element, such as a panel having a (μ) cubed ratio, and mounting means for supporting the panel free or securing the panel to a support body without providing attenuation. An electromechanical drive coupled to the radiator panel to act to excite multi-mode resonance in the radiator panel in response to an electrical input within an operating frequency band for the speaker. .

[0006] The term "transverse cell structure" as used in the above definition and used elsewhere herein refers to a honeycomb core shape having a core cell extending through the thickness of the panel material. And other cellular based core construction with non-hexagonal core cross-section
Means

In the above definition of the invention, and throughout the specification and claims, all of the units used are
MKS units, specifically in the paragraph above
It is Nm and kg / m ^2. Applicants have determined that the value of the above ratio is "T"
And the T value specified above is necessary for the radiator panel to function properly in the required manner. Preferably, the value of T should be 100 or more. This T value is determined by the loudspeaker at its matching frequency (coi
A measure of the acoustic conversion efficiency of a radiator panel when operating as intended at frequencies above the ncidence frequency (see below). High T values are most suitably obtained by using honeycomb cored panels with thin metal skins. A currently preferred panel type is a panel having a honeycomb core structure and a thin skin, both of which core and skin are made of aluminum or aluminum alloy. In such a panel, a T value of 200 or more can be obtained. In the case of a solid plate material, it would probably not be possible to provide the required minimum value of T for any material. Solid steel panels, whatever the thickness, have a T value of about 0.5, well below the required T value.
Will have a value. A solid carbon fiber reinforced plastic sheet with equiaxed reinforcement would have a T value of about 0.85, which is also well below the required minimum. The mode of operation of the claimed loudspeaker is fundamentally different from prior art diaphragm loudspeakers having a substantially "reciprocating" diaphragm movement. As mentioned above, such conventional loudspeakers are intended to cause reciprocating and in-phase motion of the diaphragm, and furthermore, the diaphragm is designed so as to eliminate the mode resonance motion of the diaphragm from the speaker frequency band. It is intended to avoid modal resonance motion of the diaphragm by doing so and / or by incorporating appropriate damping to suppress the modal resonance motion of the diaphragm. In contrast, the present invention does not incorporate any conventional diaphragms, but rather multi-mode radiation that functions by exciting the resonant mode in the panel, rather than by moving the panel in a reciprocating, non-resonant manner. A panel meeting the above criteria is used as a container. The differences in this mode of operation are based on the "stiffness" vs. "mass" criteria, the avoidance of edge attenuation and the absence of internal attenuation layers in the radiator panel, as well as the coincidence and fundamental frequencies of the composite panel. Resulting from the operation of the radiator at frequencies above both.

[0008] The "match frequency" is the frequency at which the bending wave velocity of the radiator panel matches the sound velocity in air. This matching frequency is a kind of threshold for the efficient operation of the loudspeaker, since many of the modern composite sandwich panels radiate efficiently at frequencies above the loudspeaker's matching frequency. Using the information provided herein to fabricate a radiator panel suitable for a given frequency band, where the matching frequency of the radiator panel matches or falls below the required band. It is possible, and as a result, the loudspeaker will convert almost all of the mechanical input from the electromechanical drive to an acoustic output. This is more than just a requirement, since this feature of high conversion efficiency overcomes potential problems in systems based on resonant multimode radiators. The high conversion efficiency (which can be achieved by the selection of appropriate materials according to the design rules presented here)
Obtained when panel motion is suppressed by acoustic damping, rather than by internal structure damping in the panel material or by damping imposed due to panel motion. When this is obtained, the acoustic distortion will be small.

The "B" in the "T" standard shown above
The value of is the static bending stiffness of the panel rather than the stiffness of the panel when subjected to rapid flexing. However, this bending stiffness decreases with increasing frequency due to increased shear motion effects in the core. It is important that the effect of this shearing motion is minimized, which can be obtained by using panels having a sufficiently high shear modulus. This requirement leads to a second criterion, where the shear modulus of elasticity (G) of the core is related to the relationship “μc ² / d” (where “c” is the speed of sound in air). And “d” is the depth of the panel core). It is convenient to rearrange this expression into another expression “μc ^{2 /} dG> 1”.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Two representative embodiments of the present invention are:
The embodiments will be described below with reference to the accompanying drawings.

The loudspeaker illustrated in FIG. 1 includes a resonant multimode radiator 1, a simple support frame 2 from which the radiator is suspended by a suspension loop 3, and an electromechanical exciter 4. Radiator 1 includes an aluminum alloy honeycomb sandwich rectangular panel having an aluminum alloy skin. Details of this panel and sizing rules will be described later. The electromagnetic exciter 4 has a shaft 5 which hits the back of the radiator panel 1 and
An electromagnetic exciter 4 is mounted on the support frame 2 so as to excite the radiator panel 1 by reciprocating movement of its axis when an electric signal is supplied to the radiator panel 1. At the point of contact between the shaft 5 and the panel 1, the panel is reinforced with patches 6 to resist wear and damage. In order to prevent the radiator panel 1 from being preferentially excited in the symmetric mode, the radiator panel 1 is not placed on the panel near the center point of the panel, but on the panel.
The exciter 4 is arranged so that the exciter 4 excites the radiator panel 1 at a point on the panel near one corner.
The inertial mass of the exciter 4 and the inertial mass of the radiator panel 1 are
Exciter 4 and radiator panel 1 for efficient power transmission
Is adapted to ensure an efficient inertial coupling between the two.

