Hearing aid
United States Patent 1191 Ruegg HEARING AID Inventor: Heinz Ruegg, Thalwil, Switzerland Assignee: Bommer AG, Zurich, Switzerland Filed: Jan. 24, 1973 App]. No.: 326,550  
 [30] Foreign Application Priority Data Feb. 2, 1972 Switzerland 1547/72 US. 01..... 179/107 FD, 179/121 D, 179/1 DM 1111. c1. II04p 25/00 Field of Search 179/107 R, 107 BC, 107 E, 179/107 H, 107 s,179,1s0,17s,1211),1 DM, 107 FD; 181/23 References Cited UNITED STATES PATENTS 3/1938 Lybarger 179/107 FD Primary Examiner-Ralph D. Blakesiee Attorney, Agent, or Firm-Craig &amp; Antonelli [57] ABSTRACT A hearing aid for the hard of hearing incorporating a microphone system connected with an amplifier. The f microphone system embodies a first microphone with approximately spherical-shaped sensitivity characteristics and a second microphone with directional sensitivity characteristics. The amplifier can be selectively connected with one or the other of both microphones.  
 l2 Claims, 5 Drawing Figures AMPLIFIER SHEET 10F 2 17 20 15 111 j 12 16 21 F1g.1 KS 22 LAMPLIFIER 11 25 I 3 {16 (AMPLIFIER 12 4 il] Fig.2 M f 20 21 SWITC ELEME HEARING AID The present invention relates to a new and improved construction of hearing &#39;aid for the hard of hearing of the type incorporating a microphone system coupled with an amplifier. In the context of this disclosure the expression hearing aid or hearing device, or equivalent terminology, should be understood as encompassing both the so-called behind-the-ear as well as also the so-called in-the-ear hearing aid and hearing aid eyeglasses, in other words all hearing aids worn at or about the head of the user.  
  It is well known in this particular field of technology to equip such hearing aids with microphones which possess a pronounced directional characteristic. With such hearing aids the sound waves which arrive from a predetermined direction are amplified and transmitted to the wearer of the hearing aid, this direction, as a general rule, coinciding with the line of sight or viewing direction of the wearer. Although such hearing aids provide adequate aid to the user during normal conversation with another person, they are not totally satisfactory in an environment of use where the sound emanates from all directions, since the user becomes unsure of himself. It has been particularly determined that people who are hard of hearing and who wear a hearing aid having a microphone exhibiting directional sensitivity characteristics become extremely unsure of themselves in traffic because, from the entire background of sounds, they are only able to perceive those sounds which coincide with their momentary line of sight.  
  On the other hand, there are known to the art hearing aids of the previously mentioned type in which the microphone possesses a so-called spherical sensitivity characteristic. Also such constructions of hearing aids do not satisfy all of the needs of the hard of hearing. Thus, for instance, a conversation with another person is only possible for the person who is hard of hearing when using such hearing aid if the party to whom the hard of hearing person speaks raises his voice above the general sound level of the surroundings, or then when the person who is hard of hearing, in addition to listening to the sounds of the words of the speaking person also lip reads.  
 SUMMARY OF THE INVENTION Hence, it is a primary object of the present invention to provide an improved construction of hearing aid which is capable of reliably fulfilling the needs of the hard of hearing practically for all encountered situations.  
  A further object of the present invention relates to an improved construction of hearing aid which combines the advantages of a hearing aid equipped with a microphone having directional characteristics with a hearing aid equipped with a microphone having spherical sensitivity characteristics while avoiding the drawbacks present when only using a microphone in a hearing aid having one or the other of such sensitivity characteristics.  
  Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the proposed hearing aid is manifested by&#39;the features that the microphone system possesses a first microphone having spherical sensitivity characteristics and a second microphone with directional sensitivity characteristics, and wherein the amplifier can be selectively switched to either one of both microphones.  
  Thus, a minature hand-operated reversing switch can be provided between the microphones and the amplifier, and which switch can be actuated, when required, by the user without having to remove the hearing aid. On the other hand, both of the microphones can be arranged through the agency of a controlled reversing switch following a threshold value amplifier, which upon exceeding a predetermied signal peak controls the reversing switch for switching to the second microphone, that is to say, to that microphone which has a pronounced directional characteristic. This predetermined signal peak can be set to a value which occurs when the wearer is carrying out a conversation with another person at a normal distance.  
  Both of the microphones are preferably each arranged in a respective compartment of a housing subdivided by a partition wall into two compartments or chambers, wherein in the first compartment there opens a sound inlet opening and in the second compartment two oppositely situated sound inlet openings. In order to avoid acoustical feedback it is advantageous to arrange the diaphragms or membranes of the microphones and which are capable of vibrating or oscillating such that they are each essentially parallel to the partition wall. For further avoiding acoustical feedback there can be arranged at the second compartment the one sound inlet opening at one side of the vibratable diaphragm and the other sound inlet opening at the other side thereof of the associated microphone.  
