CA1199138A - Telephone handset having close-talking microphone - Google Patents
Telephone handset having close-talking microphoneInfo
- Publication number
- CA1199138A CA1199138A CA000442207A CA442207A CA1199138A CA 1199138 A CA1199138 A CA 1199138A CA 000442207 A CA000442207 A CA 000442207A CA 442207 A CA442207 A CA 442207A CA 1199138 A CA1199138 A CA 1199138A
- Authority
- CA
- Canada
- Prior art keywords
- capsule
- telephone handset
- housing
- openings
- transducer
- 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
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
- H04M1/03—Constructional features of telephone transmitters or receivers, e.g. telephone hand-sets
Landscapes
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Telephone Set Structure (AREA)
Abstract
TELEPHONE HANDSET HAVING CLOSE-TALKING MICROPHONE
Abstract of the Disclosure An arrangement for providing close-talking in a telephone handset in which a gradient electroacoustic transducer unit is surrounded and supported by an acoustically transparent foam covering, that is substantially centrally located between relatively large holes in the front and back surfaces of the handset housing.
The covering overlays the acoustic ports in the transducer unit and thereby disperses acoustic waves passing therethrough.
Abstract of the Disclosure An arrangement for providing close-talking in a telephone handset in which a gradient electroacoustic transducer unit is surrounded and supported by an acoustically transparent foam covering, that is substantially centrally located between relatively large holes in the front and back surfaces of the handset housing.
The covering overlays the acoustic ports in the transducer unit and thereby disperses acoustic waves passing therethrough.
Description
31~
TELEPHONE HANDSET HAVING CLOSE-TALKING MICROPHUNE
This invention rela-tes to a telephone handset and more particularly to a mounting arrangemen-t wi thin the handset For a close-talking microphone.
Background of the Invention Close-talking microphones are used in telephone handsets to provide improved transmission characteristics. In the past, carbon microphones have been widely used for this purpose because of their non-linear response characteristics which provide higher sensitivity 10 For higher acoustic levels. This desirable characteristic is offset by the harmonic distortion inherent in such a microphone. In addition to this, the carbon microphone draws considerable current from the -telephone line and hence is not suited to implementation with modern electronic hybrid circuitry.
An alternative is to use a gradient microphone which is more sensitive to spherical waves than it is to planar waves at the lower audio frequencies. Because sound waves are spherical in character adjacent the speaker's mouth, whereas other sound waves, including speech which has travelled a reasonable distance, are 20 planar in nature, the gradient microphone provides noise-cancelling characteristics. This well known phenomenon is discussed in the text "Acoustical Techniques and Transducers" by M.L. Gayford, MacDonald and Evans Ltd., London 1961, pages 136-1~2. Additional discussion of the subject can be found in an article entitled "Noise-cancelling electret microphone for lightweight head telephone sets" by C.W. Reedyk, The Journal of the Acoustical Society of America, Vol. 53, Number 6, 1973, pages 1609-1615.
9 ~ 3~
In order to take full advantage of this, it is known that the acoustical path between the front and back openings to the structure holding the electroacoustic transducer, must be as short as possible and considerably less than half a wavelength otherwise unwanted cancellation efFects will result. Capsules housing electroacoustic transducers having overall dimensions of 10 mm or less, can be readily constructed utilizing current technology.
Ideally such capsules should operate in a substantially free-field environment in order to have the greatest noise-cancelling effect.
This presents a problem in mounting such a capsule in a telephone handset due to the interference presented by the handset housing which would result in increased path length, thereby degrading the noise-cancelling properties of the microphone.
Statement of the Invention The present invention substantially minimizes the interference of the housing on a sradient microphone capsule, containing an acoustical transducer, in which the capsule has a forward-facing port coupling acoustic waves to the -Front side of the transducer and at least one other port coupling acoustic waves to the back side of the transducer. The housing is characterized by openings through both its front and rear surfaces. In addition, the capsule is surrounded and supported by an acoustically transparent foam covering which overlays the ports in the capsule, and which disperses acoustic waves passing therethrough. The covering containing the capsule is mounted in the housing between the front and back surfaces with the capsule substantially axially centered in the openlngs.
erief Description of the Drawings An example embodiment of the invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a partly cutaway drawing of a telephone handset in accordance with the invention, Figure 2 is a cross-sectional view of the telephone handset taken along the line II-II of Figure 1~ and Figure 3 is a graph illustrating typical acoustic response charactPristics of a gradient microphone unit mounted in 10 the telephone handset illustrated in Figures 1 and 2.
