EP0576216B1 - Method of compensating for a change in sound pressure characteristic with temperature of an elecrtoacoustic transducer - Google Patents

Method of compensating for a change in sound pressure characteristic with temperature of an elecrtoacoustic transducer Download PDF

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Publication number
EP0576216B1
EP0576216B1 EP19930304780 EP93304780A EP0576216B1 EP 0576216 B1 EP0576216 B1 EP 0576216B1 EP 19930304780 EP19930304780 EP 19930304780 EP 93304780 A EP93304780 A EP 93304780A EP 0576216 B1 EP0576216 B1 EP 0576216B1
Authority
EP
European Patent Office
Prior art keywords
diaphragm
sound pressure
casing
resonance frequency
compensating
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 - Lifetime
Application number
EP19930304780
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0576216A3 (ja
EP0576216A2 (en
Inventor
Kazushi c/o Star Micronics Co. Ltd. Suzuki
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Star Micronics Co Ltd
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Star Micronics Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Star Micronics Co Ltd filed Critical Star Micronics Co Ltd
Publication of EP0576216A2 publication Critical patent/EP0576216A2/en
Publication of EP0576216A3 publication Critical patent/EP0576216A3/xx
Application granted granted Critical
Publication of EP0576216B1 publication Critical patent/EP0576216B1/en
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Expired - Lifetime legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K9/00—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers
    • G10K9/18—Details, e.g. bulbs, pumps, pistons, switches or casings

