Electrical audio signal processing systems and devices – Directive circuits for microphones
Reexamination Certificate
1997-06-30
2003-10-14
Mei, Xu (Department: 2644)
Electrical audio signal processing systems and devices
Directive circuits for microphones
C381S356000, C381S365000, C381S122000
Reexamination Certificate
active
06633647
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to portable computer systems having associated microphones.
2. Description of the Related Art
Portable computers are increasingly integrating multimedia functionality present in desktop computers to achieve an enhanced multimedia environment. Such multimedia functionality has predominantly been on the playback side of portable sound technology, encompassing sound devices such as CD-ROM drives, sound boards, and speakers in order to improve sound quality for portable computer users. While playback side enhancements in portable sound technology have been suited to home or office use, recording side features in portable sound technology are particularly suited to an office environment wherein voice communication applications such as audio conferencing, teleconferencing and telephony have been frequently utilized, and wherein voice recognition applications will likely become more prevalent.
On the recording side of portable sound technology, speakerphone functionality has been integrated into portable computers allowing for a portable computer with a speakerphone mode. In a full duplex, speakerphone mode, both the speaker and the microphone are on so that listening and talking may be simultaneous for a portable computer user. In addition, the speaker and microphone are acoustically coupled such that sound waves from the microphone travel to the speaker. In order to prevent acoustic feedback due to sound waves traveling from the microphone to the speaker, acoustic coupling may be reduced between the speaker and the microphone by suppressing sound waves from certain directions. This reduction in acoustic coupling is termed acoustic coupling loss.
Microphones predominantly used in portable computers are omni-directional microphones, cardioid microphones, or supercardioid microphones. An omni-directional microphone is a microphone with an even or equal response sensitivity to sound from all directions over a full 360° range. As such, the direction response pattern for an omni-directional microphone as a function of location with respect to it is a uniform level, graphically full circle. A cardioid microphone is a microphone having a heart-shaped direction response pattern resembling a graph of a mathematical cardioid function originally developed by Pascal. A cardioid microphone is improved over an omni-directional microphone in that a cardioid microphone has maximum sensitivity in the forward direction and reduced sensitivity to sounds arriving from a side or rear direction with respect to the longitudinal axis of the microphone. A supercardioid microphone has a direction response pattern more attenuated for sounds arriving from a side direction than a cardioid direction response pattern. Also, while a cardioid direction response pattern includes a single heart-shaped lobe or bulb, a supercardioid direction response pattern includes a heart-shaped front lobe for areas forward of the microphone along its longitudinal axis and an oval-shaped back or rear lobe.
Microphones in portable computers have been selected based on the general directivity associated with the microphone. That is, when marginal or minimal acoustic performance of a microphone in a portable computer is desired, omni-directional microphones have typically been chosen. When improved acoustic performance of a microphone in a portable computer is desired, cardioid or supercardioid microphones have typically been chosen. In comparison to omni-directional microphones, cardioid and supercardioid microphones produce generally improved cancellation of noise sources located external to a portable computer system. A cardioid or supercardioid microphone, however, may not be particularly suited to the spatially dependent noise sources internal to a portable computer, nor to the specific acoustic environment of a portable computer.
SUMMARY OF THE INVENTION
Briefly, according to the present invention, custom designed polar patterns for a microphone of a portable computer are achieved. It has been found that custom designing a polar pattern for a microphone of a portable computer adequately accounts for the varying locations of noise sources internal to a portable computer system and the varying acoustic environments for different designs of a portable computer system. The custom designed polar patterns are achieved by specially configuring the boot, which houses the microphone element of the portable computer microphone between the front and back portable housing surfaces. The desired polar pattern is achieved by specially configuring the hole sizes of the boot for passage of acoustic energy, and/or varying the distances between the microphone element and the front and back portable housing surfaces. Further, adding acoustic absorption material inside the boot such as foam or forming enclosed walls into the boot may be used in adjusting the shape of a particular polar pattern. Adjusting the position of the top shell of the portable computer relative to the bottom shell allows even further refinement of the polar pattern. Thus, the boot of a microphone may be specially configured for each portable computer design or configuration to achieve a directional response form-fitted to the particular portable computer configuration.
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Markow Mitchell A.
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