WO1989004106A1 - Capuchon de microphone avec filtre acoustique - Google Patents

Capuchon de microphone avec filtre acoustique Download PDF

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Publication number
WO1989004106A1
WO1989004106A1 PCT/US1988/003240 US8803240W WO8904106A1 WO 1989004106 A1 WO1989004106 A1 WO 1989004106A1 US 8803240 W US8803240 W US 8803240W WO 8904106 A1 WO8904106 A1 WO 8904106A1
Authority
WO
WIPO (PCT)
Prior art keywords
microphone
acoustic filter
acoustic
cup
air cavity
Prior art date
Application number
PCT/US1988/003240
Other languages
English (en)
Inventor
Dwight D. Lynn
Shu-Ren Chen
Original Assignee
Acs Communications, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Acs Communications, Inc. filed Critical Acs Communications, Inc.
Publication of WO1989004106A1 publication Critical patent/WO1989004106A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/08—Mouthpieces; Microphones; Attachments therefor
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/222—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only  for microphones

Definitions

  • the present invention relates to communications equipment and, in particular, to a microphone cup which is shaped to provide an acoustic filter for the associated microphone, the dimensions of the acoustic filter being chosen to provide a desired frequency response.
  • ⁇ microphone is an electroacoustic device containing a transducer which is actuated by sound waves and, in response to the incident sound waves, delivers an essentially equivalent electrical signal.
  • Microphones used in telephone handsets or headsets commonly utilize a transducer which relies on the movement of a diaphragm to generate an electrical response. The movement of the diaphragm corresponds to the pressure of the incident sound waves.
  • One of the problems encountered in using diaphragm transducers is that the diaphragm is responsive to sound waves in a band much broader than is required for voice communication. Microphones that are band limited are much more expensive than the broad band types.
  • Conventional omnidirectional microphones are also ⁇ usceptable to broadband noise from an unacceptably large distance from the microphone user.
  • Cardioid or pressure gradient diaphragm transducers significantly reduce distant background noise. These transducers have a sound port on both sides of the diaphragm. Therefore, the output of the transducer is the difference between the sound pressures entering the two ports. Sound waves dissipate as they travel. When a partially dissipated sound wave enters the two sound ports, the difference between the waves is low. A pressure gradient transducer responds minimally because of the small difference in pressure. However, at a close distance, the pressure has dissipated minimally causing a large pressure differential and a correspondingly high electrical output.
  • a specific response is required to compensate for line losses.
  • a different response may be required for other applications, e.g. microphones for order takers at a fast food outlet.
  • Broad audio band microphones introduce many undesirable sound inputs (such as typewriters, keyboard clicks and shuffled paper) outside the voice band (300 to 3300 Hertz) which need to be eliminated.
  • Microphones that utilize standardized electrical filters cannot meet these changing requirements without undue cost.
  • An acoustic resonator is a device which consists of a combination of elements having mass and compliance, the acoustical reactances of which cancel at a given frequency.
  • Acoustic resonators have found considerable application in architectural acoustics. Since it is often difficult to obtain adequate control of reverberation time at low frequencies in a large studio or auditorium using conventional acoustical materials, a number of designs for these spaces have included the construction of acoustic resonators behind walls or in the ceiling to obtain increasing low-frequency absorption and, thus, provide more satisfactory reverberation characteristics.
  • a Helmholtz resonator consists of a closed cavity of air of volume V which is connected to the air in a room by a straight cylindrical tube of length 1 and cross-sectional area S. This combination is analogous to a simple LC electrical circuit.
  • the Helmholtz resonator may prolong the reverberation time of a room.
  • the resonant frequency f 0 of a Helmholtz resonator is given by the following equation
  • the damping of acoustical waves by the Helmholtz resonator is also of interest.
  • the damping may be described in terms of the quality factor Q in analogy to the quality factor in an electrical circuit. This factor describes the ratio of energy stored to the energy dissipated, per cycle, in the resonator.
  • An acoustic filter microphone cup in accordance with the present invention comprises a housing which holds a microphone and is shaped to provide an acoustic filter for the microphone.
  • the acoustic filter consists of an interior air cavity located at the front of the microphone and a sound port which provides acoustic communication between ambient and the interior air cavity.
  • the shape of the frequency response of the microphone is determined by the dimensions of the air cavity and the sound port.
  • the acoustic filter microphone cup of the present invention provides several marked advantages over conventional microphone holders.
  • the use of the microphone cup itself as an acoustic filter provides "free" filtering for the cost of a microphone holder, ⁇ ince the need for conventional electrical filtering components is eliminated and a microphone holder is required in any event.
  • electrical filtering is expensive because of the precision components and PC board space required and, for high order filters, because of the tuning requirement of the filters.
  • the acoustic filter microphone cup of the present invention provides a high order filter without the previously-mentioned cost.
  • the filtering provided is reliable because the filter is formed from hard molding tools that do not vary in dimension.
  • the acoustic filter microphone cup of the present invention also makes it possible to meet different frequency response specifications without great expense, since as stated above, the response may be tailored by simply changing the volume combination of the air cavity and sound port.
  • the drawing is a cross-sectional schematic illustration of an acoustic filter microphone cup in accordance with the present invention.
  • the drawing shows an acoustic filter microphone cup 10 in accordance with the present invention.
  • the microphone cup 10 includes a generally cylindrically-shaped housing which holds a microphone 14.
  • the housing includes an end cap 12a which engages a generally-cylindrical barrel 12b.
  • Both the end cap 12a and the barrel 12b are molded pieces formed of DuPont Delrin 500 or its equivalent.
  • the end cap 12a is generally the shape of a truncated cone and engages the barrel 12b by means of a snap ring 16 formed at the end cap 12a which mates with a corresponding groove 18 in the barrel 12b to provide a tensioned fit between the end cap 12a and the barrel 12b.
  • a thermoplastic O-ring 20 formed of Kraton D2104, available from Shell Oil
  • a hollow cylindrical spacer 22 also formed of DuPont Delrin 500 or its equivalent, is provided within the barrel 12b to hold the microphone 14 in place.
  • the lead wires 24 of the microphone extend through the barrel 12b to conventional transmitter circuitry (not - shown) .
  • the housing is shaped to define an interior air cavity 26 forward of the microphone 14.
  • a cylindrical sound port or orifice 28 is formed through the end cap 12a to provide acoustic communication between ambient and the interior cavity 26.
  • the diameter of the cavity 26 is about 0.24 inches and its length is about 0.20 inches.
  • the sound port 28 has a diameter of about 0.02 inches and a length of about 0.04 inches. These dimensions were chosen to provide an acoustic filter which allows the microphone to meet the AT&T response specification, which requires an 8 dB peak before the cut-off frequency. Different dimensions of the air cavity 26 and sound port 28 may be utilized to obtain a desired frequency response. Basically, changing the length of the sound port alters the quality factor Q of the acoustic filter, in analogy to the C electrical circuit.
  • the microphone 14 utilizes conventional electret technology. It uses a diaphragm, commonly made from teflon or mylar, which is electrostatically charged, and then stretched over a small sealed cavity. One side of the diaphragm is exposed to the environment via the interior cavity 26 and the sound port 28 to detect sound pressure waves in the air. The back of the sealed microphone cavity is a capacitance plate. As the air moves the diaphragm, the electric charge on the plate is varied. Since the impedance of the capacitance plate is very high, an integrated field effect transistor amplifier is built into the microphone.
  • the input impedance of the field effect transistor is sufficiently high so that the capacitance effect of the microphone is not loaded and, thus, provides a linear tran ⁇ conductance amplifier to complete the transformation of acoustic energy to electrical energy.
  • a microphone of the type described above is available from Primo Microphone Inc. as its model number EM-78 or EM-94.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Details Of Audible-Bandwidth Transducers (AREA)

