Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Patent
1996-08-07
1999-05-18
Le, Huyen
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
381431, H04R25/00
Patent
active
059058056
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns an electrodynamic transducer, a diaphragm, a web of sheet having such a diaphragm and a magnet system for the transducer.
The concept electrodynamic acoustic transducer in particular comprises microphones which convert sound signals in the air into electrical signals, and sound generators which convert electrical signals into sound signals in the air. Traditionally, such transducers have a ring-shaped, wound coil of copper wire which is present in a ring-shaped air gap having a radially oriented magnetic field. Such coils are wound on automatic winding machines, and then the coils are to be mounted on a diaphragm, e.g., by gluing. After their manufacture on a winding machine, the coils and in particular their thin copper wires are vulnerable, and they must therefore be handled with great care in order not to be damaged and with great accuracy. The coils are to be mounted on the diaphragms with narrow tolerances, and also the diaphragm with the mounted coil is to be placed very precisely in the magnetic circuit.
It is increasingly required that microphones to be used in portable telephones shall have small physical dimensions, and it is simultaneously desired that such a small microphone is to have a sensitivity which is comparable to the sensitivity of a traditional, larger microphone. These requirements clash with each other, one reason being that a small diaphragm is less resilient than a corresponding larger diaphragm, and a small diaphragm therefore moves correspondingly less at the same sound pressure than a large diaphragm, which results in a smaller electrical output signal.
SUMMARY OF THE INVENTION
The object of the invention is to provide an electrodynamic transducer having a high sensitivity, which can therefore be manufactured with smaller physical dimensions and with a satisfactory high sensitivity than was possible in the past.
The present invention provides an electrodynamic acoustic transducer whose coil and magnetic circuits are of a structure that makes it possible to manufacture an electrodynamic transducer with very small dimensions so that its size is comparable to the size of electret microphones, and which, notwithstanding this, has a sensitivity which is comparable to electrodynamic transducers of considerably larger dimensions. Electret microphones of small physical dimensions and with a relatively great sensitivity are known, but electret microphones have a number of drawbacks, including extremely high electrical impedance, which requires incorporation of a transistor for signal amplification or impedance transformation, but such a transistor requires power supply. Further, electret microphones are sensitive to incident electromagnetic radiation, particularly at radio frequencies, and their acoustic sensitivity varies with the humidity of the atmosphere.
U.S. Pat. No. 3,919,498 discloses an electroacoustic transducer with a substantially flat diaphragm and a flat or disc shaped coil on the diaphragm. The diaphragm is retained along its entire periphery between a pair of magnets. This results in a relatively stiff diaphragm, which prevents miniaturisation under conservation of transducer sensitivity.
FR-A-2 128 065 likewise discloses a transducer with a flat diaphragm retained along its entire periphery.
The object of the invention is to provide an electrodynamic acoustic transducer which has all the advantages of electrodynamic transducers, including in particular stability of acoustic sensitivity, and which can simultaneously be manufactured in much smaller dimensions so that it will be a ready and attractive alternative to electret microphones.
This object is achieved with a transducer as stated in claim 1, the diaphragm being retained with respect to the magnetic system in non-contiguous regions, in contrast to known electrodynamic acoustic transducers where the diaphragm is secured to the magnetic system along its entire periphery. Since the diaphragm is secured in non-contiguous regions or in discrete points, the resilienc
REFERENCES:
patent: 3283086 (1966-11-01), Evans
patent: 3919498 (1975-11-01), Beer
patent: 4211898 (1980-07-01), Atoji et al.
patent: 4228327 (1980-10-01), Sawafuji
patent: 5021613 (1991-06-01), Garcia
patent: 5430805 (1995-07-01), Stevenson et al.
Kirk Acoustics A/S
Le Huyen
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