US3553374A

US3553374A - Acoustic coupler

Info

Publication number: US3553374A
Application number: US808979A
Authority: US
Inventors: Edgar Wolf; Francis C Marino
Original assignee: Digitronics Corp
Current assignee: Digitronics Corp; Data 100 Corp
Priority date: 1969-03-20
Filing date: 1969-03-20
Publication date: 1971-01-05
Anticipated expiration: 1988-01-05

Abstract

An acoustic coupler for coupling a telephone handset to a source of shift frequency signals representing binary information comprising an enclosure adapted to mount a handset on edge so that the microphone of the handset is oriented in a vertical position. The coupler''s speaker, having a cone with a mouth portion, is tightly sealed within a housing with the mouth portion of the speaker cone in communication with an opening in the housing and the housing is sealed within the enclosure. The mouth portion of the speaker cone is also directly opposite and axially withdrawn from an exit portion in the enclosure so that there is a passage between the mouth of the speaker cone and the interior of the enclosure. The area of the exit port is slightly smaller than the area of the mouth portion of the speaker cone, and the peripheral edge of the exit port is surrounded by a collar of elastomeric material to acoustically and sealingly engage the transmitter portion of the telephone handset. An acoustic energy absorbing material such as felt covers the mouth portion of the speaker cone to provide an acoustic low-pass filter and the walls of the enclosure to provide high audio frequency damping.

Description

United States Patent 11113,553,374

{721 Inventors Edearwolf 2,529,228 11/1950 Schwalm 179/180 N Hy 3,116,376 12/1963 Behymeretal..... 179/107 s m z m 3,299,207 1/1967 Cooke 179/](C) 1211 AppL O- 808,979 1 3,319,003 5/1967 Prager 179/1 c) [22] Filed Mar-20.1969 3,360,071 12/1967 Vogelman 181/05 Continuation-impart of Ser. No. 628,847, Aug. 17, 1967, now abandoned, which is a continuation-in-part of Ser. No. 482,340, Aug. 25, 1965. now abandoned.

[] Patented Ian. 5, 1971 [73] Assignee DigitronicsCorporation AlbertsomN-Y. a corporation of Delaware [54] ACOUSTIC COUPLER I Primary Examiner-Kath1een Claffy Assistant Examiner-Charles W. Jirauch Attorney-Yuter and Fields oriented in a vertical position. The couplers speaker, having a cone with a mouth portion, is tightly sealed within a housing 6 Claims, 2 Drawing Figs. 5 2 U s m w1th the mouth port1on of the speaker cone 1n commumcatlon 1 179/1 with an opening in the housing and the housing is sealed within c 179/2 the enclosure. The mouth portion of the speaker cone is also [51] I H28 directly opposite and axially withdrawn from an eigit port in Field ofSearcli 179/1C, 2C, the enclosure so that there is a passage between the mouth f l8 the speaker cone and the interior of the enclosure. The area of the exit port is slightly smaller than the area of the mouth por- [56] References Cited tion of the speaker cone, and the peripheral edge of the exit UNITED STATES PATENTS port is surrounded by a collar of elastomeric material to ,463 11/1954 Robbins et a1- /31(1) acoustically and sealingly engage the transmitter portion of 3, 6 L ll /3l(-l) the telephone handset. An acoustic energy absorbing material 3,146,848 9/ 1964 Fundlngsland 18l/3l( .1) such as felt covers the mouth portion of the speaker cone to 3.194.340 7/1965 Kuwayama l provide an acoustic low-pass filter and the walls of the enclo- 2,506,279 5/1950 Rowe l79/2(C) sure to provide high audio frequency damping.

o K 19. 1 2e0- sec 16 I 1. 23C 2 .1 265 I l '1 3013 I I '1 38B ass 1 I 38A 338 Ill. 15

17 11 2e 42 I 30 34 32 36A 36B 1 l 'I' I I g I PATENTEUJAN 5m! 3553374 INVENTORS Ed gar Wolf BY Francis C. Marino ATTORNEYS ACOUSTIC COUPLER This application is a continuation-in-part of copending application Ser. No. 662,847, filed Aug. 17, 1967 now abancloned which, in turn, was a continuation-in-part of application Ser. No. 482,340, filed Aug. 25, 1965 now abandoned, both of said applications being entitled Acoustic Coupler."

This invention pertains to the acoustic coupling of tones to a signal transmitter and more particularly to the coupling of tones from a source of binary information represented by shift frequency signals to a communication link.

