CA1203014A - Speaker diaphragm - Google Patents
Speaker diaphragmInfo
- Publication number
- CA1203014A CA1203014A CA000413722A CA413722A CA1203014A CA 1203014 A CA1203014 A CA 1203014A CA 000413722 A CA000413722 A CA 000413722A CA 413722 A CA413722 A CA 413722A CA 1203014 A CA1203014 A CA 1203014A
- Authority
- CA
- Canada
- Prior art keywords
- headphone
- diaphragm
- diameter
- taken
- phi
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- -1 polyethylene terephthalate Polymers 0.000 claims abstract description 5
- 229920000139 polyethylene terephthalate Polymers 0.000 claims abstract description 5
- 239000005020 polyethylene terephthalate Substances 0.000 claims abstract description 5
- 239000012260 resinous material Substances 0.000 claims abstract description 3
- 230000002093 peripheral effect Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 239000011347 resin Substances 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
- 239000000696 magnetic material Substances 0.000 description 2
- 229920002799 BoPET Polymers 0.000 description 1
- 239000005041 Mylar™ Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R7/00—Diaphragms for electromechanical transducers; Cones
- H04R7/16—Mounting or tensioning of diaphragms or cones
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only
- H04R1/225—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only for telephonic receivers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R7/00—Diaphragms for electromechanical transducers; Cones
- H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R9/00—Transducers of moving-coil, moving-strip, or moving-wire type
- H04R9/06—Loudspeakers
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Multimedia (AREA)
- Health & Medical Sciences (AREA)
- Otolaryngology (AREA)
- Diaphragms For Electromechanical Transducers (AREA)
- Headphones And Earphones (AREA)
- Laminated Bodies (AREA)
- Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A dynamic type headphone in which a diaphragm having a bobbin for a voice coil located within a magnetic circuit is formed of one sheet made of polyethylene terephthalate resinous material is disclosed, in which if a diameter of a vibrating portion of the sheet is taken as .PHI. and a thickness thereof is taken as t, its ratio
A dynamic type headphone in which a diaphragm having a bobbin for a voice coil located within a magnetic circuit is formed of one sheet made of polyethylene terephthalate resinous material is disclosed, in which if a diameter of a vibrating portion of the sheet is taken as .PHI. and a thickness thereof is taken as t, its ratio
Description
~LZ~)30:14 B~CXGROU~D ou ~IE lNVhl. ~ YON
Field of the In~ention ~ his invention relates qenerally to open alr-type headphones and more particularly rela~es to a dynamic-type headphone of a compact size which i~ c~pable of reproducing ri~h bass, tlght middle tone and higher tone.
Descri~tion of the Prior Art Rec~ntly, headphone~ have been made ~Maller. When the headphones are ~ade more compact, the resonant frequency fO
of a v~bratIng system in a speaker unit for use with the head-phone is made higher and a lower tone or bass is rendered in-sufficient thereby. For example, a headphone with a diaphragm wIth a diameter of 23 mm for the speaker unit usually employs a resinous sheet of about 12 ~
to 20 ~ in ~hickness as its diaphragm. But, ~n such a headphone, the resonant frequency fO thereof is in a range from 200 ~z to 220 Hz and therefore an adequate bass cannot be reproduced. In this case, if the sheet of diaphragm is ~ade thinner, the resonant frequency fO 1s lowered and hence the aforesaid purpose can be satisfied. In this latter case, however, higher tones cannot be ~ufficient'y reproduced thereby weakening the sound on the whole whereby tightness of sound is lost. In other words, if the thickness of the diaphragm is taken as t, Young~s modulus thereof ;fi taken as E, and the stiffness thereof is taken as S, this fitiffness S is given by S = k E t3 thus, if t becomes small, S becomes quite ~mall. ~ence resolution of fiound becomefi poor, where k represents the proportional constant.
-1- 3~, i 03~
OBJECTS ~ND SUMMARY OF T~E INv~L.llON
Accoraingly, it is an object of this invention to provid~ a dynamic-type headphone wh~ch can cbviate the above defects inherent in the prior ar headphone.
It is another object of thi6 invention to provide a dynamic~type headphone of a ~mall aperture which can nevertheless reproduce satisfactory bass and tight higher tone.
