EP1107643A2

EP1107643A2 - Insulating ring for condenser microphone

Info

Publication number: EP1107643A2
Application number: EP00306369A
Authority: EP
Inventors: Jong-Kyu Kim
Original assignee: Won-Il Communics Co Ltd
Current assignee: Won-Il Communics Co Ltd
Priority date: 1999-12-09
Filing date: 2000-07-26
Publication date: 2001-06-13
Also published as: JP2001186594A; KR20000012516A; CN1299226A

Abstract

A condenser microphone having a case (50) with a sound wave inlet hold (51) in which is sequentially stacked a spacer (40), a diaphragm (30), an integrated base ring (20), a field effect transistor (FET) (13) and a printed circuit board (10), with a gate of the FET (13) being electrically connected to a pattern of the printed circuit board (10) and the base ring (20), and the source and the drain of the FET (13) being electrically connected to patterns formed on opposite sides of the printed circuit board (10) respectively, has an improved insulating ring (60) placed in the condenser microphone which is made of an insulating material and which surrounds the circumference of the base ring (20) so as to electrically insulate the case (50) from the integrated base ring (20) the diaphragm (30). The insulating ring is made of a heat-shrinkable material whereby the integrated base ring (20) and the diaphragm (30) can readily be held in the insulating ring (60) simply by heating the latter.

Description

This invention relates to an insulating ring for a condenser microphone, more particularly, to an insulating ring for a condenser microphone and its fixing method, wherein the ring, placed inside the condenser microphone which converts the variation of capacitance caused by sound waves into electrical signals, insulates electrically a case from an integrated base ring and diaphragm, thereby facilitating the manufacture of the condenser microphone.
A conventional condenser microphone comprises, as shown in Figs. 1 and 2, a printed circuit board 101 having both sides printed in a defined pattern, a field effect transistor (FET) 102 for converting variation of potential caused by the variation of the capacitance into electrical signals, a base ring 103 connecting the FET 102 to a diaphragm 104, the diaphragm 104 vibrating by input sound waves, a spacer 105 for isolating a case 106 from the diaphragm 104, and the case 106 having a sound wave inlet hole 107.
The diaphragm 104 and the base ring 103 are electrically connected to the gate of the FET 102 via a defined pattern formed on the top surface of the printed circuit board 101, while the case 106 is electrically connected to the source of the FET 102 via a defined pattern formed on the bottom surface of the printed circuit board 101. The diaphragm 104 is electrically insulated from the base ring 103.
With regard to this, as shown in Figs. 1 and 2, insulating layers 108, 118 are formed in the case 106 prior to providing the spacer 105 and then the other components are provided. In this case, however, as the insulating layers 108, 118 not only are hard to be engaged accurately with the case 106, but require much time for being engaged, the manufacturing time of the condenser microphone is prolonged which is a considerable disadvantage.
The present invention aims to provide an insulating ring for a condenser microphone and its fixing method capable of not only efficiently isolating a case from an integrated base ring and a diaphragm, but also of simplifying a process for fixing the insulating ring in the circumference of the integrated base ring and diaphragm.
According to one aspect of the invention, there is provided an insulating ring for a condenser microphone having a case with a sound wave inlet hole in which is sequentially stacked a spacer, a diaphragm, a base ring, a field effect transistor (FET) and a printed circuit board, with the gate of said FET being electrically connected to a pattern of said printed circuit board and said base ring, and the source and the drain of said FET being electrically connected to patterns formed on opposite sides of said printed circuit board respectively, characterized in that the insulating ring is made of an insulating material which surrounds the circumference of the base ring so as to electrically insulate the case from the base ring and the diaphragm.
Preferably, the vertical thickness of the insulating ring is 75-85% of that of the base ring and the diaphragm. The insulating ring is desirably fixed in the centre of the base ring and diaphragm and is preferably made of a material which is shrinkable at a predetermined temperature.
Another aspect of the present invention provides a method for fixing an insulating ring for a condenser microphone wherein the insulation between a case and an integrated base ring and between the case and a diaphragm is maintained, characterized in that the method comprises placing said integrated base ring and diaphragm inside said insulating ring having a predetermined diameter; and heating and shrinking said insulating ring so as to fix it in the circumference of said integrated base ring and diaphragm.
Preferably, the insulating ring is fixed only in the central portion corresponding to 75-85% of the thickness of the circumference of the integrated base ring and diaphragm.
The insulating ring is desirably made of a material which is shrinkable at temperatures between 70°C and 90°C.
According to the insulating ring for a condenser microphone of the present invention, it is effective not only to efficiently isolate a case from an integrated base ring and a diaphragm, but also simplifies the process for fixing the insulating ring in the circumference of the integrated base ring and diaphragm.
The invention will now be described in detail, by way of example, with reference to the drawings, in which:-
Fig. 1 is a sectional view showing an example of a condenser microphone according to the prior art;
Fig. 2 is a sectional view showing another example of a condenser microphone according to the prior art;
Fig. 3 is an exploded perspective view of one embodiment of a condenser microphone according to the present invention;
Fig. 4 is a sectional view of the condenser microphone according to the present invention;
Figs. 5a and 5b are respectively, a plan view and a front view of a printed circuit board adapted to the condenser microphone according to the present invention; and
Fig. 6 is a side view showing the principal part of the condenser microphone according to the present invention.
As shown in Figs. 3 and 4 of the drawings, the bottom surface of a case 50 with a sound wave inlet hole 51 drilled in the centre of the lower portion thereof is completely open at first. That is, the case 50 has the form of a cylinder into which a spacer 40, a diaphragm 30, a base ring 20, an insulating ring 60 and a printed circuit board 10 having a FET 13 will be sequentially stacked later. In other words, in the inner top of the case 50 the doughnut-type spacer 40 made of an insulating material is provided, and then the diaphragm 30, the base ring 20, and the insulating ring 60 are sequentially stacked.
The diaphragm 30 and the base ring 20 are coupled to be electrically connected each other, and in the circumference of the integrated diaphragm 30 and base ring 20, the insulating ring 60 of an insulating material is fixed. Especially, the insulating ring 60 is made of a material shrinkable at a predetermined temperature (70°C-90°C), and has at first a larger diameter than the diaphragm 30 and base ring 20. By heating the insulating ring 60 after placing the diaphragm 30 and base ring 20 into the insulating ring 60, the insulating ring 60 is fixed to the central portion of the circumference of the diaphragm 30 and base ring 20 while being shrunk.
In this case, the insulating ring 60 which is fixed to the centre of the circumference of the diaphragm 30 and the base ring 20, as shown in Fig. 4, is fixed in the central portion corresponding to 75-85% of the thickness of the circumference of the integrated base ring and diaphragm so as to connect the base ring 20 to the pattern of the printed circuit board 10 precisely, while insulating the case 50 from the integrated diaphragm 30 and the base ring 20.
Next, the printed circuit board 10 having the FET 13 is provided in the case 50, lastly the bottom end of the case 50 is inwardly folded to fix the spacer 40, the diaphragm 30, the base ring 20 and the printed circuit board 10, in position in the case 50.
Fig. 5a is a plan view of the printed circuit board 10, in the circumference of which there is formed a pattern Pg having a predetermined width to be electrically connected to the gate of the FET 13 as well as to the overlying base ring 20. In the centre and the circumference away from the centre at a predetermined distance of the printed circuit board 10 are drilled vertical through holes 11 and 12 through which the source and the drain of the FET 13 are passed.
Fig. 5b is a front view of the printed circuit board 10, in the centre of which a pattern Pd to be electrically connected to the through hole 11 is formed, and in the circumference of which pattern Ps to be electrically connected to the through hole 12 and the case 50 is formed.
Next, the operation of the condenser microphone according to present invention will be described.
The diaphragm 30 is vibrated in accordance with sound waves introduced via the sound wave inlet hole 51 of the case 50, which causes a change of distance between the diaphragm 30 and the case 50, thus varying the capacitance between the diaphragm 30 and the case 50.
Accordingly, the potential of the base ring 20 inputs to the gate of the FET 13 in correspondence to the sound waves, so the currents flowing from the source to the drain of the FET 13 is amplified in correspondence to the sound waves.
Accordingly, the microphone converts the sound waves introduced through the sound wave inlet hole 51 into electrical signals and amplifies the electrical signals.
While a preferred embodiment of the present invention has been described in detail with reference to Figs 3 to 6 of the drawings, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

