CA2090681C - Noise-cancelling handset - Google Patents
Noise-cancelling handsetInfo
- Publication number
- CA2090681C CA2090681C CA002090681A CA2090681A CA2090681C CA 2090681 C CA2090681 C CA 2090681C CA 002090681 A CA002090681 A CA 002090681A CA 2090681 A CA2090681 A CA 2090681A CA 2090681 C CA2090681 C CA 2090681C
- Authority
- CA
- Canada
- Prior art keywords
- pressure
- handset
- sensing locations
- microphone
- telephone handset
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/02—Constructional features of telephone sets
- H04M1/19—Arrangements of transmitters, receivers, or complete sets to prevent eavesdropping, to attenuate local noise or to prevent undesired transmission; Mouthpieces or receivers specially adapted therefor
Abstract
A noise-cancelling telephone handset comprises a housing defining an earpiece (2) and a mouthpiece (3) housing a first order pressure gradient microphone (m). The housing is pro-vided with two pressure-sensing locations (h1 and h2) in the region of the mouthpiece (3), these locations being connected to the microphone (m) by ducts (5). The pressure-sensing locations (h1 and h2) are spaced apart by a predetermined distance which is sufficiently large to permit locally-generated speech signals to produce a pressure gradient between the pressure-sensing locations whilst sound signals from distant sources produce substantially equal pressures at the pressure-sensing locations, whereby, in use, the output from the mouthpiece is substantially entirely that resulting from the locally-generated speech sig-nals.
Description
W092/04792 PCT/GB91/01~1~
, NOIS~-~NC~T~TTNG H~ND~T
The invention relates to noise-cancelling methods for microphones, and in particular to a noise-cancelling telephone handset.
Telephones are often situated in areas with a high level of background noise, for example at railway and underground stations, airports and adjacent to busy roads.
Noise-reducing housings are not always provided for such telephones, as space may be limited, or fire regulations may not allow their use.
In a telephone handset, sound arriving from a distant sound source will tend to result in a uniform pressure over parts of the surface of the handset. Hence, at such points, a microphone system which detects pressure differences will produce little or no output. Sound propagating from a close source will, however, produce large pressure differences over the surface of the handset, and a microphone system which detects pressure differences can be made to produce a large signal.
The conventional approach to noise-cancelling handset design relies on an open mouthpiece structure around a first order pressure gradient microphone. A first order pressure gradient microphone is a microphone which detects a single pressure difference between two pressure-sensing locations. In this approach, both sides of the microphone diaphragm are exposed to the sound vibrations from a pair of holes (ports) in the mouthpiece housing, and distant noise is cancelled out because it creates substantially equal pressures on both sides of the diaphragm. The ports constitute the two pressure-sensing locations for the microphone. This approach is unsuitable for rugged payphone applications because the open structure is fragile, and would be prone to the ingress of dirt and W092/04792 PCT/~B91/01~1 2~9 0~8 1 - 2 -moisture. Traditional theory suggests that the separation of the two pressure sensing locations must be much smaller than half a wavelength for useful cancellation in order that there is sufficient correlation between the noise signals. In practice, this means that the distance between two pressure-sensing locations is of the order of 5mm, with a maximum separation of about lOmm.
In non-telephony areas, second order boom microphones are used, for example by pilots, but these are not appropriate for telephony because they rely on the microphones being placed in position close to the mouth, and do not work properly if poorly positioned.
The object of the invention is to provide an improved form of noise-cancelling in a telephone handset.
lS The invention is based upon the unexpected realisation that correlation between signals from widely-spaced pressure-sensing locations is sufficient to permit useful noise cancellation to occur.
The present invention provides a noise-cancelling telephone handset comprising a housing containing a first order pressure gradient microphone, the housing having two pressure-sensing locations which are connected to the microphone by means of ducts whereby sound travels from the pressure-sensing locations to the microphone, the pressure-sensing locations being spaced apart by a predetermineddistance which is sufficiently large to permit locally-generated speech signals to produce a pressure gradient between the pressure-sensing locations whilst sound signals from distant sources produce substantially equal pressures at the pressure-sensing locations, whereby, in use, the output of the microphone is substantially entirely that resulting from the locally-generated speech signals.
W092/04792 PCT/GB91/01~1~
20~0~gl Advantageously, said predetermined distance is at least 20mm. Prefera~ly, said predetermined distance is less than lOOmm. More preferably, said distance lies within the range of from 30mm to 80mm. In the most preferred embodiment, said predetermined distance is 65mm.