According to an aspect of the invention, there is provided a dynamic-type headphone in which a aiaphragm having a bobbin for a voice coil located within a magnetic ~ircuit i6 formed of one sheet made of polyethylene terephthalate resinous material, characterized in that if the diameter of a vibrating portion of 6aid sheet is taken as ~ and the thickness thereof is taken as.t, it~ ratio ~t i~ ~elected in a range of 4 x 10 4 to 5 x 10 4.
The other objects, features and ad~antages of the present invention will become apparent from the following description taken in conjunction with the accompanying dra~ings through which like references designate the same element6 and . _ parts.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-sectional diagram showing a dynamic-type headphone to which one embodiment of this invention can be applied: and i`'h ~;~03~)~1.4 Figs. 2 and 3 are respectively characteristic curves thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENT
After various experiments have been carried out repeatedly, the inventors of ~his invention found out a certain relation among the construction of a diaphragm itselE, diameter of movable portion of the diaphragm, thickness thereof, and the like.
Fig. 1 is a cross-sectional diagram of one example of a dynamic-type headphone unit to which this invention can be applied. Firstly, the headphone of such device wilL be described with reference to Fig 1.
In the figure, reference numeral 1 denotes a frame of the headphone unit which is made of magnetic material, namely, which serves as a magnetic circuit. Numeral 2 denotes a magnet and in this case, this magnet 2 is magnetized in the thickness direction thereof. Numeral 3 denotes a top plate, which is also made of magnetic material and which forms a magnetic gap 4 between the outer peripheral surface thereof and one portion of the frame 1 (the portion forming the inner peripheral surface thereof). Numeral 5 denotes a diaphragm the outer peripheral edge of which was bonded to an edge ring 6 beforehand. This edge ring 6 is attached to an inner periphery of an outer peripheral edge la of the Erame 1, by which the diaphragm 5 is located in a predetermined position of the frame 1. A coil i ~3~14 bobbin 7 of the diaphragm ~ is also located within the a~ore~entioned magnetic gap 4. Numeral 8 denotes a volce coil mounted on ~he coil bobbin 7.
With the arrangement made ~o far, in ~ccordance with this invention, the diaphragm S is formed of one sheet made of polyethylene terephthalate resin (trade name: Mylar ,) which i5 one of the polyester ~ystem resins. In ~ddition, if th~
diameter of the vibrating part of this diaphragm ~ (in ~his embodiment, eguated to the inner diameter of the edge rins 6) i8 taken as ~ and the thickness of ~uch diaphragm 5 is taken a~
t, its ratio ~t ~ D i5 ~elected BO as to satisfy.
D is in the range of 4 x la to 5 x 10 Next, data of respective examples of the diaphragm will be indicated on the following tables.
In the following tables, 1, 2 and 3, are 6hown the resonant frequency fO ~nd the value of D when the thickneæs t of ~he diaphragm iæ varied, where ~ - 27mm in table 1;
~ ~ ~Omm Ln tahle 2; and ~ ~ 14.4mm in table 3. Throughout tables 1 to 3 and in ~ig. 1, ~0 represents the aper~ure of the driving or headphone unit and ~1 representæ the diameter of the coil bobbin 7.
.
lZ~3~
Table 1 ~ = 27 ~m ~ 0 - 30 mm t (111 fo (~Z) D~xlO J' 9 130 3"3 12 160 ~. 4 16 210 5 .
T~ble 2 - 20 nm ~ O - 23 m~n . ..
t ~1l) fO (Hz) D(xlO 4 6 150 3. 0 9 170 4.5 ~rable 3 14.4 mm ~n = 16 mm t (t~ ) fO (Hz)D (xlO 4) 4 150 2.8 6 . 190 4.2 8 230 5.6 In each of the tables 1, 2 and 3, ~ of the un~ t is selected as 0. 52.
~ZO,3~
Figs. 2 and 3 are, r~spectively diagrams showing characteristics of tables l and 2, where the above ratio D is taken as a parameter, the frequency is indicated on the abscissa and a level or response is indicated on the ordinate. But, x 10 4 is omitted for simplicity.
In the case of the unit indicated on table 1, the unit with D = 3.3 (where x 10-4 is omitted hereinafter) it was ascertained that the resonant frequency fO was lowered sufficiently, but a so-called tightness of sound was lost in the middle and higher tone bands thereby causing an unsatisfactory sound in view of audibiity. In the un;t with D = 5.3 it was noted that the resonant frequency fO was Inade higher such as 210 Hz and therefore the so-called bass performance was unsatisfied. Regarding the unit with D = 4.4, it was noted that the resonant frequency fO was sufficiently lower that bass performance was satisfactory and the middle and higher tone bands were sufficiently smooth and tight. Thus it was discovered that the unit with D = 4.4 was quite satisfactory in audibility.