Abstract

La présente invention se rapporte à un capuchon de microphone à filtre acoustique (10), qui contient un microphone (14) et qui est conçu avec une forme lui permettant de servir de filtre acoustique pour le microphone. Ledit capuchon de microphone à filtre acoustique (10) comprend un logement (12a, 12b) contenant le microphone (14). Le filtre acoustique (10) comporte une cavité d'air interne (26) placée en face du microphone (14) en communication acoustique avec lui et une sortie de son (28) assurant une communication acoustique entre l'extérieur du logement (12a, 12b) et l'intérieur de la cavité d'air (26). Les dimensions du filtre acoustique sont sélectionnées au préalable pour que le microphone fournisse une réponse de séquence prédéterminée, dont la forme est déterminée par la grandeur de la cavité d'air (26) et de la sortie de son (28). Grâce à l'utilisation d'un filtre acoustique, il n'est plus nécessaire de recourir à des composants de filtrage électroniques traditionnels.
PCT/US1988/003240 1987-10-28 1988-09-20 Capuchon de microphone avec filtre acoustique WO1989004106A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US11446187A 1987-10-28 1987-10-28
US114,461 1987-10-28

Publications (1)

Publication Number Publication Date
WO1989004106A1 true WO1989004106A1 (fr) 1989-05-05

Family

ID=22355349

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1988/003240 WO1989004106A1 (fr) 1987-10-28 1988-09-20 Capuchon de microphone avec filtre acoustique

Country Status (1)

Country Link
WO (1) WO1989004106A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0453061A2 (fr) * 1990-01-18 1991-10-23 Motorola, Inc. Isolant acoustique pour le microphone d'un combiné téléphonique
WO1998051122A1 (fr) * 1997-05-08 1998-11-12 Ericsson Inc. Microphone a pavillon a affaiblisseur resonateur de helmholtz
EP1739933A1 (fr) * 2005-06-28 2007-01-03 Research In Motion Limited Dispositif de communication avec écran pour le microphone
US7280855B2 (en) 2005-06-28 2007-10-09 Research In Motion Limited Microphone coupler for a communication device
WO2013136063A1 (fr) * 2012-03-12 2013-09-19 The Secretary Of State For Business, Innovation & Skills Of Her Majesty's Britannic Government Système de microphones et procédé de commande de ce système de microphones
TWI513331B (fr) * 2013-02-18 2015-12-11
US11785375B2 (en) 2021-06-15 2023-10-10 Quiet, Inc. Precisely controlled microphone acoustic attenuator with protective microphone enclosure

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1278505A (en) * 1917-11-10 1918-09-10 Charles Andrew Reifel Transmitter.
US1646628A (en) * 1927-10-25 James g
US2549963A (en) * 1945-12-03 1951-04-24 Hartford Nat Bank & Trust Co Electroacoustic transducer
US3246721A (en) * 1962-04-27 1966-04-19 Siemens Ag Frequency response of an electroacoustic transducer
US3651286A (en) * 1969-01-13 1972-03-21 Akg Akustische Kino Geraete Lavalier microphone assembly protected against friction noises
DE2831401A1 (de) * 1978-07-17 1980-01-31 Siemens Ag Elektroakustischer wandler
DE3207695A1 (de) * 1982-03-04 1983-09-15 Hagenuk GmbH, 2300 Kiel Fernsprechmikrofon
FR2545302A1 (fr) * 1983-04-26 1984-11-02 Thomson Csf Mat Tel Filtre acoustique pour transducteur en particulier du type electromagnetique de combine telephonique
EP0161735A2 (fr) * 1984-03-16 1985-11-21 Northern Telecom Limited Ensemble émetteur pour combiné téléphonique

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1646628A (en) * 1927-10-25 James g
US1278505A (en) * 1917-11-10 1918-09-10 Charles Andrew Reifel Transmitter.
US2549963A (en) * 1945-12-03 1951-04-24 Hartford Nat Bank & Trust Co Electroacoustic transducer
US3246721A (en) * 1962-04-27 1966-04-19 Siemens Ag Frequency response of an electroacoustic transducer
US3651286A (en) * 1969-01-13 1972-03-21 Akg Akustische Kino Geraete Lavalier microphone assembly protected against friction noises
DE2831401A1 (de) * 1978-07-17 1980-01-31 Siemens Ag Elektroakustischer wandler
DE3207695A1 (de) * 1982-03-04 1983-09-15 Hagenuk GmbH, 2300 Kiel Fernsprechmikrofon
FR2545302A1 (fr) * 1983-04-26 1984-11-02 Thomson Csf Mat Tel Filtre acoustique pour transducteur en particulier du type electromagnetique de combine telephonique
EP0161735A2 (fr) * 1984-03-16 1985-11-21 Northern Telecom Limited Ensemble émetteur pour combiné téléphonique

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0453061A2 (fr) * 1990-01-18 1991-10-23 Motorola, Inc. Isolant acoustique pour le microphone d'un combiné téléphonique
EP0453061A3 (en) * 1990-01-18 1993-02-10 Motorola Inc. Acoustic insulator for a microphone in a telephone handset
WO1998051122A1 (fr) * 1997-05-08 1998-11-12 Ericsson Inc. Microphone a pavillon a affaiblisseur resonateur de helmholtz
EP1739933A1 (fr) * 2005-06-28 2007-01-03 Research In Motion Limited Dispositif de communication avec écran pour le microphone
US7280855B2 (en) 2005-06-28 2007-10-09 Research In Motion Limited Microphone coupler for a communication device
US7797025B2 (en) 2005-06-28 2010-09-14 Research In Motion Limited Microphone coupler for a communication device
WO2013136063A1 (fr) * 2012-03-12 2013-09-19 The Secretary Of State For Business, Innovation & Skills Of Her Majesty's Britannic Government Système de microphones et procédé de commande de ce système de microphones
TWI513331B (fr) * 2013-02-18 2015-12-11
US11785375B2 (en) 2021-06-15 2023-10-10 Quiet, Inc. Precisely controlled microphone acoustic attenuator with protective microphone enclosure

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