In the data processing and communication fields there are many instances where information from a remote source must be transmitted to a central processing location. Heretofore, special purpose communication links have been utilized. However, because of the expense in building and maintaining such links these systems can be exploited only by most affluent users. Lately there have been proposals to utilize public utility telephone systems as the communication link between a remote source and a central processor. In fact, special purpose equipment is available from the telephone utilities to provide the input and output terminals of the system. Nevertheless, such equipment is still too expensive for many potential users.

It is possible to devise a very inexpensive input device comprising a frequency shift keying tone generator which generates audio tones that binarily represent the information to be transmitted. In theory, it is only necessary to feed the audio tones into the transmitter portion of the handset of a conventional subscriber telephone connected into a public utility telephone system. At the output, a microphone is positioned against the receiver portion of a handset and the received tones are converted to binary information signals.

However, in practice, it is difficult to obtain reliable transmission. One of the major sources of unreliability comes from introducing the tones into the transmitter portion of a handset. Frequency shift representation of information utilizes a first frequency tone to represent a mark and a second frequency tone to represent a space. In order to maximize transmission rate, one frequency is typically roughly twice the other frequency. In the course of transmitting the information the tone abruptly shifts between the frequencies. Such abrupt shifts require that the transducer or coupler have excellent transient and frequency response and reasonably good sinusoidal output waveforms. In particular, there should be a minimum of phase shift and harmonic distortion. For example, it should be noted that any second harmonic distortion in the lower frequency tone would tend to look like the higher frequency tone to the handset transmitter.

Another source of unreliability is due to the fact that considerable second harmonic distortion and significant loss in amplitude arise when the handset is mounted on the transducer in the horizontal position (i.e., that position which the handset normally occupies on the telephone base). This distortion and amplitude loss may be'attributed to settling of the carbon granules used in the microphone (or granular carbon transmitter") of the handset. The effect, which shows up when the microphone is left in the horizontal position for long periods, increases the likelihood of error in the transmitted information signals. Thus a transducer or a coupler should preferably mount the handset in a position such that the harmonic distortion due to microphone granule settling is substantially eliminated.

Furthermore, in order to eliminate ambient noise the transducer or coupler should be in intimate acoustic contact with the handset transmitter. Ideally, the transducer should be fitted over the transmitter portion of the handset with a minimum of air leakage. However, subscriber telephones use many different varieties of transmitters. For example, the Western Electric Company manufactures at least three types of Granular Carbon Transmitter, i.e.', Types Tl, F1 and T2. Other manufacturers use Fl sizes and shapes of transmitters. Therefore, as a practical matter a coupler must have a universal applicability. Otherwise, a special coupler would be necessary for each type of transmitter.

In addition, the input side of the transmitter, i.e., the mouthpiece portion of the handset causes reflections of the acoustic waves back to the coupler. These reflections cause distortions in the acoustic signals emitted by the coupler. While voice communication between human beings can tolerate these distortions, digital communication cannot.

Another consideration to be taken into account includes the bass resonant frequency of the loud speaker. More particularly, it is highly undesirable to have a loudspeaker construction with a high bass resonant frequency in view of the fact that one frequency in presently used frequency shift keying systems is relatively low.

It is, accordingly, a general object of the invention to pro vide an improved binary tone coupler for transmitting shift frequency tones to a telephone transmitter It is another object of the invention to provide such a coupler which has good transient and frequency response and introduces a minimum of harmonic distortion in the tones.

Another object of the invention is the provision of a coupler which mounts a handset in such a manner so to substantially eliminate the generation of harmonic distortion and amplitude reduction.

It is a further object of the invention to provide a coupler for use with a great variety of types, sizes and shapes of telephone transmitters employed in the handsets of public utility subscriber telephones.

Briefly, the invention contemplates a transducer comprising a housing which is provided with an opening. A speaker is positioned in the housing. The speaker has a speaker cone with a mouth portion positioned in the opening of the housing. A member of material which partially absorbs acoustic energy completely covers the mouth portion of the speaker cone to provide an acoustic filter. Accordingly, when the transducer is fitted against the transmitter portion of a telephone handset? good transient and frequency response is obtained.

Other features and advantages of the present invention will become more apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a front elevational view of an acoustic coupler constructed according to the present invention; and

FIG. 2 is a partial sectional view thereof, taken along the line 24 of FIG. 1.

Referring now to FIG. 1, the coupler 10 includes an enclosure 11 having a bottom wall 12, rear wall 13, opposed sidewalls l5 and 17, a top wall 21, and a front wall 19 which is provided with two

exit ports

14 and 16. Surrounding

exit ports

14 and 16 are collars l8 and 20, respectively. When a telephone handset is rested in the coupler, the transmitter portion is received within collar 20 and the receiver portion is received within collar 18. The collars are made of an elastomer such as soft rubber to assist in proper positioning of the many differently sized handsets to the coupler and to minimize leakage of ambient sounds in the system.

