Aircraft cabin noise control apparatus

• US 4,947,356 A
• Filed: 02/10/1989
• Issued: 08/07/1990
• Est. Priority Date: 06/23/1986
• Status: Expired due to Term

• Current Assignee: The United States of America As Represented By The Secretary of Commerce
• Original Assignee: Secretary of State For Trade and Industry In Her Britannic Majesty's Government of The United Kingdom of Great Britain and Northern Ireland
• Inventors: Nelson, Philip A., Elliott, Stephen J.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): ZANELLI, MICHAEL J
• Application Number:
  US07/312,709
• Time in Patent Office: 543 Days
• Field of Search: 364/266, 364/166, 364/574, 381/71, 416/34, 244/1 N
• US Class Current: 700/280
• CPC Class Codes: B64C 1/40 Sound or heat insulation , e.g. using insulation blankets
• CPC Class Codes: B64C 11/50 Phase synchronisation between multiple propellers
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17883 the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
• CPC Class Codes: G10K 2210/123 Synchrophasors or other applications where multiple noise sources are driven with a particular phase relationship
• CPC Class Codes: G10K 2210/1281 Aircraft, e.g. spacecraft, airplane or helicopter
• CPC Class Codes: G10K 2210/3046 Multiple acoustic inputs, multiple acoustic outputs

Abstract

In propeller of fan driven aircraft, cabin noise levels may be reduced by adjustment of the phase relationship between a reference propeller or fan and some or all of the other propellers or fans. An aircraft cabin (1) contains four microphones and two loudspeakers which form the active elements of a noise control system. The microphone outputs are fed via amplifiers to a digital signal processor (11) having an adaptation algorithm in a memory store. The processor generates an error signal which is used to adjust the synchrophase angle between the reference propeller and a synchrophased propeller, controlled by a synchrophaser. Thus the synchrophase angle is varied dynamically during flight to minimize propeller noise in the cabin over a range of flying conditions.

Claims

1. Cabin noise control apparatus for an at least two propeller or fan driven aircraft, said apparatus comprising:

a plurality of transducers located inside a cabin of said aircraft;

a signal processor means for receiving and analyzing signals from said plurality of transducers wherein said signal processor means computes an estimate of the gradient of the sum of the means square outputs of the transducers with respect to the phase relationship θ

m between a reference propeller or fan and each other propeller or fan and causes the synchrophaser to increment θ

m by an amount dependent on the value of the gradient in order to minimise the sum of the mean square outputs of the transducers; and

a synchrophaser for varying, during flight, the phase relationship between a reference propeller or fan of the aircraft and at least one of the other propellers or fans of the aircraft in response to the output from said signal processor.

2. Cabin noise control apparatus as claimed in claim 1 wherein at least one of the transducers is a microphone.

3. Cabin noise control apparatus as claimed in claim 1 wherein at least one of the transducers is an accelerometer.

4. Cabin noise control apparatus as claimed in claim 1 characterised in that the signal processor forms part of an active noise control system which generates sound waves in anti-phase with ambient noise waves.

5. Cabin noise control apparatus for an at least two propeller or fan driven aircraft, said apparatus comprising:

a plurality of transducers located inside a cabin of said aircraft;

a signal processor means for receiving and analyzing signals from said plurality of transducers and for computing an estimate of a gradient of a sum of a mean square output of said transducers with respect to a phase relationship θ

m between at least one reference propeller or fan and at least one other propeller or fan; and

a synchrophaser for varying, during flight, the phase relationship between said reference propeller or fan and said at least one other propeller or fan and in response to said signal processor means, incrementing θ

m an amount dependent upon the value of said gradient in order to minimize the sum of the mean square outputs of said transducers.

6. Cabin noise control apparatus as claimed in claim 5 wherein at least one of said transducers is a microphone.

7. Cabin noise control apparatus as claimed in claim 5 wherein at least one of said transducers is an accelerometer.

8. Cabin noise apparatus as claimed in claim 5 in which said signal processor comprises at least a portion of an active noise control system which generates sound waves in anti-phase with ambinent noise waves.