  Moreover, the directional characteristics of the second microphone can be increased if the one sound inlet opening associated with such microphone possesses a greater sound absorption capacity than the other sound inlet opening.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 schematically illustrates the sensitivity charac:  
 teristics of a first microphone;  
  FIG. 4 schematically illustrates the sensitivity characteristics of a second microphone; and  
  FIG. 5 is a circuit diagram of a hearing aid equipped with manually-switchable microphones, wherein the arrangement of both microphones is illustrated in a common housing.  
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, the hearing aid 10, depicted by way of example in FIG. 1, possesses two microphones l 1 and 12, wherein the first microphone, the microphone 11, as will be understood by referring to FIG. 3, is assumed to possess a spherical-type of sensitivity characteristic, whereas the second microphone, the microphone 12, as indicated in FIG. 4, is assumed to possess a sensitivity having a pronounced directional characteristic. The microphone 11 is electrically coupledvia a conductor or line 13 with one fixed contact 15 and the microphone 12 via a conductor or line 14 with the other fixed contact 16 of a reversing switch or switch means 22. The movable contact 17 of the reversing switch 22 is connected through the agency of a conductor 18 with an amplifier 19. The output of amplifier 19 is connected via a conductor 20 with an electro-mechanical transducer, for instance a loud-speaker 21 where the electrical signals emanating from the microphone 11 or the microphone 12 are amplified by amplifier 19, and again transformed into mechanical oscillations, that is to say, sound waves.  
  The same elements will be also recognized to be present with the constructional embodiment of FIG. 2, wherein, however, in this case, instead of the reversing switch 22 there is employed an automatically controlled electronic reversing switch 23. In this embodiment the amplifier 19 is a so-called threshold value amplifier which, apart from the output or output conductor 20 which leads to the loudspeaker 21, possesses a second output 24 where there then appears a signal when the signal prevailing from one of both microphones 11 and 12 exceeds a predetermined signal peak. The output 24 is connected through the agency of a further switching element, designated by reference character 25, with the control input 26 of the reversing switch or switch means 23. The switch element can be a control or regulator, but also can be a frequencydependent discriminator stage, so that switching-over to the microphone 12 possessing the pronounced directional characteristic, not only then occurs when a sound has assumed a predetermined intensity, rather when such sound also possesses a predetermined frequency spectrum. Switching back to the microphone ll possessing the spherical sensitivity characteristic can occur both automatically upon the absence of a signal at theamplifier output 24, or also however manually, so that the user has the possibility of intentionally controlling the hearing aid.  
  It is to be observed that both in the embodiment of FIG; 1&#39; as also in the embodiment of FIG. 2 the microphones can be electro-magnetic, piezo-electrical or dielectrical microphones wherein, however, both microphones always will be of the same type owing to the nature of the different frequency characteristics. Also the amplifiers of both embodiments can be linear, AGC (automatic gain control) or non-linear controlled amplifiers.  
  Now in FIG. 5 there is illustrated a detailed circuit diagram of hearing aid with the two schematically arranged microphones of such hearing aid collectively accommodated in a single housing. Initially on the basis of the discussion of FIG. 5 there will be considered the construction of the microphone system. Both of the microphones 11 and 12 are arranged in a common housing 27, the internal compartment of which is subdiv-ided into two compartments or chambers 29 and 30 by a partition wall 28. In the compartment 29 there is arranged the microphone 11 with its diaphragm or membrane 38 and its transducer component 39, while in the compartment 30 there is arranged the microphone 12 with its diaphragm or membrane 40 and its transducer component 41. The compartment 29 possesses a&#39; sound inlet opening 31 which, as best seen by referring to FIG. 5, opens into the compartment 29 at the side or face of the diaphragm 38 facing away from the transducer component 39. On the other hand, the compartment 30 possesses two oppositely situated sound inlet openings 32 and 35, wherein the sound inlet opening 32 opens into the compartment 30 at the side of the diaphragm which faces away from the transducer component 41 and the sound inlet opening 35 opens at the side of the diaphragm 40 which confronts the transducer component 41.  
  A common sound inlet funnel 33 is arranged forwardly of both sound inlet openings 31 and 32. The sound inlet funnel 33 possesses a single inlet opening 34. On the other hand, connected in front of the sound inlet opening 35 is a stud or connection piece 36 having an opening 37. The arrangement is carried out such that the sound absorption capacity of the inlet locations formed by the openings 35, 37 and the stud 36 is greater than the sound absorption capacity of the inlet location formed by the openings 31, 32 and 34 as well as the funnel 33.  
