# US 9,438,999 B2 · Acoustic transducer assembly > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,438,999 B2 - Document ID: US9438999B2 - Status: Granted - Kind: B2 - Application number: 14/196,626 - Filed: 2014-03-04 - Published: 2014-09-11 - Granted: 2016-09-06 - Earliest claimed: 2013-03-06 - Assignees: Harman Becker Gepkocsirendszer Gyarto Korlatolt Felelossegu Tarsasag - Applicants: Harman Becker Gepkocsirendszer Gyarto Korlatolt Felelossegu Tarsasag - Inventors: John B. French - Web page: https://patentgrep.com/patent/US9438999B2 ## CPC - H04R 9/046: {Construction} - H04R 9/025: {Magnetic circuit} - H04R 9/06: Loudspeakers - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract Driver for an acoustic transducer having a moving coil of substantially equal length to the air gap. The air gap may itself be extended in length using an upper or lower lip, or both. A stationary coil is also provided. The moving and stationary coils can be controlled by suitable control blocks to form an electromagnet-based transducer with reduced distortion. The acoustic transducer may be a hybrid acoustic transducer. ## Claims ### Claim 1 A driver for an acoustic transducer comprising: a moving diaphragm; a driver body formed of magnetic material and a permanent magnet, the driver body comprising: a center post composed of a first post portion formed of the magnetic material and a second post portion formed of the permanent magnet; an outer wall coupled to the center post via a bottom portion of the driver body; and an annular plate extending inwardly toward the center post from the outer wall; a moving coil coupled to the diaphragm, the moving coil disposed at least partially within an air gap formed between the annular plate and the center post; and a stationary coil disposed within a cavity defined by the annular plate, outer wall, bottom portion and center post, wherein the annular plate includes a first lip that extends into the air gap, and wherein the first lip is positioned between the moving coil and the stationary coil in the air gap. ### Claim 2 (depends on 1) The driver of claim 1, wherein the second post portion couples the first post portion to the bottom portion of the driver body. ### Claim 3 (depends on 1) The driver of claim 1, wherein each of the outer wall, the bottom portion and the annular plate is formed of the same magnetic material. ### Claim 4 (depends on 1) The driver of claim 1, wherein the second post portion comprises an external magnetic portion that extends away from the outer wall. ### Claim 5 (depends on 1) The driver of claim 1, wherein the second post portion is formed of a shape selected from a group consisting of cylinder, a sphere, a torus and a disc. ### Claim 6 (depends on 1) The driver of claim 1, wherein the annular plate comprises an upper lip disposed at an inward end of the annular plate, the upper lip extending away from the cavity to extend the air gap. ### Claim 7 (depends on 1) The driver of claim 1, wherein the air gap has a greater width at an outward portion of an upper lip than at a central portion of the annular plate. ### Claim 8 (depends on 1) The driver of claim 1, wherein a width of an upper lip is tapered to be narrower as the upper lip extends away from the annular plate. ### Claim 9 (depends on 1) The driver of claim 1, wherein the first lip includes a lower lip disposed at an inward end of the annular plate and that extends in a parallel direction to the center post. ### Claim 10 (depends on 1) The driver of claim 1, wherein the moving coil has a moving coil length that is equal to an air gap length of the air gap. ### Claim 11 (depends on 1) The driver of claim 1, wherein the driver body has a tapered outer corner between the bottom portion and the outer wall. ### Claim 12 (depends on 1) The driver of claim 1, wherein the driver body has a tapered outer corner between the outer wall and the annular plate. ### Claim 13 (depends on 1) The driver of claim 1, wherein the driver body has a tapered upper interior portion of the center post. ### Claim 14 (depends on 1) The driver of claim 1, wherein an inward face of the annular plate is not parallel to the center post. ### Claim 15 (depends on 1) The driver of claim 1, further comprising at least one additional annular plate, the at least one additional annular plate defining at least one additional air gap and at least one additional cavity. ### Claim 16 (depends on 1) The driver of claim 1 wherein the first lip includes a lower lip positioned directly between the center post and the stationary coil. ### Claim 17 (depends on 4) The driver of claim 4, wherein: the magnetic material comprises a first magnetic material and a second magnetic material that is different from the first magnetic material; each of the outer wall, the bottom portion and the annular plate is formed of at least the first magnetic material; and the external magnetic portion is surrounded by one or more layers formed of the second magnetic material. ### Claim 18 (depends on 4) The driver of claim 4, wherein: the external magnetic portion comprises an exterior end and an interior end opposite the exterior end, the interior end engaging the cavity and the exterior end being located at the center of the driver; and the second post portion is disc-shaped. ### Claim 19 (depends on 4) The driver of claim 4, wherein: the external magnetic portion comprises an exterior end and an interior end opposite the exterior end, the interior end engaging the cavity and the exterior end being spaced from the center of the driver; and the second post portion is toroidal in shape. ### Claim 20 (depends on 9) The driver of claim 9, wherein the air gap has a greater width at an outward portion of the lower lip than at a central portion of the annular plate. ### Claim 21 (depends on 9) The driver of claim 9, wherein a width of the lower lip is tapered to be narrower as the lower lip extends away from the annular plate. ### Claim 22 (depends on 10) The driver of claim 10, wherein the moving coil length is at least 400% of a maximum excursion of the moving coil. ### Claim 23 (depends on 14) The driver of claim 14, wherein the air gap is wider at an outer portion of the air gap and narrower at a central portion of the air gap. ### Claim 24 (depends on 15) The driver of claim 15, wherein an inward portion of the at least one additional annular plate is coupled to an upper portion of the center post, further comprising an additional stationary coil disposed within the at least one additional cavity, wherein the additional stationary coil has an additional flux path rotating in thein an opposite direction to a flux path of the stationary coil. ### Claim 25 (depends on 15) The driver of claim 15, further comprising at least one additional moving coil respectively disposed within the at least one additional air gap; and at least one additional stationary coil respectively disposed within the at least one additional cavity. ### Claim 26 (depends on 17) The driver of claim 17, wherein each subsequent layer in the one or more layers surrounding the external magnetic portion decreases in length. ### Claim 27 (depends on 17) The driver of claim 17, wherein the one or more layers are tapered.