Electrical audio signal processing systems and devices – Acoustical noise or sound cancellation – Adjacent ear
Patent
1995-06-30
1997-11-25
Isen, Forester W.
Electrical audio signal processing systems and devices
Acoustical noise or sound cancellation
Adjacent ear
415119, G10K 1116
Patent
active
056920547
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a unique method of canceling noise or vibration where two or more noisy sources are employed. The tonal noise or vibration is canceled without the use of a loudspeaker or other transducer.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention refers to a method of canceling tonal noise (or vibration) generated by sources such as fans when installed into an appropriate apparatus to produce air flow. These fans usually have backward curved or backward inclined blades on the actual fan wheel. The wheel is installed into a housing with a certain scroll associated with it. Part of the scroll is a cutoff where the air flow is directed out the outlet of the housing. As the blades pass the cutoff, pressure pulses associated with them strike the cutoff and produce a tonal frequency equal to the rotational frequency times the number of blades on the wheel. Typical installations might create tonals from 50 to 2000 Hz. At these frequencies, passive silencing is not feasible due to the large amount of material necessary for these low frequencies. Therefore, active noise cancellation can be used.
In U.S. Pat. No. 5,091,953, hereby incorporated by reference herein, a repetitive phenomena canceling controller is described. The fundamental phenomenon frequencies are determined and a known electrical frequency corresponding to the fundamental and its harmonics is generated. A plurality of sensors and actuators is used to perform the canceling function with interactions between sensors and actuators taken into account by the controller. The algorithm will henceforth be referred to as MISACT.
The present invention employs some of the teachings of the MISACT algorithm. It includes the use of two or more rotating, tonal noise generating devices in conjunction with MISACT to cancel the tonal noise produced. The MISACT algorithm generates a control signal to synchronize the devices thereby minimizing the tonal noise at a specific location such as a fan inlet, outlet or both.
The invention includes methods to adjust the relative phase of noise producing pressure pulses. This can include multiple motors with single fan wheels or single motors with multiple fan wheels, for example. This can also include two or more motors mounted on a single plate.
The procedure in both systems is, given a certain motor or engine speed, to adjust the relative times at which the pressure pulses generate the noise so that at the error sensor the tonal noise is minimized. The great advantage to this approach is that no acoustic actuator such as a speaker or electromagnetic current is needed. The life of the canceling system will be as long at the motor and will not be limited by the speaker cone life.
Accordingly, it is an object of this invention to provide a unique method of canceling tonal noise generated by fans or other co-located rotating machinery.
Another object of this invention is to provide a method and device for canceling tonal noise in a system having a single fan on each multiple motor.
A further object of this invention is to provide a method and device for canceling tonal noise in a system having a single motor and multiple fans.
A still further object of this invention is to provide a method of canceling tonal noise in a system with multiple fans by adjusting the phase angle between the fans.
Another object of this invention is to provide a tonal noise canceling system without the use of an acoustic actuator.
Another object of this invention is to provide tonal vibration cancellation by adjusting the relative rotation between two co-located rotating machines without the use of an electromagnetic actuator.
These and other objects of the invention will become apparent when reference is had to the accompanying drawings in which
FIG. 1 is a diagrammatic view of a two motor, two fan system,
FIG. 2 is a diagrammatic view of a one motor, two fan system,
FIG. 3 is a semi-diagrammatic view of self cancellation using two fans as sources, and
FIGS. 4 and 5 show the effect on tonal noise when running with dual
REFERENCES:
patent: 4947356 (1990-08-01), Elliott et al.
patent: 5146505 (1992-09-01), Pfaff et al.
Parrella Michael J.
Smith Dexter G.
Isen Forester W.
Noise Cancellation Technologies, Inc.
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