Description of the Preferred Embodiment . . _ Referring to Figures 1 and 2, the telephone handset comprises a housing generally 10 having a transmit end 11, and a receive end 12. The transmit end 11 has openings 13 and 14 in the front and rear surfaces 15 and 16 respectively of the housing 10.
A linear gradient electroacoustic transducer 20 housed in a capsule 21 is surrounded and supported by a resilient acoustically transparent foam covering 22 which overlays a front port 23 and a plurality of sideward facing ports 24 in the capsule 21.
20 The transducer capsule combination has a cardioid free-field directional response characteristic.
Substantially acoustically iransparent grills 25 and 26 cover the front and back openings 13 and 14, and retain the resilient acoustically transparent foam covering 22 in the housing 10. As shown, the capsule 21 is axially centered in the t~o openings 13 and 14.
In addition the openings 13 and 14 should be as large as possible, and preferably at least as large as the dimensions of the capsule 21, in order to minimize reflections from the surfaces of the housing 10.
The transducer 20 is electrically connected by a conventional telephone cord 30 having thin electrical wires 31.
The electroacoustic trans~ucer 20 is typically an electret element but could also be a dynamic unit. Unlike the carbon microphone widely used in telephones, this transducer 20 responds linearly to acoustic signals. In addition, it has a gradient characteristic as illustrated in Figure 3. Acoustic signals (primarily voice) which are within a few centimeters of the transducer present a spherical wave front to the transducer 20, and as shown in Figure 3 result in a substantially flat frequency characteristic. However, voice and other signals more than a few centimeters away present a planar wavefront to the transducer 20 and hence have a gradient characteristic with decreased sensitivity at low frequencies. This sensitivity rises to a maximum at about 1500 Hz where there is a slight crossover as shown in Figure 3.
It is the lack of sensitivity at low frequencies to this planar wave which provides the noise cancellation.
By retaining the transducer 20 and capsule 21 in the housing 10 utilizing the resilient acoustically transparent foam covering 22, interference with the free-field characteristics are minimized. This maximizes the gradient effect thus providing the greatest noise cancellation. However some control over this cancellation can be had by varying the relative size of the two openings 13 and 1~. By surrounding the capsule 21 with the foam covering 22, acoustic waves can reach the capsule substantially unrestricted from both the front and rear of the housing 10.
~g~38 Because the foam covering 22 is resilient, it makes the transducer 20 less susceptible to mechanical vibrations picked up by the handset housing 10. In addition, the foam covering 22 helps to disperse the acoustical ~aves passing therethrough thereby minimizing any effects caused by reflections off the surfaces oF
the housing 10.
TELEPHONE HANDSET HAVING CLOSE-TALKING MICROPHUNE
This invention rela-tes to a telephone handset and more particularly to a mounting arrangemen-t wi thin the handset For a close-talking microphone.
Background of the Invention Close-talking microphones are used in telephone handsets to provide improved transmission characteristics. In the past, carbon microphones have been widely used for this purpose because of their non-linear response characteristics which provide higher sensitivity 10 For higher acoustic levels. This desirable characteristic is offset by the harmonic distortion inherent in such a microphone. In addition to this, the carbon microphone draws considerable current from the -telephone line and hence is not suited to implementation with modern electronic hybrid circuitry.
An alternative is to use a gradient microphone which is more sensitive to spherical waves than it is to planar waves at the lower audio frequencies. Because sound waves are spherical in character adjacent the speaker's mouth, whereas other sound waves, including speech which has travelled a reasonable distance, are 20 planar in nature, the gradient microphone provides noise-cancelling characteristics. This well known phenomenon is discussed in the text "Acoustical Techniques and Transducers" by M.L. Gayford, MacDonald and Evans Ltd., London 1961, pages 136-1~2. Additional discussion of the subject can be found in an article entitled "Noise-cancelling electret microphone for lightweight head telephone sets" by C.W. Reedyk, The Journal of the Acoustical Society of America, Vol. 53, Number 6, 1973, pages 1609-1615.