Definitions

  • This invention defined in the appended claims relates to a method of compensating for a change in sound pressure characteristic with temperature of an electroacoustic transducer, used in the form of a buzzer or sound alarm means, for converting electric signals into sound.
  • the document GB-A-2 041 616 discloses a sound alarm means provided with a temperature compensation means.
  • Electroacoustic transducers convert electric signals into sound. They can be used in the form of buzzers or sound alarm means in various electronic equipments to provide acoustic output corresponding to input electric signals. They have sound pressure characteristics determined by their own structure and materials. Sound pressure characteristics vary with temperature, and a change in sound pressure characteristic has effects on acoustic output.
  • Fig. 6 shows a prior art electroacoustic transducer using an electromagnetic coil in a driving source.
  • This transducer has a cylindrical casing 2 made of synthetic resin.
  • On the inner wall surface of the casing 2 are axially provided a plurality of ribs 3.
  • On the back side of the ribs 3 a diaphragm 4 is disposed orthogonally to the axis of the casing 2.
  • a resonance chamber 6 is defined on the front side of the diaphragm 4.
  • a driving source 8 is provided for producing vibrations of the diaphragm 4.
  • a sound emitting hole 10 is provided on the closing surface of the casing 2 extending parallel to the diaphragm 4.
  • the hole 10 has a cylindrical shape projecting into the resonance chamber 6. This allows the resonance chamber 6 to communicate with atmosphere to emit a sound produced by the diaphragm 4 in the resonance chamber 6 to the outside of the casing 2.
  • the driving source 8 is a means for-producing acoustic vibrations of the diaphragm 4. It is externally supplied with a driving current via terminals 12 and 14 to generate an alternating magnetic field acting on the diaphragm 4 for acoustic vibration.
  • the diaphragm 4 is a magnetizable thin metal plate and at the central portion a disk-like magnetic piece 16 is mounted.
  • the magnetic piece 16 is an additional mass means for increasing the mass of the diaphragm 4. It is made of a magnetic material to constitute a magnetic circuit in combination with the diaphragm 4.
  • the diaphragm 4 is at the periphery magnetically fixed to the top of a cylindrical magnet 18 contained in the casing 2.
  • the diaphragm 4 is magnetized and secured in position by the magnetic attraction of the magnet 18.
  • the magnet 18 is firmly fixed within the casing 2 by a magnetizable metal base 20 closing the back space of the casing 2.
  • a substrate 22 With the terminals 12 and 14 mounted thereon.
  • the central portions of the base 20 and substrate 22 are penetrated by a cylindrical core 24 extending along the center axis of the magnet 18.
  • a gap 26 is defined between an end of the core 24 and the diaphragm 4 for permitting magnetic coupling and vibrations of the diaphragm 4.
  • a coil 30 is wound around the core 24 via a bobbin 28 and connected to the terminals 12 and 14. Via the terminals 12 and 14, a driving current is supplied to the coil 30 as an input current for producing vibrations.
  • the diaphragm 4 and resonance chamber 6 have natural resonance frequencies (fo) and (fv) respectively.
  • the resonance frequency (fo) is determined by physical parameters such as the material and shape of the diaphragm 4, the shape and mass of the magnetic piece 16, the size of the gap 26, the magnetic force of the magnet 18, the size of the back space 32 of the diaphragm 4, and the diameter of the core 24.
  • the equation (1) is the Helmholtz equation, where V stands for the volume of the resonance chamber 6, D and L for the diameter and length of the sound emitting hole 10, and C for the sound velocity (approx. 344,000 mm/sec.). That is, the frequency (fv) is determined by the diameter and length of the sound emitting hole 10 and the volume of the resonance chamber 6. If the diameter and length of the sound emitting hole 10 are constant, the frequency (fv) only depends on the volume of the resonance chamber 6.
  • Fig. 8 shows a measure to broaden the frequency range of the sound pressure characteristic, where the frequency (fv) is set slightly higher (fv>fo) than the frequency (fo).
  • a reproduced frequency (fw) is set at the frequency (fo) in the former case and to be in the range of (fo) to (fv) in the latter case.
  • the frequency (fv) also varies with temperature, that is, it is increased at high temperatures and decreased at low temperatures.
  • T H 85°C
  • T s 25 °C
  • the frequency interval (fov) at ordinary temperature is expanded to (fov H ) (>fov) to cause a remarkable drop in sound pressure.
  • the resonance frequency (fo) at ordinary temperature is shifted to (fo L )(>fo) and the frequency (fv) to (fv L )( ⁇ fv).
  • the frequency interval (fov) at ordinary temperature is narrowed to (fov L )( ⁇ fov) to cause a remarkable rise in sound pressure. Above result in a remarkable change in sound pressure of 10 dB or more at the reproduced frequency (fw). Required and sufficient acoustic output is not available.
  • Fig. 10 also shows the change in the resonance frequencies (fo) and (fv) with temperature when they are relativley set to be (fv>fo) as shown in Fig. 8.
  • T H 85°C
  • T s 25 °C
  • the frequency interval (fov) at ordinary temperature is expanded to (fov H ) (>fov) to cause a remarkable drop in sound pressure.
  • the resonance frequency (fo) at ordinary temperature is shifted to (fo L ) (>fo) and the frequency (fv) to (fv L ) ( ⁇ fv).
  • the frequency interval (fov) at ordinary temperature is narrowed to (fov L ) ( ⁇ fov) to cause a remarkable rise in sound pressure. Above also result in a remarkable change in sound pressure of 10 dB or more at the reproduced frequency (fw).
  • Fig. 11 shows the sound pressure characteristics of the prior art electroacoustic transducer, where T s represents the characteristic at 25°C, T H at 85 °C, and T L at -40 °C.
  • Fig. 12 shows the coil current characteristics corresponding to Fig. 11, where Ts represents the characteristic at 25°C, T H at 85 °C, and T L at -40 °C.
  • a difference in sound pressure at -40 °C and 85°C is about 10 dB at the reproduced frequency range (fw) of 2 kHz to 3 kHz.
  • the sound pressure characteristic varies with temperature to the extent that the change is sensible by hearing in various applications and seasons.
  • An object of the invention is to provide a method of compensating for a change in sound pressure characteristic with temperature of an electroacoustic transducer by utilizing the tendency of the resonance frequencies (fo) and (fv) to vary with temperature.
  • the invention provides a method of compensating for a change in sound pressure characteristic with temperature without a major change in the basic structure of a conventional electroacoustic transducer.
  • the invention provides a method of compensating for a change in sound pressure characteristic with temperature of an electroacoustic transducer comprising a casing, a diaphragm disposed in the casing and having a natural resonance frequency, a resonance chamber provided on the front side of the diaphragm in the casing and having a resonance frequency which is set lower than the resonance frequency of the diaphragm at ordinary temperature to resonate with vibration of the diaphragm, a driving source provided on the back side of the diaphragm, and the diaphragm being vibrated by the driving source to produce a sound to be emitted through the resonance chamber, the method being characterized by comprising:
  • the invention provides a method of compensating for a change in sound pressure characteristic with temperature of an electroacoustic transducer comprising a casing, a diaphragm disposed in the casing and having a natural resonance frequency, a resonance chamber provided on the front side of the diaphragm in the casing and having a resonance frequency which is set lower that the resonance frequency of the diaphragm at ordinary temperature to resonate with vibration of the diaphragm, a driving source provided on the back side of the diaphragm, and the diaphragm being vibrated by the driving source to produce a sound to be emitted through the resonance chamber, the method being characterized by comprising:
  • the resonance frequencies (fo) and (fv) of the diaphragm and resonance chamber are relatively set so that the frequency (fv) is lower than the frequency (fo) at ordinary temperature.