In the case of the units indicated on table 2, it was found that regarding the unit with D = 4.5 bass performance was satisfactory and the middle and higher tones were very smooth.
Relative to the unit with D = 3.0 the tightness of sound was lost, and it was ound that in the unit with D = 6 bass performance was unsatisfactory.
., ~20~0~L~
According to the results of various other experiments, it was ascertained that if the diaphragm 5 was formed of one sheet made of polyethylene terephthalate resin and the ratio D or t was selected in a range from 4 x 10 4 to 5 x 10 4, even though the dynamic-t~pe headphone is formed verv compact, a headphone unit which was able to reproduce good sound with a satisfactory bass performance and tightness in view of audibility, could be obtained whatever its size.
The above description is given on a single preferred embodiment of the invention, but it will be apparent that many modifications and variations could be effected by one skilled in the art without departing from the spirit or scope of the novel concepts of the invention, so that the scope of the invention should be determined by the hereinafter appended clalms only.
Field of the In~ention ~ his invention relates qenerally to open alr-type headphones and more particularly rela~es to a dynamic-type headphone of a compact size which i~ c~pable of reproducing ri~h bass, tlght middle tone and higher tone.
Descri~tion of the Prior Art Rec~ntly, headphone~ have been made ~Maller. When the headphones are ~ade more compact, the resonant frequency fO
of a v~bratIng system in a speaker unit for use with the head-phone is made higher and a lower tone or bass is rendered in-sufficient thereby. For example, a headphone with a diaphragm wIth a diameter of 23 mm for the speaker unit usually employs a resinous sheet of about 12 ~
to 20 ~ in ~hickness as its diaphragm. But, ~n such a headphone, the resonant frequency fO thereof is in a range from 200 ~z to 220 Hz and therefore an adequate bass cannot be reproduced. In this case, if the sheet of diaphragm is ~ade thinner, the resonant frequency fO 1s lowered and hence the aforesaid purpose can be satisfied. In this latter case, however, higher tones cannot be ~ufficient'y reproduced thereby weakening the sound on the whole whereby tightness of sound is lost. In other words, if the thickness of the diaphragm is taken as t, Young~s modulus thereof ;fi taken as E, and the stiffness thereof is taken as S, this fitiffness S is given by S = k E t3 thus, if t becomes small, S becomes quite ~mall. ~ence resolution of fiound becomefi poor, where k represents the proportional constant.
-1- 3~, i 03~
OBJECTS ~ND SUMMARY OF T~E INv~L.llON
Accoraingly, it is an object of this invention to provid~ a dynamic-type headphone wh~ch can cbviate the above defects inherent in the prior ar headphone.
It is another object of thi6 invention to provide a dynamic~type headphone of a ~mall aperture which can nevertheless reproduce satisfactory bass and tight higher tone.
According to an aspect of the invention, there is provided a dynamic-type headphone in which a aiaphragm having a bobbin for a voice coil located within a magnetic ~ircuit i6 formed of one sheet made of polyethylene terephthalate resinous material, characterized in that if the diameter of a vibrating portion of 6aid sheet is taken as ~ and the thickness thereof is taken as.t, it~ ratio ~t i~ ~elected in a range of 4 x 10 4 to 5 x 10 4.
The other objects, features and ad~antages of the present invention will become apparent from the following description taken in conjunction with the accompanying dra~ings through which like references designate the same element6 and . _ parts.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-sectional diagram showing a dynamic-type headphone to which one embodiment of this invention can be applied: and i`'h ~;~03~)~1.4 Figs. 2 and 3 are respectively characteristic curves thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENT
After various experiments have been carried out repeatedly, the inventors of ~his invention found out a certain relation among the construction of a diaphragm itselE, diameter of movable portion of the diaphragm, thickness thereof, and the like.
Fig. 1 is a cross-sectional diagram of one example of a dynamic-type headphone unit to which this invention can be applied. Firstly, the headphone of such device wilL be described with reference to Fig 1.