A member in the form of disc 22 completely covers exit port 16. The member 22 may be made of felt or some other rnateri al having soundabsorbent characteristics. This member serves to eliminate standing waves between a speaker or an output transducer 28 and the hard plastic cover of the telephone handsets transmitter. Additionally, the member 22 functions as an acoustical low-pass filter thereby to eliminate most of the undesirable higher frequency harmonics.

Bushinglike spacers 26A and 268 support output transducer 28 in spaced relationship to the wall of the enclosure 11. Similarly bushinglike spacers 26C and 26D support input transducer 30 in spaced relationship to the wall of enclosure 11. The spacing is best seen with respect to transducer 30.

The output transducer 28 includes the cup shaped housing 32 of a dense, rigid material such as aluminum. Within the housing 32 are a felt base disc 34, and a plurality of felt washers 36A36C. Fitted in the housing and cushioned by the disc 34 and washers 36 is a speaker 38 including a permanent magnet 38A, a speaker cone 38C and a voice coil (not shown) which is energized by leads 38. The speaker cone 38C is in the open end of housing 32 and the mouth of speaker cone 38 faces exit port 16. The flange 38E of speaker cone 38C is supported between felt washer 40 and spacers 26A, 26B. Screws (not shown) start from the wall of enclosure 11, pass through spacers 26A, 26B flange 38E and washer 40 and terminate in threaded openings in the wall of housing 32.

It should be noted that by virtue of flange 38B and washer 40, housing 32 is completely sealed to prevent the escape of any acoustic backwaves. In addition, by virtue of spacers 26A, 268 there is an air passageway between the mouth of speaker cone 38C and the interior of enclosure 11 which is lined with sound-absorbing material 42. Such a passageway makes the coupling between the speaker and the handset transmitter equivalent to a transformer with a low k. Thus, the coupling is improved and the low frequency response is controlled.

In an enclosure of the type under consideration, the bass frequency response of the transducer increases with decreasing volume. To reduce any upward shift of the bass resonant frequency and to effect adequate acoustical damping, the area of the exit port 16 is made to be slightly smaller than the area of the mouth of the speaker cone. 38C. Additionally, the I sound-absorbent material 42, which may be felt or the like, serves to dampen or eliminate standing waves in the higher audio frequency-range while having little effect on the lower frequencies. That is, all the material lies within a small fraction of a wavelength of the inner wall, which is effecting a velocity node, so there is no motion of the air particles at the boundary of the acoustical material. Thus, the combination acts as an acoustic coupler having a controlled passband.

The input transducer portion is similar to the above described output transducer portion except that a further felt washer 44 is provided to minimize acoustic communication from the mouth of the speaker cone and the interior of enclosure 12.

There has thus been shown an improved coupler which, b utilizing a member of material which partially absorbs acoustic energy across the exit port of an enclosure adjacent to the mouth of a speaker cone, provides good transient and frequency response and minimizes harmonic distortion because the member acts as a low-pass filter. In addition, by providing in such a combination an air passageway between the mouth of the speaker cone and the interior of the enclosure and by properly dimensioning the exit port, the low frequency response of the coupler is controlled so that the coupler in effect includes a band-pass filter.

It will also be appreciated that the coupler l0 mounts the microphone of a handset in a vertical position rather than the conventional horizontal position thereby to substantially reduce the generation of harmonic distortion and minimize amplitude reduction which would otherwise arise if the handset were oriented in the horizontal position for long periods of time. To be more specific, it has been found that second harmonic distortion of signals is substantially eliminated when the handset is placed with the microphone or transmitter in a vertical position rather than a horizontal position. Accordingly, when the coupler of the present invention is utilized in the manner described above, with the bottom-wall 12 resting on a supporting surface, the handset will be positioned on edge. Hence, the microphone will be oriented in a vertical plane to reduce the aforementioned distortion.

While only one embodiment of the invention has been shown and described in detail, there will now be obvious to those skilled in the art many modifications and variations which satisfy many or all of the objects of the invention but which do not depart from the spirit thereof as defined in the appended claims.

We claim:

1. A transducer for use with a telephone handset and the like comprising a housing, said housing being provided with an opening, a speaker positioned in said housing, said speaker ineluding a speaker cone with a mouth portion positioned in the opening of said housing, and a low-pass filter means com letely covering the mouth portion of said speaker cone, sai lowpass filter means comprising a felt disc, said transducer further including sealing means for sealing said speaker in said housing so that only the mouth portion of said speaker cone can communicate with the region external to said housing, an enclosure provided with an exitport enclosing said housing and said speaker with the mouth portion of said speaker cone directly opposite the exit port, said sealing means including spacing means for supporting said speaker so that the mouth portion of the speaker cone is within said enclosure and axially withdrawn from said exit port, and a passage between the mouth of the speaker and the interior of the enclosure to control low frequency response of said speaker.