  • the frequency (fv) tends to rise, the frequency (fo) tends to fall and a magnetic driving force is weakened to decrease the sound pressure.
  • the frequency (fv) tends to fall, the frequency (fo) tends to rise, and a magnetic driving force is improved to increase the sound pressure.
  • the interval between the resonance frequencies (fo) and (fv) is narrowed to increase the sound pressure, thus offsetting the decrease in sound pressure due to the weakened magnetic driving force.
  • the interval is expanded to decrease the sound pressure, thus offsetting the increase in sound pressure due to the improved magnetic driving force. That is, the change in the interval between the resonance frequencies is inversely related to that of the conventional transducer.
  • a change in sound pressure caused by a change in driving force is offset by a change in sound pressure caused by a change in frequency interval, thus compensating for a change in sound pressure with temperature to provide a sound pressure characteristic with only a negligible change with temperature.
  • Fig. 1 is a graph showing an embodiment of the method of compensating for a change in sound pressure characteristic with temperature of an electroacoustic transducer according to the invention.
  • Fig. 2 is a longitudinal sectional view of an embodiment of the electroacoustic transducer implementing the method shown in Fig. 1.
  • Fig. 3 is a longitudinal sectional view showing the dimensional difference between the electroacoustic transducer shown in Fig. 2 and the prior art electroacoustic transducer shown in Fig. 6.
  • Fig. 4 is a graph showing the sound pressure characteristics obtained in the electroacoustic transducer shown in Fig. 2.
  • Fig. 5 is a graph showing the coil current characteristics obtained in the electroacoustic transducer shown in Fig. 2.
  • Fig. 6 is a longitudinal sectional view of a prior art electroacoustic transducer.
  • Fig. 7 is a graph showing the sound pressure characteristic obtained in the prior art electroacoustic transducer.
  • Fig. 8 is a graph showing the sound pressure characteristic obtained in the prior art electroacoustic transducer.
  • Fig. 9 is a graph showing the change in sound pressure characteristics with temperature obtained in the prior art electroacoustic transducer.
  • Fig. 10 is a graph showing the change in sound pressure characteristics with temperature obtained in the prior art electroacoustic transducer.
  • Fig. 11 is a graph showing the sound pressure characteristics obtained in the prior art electroacoustic-transducer.
  • Fig. 12 is a graph showing the coil current characteristics obtained in the prior art electroacoustic transducer.
  • Fig. 1 shows an embodiment of the method of compensating for a change in sound pressure characteristic with temperature of an electroacoustic transducer according to the invention.
  • This electroacoustic transducer has natural resonance frequencies (fo) and (fv).
  • This invention is characterized in that they are relatively set so that the resonance frequency (fv) of the resonance chamber 6 is lower than the resonance frequency (fo) of the diaphragm 4.
  • the present invention intends not to suppress changes in the resonance frequencies (fo) and (fv), but, taking into account possible changes in the frequencies with temperature, to differentially set them to the extent that they may approach each other but they are never inversely related.
  • the resonance frequency (fo) is determined by the material and shape of the diaphragm 4, the shape and mass of the magnetic piece 16 as an additional mass means, the size of the gap 26, the magnetic force of the magnet 18, the size of the back space 32 of the diaphragm 4, and the diameter of the core 24.
  • the resonance frequency (fv) is determined by the equation (1).
  • the frequency (fv) of the resonance chamber 6 can be easily adjusted by the volume of the resonance chamber 6 since it is in close relation with its volume.
  • the resonance frequency (fo) is decreased to (fo H )( ⁇ fo) at high temperatures and increased to (fo L ) (>fo) at low temperatures.
  • Fig. 2 shows an embodiment of the electroacoustic transducer implementing the method according to the invention. It is structually similar to that of the prior art transducer shown in Fig. 6, therefore having the same reference numbers for the parts.
  • This transducer has a cylindrical casing 2 made of synthetic resin. On the inner wall surface of the casing 2 are axially provided a plurality of ribs 3. On the back of the ribs 3 a diaphragm 4 is disposed orthogonally to the axis of the casing 2. A resonance chamber 6 is defined on the front side of the diaphragm 4. On the back side thereof a driving source 8 is provided for producing vibrations of the diaphragm 4. A sound emitting hole 10 is provided on the closing surface of the casing 2 extending parallel to the diaphragm 4. The hole 10 has a cylindrical shape projecting into the resonance chamber 6. This allows the resonance chamber 6 to communicate with atmosphere to emit a sound produced by the diaphragm 4 in the resonance chamber 6 to the outside of the casing 2.
  • the driving source 8 is a means for producing acoustic vibrations of the diaphragm 4. It is externally supplied with a driving current via terminals 12 and 14 to generate an alternating magnetic field acting on the diaphragm 4 for acoustic vibration.
  • the diaphragm 4 is a magnetizable thin metal plate and at the central portion a disk-like magnetic piece 16 is mounted.
  • the magnetic piece 16 is an additional mass means for increasing the mass of the diaphragm 4. It is made of a magnetic material to constitute a magnetic circuit in combination with the diaphragm 4. It may be made of a non-magnetizable material only for the purpose of increasing the mass.
  • the diaphragm 4 is at the periphery magnetically fixed to the top of a cylindrical magnet 18 contained in the casing 2. That is, the diaphragm 4 is magnetized and secured in position by the magnetic attraction of the magnet 18.
  • the magnet 18 is firmly fixed within the casing 2 by a magnetizable metal base 20 closing the back space of the casing 2.
  • a substrate 22 To the back surface of the base 20 is secured a substrate 22 with the terminals 12 and 14 mounted thereon.
  • the central portions of the base 20 and substrate 22 are penetrated by a cylindrical core 24 extending along the center axis of the magnet 18.
  • a gap 26 is defined between an end of the core 24 and the diaphragm 4 for permitting magnetic coupling and vibrations of the diaphragm 4.
  • a coil 30 is wound around the core 24 via a bobbin 28 and connected to the terminals 12 and 14.
  • An alternating drive current is supplied to the terminals 12 and 14 as an input current to generate an alternating magnetic field at the coil 30 for interlinkage with the diaphragm 4.
  • the driving source 8 is surrounded by the cylindrical magnet 18.
  • the diaphragm 4, the magnetic piece 16 as an additional mass means, the driving source 8, the cylindrical magnet 18, and the base 20 in combination constitute a closed magnetic circuit.
  • the additional mass means is excluded from the closed magnetic circuit if a non-magnetizable material is used instead of the magnetic piece 16.
  • Fig. 3 compares this electroacoustic transducer with the prior art transducer.
  • the references b 2 , c 2 , d 2 , and e 2 show the corresponding dimensions of the prior art transducer. The dimensional relationship are as follows: b 1 ⁇ b 2 , c 1 >c 2 , d 1 ⁇ d 2 , and e 1 >e 2 .
  • the volume ratio of the resonance chamber 6 to the casing 2 can be increased to considerably decrease the resonance frequency (fv). This allows easy setting of the resonance frequency interrelation of (fv ⁇ fo).
  • setting the resonance frequency of the resonance chamber lower than the resonance frequency of the diaphragm may compensate for a change in sound pressure characteristic with temperature to provide stable sound pressure characteristic regardless of temperatures. This is also true when a plastic magnet is used, which likely presents a remarkable change in sound pressure characteristic with temperature.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
  • Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)
EP19930304780 1992-06-20 1993-06-18 Method of compensating for a change in sound pressure characteristic with temperature of an elecrtoacoustic transducer Expired - Lifetime EP0576216B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP18613892A JPH066899A (ja) 1992-06-20 1992-06-20 電気音響変換器の音圧特性の温度補償方法
JP186138/92 1992-06-20

Publications (3)

Publication Number Publication Date
EP0576216A2 EP0576216A2 (en) 1993-12-29
EP0576216A3 EP0576216A3 (ja) 1994-08-31
EP0576216B1 true EP0576216B1 (en) 1999-03-17

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ID=16183046

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19930304780 Expired - Lifetime EP0576216B1 (en) 1992-06-20 1993-06-18 Method of compensating for a change in sound pressure characteristic with temperature of an elecrtoacoustic transducer

Country Status (4)

Country Link
EP (1) EP0576216B1 (ja)
JP (1) JPH066899A (ja)
CN (1) CN1038095C (ja)
DE (1) DE69323930T2 (ja)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2001204096A (ja) * 2000-01-24 2001-07-27 Star Micronics Co Ltd 電磁音響変換器およびその製造方法
JP4802998B2 (ja) * 2005-12-19 2011-10-26 セイコーエプソン株式会社 静電型超音波トランスデューサの駆動制御方法、静電型超音波トランスデューサ、これを用いた超音波スピーカ、音声信号再生方法、超指向性音響システム及び表示装置
EP3382691B1 (en) * 2017-03-30 2021-05-26 Mitsuba Corporation Horn device
CN112827787B (zh) * 2021-01-07 2022-06-21 歌尔微电子股份有限公司 超声波换能器

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE435777B (sv) * 1979-01-29 1984-10-15 Ibuki Kogyo Co Ltd Elektriskt horn
JPS59150880A (ja) * 1983-02-14 1984-08-29 国産金属工業株式会社 ドア錠

Also Published As

Publication number Publication date
CN1038095C (zh) 1998-04-15
JPH066899A (ja) 1994-01-14
EP0576216A3 (ja) 1994-08-31
DE69323930D1 (de) 1999-04-22
EP0576216A2 (en) 1993-12-29
CN1083300A (zh) 1994-03-02
DE69323930T2 (de) 1999-08-26

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