Conveniently, the pressure-sensing locations are positioned substantially along the longitudinal axis of the handset, and are constituted by holes formec in the housing.
In a preferred embodiment, the ducts comprise tubes extending in the handset from the pressure-sensing locations to the microphone. Alternatively, the handset is fabricated in part by moulding, and the ducts are moulded integrally with the handset.
A noise-cancelling handset constructed in accordance with the invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:
Figure l is a schematic plan view of the telephone handset; and Figure 2 shows the acoustic connection.
Referring to the drawings, Figure l shows a handset l having a standard earpiece 2, and a mouthpiece 3 located in a recess 4. A hole h1 is located in the mouthpiece recess 2S 4, and a second hole h2 is located approximately 65mm further up the handset l towards the earpiece 2. The holes h1 and h2 lead via acoustic tubes to a microphone m (see Figure 2) located within the handset.
An important advantage of a noise-cancelling handset of the type shown, relying on direct acoustic noise cancellation rather than on an electrical or electronic noise cancellation technique, is that such a handset could W092/04792 PCT/GB91/0151~
2090~81 4 be used to replace a standard handset, without having to change the circuitry in an associated telephone base unit.
The use of a single microphone m connected via tubes to the holes h1 and h2 with no special matching provides excellent noise cancellation, provided the holes are spaced to coincide with the practical pressure gradient discussed.
As well as having ma~or advantages for payphone applications, it is envisaged that this technique will have applications in many other areas. In particular, the increasing number of mobile communications systems would benefit from effective noise-cancelling.
Figure 2 shows an arrangement of tubes and microphone for use with the handset of Figure l. The system has a single, first order pressure gradient microphone (such as a Primo EM75B) m positioned within the handset housing substantially centrally with respect to the holes h1 and h2, and connected thereto by tubes 5. The microphone includes a diaphragm 6 and the holes h1 and h2 are connected to appropriate sides of this diaphragm 6. Noise from a distant source produces substantially equal pressures at the holes h1 and h2, whereas speech produces significantly different pressures at the two holes. These pressure differences are transmitted via the tubes 5, to opposite sides of the diaphragm 6 so that the microphone m will produce an output signal that is substantially entirely speech dependent.
As the microphone m is a pressure gradient microphone, it detects pressure differences directly.
The principal advantages of the type of noise-cancelling handset described above are:-it can be designed as a simple, compact arrangementincorporating a lightweight, proprietary microphone;
W092/04792 PCT/GB9~/01~13 209068~
because it relies on the use of a face-side pressure gradient, there is no requirement for any openings on the back of the handset, where they could be blocked by the user's hand; and the use of a first order solution is tolerant of a wide range of positions of the handset with respect to the user's head.
A user at a noisy location will benefit from reduced noise in the "telephony ear" via the local side tone path, and the far end user will benefit from reduced background noise sent to line.
It will be apparent that modifications could be made to the telephone handset described above. In particular, the distance between the holes h1 and h2 can be varied to lS suit different handset constructions. A theoretical useful range for this distance is from 20mm to lOOmm, but in practice this may be reduced to from 30mm to 80mm.
In another alternative construction, instead of tubes 5 being provided independently in the handset, ducts could be moulded into the handset body. This provides a more robust construction.
, NOIS~-~NC~T~TTNG H~ND~T
The invention relates to noise-cancelling methods for microphones, and in particular to a noise-cancelling telephone handset.
Telephones are often situated in areas with a high level of background noise, for example at railway and underground stations, airports and adjacent to busy roads.
Noise-reducing housings are not always provided for such telephones, as space may be limited, or fire regulations may not allow their use.
In a telephone handset, sound arriving from a distant sound source will tend to result in a uniform pressure over parts of the surface of the handset. Hence, at such points, a microphone system which detects pressure differences will produce little or no output. Sound propagating from a close source will, however, produce large pressure differences over the surface of the handset, and a microphone system which detects pressure differences can be made to produce a large signal.
