WO2012038981A1

WO2012038981A1 - Linear actuation loudspeaker driver

Info

Publication number: WO2012038981A1
Application number: PCT/IN2011/000658
Authority: WO
Inventors: Praveen Vallabhaneni
Original assignee: Praveen Vallabhaneni
Priority date: 2010-09-23
Filing date: 2011-09-22
Publication date: 2012-03-29
Also published as: WO2012038981A9

Abstract

Electrodynamic loudspeaker (electroacoustic transducer) driver where the coil is connected to the diaphragm via surface gap(s) in the magnetic field assembly part(s) enclosing the coil or enclosed by the coil or both, thereby making it possible to build loudspeakers that are compact with respect to diaphragm excursion, capable of mirror symmetry motor construction and least non-linear distortions, capable of producing high diaphragm exclu sions and able to optimize the magnetic field incident on the coil.

Description

Linear actuation loudspeaker driver

BACKGROUND

Technical Field

[001 ]The present invention relates to a loudspeaker assembly. More particularly the inv ntion relates to an electrodynamic loudspeaker (electroacoiistic transducer) that can comprise of symmetric mirror image motor halves and that can provide diaphragm excursion less lhaii, closer to or greater than the cross sectional dimension (diameter etc) of the diaphragm

Description of the Related Art

[002]Compact, slim loudspeakers, be they subwoofers or midrange or tweeters have the obvious advantage of portability and integration in small spaces.

At lower sound frequencies, more amount of air needs to be moved to maintain higher volume levels.

[003] Loudspeakers with high excursion levels are able to produce low frequency sound as they can move larger volumes of air without increasing the size of the diaphragm and thereby increasing the size of the cabinet and increasing cabinet costs, shipping costs, finishing costs and other disadvantages associated with increased cabinet size for the approximately same sonic performance.

[004]Since most current subwoofer design technologies provide a fraction of excursion lor a given speaker length/height, larger diaphragm subwooleis are used to compensate for the small excursions possible. Even though larger speakers are used, they are not a complete substitute for increased diaphragm excursion to produce lower frequency sound.

[005]The limits of the common design for electrodynamic loudspeaker drivers is due to the design limitations and stability problems brought up by long formers (hollow cylindrical structures on which the coils are wound) in small magnetic spaces, suspensions required, increase in structural size and weight imbalance (with the motor structure on one end and diaphragm on the other end). It becomes harder to keep the coil and former centered in the air gap as the excursion levels get higher.

[007]In US7088841 , this particular prior art has segmented magnets which have gaps between them, but the gaps are not utilized for connecting the coil, this above art uses a regular cylindrical former to tap the mechanical energy of the coil to the diaphragm via Hie magnetic space only.

[008]In US20100150392, method described in this method uses regular cylindrical I rmcr to tap the mechanical energy of the coil to the diaphragm via the magnetic space only.

In US20090190791 This prior art, uses cylindrical former in the magnetic space lo t ransmit mechanical energy from the coil to the diaphragms.

[009]In US20080056527, the method described in this patent uses regular cylindrical former to tap the mechanical energy of the coil to the diaphragm.

[010]In US20040218778 and US6778677 the suspension components are tapped directly from the coil structure within the magnetic field assembly structure, but still a cylindrical former is used to tap the mechanical energy from the coil to the diaphragm- through the magnetic space only.

[01 l ]In US7317810, opposing magnets are used to push the Held towards the coil creating a magnetic space without the need for a pole inside the coi l and the coil is connected to the diaphragm via a cylindrical former / bobbin through the magnetic space and not via any surface gap(s) in the magnetic field assembly part(s) surrounding the coil. [012]In the prior art, we see that the coil is placed in a magnetic space with gaps between the coil and the field structure so as to allow for linear motion of the coil. The force produced by the coil is transferred to the diaphragm via the former which is a cylindrical hollow pipe-like structure that has to excurse in the gap along with the coil.

[013]As the magnetic assembly is made deeper to allow the existing design to provide more linear motion, longer voice coils (in overhung coils) and formers have to be used which not only become heavy but also make the system unstable as the coil and former are support d outside the magnetic structure, but inside the structure, they are freely suspended without support and as the length increases it becomes very difficult and unstable to keep the voice coil and former centered in the air gap, hence the length of the former (coil-diaphragm connection) becomes directly proportional to the length of coil-diaphragm excursion.