FIG. 2 shows a second embodiment of the speaker of the present invention.
This embodiment is analogous to the loudspeaker embodiment described above with reference to FIG. 1, except for some less important details described below. Common reference numbers are used for common parts in these two figures.

This second embodiment of the loudspeaker is suspended from the ceiling 7 rather than suspended from the support frame. Instead of the two suspension loops in the first embodiment described above, four suspension loops are used so that the radiator panel is placed under the ceiling rather than hanging from the ceiling. The exciter 4 is arranged above the radiator 1.

The two loudspeaker embodiments described above operate in exactly the same way and follow the same design rules with respect to the choice of panel material and the structure and size of the panel in relation to the required frequency band of the loudspeaker. The "T" and "shear modulus" criteria both described above relate to panel shape and panel material rather than panel size and speaker frequency range. In order to produce a speaker optimized for a particular frequency range, it is instructive to refer to some design rules set forth below.

Since the fundamental frequency of the panel must be lower than the lowest frequency of the required frequency range of the speaker, the lower limit of the required frequency range of the speaker limits the fundamental frequency of the panel. In addition, the matching frequency of the panel must be lower than the lowest frequency in the required frequency range of the speaker. The match frequency (f ₁ ) is independent of the panel area and is given by:

[0016] _{f c} ² = _μ. c ^4/4 . π ² . Necessary bandwidth about B specific speaker, determines the value of f _c, thus causing the relationship between μ and B. If the value of the fundamental frequency (f ₁ ) is also determined, then the value of this fundamental frequency will determine the approximate value for the panel area, since f ₁ is given by the following approximation:

F₁ ^Two = B / μ. A^Two  Finally, the frequency at which the first air resonance occurs in the panel core
Number must be higher than the upper frequency limit of the speaker.
No. This frequency (f_a) Is the following equation
Given, f_a= C / 2. d In the above equation, d is the depth of the panel core. Therefore, this equation
Adjusts the depth of the panel core according to the frequency band of the speaker.
Decide.

In the following, the point to be considered in the design is 1 m
This is described by way of example with reference to one loudspeaker embodiment using a radiator panel comprising an aluminum honeycomb core composite with a x1 m square aluminum skin. For this panel, the core depth is 0.04 m and the thickness of each skin is 0.0003 m. In this panel, B is
18850 Nm, μ is 3.38 kg / m ² , and T is 488 Nm ⁷ / k
a g ^2.

From the f ₁ equation, f ₁ is [18850 / 3.38 × 1]
^1/2 = 75 Hz.

[0020] from _{f c} equation, _{f c} is [3.38 × 340 ^4/4
× 3.1416 ² × 18850] ^1/2 = 246 Hz.

From the equation f _a , f _a is 340/2 × 0.04 = 4
250 Hz.

The shear stiffness of the panel varies depending on the direction in the plane of the panel. For the axis with the minimum value of “G”, the expression “μ.c ² /G.d” has a value of 0.056, and for the axis with the maximum value of “G”, Has a value. Both of these values are much smaller than the limit value "1", thus indicating that over the intended frequency band, the performance of the loudspeaker will not be limited by the core shear motion. .

Based on these calculations, the claimed loudspeaker using a 1 m × 1 m square shaped radiator panel made of the materials detailed above has a high conversion efficiency and low distortion. It will be inferred that one would have a frequency band between 250 Hz and 4 kHz that has within that band. It is expected that such a band would be very appropriate for a loudspeaker speaker.

[Brief description of the drawings]

FIG. 1 is an isometric view from the back of a speaker mounted on a frame.

FIG. 2 is a side view of a speaker mounted on a ceiling.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04R 7/08 H04R 1/00 310 H04R 9/00

Claims (5)

(57) [Claims] 1. A panel-type loudspeaker, comprising a single sandwich panel formed of two material skins, having a spacing core of a transverse cellular structure;
A resonant multi-mode radiator element wherein the panel has a ratio of "bending stiffness (B)" to "panel mass per unit surface area (μ) cubed" in all directions of at least 10; Mounting means for supporting the panel in a free state or securing the panel to a support body, and exciting multi-mode resonance in the radiator panel in response to an electrical input within an operating frequency band for the speaker Electromechanical drive means coupled to the radiator panel to operate the loudspeaker panel. 2. The panel-type speaker according to claim 1, wherein the sandwich panel constituting the radiator element is a panel having a “B / μ ³ ” ratio of at least 100. 3. The panel-type speaker according to claim 1, wherein an outer plate of the sandwich panel constituting the radiator element contains aluminum or an aluminum alloy. 4. The panel-type speaker according to claim 1, wherein the core of the sandwich panel is a honeycomb core made of aluminum or an aluminum alloy. 5. The electromechanical driving means according to claim 1, wherein the electromechanical driving means is supplied with an electric driving signal having a fundamental frequency component exceeding both a first resonance frequency and a coincidence frequency of the radiator panel. A panel-type speaker according to the item.