The conventional approach to noise-cancelling handset design relies on an open mouthpiece structure around a first order pressure gradient microphone. A first order pressure gradient microphone is a microphone which detects a single pressure difference between two pressure-sensing locations. In this approach, both sides of the microphone diaphragm are exposed to the sound vibrations from a pair of holes (ports) in the mouthpiece housing, and distant noise is cancelled out because it creates substantially equal pressures on both sides of the diaphragm. The ports constitute the two pressure-sensing locations for the microphone. This approach is unsuitable for rugged payphone applications because the open structure is fragile, and would be prone to the ingress of dirt and W092/04792 PCT/~B91/01~1 2~9 0~8 1 - 2 -moisture. Traditional theory suggests that the separation of the two pressure sensing locations must be much smaller than half a wavelength for useful cancellation in order that there is sufficient correlation between the noise signals. In practice, this means that the distance between two pressure-sensing locations is of the order of 5mm, with a maximum separation of about lOmm.
In non-telephony areas, second order boom microphones are used, for example by pilots, but these are not appropriate for telephony because they rely on the microphones being placed in position close to the mouth, and do not work properly if poorly positioned.
The object of the invention is to provide an improved form of noise-cancelling in a telephone handset.
lS The invention is based upon the unexpected realisation that correlation between signals from widely-spaced pressure-sensing locations is sufficient to permit useful noise cancellation to occur.
The present invention provides a noise-cancelling telephone handset comprising a housing containing a first order pressure gradient microphone, the housing having two pressure-sensing locations which are connected to the microphone by means of ducts whereby sound travels from the pressure-sensing locations to the microphone, the pressure-sensing locations being spaced apart by a predetermineddistance which is sufficiently large to permit locally-generated speech signals to produce a pressure gradient between the pressure-sensing locations whilst sound signals from distant sources produce substantially equal pressures at the pressure-sensing locations, whereby, in use, the output of the microphone is substantially entirely that resulting from the locally-generated speech signals.
W092/04792 PCT/GB91/01~1~
20~0~gl Advantageously, said predetermined distance is at least 20mm. Prefera~ly, said predetermined distance is less than lOOmm. More preferably, said distance lies within the range of from 30mm to 80mm. In the most preferred embodiment, said predetermined distance is 65mm.
Conveniently, the pressure-sensing locations are positioned substantially along the longitudinal axis of the handset, and are constituted by holes formec in the housing.
In a preferred embodiment, the ducts comprise tubes extending in the handset from the pressure-sensing locations to the microphone. Alternatively, the handset is fabricated in part by moulding, and the ducts are moulded integrally with the handset.
A noise-cancelling handset constructed in accordance with the invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:
Figure l is a schematic plan view of the telephone handset; and Figure 2 shows the acoustic connection.
Referring to the drawings, Figure l shows a handset l having a standard earpiece 2, and a mouthpiece 3 located in a recess 4. A hole h1 is located in the mouthpiece recess 2S 4, and a second hole h2 is located approximately 65mm further up the handset l towards the earpiece 2. The holes h1 and h2 lead via acoustic tubes to a microphone m (see Figure 2) located within the handset.
An important advantage of a noise-cancelling handset of the type shown, relying on direct acoustic noise cancellation rather than on an electrical or electronic noise cancellation technique, is that such a handset could W092/04792 PCT/GB91/0151~
2090~81 4 be used to replace a standard handset, without having to change the circuitry in an associated telephone base unit.
The use of a single microphone m connected via tubes to the holes h1 and h2 with no special matching provides excellent noise cancellation, provided the holes are spaced to coincide with the practical pressure gradient discussed.
As well as having ma~or advantages for payphone applications, it is envisaged that this technique will have applications in many other areas. In particular, the increasing number of mobile communications systems would benefit from effective noise-cancelling.
Figure 2 shows an arrangement of tubes and microphone for use with the handset of Figure l. The system has a single, first order pressure gradient microphone (such as a Primo EM75B) m positioned within the handset housing substantially centrally with respect to the holes h1 and h2, and connected thereto by tubes 5. The microphone includes a diaphragm 6 and the holes h1 and h2 are connected to appropriate sides of this diaphragm 6. Noise from a distant source produces substantially equal pressures at the holes h1 and h2, whereas speech produces significantly different pressures at the two holes. These pressure differences are transmitted via the tubes 5, to opposite sides of the diaphragm 6 so that the microphone m will produce an output signal that is substantially entirely speech dependent.
As the microphone m is a pressure gradient microphone, it detects pressure differences directly.