2. A transducer as in claim 1, in which said sealing means further includes a washer of acoustically-absorbing material between said housing and said speaker cone.

3. A transducer for coupling tones to the transmitter portion of a telephone handset comprising a housing provided with an opening, a speaker including a speaker cone having a mouth portion, said speaker being disposed in said housing with the mouth portion of said speaker cone being disposed in said opening, means for tightly sealing said speaker in said housing so that only the mouth portion of said speaker cone can communicate with the region external to said housing, an enclosure provided with an exit port, said housing and said speaker being disposed in said enclosure with the mouth portion of said speaker cone directly opposite the exit port, and a collar of elastomeric material around the peripheral edge of the exit port for acoustically sealingly engaging the transmitter portion of the telephone handset, the area of said exit port being slightly smaller than the area of the mouth of said speaker, said transducer further including means for supporting said housing and said speaker so that the mouth portion of the speaker cone is within said enclosure and axially withdrawn from the exit port, and a passage between the mouth of the speaker and the interior of the enclosure to control low frequency response of said speaker.

4. A transducer as in claim 3, in which said enclosure includes a bottom wall, a top wall, opposed sidewalls, a front wall, and a rear wall; said exit port being provided in said front wall, whereby a telephone handset is oriented with the granular carbon transmitter in a vertical position when connected with said transducer.

5. A transducer as in claim 3, and high audio frequency damping means disposed on the interior wall portions of said enclosure.

6. A transducer for coupling tones to the transmitter portion of a telephone handset comprising a housing provided with an opening, a speaker including a speaker cone having a mouth portion, said speaker being disposed in said housing with the mouth portion of 'said speaker cone being disposed in said opening, means for sealing said speaker in said housing so that only the mouth portion of said speaker cone can communicate with the region external to said housing, and enclosure provided with an exit port, said housing and said speaker being disposed in said enclosure with the mouth portion of said speaker cone directly opposite the exit port, a member of material which partially absorbs acoustic energy completely covering said exit port to provide and acoustic filter, a collar of elastomeric material around the peripheral edge of the exit port for acoustically sealingly engaging the transmitter portion of the telephone handset, means for supporting said housing and said speaker so that the mouth portion of the speaker cone is within said enclosure and axially withdrawn from the exit port and the face of said housing is spaced from the interior side of the wall defining said exit port, and acoustic energy absorbing means disposed on the interior wall portions of said enclosure. 1

Patent No. 3,553,374 Dated January 5, 1971 Edgar Wolf et a1 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet the illustrative drawing and FIG. 2, the reference character "38B", each occurrence, should read 38 Column 3, line 1, "38" should read 38D line "38" should read 38C Column 4, line 56, "and" should re an line 61 "and" should read an Signed and sealed this 16th day of May 1972 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

1. A transducer for use with a telephone handset and the like comprising a housing, said housing being provided with an opening, a speaker positioned in said housing, said speaker including a speaker cone with a mouth portion positioned in the opening of said housing, and a low-pass filter means completely covering the mouth portion of said speaker cone, said low-pass filter means comprising a felt disc, said transducer further including sealing means for sealing said speaker in said housing so that only the mouth portion of said speaker cone can communicate with the region external to said housing, an enclosure provided with an exit port enclosing said housing and said speaker with the mouth portion of said speaker cone directly opposite the exit port, said sealing means including spacing means for supporting said speaker so that the mouth portion of the speaker cone is within said enclosure and axially withdrawn from said exit port, and a passage between the mouth of the speaker and the interior of the enclosure to control low frequency response of said speaker.

6. A transducer for coupling tones to the transmitter portion of a telephone handset comprising a housing provided with an opening, a speaker including a speaker cone having a mouth portion, said speaker being disposed in said housing with the mouth portion of said speaker cone being disposed in said opening, means for sealing said speaker in said housing so that only the mouth portion of said speaker cone can communicate with the region external to said housing, and enclosure provided with an exit port, said housing and said speaker being disposed in said enclosure with the mouth portion of said speaker cone directly opposite the exit port, a member of material which partially absorbs acoustic energy completely covering said exit port to provide and acoustic filter, a collar of elastomeric material around the peripheral edge of the exit port for acoustically sealingly engaging the transmitter portion of the telephone handset, means for supporting said housing and said speaker so that the mouth portion of the speaker cone is within said enclosure and axially withdrawn from the exit port and the face of said housing is spaced from the interior side of the wall defining said exit port, and acoustic energy absorbing means disposed on the interior wall portions of said enclosure.