The present invention relates in general to headset noise reduction and, more particularly, concerns novel apparatus and techniques for actively and/or passively reducing the noise perceived by the user of a headset.

For background, reference is made to U.S. Patent Nos. 5,305,387, 5,208,868, 5,181,252, 4,989,271, 4,922,542, 4,644,581 and 4,455,675. Reference is also made to the Bose active noise-reducing headsets that are or were commercially available from Bose Corporation and that are incorporated by reference herein.

It is an important object of the invention to provide improved noise-reduction for headsets.

According to the invention, there is an earcup closed at the back away from the ear of a user and open at the front adjacent to the ear of the user. There is a driver inside the earcup. The earcup has a cushion that is seated in the front opening and formed with an ear opening for accommodating the ear of the user and an annular ridge surrounding the ear opening formed with a plurality of openings with adjacent openings typically spaced from each other by of the order of the width of an opening measured along the circumference of the ear opening with each opening having a radial width generally perpendicular to the circumference of the ear opening slightly less than the radial width of the annular ridge.

For active noise reduction, there is a microphone adjacent to the driver coupled to the driver by electronic circuitry that furnishes active noise reduction and an acoustical load around the microphone and driver.

The acoustic load may comprise a resistive mesh screen and/or air in a tube.

Other features, objects and advantages will become apparent from the following detailed description when read in connection with the accompanying drawings in which:

• Figure 1 A is a perspective view of a headset earcup assembly embodying the invention with the cushion shown in Figure 1 B according to the invention removed;
• Figure 2 is a sectional view of an earcup assembly according to the invention;
• Figure 3 is a pictorial perspective view into the earcup assembly with the microphone and resistive cover plate removed;
• FIG. 4 is a perspective view showing the outside of an earcup; and
• FIG. 5 is a block diagram of a system embodying the invention.

With reference now to the drawings and, more particularly, Figures 1 A and 1 B thereof, there is shown, in Figure 1A, a perspective view of an earcup assembly according to the invention with the perforated cushion of FIG. 1 B removed. Earcup 11 is closed at the rear away from the ear of a user and supports driver 12 and a closely adjacent microphone 13 (shown in Figure 2) that is covered by resistive mesh screen 13, typically formed with an opening 13A exposing the microphone, and comprising an acoustical load. Electronic circuitry intercouples the microphone and driver 12 to provide active noise reduction and exchange audio signals through cable 14 for transduction by driver 12 into desired sound signal for the wearing user and by the microphone into a noise-reducing audio signal.

Referring also to FIG. 1 B, cushion 15 covers the exposed front opening adjacent to the ear of the wearing user and is formed with an ear opening 15A for accommodating the ear of the wearing user. An annular ridge 16, surrounding ear opening 15A, is formed with a plurality of openings, such as 16A, through which an annular ring of foam is visible that rests against driver 12 when assembled.

Referring to Figure 2, there is shown a diagrammatic sectional view through an assembled earcup. Driver 12 is seated in earcup 11 with driver plate 12A extending rearward from a lip 11 A of earcup 11 to a ridge 11 B. Microphone 17 is located adjacent to driver 12 and is covered by wire mesh resistive cover 13. Cushion 15 covers the front opening of earcup 11 and includes foam 15B.

Referring to Figure 3, there is shown a pictorial perspective view into the earcup 11 with cushion 15, microphone 17 and wire mesh resistive cover 13 removed to illustrate certain structural details. Earcup 11 is formed with a cable entry IIC for accommodating cable 14 (shown in Figure 1A) for receiving audio signals for transduction by driver 12 and for intercoupling external electronic circuitry with the drive and microphone. Driver plate 12A carries resistive cover holders 21A and 21B for supporting the wire mesh resistive cover 13. Microphone holder 22 extends from the rear wall of earcup 11 for supporting microphone 17 and encloses air that comprises acoustical loading. Driver plate mounting bosses 12B and 12C furnish a means for attaching driver 12 to earcup 11. Driver 12 divides earcup 11 into a front volume, typically about 50cc, adjacent to the front opening and a rear volume, typically about 15cc, enclosed by the closed end of earcup 11.

Referring to Figure 4, there is shown a rear view of earcup 11 showing mass port 11 E and resistive port 11 D covered by a wire mesh.

With reference now to Figure 5, there is shown a block diagram illustrating the logical arrangement of a system incorporating the invention corresponding substantially to FIG. 1 of US 4644581. A signal combiner 30 algebraically combines the signal to be reproduced by the earphone on input terminal 24 with a feedback signal provided by microphone preamplifier 35. Signal combiner 30 provides the combined signal to compressor 31 which limits the level of the high level signals. The output of compressor 31 is applied to compensator 31 A. Compensator 31 A includes compensation circuits to insure that the open loop gain meets the Nyquist stability criteria, so that the system will not oscillate when the loop is closed. The system shown is duplicated once each for the left and right ears.

Power amplifier 32 amplifies the signal from compensator 31A and energizes earphone driver 12 to provide an acoustical signal in the front cavity that is combined with an outside noise signal that enters the front cavity from a region, represented as acoustical input terminal 25, to produce a combined acoustic pressure signal in the front cavity, represented as a circle 36, to provide a combined acoustic pressure signal applied to and transduced by microphone 17. Microphone amplifier 35 amplifies the transduced signal and delivers it to signal combiner 30.

Having described the structural arrangement of an embodiment of the invention, principles of operation will be described. A problem in active noise-reducing circumaural headphones arises from earcup resonances causing a rough acoustic response that is a function of the head of the user, making electronic compensation difficult.

One approach for smoothing the acoustic response is to place damping material, typically highly absorptive foam, around the walls of the earcup. This approach typically requires a significant thickness of foam to provide sufficient damping and requires earcups of relatively large volume to accommodate the thick foam. Furthermore, the damping of the highly absorptive foam is a sensitive function of the physical dimensions of the foam and atmospheric conditions, causing inconsistent acoustical response.

Resonance in the earcup may produce instability by causing oscillation at certain frequencies that typically limits the amount of feedback for active noise reduction. By acoustically loading the microphone and driver with the wire mesh resistive cover 13 and/or the enclosed air, resonances are significantly reduced, allowing increased gain in the feedback loop and significantly improved active noise reduction in an earcup of relatively small volume. By forming openings in annular ridge 16 of cushion 15 to expose foam material 15B, the effective volume of the earcup is significantly increased to embrace the volume and provides additional damping to help smooth the audio response at the ear and control stability with the headset off the head occupied by cushion 15 and thereby increase passive attenuation.

The invention has a number of advantages. Cup size is relatively small, yet there is considerable effective volume with the additional effective volume afforded by cushion 15 accessed through openings such as I6A. The effect of resonances inside earcup 11 is significantly reduced with wire mesh resistive cover 13 and/or the enclosed air, thereby allowing a significant increase in loop gain of the active noise reducing system.