# US 12,010,481 B2 · Acoustic filter for a coaxial electro-acoustic transducer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,010,481 B2 - Document ID: US12010481B2 - Status: Granted - Kind: B2 - Application number: 17/260,896 - Filed: 2019-07-12 - Published: 2021-09-23 - Granted: 2024-06-11 - Earliest claimed: 2018-07-17 - Assignees: Blueprint Acoustics Pty Ltd - Applicants: Blueprint Acoustics Pty Ltd - Inventors: Zeljko Velican - Web page: https://patentgrep.com/patent/US12010481B2 ## CPC - H04R 1/2869: {Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself} - H04R 1/24: Structural combinations of separate transducers or of two parts of the same transducer and responsive respectively to two or more frequency ranges - H04R 1/2849: {for loudspeaker transducers} - H04R 3/14: Cross-over networks - 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 An acoustic filter suitable for an electro-acoustic transducer includes a relatively high frequency driver and a relatively low frequency driver situated on a common axis. The acoustic filter includes a baffle body having an outer side and an inner side, such that the outer side serves as a baffle for the high frequency driver. The inner side forms a first wall of a Helmholtz resonator including a chamber and a vent duct communicating with the chamber. ## Claims ### Claim 1 An acoustic filter suitable for an electro-acoustic transducer having a relatively high frequency driver and a relatively low frequency driver situated on a common axis, said acoustic filter comprising: a baffle body having an outer side and an inner side, such that said outer side serves as a baffle for said high frequency driver and said inner side forms a first wall of at least one Helmholtz resonator including a chamber and a vent duct communicating with said chamber wherein the baffle body is arranged to convert low end response of the high frequency driver to half space radiation (2 pi steradian); wherein said Helmholtz resonator acts with said baffle body to provide an acoustic crossover between said drivers, and wherein said Helmholtz resonator is adapted to boost output of said low frequency driver above piston range both on-axis and off-axis to provide a response perceived by a listener to be substantially flat over a wide range of listening angles; and wherein said low frequency driver includes a cone and wherein said cone forms a second wall of said Helmholtz resonator. ### Claim 2 (depends on 1) An acoustic filter according to claim 1 wherein said Helmholtz resonator is tuned to a crossover frequency above which it acoustically rolls off. ### Claim 3 (depends on 1) An acoustic filter according to claim 1 wherein said baffle body in combination with said high frequency driver is adapted to cover a piston area associated with said low frequency driver defined by a circular section with a radius about the main axes of at least 80% of a piston radius associated with said low frequency driver. ### Claim 4 (depends on 1) An acoustic filter according to claim 1 wherein said baffle body is adjusted to contribute to vent dimensions and/or to contribute to tuning said Helmholtz resonator to a crossover frequency. ### Claim 5 (depends on 1) An acoustic filter according to claim 1 wherein said high frequency driver includes a diaphragm and said baffle body provides separation between said diaphragm of said high frequency driver and the cone of said low frequency driver to reduce cross-talk between said high and low frequency drivers. ### Claim 6 (depends on 1) An electro-acoustic transducer according to claim 1 including an acoustic filter. ### Claim 7 A method of acoustically filtering an electro-acoustic transducer having a relatively high frequency driver and a relatively low frequency driver situated on a common axis to form an acoustic crossover between said drivers, said method comprising: forming a baffle body having an outer side and an inner side, such that said outer side acts as a baffle for said high frequency driver and said inner side forms a first wall of at least one Helmholtz resonator including a chamber and a vent duct communicating with said chamber wherein the baffle body is arranged to convert low end response of the high frequency driver to half space radiation (2 pi steradian); wherein said Helmholtz resonator acts with said baffle body to provide an acoustic crossover between said drivers; adapting said Helmholtz resonator to boost output of said low frequency driver above piston range both on-axis and off-axis to provide a response perceived by a listener to be substantially flat over a wide range of listening angles; and wherein said low frequency driver includes a cone and wherein said cone forms a second wall of said Helmholtz resonator. ### Claim 8 (depends on 7) A method according to claim 7 including tuning said Helmholtz resonator to a crossover frequency above which it acoustically rolls off. ### Claim 9 (depends on 7) A method according to claim 7 including adapting said baffle body in combination with said high frequency driver to cover a piston area associated with said low frequency driver defined by a circular section with a radius about the main axes of at least 80% of a piston radius associated with said low frequency driver. ### Claim 10 (depends on 7) A method according to claim 7 including adjusting said baffle body such that it contributes to vent dimensions and/or contributes to tuning said Helmholtz resonator to a crossover frequency. ### Claim 11 (depends on 9) A method according to claim 9 wherein said high frequency driver includes a diaphragm and including arranging said baffle body to provide separation between said diaphragm of said high frequency driver and the cone of said low frequency driver to reduce cross-talk between said high and low frequency drivers.