9 ~ 3~
In order to take full advantage of this, it is known that the acoustical path between the front and back openings to the structure holding the electroacoustic transducer, must be as short as possible and considerably less than half a wavelength otherwise unwanted cancellation efFects will result. Capsules housing electroacoustic transducers having overall dimensions of 10 mm or less, can be readily constructed utilizing current technology.
Ideally such capsules should operate in a substantially free-field environment in order to have the greatest noise-cancelling effect.
This presents a problem in mounting such a capsule in a telephone handset due to the interference presented by the handset housing which would result in increased path length, thereby degrading the noise-cancelling properties of the microphone.
Statement of the Invention The present invention substantially minimizes the interference of the housing on a sradient microphone capsule, containing an acoustical transducer, in which the capsule has a forward-facing port coupling acoustic waves to the -Front side of the transducer and at least one other port coupling acoustic waves to the back side of the transducer. The housing is characterized by openings through both its front and rear surfaces. In addition, the capsule is surrounded and supported by an acoustically transparent foam covering which overlays the ports in the capsule, and which disperses acoustic waves passing therethrough. The covering containing the capsule is mounted in the housing between the front and back surfaces with the capsule substantially axially centered in the openlngs.
erief Description of the Drawings An example embodiment of the invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a partly cutaway drawing of a telephone handset in accordance with the invention, Figure 2 is a cross-sectional view of the telephone handset taken along the line II-II of Figure 1~ and Figure 3 is a graph illustrating typical acoustic response charactPristics of a gradient microphone unit mounted in 10 the telephone handset illustrated in Figures 1 and 2.
Description of the Preferred Embodiment . . _ Referring to Figures 1 and 2, the telephone handset comprises a housing generally 10 having a transmit end 11, and a receive end 12. The transmit end 11 has openings 13 and 14 in the front and rear surfaces 15 and 16 respectively of the housing 10.
A linear gradient electroacoustic transducer 20 housed in a capsule 21 is surrounded and supported by a resilient acoustically transparent foam covering 22 which overlays a front port 23 and a plurality of sideward facing ports 24 in the capsule 21.
20 The transducer capsule combination has a cardioid free-field directional response characteristic.
Substantially acoustically iransparent grills 25 and 26 cover the front and back openings 13 and 14, and retain the resilient acoustically transparent foam covering 22 in the housing 10. As shown, the capsule 21 is axially centered in the t~o openings 13 and 14.
In addition the openings 13 and 14 should be as large as possible, and preferably at least as large as the dimensions of the capsule 21, in order to minimize reflections from the surfaces of the housing 10.
The transducer 20 is electrically connected by a conventional telephone cord 30 having thin electrical wires 31.
The electroacoustic trans~ucer 20 is typically an electret element but could also be a dynamic unit. Unlike the carbon microphone widely used in telephones, this transducer 20 responds linearly to acoustic signals. In addition, it has a gradient characteristic as illustrated in Figure 3. Acoustic signals (primarily voice) which are within a few centimeters of the transducer present a spherical wave front to the transducer 20, and as shown in Figure 3 result in a substantially flat frequency characteristic. However, voice and other signals more than a few centimeters away present a planar wavefront to the transducer 20 and hence have a gradient characteristic with decreased sensitivity at low frequencies. This sensitivity rises to a maximum at about 1500 Hz where there is a slight crossover as shown in Figure 3.
It is the lack of sensitivity at low frequencies to this planar wave which provides the noise cancellation.
By retaining the transducer 20 and capsule 21 in the housing 10 utilizing the resilient acoustically transparent foam covering 22, interference with the free-field characteristics are minimized. This maximizes the gradient effect thus providing the greatest noise cancellation. However some control over this cancellation can be had by varying the relative size of the two openings 13 and 1~. By surrounding the capsule 21 with the foam covering 22, acoustic waves can reach the capsule substantially unrestricted from both the front and rear of the housing 10.
~g~38 Because the foam covering 22 is resilient, it makes the transducer 20 less susceptible to mechanical vibrations picked up by the handset housing 10. In addition, the foam covering 22 helps to disperse the acoustical ~aves passing therethrough thereby minimizing any effects caused by reflections off the surfaces oF
the housing 10.