[014] Also, in the current design, more the diaphragm excursion desired, sti lTer or more number ol^' spiders/suspensions placed away from each other have to be employed to k the former in place and to connect to the diaphragm. Still the length of linear excursion remains a fraction of the whole length of the speaker structure, causing the whole speaker structure to be huge with respect to the actual length being used for diapliragm excursion. Also the former covers a whole surface area of the coil interfering with the field incident on the coil and the magnetic space has to accommodate the thickness of the layer of the former jjjaced in the magnetic space along with the coil.

[015]Also, in current drivers, there is less possibility of mirror image metal & thermal environments for the coil during its excursion and mirror image symmetry flux distribution, including fringe fields, at the magnetic space/gap due to the way the drivers are constructed without symmetric magnetic assembly structures, comprising of mirror image halves, not necessarily meaning two separate halves, but the design of the magnetic circuit itself due to the coil-diaphragm connection via the voice coil former. 75 Present invention helps address some or all of the above mentioned problems.

Statement of the invention:

80 [016]Electrodynamic loudspeaker (electroacoustic transducer) driver motor where the coil is connected to the diaphragm via surface gaps in the magnetic field assembly parts enclosing the coil or enclosed by the coil or both, (hereby making is possible to build loudspeaker drivers/transducers with mirror symmetry motor structures that are compact with respect to diaphragm excursion, capable of producing high excursions and capable of less interference

85 between magnetic field and coil.

Summary:

| 01 7]An electrodynamic loudspeaker driver that is capable of high diaphragm excursion and being compact with respect to its diaphragm excursion length and capable of optimizing the

90 magnetic field incident on the coil(s) by the virtue of the coil(s) being connected to the diaphragm(s) via surface gap(s) in the magnetic field assembly part(s) enclosing the coil or enclosed by the coil or both. Some of the embodiments/iterations of thejDresent invention include slim profile speakers, speakers with mirror symmetry motor structures, speakers with high diaphragm excursion, speakers with optimized magnetic field interaction with the coil,

95 multi-point speakers, multi-concentric speakers, spiral diaphragm excursion speakers. 100 Brief description of drawings

[018]The invention will now be described with reference to accompanying drawings in which,

Figure - 1 shows side view of the horizontal gap connection type loudspeaker.

Figure - 2 shows inner and outer diaphragm type variation

105 Figure- 3 shows a multi-point type loudspeaker with multiple coils

Figure - 4 shows side view of high excursion type driver

Figure - 5 shows sectional view of few basic types of connections between coil and diaphragm

Figure - 6 shows sectional view of angular connection from the coil surface to the diaphragm

1 10

Detailed Description

[019]The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing

1 15 from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will rceogni e

120 that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims. Definitions:

125 Certain parts are defined for the purpose of this invention. [020]Magnetic field assembly:

When a magnetic field producing part such as a permanent magnet, field coil etc, is incorporated into a housing or mounted to other part(s), which may be magnetically conducting in nature (ferromagnetic), it is be called a magnetic field assembly.

130

[021 ]Magnetic space:

Also known as 'Magnetic Gap', is the space between two magnetic pole faces. A voice coil placed in a magnetic space of high flux density, which is usually also an air gap in a loudspeaker driver, interacts with the magnetic field when a signal is passed through I he coil 135 and vibrates.

[022]Voice coil:

The element in a loudspeaker that vibrates according to a varying electrical signal and so produces sound waves when rigidly connected to a diaphragm. Generally comprises of a coil 140 of wire which is placed in a magnetic field in a magnetic space and vibrates when an audio signal is supplied to it. The voice coil generally may be wound on a cylindrical structure known as 'former'.

[023]Diaphragm:

145 The element or membrane in a loudspeaker that couples with a medium such as air, producing sound waves. The diaphragm is the most significant sound producing element in a loudspeaker. Usually referred to as the cone due to the shape that is most widely used in the loudspeaker industry. However, flat, elliptical, square, rectangular, polygon and other shape diaphragms can be used as well.

150

[024]Geometrically Symmetric Mirror Image Halves:

Meaning the construction of the motor assembly made of one or more magnetic field assemblies comprises of symmetrical construction of the ferromagnetic return structures/poles or the magnetic field producing parts such as permanent magnets or field 155 coils (not limited to physically separated halves assembled together) on either sides of the axis of symmetry which in many iterations can be across the magnetic space(s).

[025]The invention helps provide loudspeakers that are compact with regards to the diaphragm excursion levels, able to provide linear excursion comparable to the dimensions of the cone/diaphragm itself and loudspeakers with less physical interference between the 160 magnetic poles and the coil(s).

| 026]The need for the invention is to be able lo tap the mechanical energy of (he coi l( s) lo th diaphragm(s) via one or more surface gaps in the magnetic assembly part(s) surrounding (li surface(s) of the coil(s) so that the field exerted on the coil(s) can be max nizgd and/or to be able to keep the loudspeaker compact with respect to its diaphragm excursion by excursing 165 along the length of the speaker structure whilst keeping the size of the connection (analogous to the former in common loudspeakers) between coil and diaphragm compact and dependent on the size of the coil and the surface gaps rather than the excursion level. Hence, slim profile speakers (subwoofers, mid-range etc) can be made or longer loudspeakers can have higher diaphragm excursion to move larger volumes of air at low frequencies. 170 [027]Here, a coil (considering only one coil) is placed in the magnetic space (air gap) facilitated by one or more magnetic assembly parts, be they magnets or parts connected to magnets or both. Since magnetic field flows from one magnetic pole to the other, the magnetic assembly parts exert magnetic field on the coil from the part inside the coil to the part outside or vice versa.

175 [028]In the present invention, the coil in the magnetic space is connected to the diaphragm via surface gaps in the magnetic assembly part(s) enclosing the coil or enclosed by the coil or both. This can be done by incorporating the gap(s) in the magnetic assembly part or arranging the said parts (segmented magnets, focusing plates etc) to have the surface gap(s) between them. The said surface gap(s) leading into the magnetic space(s).

180 [029]TheoreticalIy, one surface gap is enough for the connection to be established, however in practicality more evenly spaced surface gaps around the coil help tap the energy from the coil more evenly and stably.

[030] The connection between coil and diaphragm through the surface gap(s) surrounding the inner/outer surfaces of the coil can range from vertical to horizontal with respect to the

185 coil and diaphragm, hence allowing these type of connections to facilitate diaphragm

excursion through the magnetic assembly enclosing it or enclosed by it, utilizing the length of the loudspeaker structure for excursion, hence keeping the whole loudspeaker structure compact with respect to the diaphragm excursion and having the dimensions of the coil- diaphragm connection(s) depend on coil and surface gap dimensions rather than excursion

190 length.

[031 ]Also, the loudspeaker can have the diaphragm excurse outside the magnet ic structure (like in common electrodynamic loudspeakers) via horizontally oriented connection(s ) via the surface gap(s) with the length of diaphragm excursion and the length of the motor structure (magnetic assembly and coil) arranged in series to each other, adding to the total length of the 195 loudspeaker driver . The coil(s) can be connected to the amplifier or signal source via the connectors (or concentric ribbed structures) through the surface gaps and the suspension or diaphragm etc.

[032]The coil(s) may be Underhung, Hqual-hung or Overhung type. Vast number of mirror symmetric magnetic circuits can be constructed in this t chnique of coil-diaphragm

200 connection - one example being, coupling magnets/field coils with opposite magnetic

orientations to either side of a plate which forms a magnetic space along with the flux return structures of the magnets/field coils and the coil-diaphragm connection gaps implemented in the return structures surrounding the voice coil(s) outer/inner surface depending on whether the flux return structures are outside/inside the magnets/field coils.

205 [033]Shorting rings, slots and holes in parts, fcrrofluids, retardation magnets, sensors,

multiple coils, diaphragms placed coaxially along the length of the speaker structure, cooling vents, cooling systems etc can be incorporated as desired. Although compact and powerful magnets (like rare earth magnets) are preferred for the invention, other magnetic materials may be used as well.

210

[034]Following are the components and their reference numbers

10 - Surround of diaphragm

20 - Diaphragm

30 - Connector/Connection between coil and diaphragm

40 - Coil

50 - Magnetic assembly and associated parts

60 - Suspension

70 - Supporting frame

[035]Figure -1 shows side view of the horizontal connection from the coil surface to the diaphragm, through the surface gap. Coil 40 is placed in the magnetic space between magnetic assembly parts 50-A and 50-B, 40 is horizontally connected to 20 via 30 through the gap in 50-A. [036]Figure -2 shows inner and outer diaphragm type variation with connections between coil and diaphragms via surface gaps. Coil 40 is placed in the magnetic space between 50-Λ and 50-B, 40 is connected to outer diaphragm 20-A via 30-A through the gaps in 50-A, coil 40 is also connected to inner diaphragm 20-B via 30-B through the gaps in 50-B. The iteration can also have either inner diaphragm or outer diaphragm only, if desired.

[037]Figure-3 shows a multi-point type variation with multiple coils connected to the diaphragm at different points on the diaphragm via the surface gaps. Magnets 50-A, pole pieces 50-B and three assembly variations arc shown as examples for the multiple point connections on the diaphragm 20. In each point application, coil 40 is placed in the magnetic space between magnetic assembly parts, coil 40 is connected to diaphragm 20 via connection 30 through the surface gaps in the magnetic assembly parts surrounding the coil, this is repeated at multiple points on diaphragm as shown.

[038]Figure-4 shows side view of high excursion type driver with bellow type suspension 60, surround 10 and supporting skeletal frame 70, where diaphragm20 is connected by connector 30 to the coil 40 via surface gaps. Coil 40 is placed in the magnetic space between magnetic assembly parts 50-A and 50-B, 40 is connected to diaphragm 20 via connection 30 through the gaps in 50-A. Suspension 60 connects either 20 or 30 or both with frame 70.

[039]Figure -5 shows sectional view of the connection between coil and diaphragm by 30 which is connected to coil 40.

Top left depicts an iteration of a vertical type coil connection

Top right depicts the vertical connection with a reinforcing frame and 30-C for support from inside the coil 40.

Bottom left depicts iterations of horizontal type gap connection 30, where 30-Λ is the part of the connection going into the gap and 30-B is the supporting/reinforcing frame which can he integrated with 30- A or an attachment.

Bottom right depicts the horizontal connection 30-A with a reinforcing frame 30-13 attached to the edge of the coil 40 and the thickness of the reinforcing frame 30-B preferably not exceeding the thickness of coil 40.

[040]Figure -6 shows sectional view of angular connection from the coil surface to the diaphragm. Coil 40 is placed in the magnetic space between magnetic Held assembly parts 50-A and 50-B. Coil 40 is angularly connected to diaphragm 20 via angular conneclion 0 through the surface gap in 50-A.

Claims

I claim:

1 ) An electromagnetic transducer comprising:

One or more magnetic field assembly part(s) with one or more gap(s) through the surface(s) of the said magnetic field assembly part(s) and said part(s) having one or more magnetic space(s) between them;

One or more voice coil(s) placed in the said magnetic space(s);

One or more diaphragm(s) connected to the said voice coil(s) through (he said one or more surface gap(s) in the said magnetic field assembly part(s).

2) Transducer arrangement of the claim 1 wherein the diaphragm(s) are placed either a) concentrically on the inner portion of the part(s) of the said magnetic field assembly part(s) enclosed by the voice coil(s); or

b) concentrically on the outer portion of the said magnetic field assembly part(s) thai enclose the voice coil(s); or

c) concentrically on the inner portion and the outer portion of the said magnetic field assembly part(s) that enclose the voice coil(s) and are enclosed by the voice coil(s); or d) Coaxial or serial to the said magnetic field assembly or assemblies.

3) Transducer arrangement of the claim 1 wherein the diaphragm(s) excurses ]ess than, equal to or greater than the dimension of the diaphragm(s).

4) Transducer arrangement of the claim 1 wherein the cross section can be circular, elliptical, oval, polygon or other closed geometries.

5) Transducer arrangement of the claim 1 wherein the diaphragm or coil assembly restoring force can be provided by one or more suspension mechanism(s). 6) Transducer arrangement of the claim 5 wherein the suspension system(s) are spring structure(s), or bellow structure(s) , or elastic structure(s) , or spider suspension(s) , or a combination of them.

7) Transducer of claim 1 wherein voice coil(s) and diaphragm(s) may be connected usi g concentrically ribbed structure(s).

8) Loudspeaker/ electromagnetic transducer of claim 1 wherein; the magnetic iield assembly structure(s) comprise substantially geometrically symmetric mirror image halves.

9) An electromagnetic transducer, comprising of one or more magnetic assembly stnicliire(s) with one or more diaphragm(s) connected to one or more voice coil(s) placed in one or more magnetic space(s), through one or more gap(s) in the magnetic iield assembly part(s);

-surrounding the outer surface of the voice coil(s); or

-surrounded by the inner surface of the voice coil(s); or

-surrounding the outer surface of the voice coil(s) and surrounded by the inner surface of the voice coil(s);

the connection(s) through the gap(s) may be provided by one or more rib(s) in concentric section(s), said diaphragm(s) and voice coil(s) may be placed on the said concentric section(s) or away from the said concentric section(s );

said transducer having one or more suspension mechanism(s); said suspensi£¾ mechanism(s) may comprise of spring structure(s), or bellow structure! s), or elastic structure(s), or spider suspension(s), or a combination of them;

said magnetic field assembly structure(s) having one or more permanent magnet(s), or Iield coil(s), or both;

said magnetic field assembly structure(s) may comprise of substantially geometrically symmetric mirror image halves.