In the figure, reference numeral 1 denotes a frame of the headphone unit which is made of magnetic material, namely, which serves as a magnetic circuit. Numeral 2 denotes a magnet and in this case, this magnet 2 is magnetized in the thickness direction thereof. Numeral 3 denotes a top plate, which is also made of magnetic material and which forms a magnetic gap 4 between the outer peripheral surface thereof and one portion of the frame 1 (the portion forming the inner peripheral surface thereof). Numeral 5 denotes a diaphragm the outer peripheral edge of which was bonded to an edge ring 6 beforehand. This edge ring 6 is attached to an inner periphery of an outer peripheral edge la of the Erame 1, by which the diaphragm 5 is located in a predetermined position of the frame 1. A coil i ~3~14 bobbin 7 of the diaphragm ~ is also located within the a~ore~entioned magnetic gap 4. Numeral 8 denotes a volce coil mounted on ~he coil bobbin 7.
With the arrangement made ~o far, in ~ccordance with this invention, the diaphragm S is formed of one sheet made of polyethylene terephthalate resin (trade name: Mylar ,) which i5 one of the polyester ~ystem resins. In ~ddition, if th~
diameter of the vibrating part of this diaphragm ~ (in ~his embodiment, eguated to the inner diameter of the edge rins 6) i8 taken as ~ and the thickness of ~uch diaphragm 5 is taken a~
t, its ratio ~t ~ D i5 ~elected BO as to satisfy.
D is in the range of 4 x la to 5 x 10 Next, data of respective examples of the diaphragm will be indicated on the following tables.
In the following tables, 1, 2 and 3, are 6hown the resonant frequency fO ~nd the value of D when the thickneæs t of ~he diaphragm iæ varied, where ~ - 27mm in table 1;
~ ~ ~Omm Ln tahle 2; and ~ ~ 14.4mm in table 3. Throughout tables 1 to 3 and in ~ig. 1, ~0 represents the aper~ure of the driving or headphone unit and ~1 representæ the diameter of the coil bobbin 7.
.
lZ~3~
Table 1 ~ = 27 ~m ~ 0 - 30 mm t (111 fo (~Z) D~xlO J' 9 130 3"3 12 160 ~. 4 16 210 5 .
T~ble 2 - 20 nm ~ O - 23 m~n . ..
t ~1l) fO (Hz) D(xlO 4 6 150 3. 0 9 170 4.5 ~rable 3 14.4 mm ~n = 16 mm t (t~ ) fO (Hz)D (xlO 4) 4 150 2.8 6 . 190 4.2 8 230 5.6 In each of the tables 1, 2 and 3, ~ of the un~ t is selected as 0. 52.
~ZO,3~
Figs. 2 and 3 are, r~spectively diagrams showing characteristics of tables l and 2, where the above ratio D is taken as a parameter, the frequency is indicated on the abscissa and a level or response is indicated on the ordinate. But, x 10 4 is omitted for simplicity.
In the case of the unit indicated on table 1, the unit with D = 3.3 (where x 10-4 is omitted hereinafter) it was ascertained that the resonant frequency fO was lowered sufficiently, but a so-called tightness of sound was lost in the middle and higher tone bands thereby causing an unsatisfactory sound in view of audibiity. In the un;t with D = 5.3 it was noted that the resonant frequency fO was Inade higher such as 210 Hz and therefore the so-called bass performance was unsatisfied. Regarding the unit with D = 4.4, it was noted that the resonant frequency fO was sufficiently lower that bass performance was satisfactory and the middle and higher tone bands were sufficiently smooth and tight. Thus it was discovered that the unit with D = 4.4 was quite satisfactory in audibility.
In the case of the units indicated on table 2, it was found that regarding the unit with D = 4.5 bass performance was satisfactory and the middle and higher tones were very smooth.
Relative to the unit with D = 3.0 the tightness of sound was lost, and it was ound that in the unit with D = 6 bass performance was unsatisfactory.
., ~20~0~L~
According to the results of various other experiments, it was ascertained that if the diaphragm 5 was formed of one sheet made of polyethylene terephthalate resin and the ratio D or t was selected in a range from 4 x 10 4 to 5 x 10 4, even though the dynamic-t~pe headphone is formed verv compact, a headphone unit which was able to reproduce good sound with a satisfactory bass performance and tightness in view of audibility, could be obtained whatever its size.
