JPS6231879B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrodynamic speaker using a rectangular flat diaphragm, and an object of the present invention is to expand the reproduction band. FIGS. 1A and 1B show conventional electrodynamic speakers of this type. In FIGS. 1A and B, 1 is a yoke in which a center pole 2 is integrally formed;
This yoke 1 is fixed within a frame 3. 4 is an annular magnet fixed to the upper surface of the yoke 1; 5 is an annular plate fixed to the upper surface of the magnet 4; between the inner circumferential surface of this plate 5 and the outer circumferential surface of the center pole 2; An annular magnetic gap is formed. 6 is a rectangular flat plate diaphragm, and the outer circumference of this diaphragm 6 is an edge member 7.
It is supported by the frame 3 via. A cylindrical coil bobbin 8 is fixed to the center of the lower surface of the diaphragm 6, and a voice coil 9 is wound around the coil bobbin 8. This voice coil 9 is arranged within the magnetic gap. 10
is a damper that supports the coil bobbin 8. FIGS. 2A and 2B show the vibration modes of the diaphragm 6 of the conventional electrodynamic speaker. When an electric signal is applied to the voice coil 9, vibration occurs, and the diaphragm 6 is driven by the coil bobbin 8 and vibrates, but the frequency
₁ , the vibration mode M is such that two nodal lines m ₁ and m ₂ parallel to the short side of the diaphragm 6 occur. Further, when the frequency becomes higher than ₁ and reaches ₃ , the diaphragm 6 becomes a vibration mode N in which four nodal lines n ₁ , n ₂ , n ₃ , and n ₄ occur. In this type of speaker, the reproduction band is determined by the frequency at which the vibration mode occurs. FIG. 3 shows the sound pressure frequency characteristics of the conventional electrodynamic speaker. In Figure 3 _{, 1} is the second
In the figure, 3 is the frequency at which vibration mode M occurs, and ₃ is the frequency at which vibration mode N occurs;
₁ and ₃ , the sound pressure peaks occur. Third
As is clear from the figure, the reproduction band of the conventional electrodynamic speaker is a flat band up to frequency ₁ . In general, speakers using a rectangular flat diaphragm have lower values of ₁ and ₃ than cone-shaped speakers. As described above, conventional electrodynamic speakers have the drawback of having a narrow band. The present invention eliminates the above-mentioned conventional drawbacks and expands the reproduction band. An embodiment of the present invention will be described below with reference to FIGS. 4A and 4B and 5A and 5B. Note that in FIGS. 4A, B and 5A and B, the same parts as in FIGS. 1A and B and FIGS. 2A and B are given the same numbers. In Figures 4A and B, 1' is a yoke, 2' is a center pole, 4' is an annular magnet, 5' is an annular plate, 8' is a coil bobbin, 9' is a voice coil, and 10' is a damper. , the diaphragm 6 is driven by two similar magnetic drive mechanisms. 5A and 5B show the relationship between the attachment points of the coil bobbins 8 and 8' to the diaphragm 6 in the above embodiment and the vibration modes M and N in the conventional example. As is clear from FIGS. 5A and 5B, in this embodiment, when the coil bobbin 8 is driven at the center of the rectangular flat diaphragm 6 as in the conventional example,
The nodal line _m in the vibration mode M that occurs at frequency 3 is fixed at _one part, and the nodal line n in the vibration mode N that occurs at frequency ₃ when the other coil bobbin 8' is driven at the center of the rectangular flat plate 6 It is fixed in ₄ parts. In this way, if one nodal line _m1 of vibration mode M occurring at frequency ₁ and one nodal line _n4 of vibration mode N at frequency ₂ are driven, the vibration modes M and N are irregular, but each It will be node driven. The vibration displacement ξ (vibration mode) of the diaphragm during such irregular nodal driving is determined by the following equation (1). ξ=Fx/ρSl [-1/ω ₂ +P] ^ejwt ...(1) However,

[Formula] Here, X=x/l y=X/l m=1, 2, 3,... F _x : Driving force, x: Driving position, ρ: Density of diaphragm, y: Point of interest of vibration displacement, s: cross-sectional area of the diaphragm, 1: length of the diaphragm, ω: angular frequency, ω _n : natural angular frequency, Ξ _n (X), Ξ _n (y): standard functions representing vibration mode. By substituting X = x / l = 0.224, which indicates the position of the nodal line m ₁ of ₁ , into P in equation (1) and comparing it with the case of center drive where X = x / l = 0.5, Figure 10A As shown in , the vibration mode is greatly suppressed. Also, assuming that X=x/l=0.906, driving the position of node line _n4 of ₂ results in the 10th
As shown in Figure B, the vibration mode is suppressed similarly to ₁ . That is, since the vibration modes M and N are nodally driven by the voice coils 9 and 9', disturbances in the sound pressure can be suppressed to a level that is hardly a problem in practice, as shown in FIG. 6, and the reproduction band can be It is possible to expand the resonance frequency to a higher-order resonance frequency _H. FIGS. 7A and 7B and FIG. 8 show other embodiments of the present invention. In this embodiment, the diameters of the coil bobbins 8 and 8' are increased, and the coil bobbin 8 allows the node lines n ₁ ,
m ₁ is driven, and the node lines m ₂ and n ₄ are connected by the coil bobbin 8'.
It is what drives the. In this embodiment, the flatness of the sound pressure is improved by removing the portions of the upper edges of the coil bobbins 8, 8' that are not in contact with the nodal lines, as shown in FIG. FIGS. 9A and 9B show still another embodiment of the present invention. This embodiment has a substantially truncated conical cylinder 11,1.
The small diameter end of 1' is fixed to the coil bobbins 8, 8', the large diameter end is fixed to the diaphragm 6, and the nodal line is connected by the cylinder 11.
n ₁ and m ₁ are driven, and nodal lines m ₂ and n ₄ are driven by the cylindrical body 11'. According to this embodiment, the reproduction band can be expanded. The present invention has the above configuration, and has the advantage that the reproduction band of an electrodynamic speaker can be expanded by using a rectangular flat diaphragm. Furthermore, compared to a multi-point drive type speaker that drives all the nodal line parts, the number of magnetic drive mechanisms is smaller, which is advantageous in terms of cost and is excellent in mass production.

[Brief explanation of the drawing]

Figures 1A and B are a top view and side sectional view of a conventional electrodynamic speaker, Figures 2A and B are diagrams showing the vibration modes of the diaphragm of the same speaker, and Figure 3 is the sound pressure of the same speaker. Frequency characteristic diagrams, FIGS. 4A and 4B are a top view and a side sectional view of an electrodynamic speaker according to an embodiment of the present invention, FIGS. 5A and B are a top view and a side sectional view of the main parts of the same speaker, FIG. 6 is a sound pressure frequency characteristic diagram of the same speaker, FIGS. 7A and B are a top view and side sectional view of main parts of another embodiment of the present invention, and FIG. 8 is a perspective view of the coil bobbin of the same speaker. FIGS. 9A and 9B are a top view and a side sectional view of essential parts of still another embodiment of the present invention, and FIGS. 10A and 10B are state diagrams showing drive modes of the speaker shown in FIG. 5. 1, 1'... Yoke, 2, 2'... Center pole, 3... Frame, 4, 4'... Magnet,
5, 5'...Plate, 6...Rectangular flat plate diaphragm,
7... Etsy member, 8, 8'... Coil bobbin,
9, 9'... Voice coil, 10, 10'... Damper, 11, 11'... Cylindrical body.

Claims (1)

[Claims] 1. In an electrodynamic speaker in which two parts of a rectangular flat diaphragm are driven by a magnetic drive mechanism, the frequency ₁ when driving the central part of the rectangular flat diaphragm,
₃ , at least one of two nodal lines m ₁ , m ₂ and four nodal lines n ₁ , n ₂ , n ₃ , n ₄ each occurring parallel to the short side of the rectangular flat diaphragm.
An electrodynamic speaker characterized in that two nodal lines are driven by each of the magnetic drive mechanisms so as to eliminate peak dips in sound pressure frequency characteristics due to primary and secondary resonances. 2. In the electrodynamic speaker according to claim 1, one magnetic drive mechanism drives one of the nodal lines m ₁ , m ₂ , and the other magnetic drive mechanism drives the nodal lines n ₁ , m 2 .
An electrodynamic speaker characterized by driving one of n ₂ , n ₃ , and n ₄ . 3. In the electrodynamic speaker according to claim 1, one of the nodal lines m ₁ and m ₂ and one of the nodal lines n ₁ , n ₂ , n ₃ , and n ₄ in one magnetic drive mechanism. , and the other of the nodal lines m ₁ and m ₂ and the other one of the nodal lines n ₁ , n ₂ , n ₃ , and n ₄ are driven by the other magnetic drive mechanism. Electric speaker.