The principal advantages of the type of noise-cancelling handset described above are:-it can be designed as a simple, compact arrangementincorporating a lightweight, proprietary microphone;
W092/04792 PCT/GB9~/01~13 209068~
because it relies on the use of a face-side pressure gradient, there is no requirement for any openings on the back of the handset, where they could be blocked by the user's hand; and the use of a first order solution is tolerant of a wide range of positions of the handset with respect to the user's head.
A user at a noisy location will benefit from reduced noise in the "telephony ear" via the local side tone path, and the far end user will benefit from reduced background noise sent to line.
It will be apparent that modifications could be made to the telephone handset described above. In particular, the distance between the holes h1 and h2 can be varied to lS suit different handset constructions. A theoretical useful range for this distance is from 20mm to lOOmm, but in practice this may be reduced to from 30mm to 80mm.
In another alternative construction, instead of tubes 5 being provided independently in the handset, ducts could be moulded into the handset body. This provides a more robust construction.
Claims (7)
1. A noise-cancelling telephone handset comprising a housing containing a first order pressure gradient microphone, the housing having on a face-side thereof two pressure-sensing locations which are connected to the microphone by means of ducts whereby sound travels from the pressure-sensing locations to the microphone, the pressure-sensing locations being spaced apart by a predetermined distance which is sufficiently large to permit locally-generated speech signals to produce a pressure gradient between the pressure-sensing locations whilst sound signals from distant sources produce substantially equal pressures at the pressure-sensing locations, whereby, in use, the output of the microphone is substantially entirely that resulting from the locally-generated speech signals, the predetermined distance being at least 20 mm. and preferably between 30 mm. and 80 mm.
2. A telephone handset as claimed in claim 1, wherein said predetermined distance is less than 100 mm.
3. A telephone handset as claimed in claim 1, wherein said predetermined distance is 65 mm.
4. A telephone handset as claimed in claim 1, wherein the pressure-sensing locations are positioned substantially along the longitudinal axis of the handset.
5. A telephone handset as claimed in claim 1, wherein the pressure-sensing locations are constituted by holes formed in the housing.
6. A telephone handset as claimed in claim 1, wherein the ducts comprise tubes extending in the handset from the pressure-sensing locations to the microphone.
7. A telephone handset as claimed in claim 1, wherein the handset is fabricated in part by moulding, and the ducts are moulded integrally with the handset.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9019448.1 | 1990-09-06 | ||
| GB909019448A GB9019448D0 (en) | 1990-09-06 | 1990-09-06 | Noise-cancelling handset |
| GB9025853.4 | 1990-11-28 | ||
| GB909025853A GB9025853D0 (en) | 1990-11-28 | 1990-11-28 | Noise-cancelling handset |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2090681A1 CA2090681A1 (en) | 1992-03-07 |
| CA2090681C true CA2090681C (en) | 1994-12-13 |
Family
ID=26297605
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002090681A Expired - Fee Related CA2090681C (en) | 1990-09-06 | 1991-09-05 | Noise-cancelling handset |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US5341420A (en) |
| EP (1) | EP0547138B1 (en) |
| JP (1) | JPH06505132A (en) |
| KR (1) | KR100199454B1 (en) |
| AU (1) | AU645136B2 (en) |
| CA (1) | CA2090681C (en) |
| DE (1) | DE69120542T2 (en) |
| ES (1) | ES2090350T3 (en) |
| HK (1) | HK112297A (en) |
| IE (1) | IE77869B1 (en) |
| NZ (1) | NZ239695A (en) |
| WO (1) | WO1992004792A1 (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5473684A (en) * | 1994-04-21 | 1995-12-05 | At&T Corp. | Noise-canceling differential microphone assembly |