An insulating ring for a condenser microphone having a case (50) with a sound wave inlet hole (51) in which is sequentially stacked a spacer (40), a diaphragm (30), a base ring (20), a field effect transistor (FET) (13) and a printed circuit board (10), with the gate of said FET (13) being electrically connected to a pattern of said printed circuit board (10) and said base ring (20), and the source and the drain of said FET (13) being electrically connected to patterns formed on opposite sides of said printed circuit board (10) respectively, characterized in that the insulating ring (60) is made of an insulating material which surrounds the circumference of the base ring (20) so as to electrically insulate the case (50) from the base ring (20) and the diaphragm (30).
An insulating ring according to claim 1, characterized in that the vertical thickness of said insulating ring (60) is 75-85% of that of said base ring (20) and diaphragm (30).
An insulating ring according to claim 1 or claim 2, characterized in that the insulating ring (60) is fixed in the centre of said base ring (20) and diaphragm (30).
An insulating ring according to any one of the preceding claims, characterized in that the insulating ring (60) is made of a material which is shrinkable at a predetermined temperature.
An insulating ring according to claim 4, characterized in that said temperature is within the range of 70°C to 90°C.
A method for fixing an insulating ring (60) for a condenser microphone wherein the insulation between a case (50) and an integrated base ring (20) and between the case (50) and a diaphragm (30) is maintained, characterized in that the method comprises:

placing said integrated base ring (20) and diaphragm (30) inside said insulating ring (60) having a predetermined diameter; and

heating and shrinking said insulating ring (60) so as to fix it in the circumference of said integrated base ring (20) and diaphragm (30).
A method for fixing an insulating ring according to claim 6, characterized in that said method comprises fixing said insulating ring (60) only in the central portion corresponding to 75-85% of the thickness of the circumference of said integrated base ring (20) and diaphragm (30).
A method for fixing an insulating ring according to claim 6 or claim 7, characterized in that the insulating ring (60) is made of a material shrinkable at a predetermined temperature.
A method for fixing an insulating ring according to any one of claims 6 to 8, characterized in that the insulating ring (60) is made of a material which is shrinkable at temperatures between 70°C and 90°C.