Method and apparatus for reducing noise radiated from a complex vibrating surface

• US 5,410,607 A
• Filed: 09/24/1993
• Issued: 04/25/1995
• Est. Priority Date: 09/24/1993
• Status: Expired due to Fees

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Mason, V. Bradford, Naghshineh, Koorosh
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US08/126,493
• Time in Patent Office: 578 Days
• Field of Search: 381/71, 381/94
• US Class Current: 381/71.2
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward
• CPC Class Codes: G10K 2210/102 Two dimensional
• CPC Class Codes: G10K 2210/1053 Hi-fi, i.e. anything involving music, radios or loudspeakers
• CPC Class Codes: G10K 2210/1291 Anti-Vibration-Control, e.g. reducing vibrations in panels or beams
• CPC Class Codes: G10K 2210/3011 Single acoustic input
• CPC Class Codes: G10K 2210/3013 Analogue, i.e. using analogue computers or circuits
• CPC Class Codes: G10K 2210/501 Acceleration, e.g. for accelerometers
• CPC Class Codes: G10K 2210/512 Wide band, e.g. non-recurring signals

Abstract

An apparatus for reducing noise radiated from a complex vibrating surface includes: a motion sensor responsive to a region of the vibrating surface that contributes to a noise field in a fluid medium; a controller having a substantially fixed transfer function, where the controller is responsive to an electrical motion signal produced by the motion sensor and is operative to produce an electrical antinoise signal; and an acoustic driver responsive to the electrical antinoise signal and operative to produce and an acoustic antinoise field that is substantially 180° out-of-phase with the original noise field. The antinoise field reduces the original noise field by the process of destructive interference without substantially affecting the motion of the vibrating surface. If the medium is air, the acoustic driver is preferably a loudspeaker which is operated so that its cone velocity is approximately equal to the ratio of a noise-source area weighting to a cone area weighting multiplied by the velocity of the noise source. A method for reducing noise radiated from a complex vibrating surface in accordance with the present invention includes: dividing the vibrating surface into a plurality of regions, each of which contributes to a noise field in a fluid medium; and, for each region of the vibrating surface, developing an antinoise field that effectively reduces the original noise field associated with that region. The plurality of antinoise fields provides wideband noise reduction in a quiet zone of arbitrary size and shape.

Claims

1. An apparatus for reducing noise radiated from a vibrating surface comprising:

a motion sensor to sense the mechanical movement of a vibrating surface, said vibrating surface developing a broadband noise field having multiple propagation modes in a fluid medium, said motion sensor being operative to convert movement of said vibrating surface into a motion signal;

a controller having a substantially fixed transfer function, said controller being responsive to said motion signal and operative to produce an antinoise signal; and

an output transducer responsive to said antinoise signal and operative to produce a broadband antinoise field having multiple propagation modes which is approximately the same amplitude and which is approximately 180°

out-of-phase with said noise field, such that said antinoise field and said noise field combine to reduce noise in a quiet zone in said fluid medium without substantially affecting vibrations of said vibrating surface;

wherein at least one of said controller and said output transducer are physically attached to said vibrating surface.

2. An apparatus as recited in claim 1 wherein said motion sensor is selected from a group comprising strain gauges, displacement sensors, velocity sensors, and acceleration sensors.

3. An apparatus as recited in claim 1 wherein said output transducer comprises an acoustic driver having a predetermined piston area and a variable piston velocity.

4. An apparatus as recited in claim 1 wherein said output transducer comprises a loudspeaker.

5. An apparatus as recited in claim 1 wherein said motion sensor is mechanically coupled to said vibrating surface.

6. An apparatus as recited in claim 5 wherein said motion sensor comprises an accelerometer.

7. An apparatus as recited in claim 1 wherein said noise field is a component of a sound field, and wherein said sensor:

is substantially unaffected by said sound field.

8. An apparatus for reducing noise radiated from a vibrating surface comprising:

a motion sensor coupled to a vibrating surface, said vibrating surface developing a broadnoise noise field in a fluid medium, said motion sensor being operative to convert movement of said vibrating surface into a motion signal;

a controller having a substantially fixed transfer function, said controller being responsive to said motion signal and operative to produce an antinoise signal; and

an output transducer mechanically coupled to said vibrating surface and responsive to said antinoise signal and operative to produce a broadhand antinoise field which is approximately the same amplitude and which is approximately 180°

out-of-phase with said broadhand noise field, such that said antinoise field and said noise field combine to reduce noise in a quiet zone in said fluid medium without substantially affecting vibrations of said vibrating surface.

9. An apparatus for reducing noise radiated from a vibrating surface comprising:

a motion sensor coupled to a vibrating surface, said vibrating surface developing a noise field in a fluid medium, said motion sensor being operative to convert movement of said vibrating surface into a motion signal;

a controller having a substantially fixed transfer function, said controller being responsive to said motion signal and operative to produce an antinoise signal; and

an output transducer responsive to said antinoise signal and operative to produce an antinoise field which is approximately the same amplitude and which is approximately 180°

out-of-phase with said noise field, such that said antinoise field and said noise field combine to reduce noise in a quiet zone in said fluid medium without substantially affecting vibrations of said vibrating surface;

wherein said output transducer comprises an acoustic driver having a predetermined piston area and a variable piston velocity and wherein said antinoise signal excites said acoustic driver such that its piston velocity is approximately equal to the ratio of said noise source area to said piston area, multiplied by the velocity of said noise source.

10. An apparatus for reducing noise radiated from a vibrating surface comprising:

a motion sensor comprising an accelerometer mechanically coupled to a vibrating surface, said vibrating surface developing a noise field in a fluid medium, said motion sensor being operative to convert movement of said vibrating surface into a motion signal;

a controller having a substantially fixed transfer function, said controller being responsive to said motion signal and operative to produce an antinoise signal; and

an output transducer responsive to Said antinoise signal and operative to produce an antinoise field which is approximately the same amplitude and which is approximately 180°

out-of-phase with said noise field such that said antinoise field and said noise field combine to reduce noise in a quiet zone in said fluid medium without substantially affecting vibrations of said vibrating surface;

wherein said motion sensor, said controller, and said output transducer are attached to said vibrating surface such that the combination of said motion sensor, said controller, and said output transducer does not cover substantially more area of said vibrating surface than the dimensionally largest of said motion sensor, said controller, and said output transducer.

11. A system for reducing broadhand noise radiated from a vibrating surface comprising:

a plurality of active noise-reduction apparatus associated with a plurality of regions of a vibrating surface, wherein each of said plurality of active noise-reduction apparatus includes;

(a) a motion sensor associated with a region of said vibrating surface and operative to convert mechanical motion of said region into a motion signal, said region of said vibrating surface producing a regional broadband noise field in a fluid medium;

(b) a controller having a substantially fixed transfer function, said controller being responsive to said motion signal and operative to produce a regional antinoise signal; and

(c) an output transducer responsive to said regional antinoise signal and located proximate to said region and operative to produce a regional broadhand antinoise field in said fluid medium that is substantially the same amplitude and substantially 180°

out-of-phase with said regional broadband noise field;

such that at least one of said controller and said transducer are physically attached to said vibrating surface; and

such that a noise field comprising a plurality of regional noise fields is at least partially canceled by a cumulative antinoise field comprising a plurality of said regional antinoise fields.

12. A system as recited in claim 11 wherein said plurality of regions of said vibrating surface are substantially regularly spaced.

13. A system as recited in claim 11 wherein said plurality of regions of said vibrating surface are chosen based on knowledge of the structure of said vibrating surface.

14. A system as recited in claim 11 wherein said plurality of regions of said vibrating surface are chosen as areas which create the strongest noise fields.

15. A system for reducing noise radiated from a vibrating surface comprising:

a plurality of active noise-reduction apparatus associated with a plurality of regions of a vibrating surface, wherein said plurality of regions of said vibrating surface are substantially randomly spaced, and wherein each of said plurality of active noise-reduction apparatus includes;

(a) a motion sensor attached to a region of said vibrating surface and operative to convert mechanical motion of Said region into a motion signal said region of said vibrating surface producing a regional noise field in a fluid medium;

(b) a controller having a substantially fixed transfer function, said controller being responsive to said motion signal and operative to produce a regional antinoise signal;

(c) an output transducer responsive to said regional antinoise signal and located proximate to said region and operative to produce a regional antinoise field in said fluid medium that is substantially the same amplitude and substantially 180°

out-of-phase with said regional noise field;

such that a noise field comprising a plurality of regional noise fields is at least partially canceled by a cumulative antinoise field comprising a plurality of said regional antinoise fields.

16. A method for reducing noise radiated from a vibrating surface comprising the steps of:

developing a motion signal from the mechanical movement of a vibrating surface which is producing a broadhand noise field in a fluid medium;

transforming said motion signal into an antinoise signal with a controller having a substantially fixed transfer function; and

developing with an output transducer a broadhand antinoise field from said antinoise signal, said antinoise field being approximately 180°

out-of-phase with said noise field and combining with said noise field in said fluid medium without substantially affecting said mechanical movement of said vibrating surface;

wherein at least one of said controller and said transducer is physically attached to said vibrating surface.

17. A method for reducing noise radiated from a complex vibrating surface comprising the steps of:

dividing said vibrating surface into a plurality of regions, each of which contributes to a broadhand noise field in a fluid medium; and

for each selected region of said plurality of regions;

(a) developing a motion signal from the mechanical movement of said selected region;

(b) transforming said motion signal into an antinoise signal with a controller having a substantially fixed transfer function; and

(c) developing with an output transducer a broadband antinoise field from said antinoise signal, said antinoise field being approximately 180°

out-of-phase with said broadhand noise field and combining with said broadhand noise field in said fluid medium without substantially affecting said mechanical movement of said vibrating surface;

wherein at least one of said controller and said transducer is physically attached to said vibrating surface.

18. An apparatus for reducing noise radiated from a vibrating surface comprising:

a motion sensor coupled to a vibrating surface, said vibrating surface developing a noise field in a fluid medium, said motion sensor being operative to convert movement of said vibrating surface into a motion signal;

a controller having a substantially fixed transfer function, said controller being responsive to said motion signal and operative to produce an antinoise signal; and

an output transducer responsive to said antinoise signal and operative to produce an antinoise field which is approximately the same amplitude and which is approximately 180°

out-of-phase with said noise field, such that said antinoise field and said noise field combine to reduce noise in a quiet zone in said fluid medium without substantially affecting vibrations of said vibrating surface;

wherein said output transducer comprises an acoustic driver having a predetermined piston area and a variable piston velocity, and wherein said controller has a transfer function given by;

##EQU3## where H is the transfer function of said controller, T is the acoustic driver transmission transfer function of the acoustic driver, A_p is the noise source area, A_s is the driver piston area, X_s is the driver voltage-to-acceleration transfer function, and X_a is the acceleration-to-voltage transfer function of said motion sensor.