| JP2550914B2 (en) * | 1994-06-21 | 1996-11-06 | 日本電気株式会社 | Foldable mobile phone device |
| US5651074A (en) * | 1995-05-11 | 1997-07-22 | Lucent Technologies Inc. | Noise canceling gradient microphone assembly |
| USD384673S (en) * | 1995-11-09 | 1997-10-07 | Lucent Technologies Inc. | Telephone handset |
| GB2316814B (en) * | 1996-08-30 | 2001-02-28 | Nokia Mobile Phones Ltd | A radio telephone connector |
| US5854848A (en) * | 1996-10-08 | 1998-12-29 | Umevoice, Inc. | Noise control device |
| US6009184A (en) * | 1996-10-08 | 1999-12-28 | Umevoice, Inc. | Noise control device for a boom mounted noise-canceling microphone |
| USD427999S (en) * | 1999-07-20 | 2000-07-11 | Umevoice, Inc. | Element for a noise cancellation device |
| USD428408S (en) * | 1999-07-20 | 2000-07-18 | Ume Voice, Inc. | Element for a noise cancellation device |
| USD427998S (en) * | 1999-07-20 | 2000-07-11 | Umevoice, Inc. | Noise cancellation device |
| US6285772B1 (en) | 1999-07-20 | 2001-09-04 | Umevoice, Inc. | Noise control device |
| US6396932B1 (en) | 1999-07-21 | 2002-05-28 | Umevoice, Inc. | Pluggable noise-controlling apparatus and method |
| NO326892B1 (en) * | 2007-12-21 | 2009-03-16 | Tandberg Telecom As | microphone device |
| US9628596B1 (en) | 2016-09-09 | 2017-04-18 | Sorenson Ip Holdings, Llc | Electronic device including a directional microphone |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3004103A (en) * | 1958-12-22 | 1961-10-10 | Chance Vought Corp | Noise-reducing microphone assembly |
| US3204031A (en) * | 1961-08-29 | 1965-08-31 | Akg Akustische Kino Geraete | Moving-coil microphone arrangement |
| US3573400A (en) * | 1968-08-14 | 1971-04-06 | Bell Telephone Labor Inc | Directional microphone |
| US3835263A (en) * | 1973-02-05 | 1974-09-10 | Industrial Research Prod Inc | Microphone assembly operable in directional and non-directional modes |
| US4463222A (en) * | 1981-12-23 | 1984-07-31 | Roanwell Corporation | Noise canceling transmitter |
| US4555598A (en) * | 1983-09-21 | 1985-11-26 | At&T Bell Laboratories | Teleconferencing acoustic transducer |
| US4584702A (en) * | 1983-12-19 | 1986-04-22 | Walker Equipment Corporation | Noise cancelling telephone transmitter insertable in telephone handset receptacle |
| JPS62110349A (en) * | 1985-11-08 | 1987-05-21 | Matsushita Electric Ind Co Ltd | Transmitter |
| US5239578A (en) * | 1990-05-15 | 1993-08-24 | Plantronics, Inc. | Noise cancelling apparatus for a telephone handset |
-
1991
- 1991-09-05 CA CA002090681A patent/CA2090681C/en not_active Expired - Fee Related
- 1991-09-05 WO PCT/GB1991/001513 patent/WO1992004792A1/en active IP Right Grant
- 1991-09-05 AU AU85033/91A patent/AU645136B2/en not_active Ceased
- 1991-09-05 US US08/039,370 patent/US5341420A/en not_active Expired - Lifetime
- 1991-09-05 DE DE69120542T patent/DE69120542T2/en not_active Expired - Fee Related
- 1991-09-05 JP JP3514963A patent/JPH06505132A/en active Pending
- 1991-09-05 EP EP91916510A patent/EP0547138B1/en not_active Expired - Lifetime
- 1991-09-05 ES ES91916510T patent/ES2090350T3/en not_active Expired - Lifetime
- 1991-09-06 NZ NZ239695A patent/NZ239695A/en unknown
- 1991-09-06 IE IE313491A patent/IE77869B1/en not_active IP Right Cessation
-
1993
- 1993-03-05 KR KR1019930700664A patent/KR100199454B1/en not_active IP Right Cessation
-
1997
- 1997-06-26 HK HK112297A patent/HK112297A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| US5341420A (en) | 1994-08-23 |
| CA2090681A1 (en) | 1992-03-07 |
| DE69120542D1 (en) | 1996-08-01 |
| IE913134A1 (en) | 1992-03-11 |
| IE77869B1 (en) | 1998-01-14 |
| AU645136B2 (en) | 1994-01-06 |
| JPH06505132A (en) | 1994-06-09 |
| KR930702844A (en) | 1993-09-09 |
| AU8503391A (en) | 1992-03-30 |
| NZ239695A (en) | 1994-08-26 |
| EP0547138B1 (en) | 1996-06-26 |
| WO1992004792A1 (en) | 1992-03-19 |
| EP0547138A1 (en) | 1993-06-23 |
| ES2090350T3 (en) | 1996-10-16 |
| DE69120542T2 (en) | 1996-11-28 |
| KR100199454B1 (en) | 1999-06-15 |
| HK112297A (en) | 1997-08-29 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |