Active noise control in a duct with highly turbulent airflow

• US 5,606,622 A
• Filed: 09/29/1994
• Issued: 02/25/1997
• Est. Priority Date: 09/29/1994
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Christenson, Terry N.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US08/315,011
• Time in Patent Office: 880 Days
• Field of Search: 415/119, 381/71
• US Class Current: 381/71.5
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17861 using additional means for damping sound, e.g. using sound absorbing panels
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 2210/1082 Microphones, e.g. systems using "virtual" microphones
• CPC Class Codes: G10K 2210/112 Ducts
• CPC Class Codes: G10K 2210/1281 Aircraft, e.g. spacecraft, airplane or helicopter
• CPC Class Codes: G10K 2210/507 Flow or turbulence

Abstract

A system for providing active noise control for turbulent airflow in a duct utilizing flow straightening upstream of bullet shaped microphones coupled to the noise control electronics thereby improving noise coherence between the input and error microphones and achieving noise reduction.

Claims

1. In combination in an active noise cancellation system in a duct having an input microphone, a control speaker, and an error microphone;

a turbulent airflow control device disposed upstream in said duct from said input microphone;

said input microphone and said error microphone having bullet shaped profiles;

the combination wherein said turbulent airflow control device comprises a perforated plate wherein a honeycomb section is attached to said perforated plate.

2. In combination in an active noise cancellation system in a duct having an input microphone, a control speaker, and an error microphone;

a turbulent airflow control device disposed upstream in said duct from said input microphone;

said input microphone and said error microphone having bullet shaped profiles;

the combination wherein said turbulent airflow control device comprises a perforated plate wherein a honeycomb section is attached to said perforated plate wherein said honeycomb section has a dimension L/D≧

2 where L is the length of said honeycomb section and D is the average cell diameter.

3. In combination in an active noise control system having an input microphone disposed in a duct, said input microphone coupled to an active noise controller;

a turbulent airflow control device for removing large structured turbulence moving parallel to the sidewalls of said duct and the swirling of air in he said duct tangential to the sidewalls of said duct, said turbulent airflow control device disposed in said duct upstream from said input microphone wherein said turbulent airflow control device comprises a perforated plate and a honeycomb section.