Classifications

• • 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
  • H04R9/02—Details
  • H04R9/025—Magnetic circuit
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2209/00—Details of transducers of the moving-coil, moving-strip, or moving-wire type covered by H04R9/00 but not provided for in any of its subgroups
  • H04R2209/022—Aspects regarding the stray flux internal or external to the magnetic circuit, e.g. shielding, shape of magnetic circuit, flux compensation coils
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2209/00—Details of transducers of the moving-coil, moving-strip, or moving-wire type covered by H04R9/00 but not provided for in any of its subgroups
  • H04R2209/041—Voice coil arrangements comprising more than one voice coil unit on the same bobbin

Definitions

• the present invention relates to the field of electromagnetic transducers and actuators, and more particularly it relates to improvements in loudspeaker drivers of the type having dual voice coils axially located in corresponding dual annular magnetic air gaps on a common axis.
• U.S. patent 5,381,483 to Grau discloses a minimal inductance electrodynamic transducer having ferromagnetic shunting rings coated with a highly conductive material to increase the induced current carrying capacity of the transducer.
• U.S. patent 3,830,986 to Yamamuro discloses a MAGNETIC CIRCUIT FOR AN ELECTRO-ACOUSTIC CONVERTER having an air gap formed of a magnetic material laminated with a conductive layer for acting as shorting rings to decrease the inductance of the voice coil .
• Japanese patent WO 81/02501 discloses a MAGNETIC CIRCUIT FOR AN ELECTRO-MECHANICAL TRANSDUCER OF A DYNAMIC ELECTRICITY TYPE wherein compensating coils or conductors within the magnetic gaps are supplied with signal current to prevent disturbances in the magnetic field.
• Japanese patent 198208 discloses an ELECTROMAGNETIC CONVERTER wherein a magnetic ring is located in the air gap so that it can be moved axially between a circumferential yoke and a center yoke to provide good conversion efficiency by using a hollow disk permanent magnet that is magnetized in different poles at the center and external circumference.
• U.S. patent 3,783,311 to Sato et al discloses a MAGNETIC DEVICE FOR USE IN ACOUSTIC APPARATUS wherein a metallic member in a voice coil gap permits the lines of magnetic force to move substantially in one direction only, for distortion reduction.
• Patents that disclose dual voice coil dual magnetic gap drivers/actuators include U.S. patents 4,612,592 to Frandsen, 5,231,336 to Van Namen, and French patent 1,180,456 to Kritter; however these do not disclose the use of shorting rings.
• U.S. patent 4,914,707 to Kato et al for a BALANCE VEHICULAR SPEAKER SYSTEM suggests attaching a shorting ring to a coil of a dual -coil dual -gap front speaker in a vehicle to decrease the high frequency impedance as an alternative to connecting a resistor in series with a rear speaker, for purposes of making the impedance of the rear speaker higher than that of the front one.
• the location of the shorting rings determines their effect : location close to a voice coil reduces the voice coil inductance, location entirely within the magnetic flux loop centerline favors reduction of second harmonic and higher order even harmonic distortion, a centered location on the flux loop centerline, i.e. centered in the magnetic gap, favors reduction of third harmonic and higher odd order harmonic distortion, while location outside the flux loop centerline but near the voice coil acts generally to reduce harmonic distortion.
• a plurality of rings can be differently located so as to optimally suppress both even and odd order harmonic distortion and reduce the voice coil inductance.
• FIGs . 1-3 show shorting rings located inside the flux loop for reducing even order harmonic distortion.
• FIGs. 4-5 show shorting rings located outside the flux loop.
• FIGs. 6-7 show at least two shorting rings located inside the flux loop and at least two located outside the flux loop.
• FIGs. 8-10 show shorting rings centered on the flux loop for best suppression of odd order harmonics.
• FIGs. 11 and 12 show shorting rings in tubular form extending through both gaps .
• FIGs. 1-12 are basic functional representations of a dualgap dual -voice-coil loudspeaker driver, shown in half crosssection with a voice coil assembly 10 carrying voice coils 10A and 10B suspended in a pair of magnetized air gaps formed from a permanent magnet M disposed between a first steel pole piece N, at the north pole of magnet M and a second steel pole S at the south pole of magnet M, and a yoke 12 which is made of magnetic material and which can be considered to define, in effect, a pair of pole pieces that would substantially mirror the articulated pole pieces N and S of magnet M and thus form the two magnetic gaps.
• the magnetic system of the foregoing structure sets up a magnetic flux loop in the path shown as a dashed line, i.e. flux loop center line 14, which is typically centered within each magnetic gap and within each voice coil 10A and 10B.
• Voice coil assembly 10 is constrained by well known spring suspension diaphragm structure (not shown) so that it travels axially, typically driving a conventional speaker cone diaphragm (not shown) in response to AC (alternating current) applied to coils 10A and 10B, in accordance with the well known Right Hand Rule of electro-magnetic mechanics and in the general manner of loudspeakers, the two coils being phase-connected accordingly.
• the half cross-section shown in FIGs. 1-12 represents a coaxial loudspeaker motor structure that can have either of two basic configurations that are inverse of each other:
• a common inherent shortcoming in loudspeakers is that the magnetic flux in the region of the voice coil (s) is subject to pattern deformation or modulation as a reaction to drive current in the voice coil (s) ; this in turn can distort the acoustic output as well as increase the inductance of the coil winding (s), altering the frequency response .
• Such shorting rings have no effect on the flux pattern as long as it remains constant and stationary, however the rings react with an internal flow of current that opposes any change in the flux pattern such as would be caused by the drive current in the voice coils, thus the rings can substantially reduce distortion in the acoustic output. Also a shorting ring located near a voice coil tends to reduce the inductance of the voice coil .
• the present inventors in research directed to improvements in dual-gap dual -coil transducer drivers, have identified key locations and configurations for such shorting rings, particularly with regard to distortion reduction, and have developed such locations and configurations for reducing second and/or third harmonic distortion selectively.
• FIGs. 1-3 show locations of tubular-shaped shorting rings Shat are located within the flux loop as defined by its center line 14 and that therefore act in a manner to reduce even order harmonic distortion including particularly second harmonic distortion in accordance with the present invention.
• the tubular shorting ring 16A is located adjacent to permanent magnet M, essentially extending between the two pole pieces N and S in a location adjacent to voice coil assembly 10 and entirely within the flux loop defined by center line 14.
• the tubular shorting ring 16B is embedded in a recessed region of yoke 12, essentially extends between the two yoke pole pieces in a location adjacent to voice coil assembly 10 and entirely within the flux loop defined by center line 14.
• two rings are incorporated in a driver unit: ring 16A, as in FIG. 1 and ring 16B, as in FIG. 2; since both rings are located within the flux loop defined by center line 14, the even order harmonic distortion suppression is greater than in either FIG. 1 or FIG. 2.
• FIGs. 4 and 5 show locations of annular shorting rings 16D and 16E configured as disks that have an edge positioned close to the voice coils of assembly 10 and that, being located outside the flux loop center line 14, act generally to reduce harmonic distortion and reduce voice coil inductance in accordance with the present invention.
• a first pair of shorting rings 16C are located on the outer surfaces of pole pieces N and S respectively and a second pair of shorting rings 16D are located on each end of yoke 12, all having an edge in close proximity to the voice coils of assembly 10.
• the shorting rings 16C and 16D are shaped as annular disks, i.e. flat washers, however, depending on the configuration, i.e. whether CL1 or CL2 is the central axis, the pair of shorting rings that are centered on the axis need not have a central hole and thus could be shaped simply as circular disks.
• two shorting rings 16E are fitted in the outer corners of yoke 12 , in close proximity to the voice coils of assembly 10, but outside the flux loop as defined by center line 14.
• FIGs. 6 and 7 show configurations with shorting ring locations near the voice coils both inside and outside the flux loop as defined by center line 14, thus acting mainly to suppress second harmonics and higher order even harmonics and to reduce voice coil inductance.
• two shorting rings 16F 1 are located in the inner corners of each of the magnet pole pieces N and
• FIG. 7 a total of eight rings are deployed; a pair of shorting rings 16G and 16G' embedded in each of the pole pieces N and S as shown, and two corresponding pairs of shorting rings 16H and 16H 1 embedded in corresponding locations in yoke 12, so that four of the rings are inside the flux loop and the other four are outside the flux loop.
• FIGs. 8-10 show shorting rings located substantially centered on the flux loop center line 14: this is the optimal location for suppression of odd order harmonics, particularly third harmonics.
• shorting rings 16J and 16K are embedded in a center location, one each in all four pole pieces defining the two magnetic gaps, substantially centered on the flux loop center line 14.
• the total faces of poles N and S are configured with laminated shorting ring structures 16L, and corresponding laminated shorting ring structures 16H are embedded in the upper pole piece regions of yoke 12 adjacent the voice coils as shown.
• These laminated shorting ring structures 16L and 16H consist of sheets of electrically conductive metal (typically copper or aluminum) interleaved with magnetic grade steel laminations.
• FIG. 10 depicts essentially an unlaminated version of FIG. 9: lower faces of pole pieces N and S are fitted with shorting rings 16P of tubular shape, and yoke 12 is fitted with embedded shorting rings 16Q of tubular shape, somewhat longer than rings 16P and thus extending inwardly from the outer corners past the voice coils of assembly 10, acting to lower the voice coil inductance as well as to reduce harmonic distortion optimally.
• a single tubular shorting ring 16R extending full length of the magnet assembly including a surface layer added onto the faces of pole pieces N and S close to the voice coils, thus acting to reduce voice coil inductance as well as to reduce harmonic distortion.
• FIG. 12 depicts essentially a version of FIG. 11 with the tubular shorting ring 16S deployed as a surface layer extending full length along the upper surface of yoke 12 including its pole regions, close to the voice coils, thus providing further reduction in voice coil inductance.
• FIGs. 10-12 Alternative viable combinations of FIGs. 10-12 include: ring 16R (FIG. 11) deployed in place of rings 16P in FIG. 10; ring 16S (FIG. 12) deployed in place of rings 16Q in FIG. 10; ring 16S (Fig. 12) deployed in yoke 12 in FIG. 11.
• Shorting rings are most effective in reducing harmonic distortion in the audio frequency range 200 to 2,000 Hertz.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
• Circuit For Audible Band Transducer (AREA)

Applications Claiming Priority (3)

Publications (3)

Family

ID=22145231

Family Applications (1)

Country Status (8)

Families Citing this family (10)

Citations (5)

Family Cites Families (4)

• 1999
  • 1999-03-19 CN CNB998054852A patent/CN1152601C/zh not_active Expired - Lifetime
  • 1999-03-19 CA CA002324394A patent/CA2324394C/en not_active Expired - Lifetime
  • 1999-03-19 AT AT99913989T patent/ATE414395T1/de not_active IP Right Cessation
  • 1999-03-19 AU AU31941/99A patent/AU3194199A/en not_active Abandoned
  • 1999-03-19 JP JP2000537404A patent/JP3574403B2/ja not_active Expired - Lifetime
  • 1999-03-19 EP EP99913989A patent/EP1072168B1/de not_active Expired - Lifetime
  • 1999-03-19 WO PCT/US1999/006084 patent/WO1999048329A1/en active Application Filing
  • 1999-03-19 DE DE69939898T patent/DE69939898D1/de not_active Expired - Lifetime

Patent Citations (5)

Non-Patent Citations (1)

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