Claims (4)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A telephone handset and the like, comprising:
an elongated housing having a transmit end;
a gradient electroacoustic transducer, housed in a capsule having a forward facing port coupling acoustic waves to the front side of the transducer and at least one other port coupling acoustic waves to the back side of the transducer, said ports coacting with the electroacoustic transducer to provide a preselected free-field directional response characteristic;
characterized by:
the transmit end has openings through front and back surfaces of the housing;
the capsule is surrounded and supported by an acoustically transparent foam covering which overlays the ports and which disperses acoustic waves passing therethrough;
the covering containing the capsule is mounted in the housing between the front and back surfaces with the capsule substantially axially centered in said openings.
an elongated housing having a transmit end;
a gradient electroacoustic transducer, housed in a capsule having a forward facing port coupling acoustic waves to the front side of the transducer and at least one other port coupling acoustic waves to the back side of the transducer, said ports coacting with the electroacoustic transducer to provide a preselected free-field directional response characteristic;
characterized by:
the transmit end has openings through front and back surfaces of the housing;
the capsule is surrounded and supported by an acoustically transparent foam covering which overlays the ports and which disperses acoustic waves passing therethrough;
the covering containing the capsule is mounted in the housing between the front and back surfaces with the capsule substantially axially centered in said openings.
2. A telephone handset as defined in claim 1 additionally characterized by:
front and back substantially acoustically transparent grill networks which enclose the openings in the front and back surfaces respectively, and retain the acoustically transparent foam covering;
the openings in the front and back surfaces of the housing are dimensionally greater than the facing dimensions of the capsule.
front and back substantially acoustically transparent grill networks which enclose the openings in the front and back surfaces respectively, and retain the acoustically transparent foam covering;
the openings in the front and back surfaces of the housing are dimensionally greater than the facing dimensions of the capsule.
3. A telephone handset as defined in claim 1 further characterized by:
the capsule being cylindrical in shape, the forward facing port being in one end of the cylindrical capsule and the at least one other port being a plurality of sideward facing ports spaced around the circumference of the capsule.
the capsule being cylindrical in shape, the forward facing port being in one end of the cylindrical capsule and the at least one other port being a plurality of sideward facing ports spaced around the circumference of the capsule.
4. A telephone handset as defined in claim 1 in which the preselected free-field directional response characteristic is a cardioid pattern in the direction of the forward facing port.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000442207A CA1199138A (en) | 1983-11-29 | 1983-11-29 | Telephone handset having close-talking microphone |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000442207A CA1199138A (en) | 1983-11-29 | 1983-11-29 | Telephone handset having close-talking microphone |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1199138A true CA1199138A (en) | 1986-01-07 |
Family
ID=4126631
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000442207A Expired CA1199138A (en) | 1983-11-29 | 1983-11-29 | Telephone handset having close-talking microphone |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1199138A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4773091A (en) * | 1986-06-16 | 1988-09-20 | Northern Telecom Limited | Telephone handset for use in noisy locations |
| US4845760A (en) * | 1985-10-25 | 1989-07-04 | Siemens Aktiengesellschaft | Electro-acoustic transducer arranged within the handset of a telephone instrument |
| US4850016A (en) * | 1987-01-29 | 1989-07-18 | Crystalate Electronics Limited | Microphone |
| US5790679A (en) * | 1996-06-06 | 1998-08-04 | Northern Telecom Limited | Communications terminal having a single transducer for handset and handsfree receive functionality |
| US6421444B1 (en) | 1995-09-28 | 2002-07-16 | Nortel Networks Limited | Embedded higher order microphone |
-
1983
- 1983-11-29 CA CA000442207A patent/CA1199138A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4845760A (en) * | 1985-10-25 | 1989-07-04 | Siemens Aktiengesellschaft | Electro-acoustic transducer arranged within the handset of a telephone instrument |
| US4773091A (en) * | 1986-06-16 | 1988-09-20 | Northern Telecom Limited | Telephone handset for use in noisy locations |
| US4850016A (en) * | 1987-01-29 | 1989-07-18 | Crystalate Electronics Limited | Microphone |
| US6421444B1 (en) | 1995-09-28 | 2002-07-16 | Nortel Networks Limited | Embedded higher order microphone |
| US5790679A (en) * | 1996-06-06 | 1998-08-04 | Northern Telecom Limited | Communications terminal having a single transducer for handset and handsfree receive functionality |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |