# US 10,309,421 B2 · Fan noise reduction using an adaptive helmholtz chamber > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,309,421 B2 - Document ID: US10309421B2 - Status: Granted - Kind: B2 - Application number: 15/041,698 - Filed: 2016-02-11 - Published: 2017-08-17 - Granted: 2019-06-04 - Earliest claimed: 2016-02-11 - Assignees: Lenovo Enterprise Solutions (Singapore) Pte. Ltd. - Applicants: Lenovo Enterprise Solutions (Singapore) Pte. Ltd. - Inventors: Daniel P. Kelaher; Kevin Perveiler - Web page: https://patentgrep.com/patent/US10309421B2 ## CPC - F04D 29/665: {by means of resonance chambers or interference} - F04D 19/002: {Axial flow fans} - F04D 27/004: {by varying driving speed} - F04D 29/522: {especially adapted for elastic fluid pumps} - F04D 29/545: {Ducts} - Y02B 30/70: Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating - F04D: NON-POSITIVE-DISPLACEMENT PUMPS (engine fuel-injection pumps F02M; ion pumps H01J41/12; electrodynamic pumps H02K44/02) - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract A fan assembly includes a fan having an outlet side, a fan duct positioned at the fan outlet side, and a hollow cylindrical chamber positioned within the fan duct, wherein the chamber has two closed ends, a cylindrical side wall, and an inlet port. The dimensions of the chamber are determined to suppress one or more noise frequencies emitted by the fan. In one example, one or more dimensions of a chamber disposed in an outlet duct of an axial fan is automatically adjusted to suppress a noise frequency that is a function of a rotational speed of the axial fan. ## Claims ### Claim 1 An apparatus, comprising: a fan having an outlet side; a fan duct positioned at the fan outlet side; and a hollow cylindrical chamber positioned within the fan duct, wherein the chamber has two closed ends, a cylindrical side wall, and an inlet port formed in the cylindrical side wall. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the inlet port is adjacent to a distal end of the chamber. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the inlet port of the chamber is formed by a series of open slots or an open ring. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein one or more dimension of the chamber is varied in response to a change in fan rotational speed. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the one or more dimension of the chamber is varied to an extent that is predetermined to cause suppression of a rotational speed-dependent noise frequency. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein the inlet port has a width that is varied in response to the change in fan rotational speed. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the fan is a variable speed fan. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the fan is an axial fan having a fan hub, and wherein the cylindrical chamber is axially aligned with the fan hub. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein the cylindrical chamber has an outer diameter matching a diameter of the fan hub. ### Claim 10 (depends on 8) The apparatus of claim 8, further comprising: a metal pickup formed at a proximal end of the chamber; and one or more magnets secured to the fan hub adjacent the metal pickup, wherein the rotation of the fan hub causes the magnets to induce angular displacement of the metal pickup about an axis of the fan. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein the angular displacement of the metal pickup causes a variation in one or more dimension of the chamber in order to vary a noise frequency that will be suppressed. ### Claim 12 (depends on 11) The apparatus of claim 11, wherein the one or more dimension of the chamber is selected from the group consisting of chamber length, inlet port length, inlet port width and combinations thereof. ### Claim 13 (depends on 10) The apparatus of claim 10, further comprising: a fixed bearing that secures the metal pickup in axial alignment with the axial fan and allowing the metal pickup to rotate within the bearing. ### Claim 14 (depends on 13) The apparatus of claim 13, further comprising: a spring biasing the metal pickup to a default angular orientation. ### Claim 15 (depends on 10) The apparatus of claim 10, wherein the chamber includes a proximal chamber portion and a distal chamber portion; wherein the proximal chamber portion is coupled to the metal pickup, supported by a fixed bearing that allows the proximal chamber portion to rotate in place while maintaining axial alignment with the axial fan, and includes a spiral groove; and wherein the distal chamber portion is concentric with the proximal chamber portion and includes a pin received in the spiral groove of the proximal chamber portion such that rotation of the proximal chamber portion causes longitudinal movement of the distal chamber portion relative to the proximal chamber portion. ### Claim 16 (depends on 15) The apparatus of claim 15, wherein the chamber further includes an intermediate chamber portion including a pin received in a second spiral groove of the proximal chamber such that rotation of the proximal chamber portion further causes longitudinal movement of the intermediate chamber portion relative to the proximal chamber portion. ### Claim 17 (depends on 16) The apparatus of claim 16, further comprising: a seal disposed between the proximal and intermediate chamber portions to form an air-tight seal while allowing the chamber portions to move longitudinally relative to each other. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein rotation of the proximal chamber portion in a first direction causes longitudinal movement of the intermediate chamber portion to extend a length of the chamber and causes longitudinal movement of the distal chamber portion to increase a width of the inlet port and decrease the inlet port passage length. ### Claim 19 (depends on 18) The apparatus of claim 18, wherein the slopes of the first and second spiral grooves are independently selected to cause longitudinal movement of the distal and intermediate chamber portions at rates determined to suppress a rotational speed-dependent noise frequency. ### Claim 20 A method comprising: automatically adjusting one or more dimensions of a Helmholtz chamber disposed in an outlet duct of an axial fan to suppress a noise frequency that is a function of a rotational speed of the axial fan, wherein eddy currents induced by rotation of the axial fan are used to drive the adjustments in the one or more dimensions of the Helmholtz chamber as a function of the rotational speed of the axial fan. ### Claim 21 (depends on 20) The method of claim 20, wherein the one or more dimension of the Helmholtz chamber is selected from the group consisting of a length of the chamber, a length of an inlet port to the chamber, a width of an inlet port to the chamber, and combinations thereof. ### Claim 22 An apparatus, comprising: a fan having an outlet side; a fan duct positioned at the fan outlet side; and a hollow cylindrical chamber positioned within the fan duct, wherein the chamber has two closed ends, a cylindrical side wall, and an inlet port, wherein one or more dimension of the chamber is varied in response to a change in fan rotational speed.