The above description is given on a single preferred embodiment of the invention, but it will be apparent that many modifications and variations could be effected by one skilled in the art without departing from the spirit or scope of the novel concepts of the invention, so that the scope of the invention should be determined by the hereinafter appended clalms only.
Claims (3)
1. A dynamic-type speaker for use in a headphone, in which a diaphragm having a bobbin for a voice coil located within a magnetic circuit is formed of one sheet made of polyethylene terephthalate resinous material, characterized in that where the diameter of the vibrating portion of said sheet is taken as .PHI. and the thickness thereof is taken as t, its ratio is selected in the range of 4 x 10-4 to 5 x 10 4 wherein the diameter .PHI. is less than 30 mm.
2. A headphone as set forth in claim 1 wherein the bobbin diameter is approximately one-half the diameter .PHI..
3. A headphone as set forth in claim 1, wherein the diameter .PHI. is selected in the range of 14mm to 27mm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP56171207A JPS5871798A (en) | 1981-10-26 | 1981-10-26 | Dynamic headphone |
| JP171207/81 | 1981-10-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1203014A true CA1203014A (en) | 1986-04-08 |
Family
ID=15919008
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000413722A Expired CA1203014A (en) | 1981-10-26 | 1982-10-19 | Speaker diaphragm |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5871798A (en) |
| KR (1) | KR860001103B1 (en) |
| AU (1) | AU556442B2 (en) |
| CA (1) | CA1203014A (en) |
| DE (1) | DE3239616A1 (en) |
| FR (1) | FR2515468B1 (en) |
| GB (1) | GB2110502B (en) |
| NL (1) | NL191226C (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DK176614B1 (en) * | 1999-02-17 | 2008-11-17 | Tymphany Denmark As | Speaker |
| JP2002152885A (en) * | 2000-11-14 | 2002-05-24 | Sony Corp | Speaker system |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB525154A (en) * | 1938-02-16 | 1940-08-22 | British Thomson Houston Co Ltd | Improvements in and relating to dynamic sound-converting apparatus |
| DE2241445A1 (en) * | 1972-08-23 | 1974-03-21 | Gottlob Widmann & Soehne Gmbh | Dome shaped loudspeaker diaphragm of rigid foam - e.g. polyurethane is resistant to high amplitude distortion, has good damping properties and is cheap |
| JPS5343515A (en) * | 1976-09-30 | 1978-04-19 | Matsushita Electric Ind Co Ltd | Diaphragm for speaker |
| JPS53137129A (en) * | 1977-05-07 | 1978-11-30 | Matsushita Electric Ind Co Ltd | Vibratory diaphragm for acousitic device |
| DE3049222A1 (en) * | 1980-12-27 | 1982-07-29 | Elektrotechnik Ehmann Gmbh, 6953 Gundelsheim | ELECTRODYNAMIC SPEAKER SYSTEM WITH CALL-SHAPED MEMBRANE |
-
1981
- 1981-10-26 JP JP56171207A patent/JPS5871798A/en active Granted
-
1982
- 1982-10-19 KR KR8204711A patent/KR860001103B1/en active
- 1982-10-19 CA CA000413722A patent/CA1203014A/en not_active Expired
- 1982-10-19 AU AU89476/82A patent/AU556442B2/en not_active Expired
- 1982-10-25 NL NL8204113A patent/NL191226C/en not_active IP Right Cessation
- 1982-10-25 GB GB08230446A patent/GB2110502B/en not_active Expired
- 1982-10-26 DE DE19823239616 patent/DE3239616A1/en active Granted
- 1982-10-26 FR FR8217925A patent/FR2515468B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5871798A (en) | 1983-04-28 |
| DE3239616C2 (en) | 1990-07-26 |
| JPH0235520B2 (en) | 1990-08-10 |
| AU556442B2 (en) | 1986-11-06 |
| FR2515468B1 (en) | 1986-03-14 |
| FR2515468A1 (en) | 1983-04-29 |
| GB2110502B (en) | 1985-05-15 |
| KR860001103B1 (en) | 1986-08-07 |
| DE3239616A1 (en) | 1983-05-05 |
| NL8204113A (en) | 1983-05-16 |
| AU8947682A (en) | 1983-05-05 |
| NL191226C (en) | 1995-03-16 |
| KR840002388A (en) | 1984-06-25 |
| NL191226B (en) | 1994-10-17 |
| GB2110502A (en) | 1983-06-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |