Gas flow sensor, speaker system and microphone, utilizing measurement absolute of time-variations in absolute pressure

• US 20040101153A1
• Filed: 09/15/2003
• Published: 05/27/2004
• Est. Priority Date: 05/08/2001
• Status: Abandoned Application

• Current Assignee: Microbridge Technologies Inc.
• Original Assignee: Microbridge Technologies Inc.
• Inventors: Landsberger, Leslie M., Grudin, Oleg, Frolov, Gennadiy
• Application Number:
  US10/275,255
• Publication Number:
  US 20040101153A1
• Time in Patent Office: Days
• US Class Current: 381/357
• CPC Class Codes: H04R 29/001 for loudspeakers H04R29/007 takes precedence

Abstract

This invention addresses a fundamental weakness in currently common microphones, and their applications in feedback for audio speaker systems. This limitation stems from the fundamental difficulties of typical membrane-type microphones in the frequency range 1-100 Hz. The self-noise of membrane-type microphones increases in this range approximately as 1/f, and membrane-type microphones are sensitive to parasitic inertial vibrations, which are usually very important in this frequency range. The removal of these limitations enables the use of such a sensor (APV sensor) for effective feedback in audio speakers, dramatically improving performance in the low-frequency range of 10-100 Hz. Without feedback, typical audio speakers suffer severe attenuation and/or distortion in this range.

Claims

1. A transducer device for time variations of pressure comprising a chamber, a restrictive flow channel communicating gas from ambient to said chamber across a thermal gas flow sensor,

characterized in that

said sensor comprises thermoanemometer-type sensing elements integrated on a substrate and having a low thermal inertia.

2. The device as claimed in claim 1, wherein said low thermal inertia allows said device to have an upper cut-off frequency higher than about 50 Hz.

3. The device as claimed in claim 1, wherein said low thermal inertia allows said device to have an upper cut-off frequency higher than about 100 Hz.

4. The device as claimed in claim 1, wherein said low thermal inertia allows said device to have an upper cut-off frequency higher than about 150 Hz.

5. The device as claimed in any one of claims 1 to 4, wherein said channel is coupled with said sensor such that gas flow velocity over said sensing elements is the same as or greater than in said channel.

6. The device as claimed in any one of claims 1 to 5, wherein said sensor is provided inside said chamber.

7. The device as claimed in claim 6, wherein said channel is also provided inside said chamber.

8. The device as claimed in any one of claims 1 to 7, wherein said thermoanemometer-type sensing elements are inside said channel and a remainder of said sensor being outside said channel.

9. The device as claimed in any one of claims 1 to 8, comprising at least two said sensors, said sensors and said channel being arranged geometrically to provide signals which can be combined to cancel an inertial vibration-related component.

10. A hybrid microphone comprising a membrane-based microphone sensitive for a normal range of audio signals, a thermoanemometer-based microphone comprising a transducer device as defined in any one of claims 1 to 9 for detecting low-frequency audio signals, and a combiner circuit for combining an output of said membrane-based microphone and said thermoanemometer-based microphone to provide a combined output signal with good response from low audio frequency to at least normal audio frequency.

11. A motional feedback (MFB) speaker apparatus comprising a speaker, a circuit for modifying an input audio signal to compensate for low frequency attenuations and distortions introduced by said speaker in response to a feedback signal, and a microphone for generating a feedback signal,

characterized in that

said microphone comprises a microphone comprising one of:

a transducer device as defined in any one of claims 1 to 9; and

a hybrid microphone as defined in claim 10.

12. The speaker apparatus as claimed in claim 11, wherein said circuit applies a variable attenuation to said audio signal between an amplifier source and said speaker, said variable attenuation having a base level which is modulated to provide said compensation.

13. The speaker apparatus as claimed in claim 11 or 12, wherein said channel is perpendicular to an axis of sound propagation of said speaker.

15. The speaker apparatus as claimed in any one of claims 11 to 14, wherein said circuit is powered by said audio signal.

16. The speaker apparatus as claimed in any one of claims 11 to 15, wherein said circuit is housed in a housing adapted to be positioned next to said speaker, said housing comprising a mounting for holding said microphone in front of said speaker.

17. The speaker apparatus as claimed in claim 16, wherein said housing provides a base or stand for said speaker.

18. The speaker apparatus as claimed in any one of claims 12 to 17, wherein said variable attenuation is provided by a pulse width modulation (PWM) circuit operating at a high frequency which does not cause audible interference in said speaker.

19. The speaker apparatus as claimed in claim 18, wherein said circuit separates a low frequency component of said audio signal from a medium/high frequency component, modifies only said low frequency component for said compensation, demodulates said compensated low frequency component, and mixes said compensated demodulated low frequency component with said medium/high frequency component.

20. The speaker apparatus as claimed in any one of claims 12 to 17, wherein said circuit separates a low frequency component of said audio signal from a medium/high frequency component, modifies only said low frequency component for said compensation, and mixes said compensated low frequency component with said medium/high frequency component.

14. A motional feedback (MFB) speaker apparatus comprising a speaker, a circuit for modifying an input audio signal to compensate for low frequency attenuations and distortions introduced by said speaker in response to a feedback signal, and a microphone for generating a feedback signal,

characterized in that

said circuit applies a variable attenuation to said audio signal between an amplifier source and said speaker, said variable attenuation having a base level which is modulated to provide said compensation.