  Now if this arrangement is subjected to sound vibrations or oscillations, then initially the entire outside of the housing 27 will be uniformly impinged by the sound pressure, something which for itself will not have any effect upon the microphone l 1 and 12. The parts of the compartments 29 and 30 which are located, on the one hand, between the partition wall 28 and, on the other hand, the respective diaphragms 38 and 40 will be subjected to the action of the sound pressure which enters via the openings 31 and 32. The partition wall 28 will therefore so to speak be impinged in a push-pull mode from both sides by the sound oscillations or vibrations, so that as a practical matter it does not begin to vibrate or oscillate, whereby there is practically eliminated the possibility of acoustical feedback between the compartments 29 and 30. Since the microphone 11 only has associated therewith one sound inlet opening, namely the opening 31, the diaphragm 38 will be activated by its receiving sensitivity is concerned, possesses a spherical-type characteristic as same has been schematically depicted in FIG. 3. The conditions are different for the microphone 12. In this case both sides of the diaphragm or membrane 40 are impinged by the sound pressure, wherein, however, the sound waves which enter the opening 35 are dampened to a greater extent than the sound waves which enter through the opening 32. Consequently, the diaphragm 40 is placed into oscillation which, however, is only predicated upon the magnitude of the pressure differential in the compartment 30 which prevails between both faces or sides of the diaphragm 40. Since additionally the sound inlet openings 32 and 35 are arranged opposite one another the microphone 12 possesses, as concerns its receiving sensitivity, a pronounced directional characteristic,  
 and specifically such microphone possesses in the posi-- tion depicted in FIG. 5 a considerably greater sensitivity for sound waves which emanate from the left than for those which can enter from the right through the opening 35.  
 Both of the microphones 11 and 12 are each coupled through the agency of the conductor lines 13 and 14 respectively, with the reversing switch 22 and the amplifier 19. At such conductor lines 13 and 14 there is shown in phantom lines a supply conductor for the situation where the microphones 11 and 12 are of the type belonging to the class of piezo-electrical or dielectrical microphones. The illustrated amplifier 19 is a conventional miniaturized hearing aid-amplifier. The power supply to such amplifier 19 takes place through the agency of a suitable and therefore not particularly illustrated current source coupled with the terminals 45 and 46, wherein an installed switch 44 serves to switchon the amplifier 19. The weak tone-frequency signal which emanates from one of the microphones 11 and 12, depending upon the position of the reversing switch 22, is delivered to the amplifier 19 through the agency of the input terminal 43. Amplifier 19 is composed of the resistors Rl-R6, the capacitors C1-C7, the transistors Tl-T3 as well as the potentiometer Rv serving as the loud-speaker control and the variable resistor Rtl. A non-linear network is arranged in circuit with the conductor 47 leading to the loud-speaker 21, and this non-linear network consists of the resistor R7, both of the diodes D1 and D2 which are arranged in an antiparallel circuit configuration and the variable resistor Rt2. This network produces a non-linear alternatingcurrent feedback which, in turn, produces an amplificationor output-dependent, approximately logarithmic feedback or output limiting effect.  
  It should be understood that those skilled in the art will have considerable leeway as concerns the construction of the amplifier. Purely by way of example it is mentioned that the circuit components enclosed by the phantom-line box 42 can be constructed as an integrated circuit, at which there are coupled the adjustable or regulatable switching elements, namely the switch 44, the potentiometer Rv as well as the variable resistors Rtl and Rt2. It is, however, also possible to provide, instead of the illustrated amplifier 19, a linearamplifying amplifier which is controlled by a DC- voltage or limited by so-called peak clipping, and which constitutes electrical hardware particularly well known to those skilled in the hearing aid art.  
  While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,  
 What is claimed is:  
  1. An individual hearing aid for wearing by the hard of hearing, the hearing aid being transportable by the wearer and comprising amplifier means, a microphone system electrically coupled with said amplifier means, said microphone system comprising a first microphone having approximately spherical sensitivity chatacteristics and a second microphone with directed sensitivity characteristics, and means for selectively connecting the amplifier means with one or the other of both microphones.  
  2. A hearing aid for the hard of hearing comprising amplifier means, a microphone system electrically coupled with said amplifier means, said microphone system comprising a first microphone having approximately spherical sensitivity characteristics and a second microphone with directed sensitivity characteristics, means for selectively connecting the amplifier means with one or the other of both microphones, and further including a housing, a partition wall for subdividing the housing into two compartments, each of the microphones being arranged in a respective compartment of the housing, means defining a sound inlet opening which opens into one of the compartments and means defining two oppositely situated sound inlet openings opening into the other compartment.  
  3. The hearing aid as defined in claim 2, wherein each of the microphones has a diaphragm which can be placed into oscillation, and wherein said diaphragms are arranged substantially parallel to the partition wall.  
  4. The hearing aid as defined in claim 3, wherein for said other compartment one sound inlet opening is arranged atone side of the diaphragm which can be oscillated and the other sound inlet opening is arranged at the other side of said diaphragm of the associated microphone.  
  5. The hearing aid as defined in claim 4, wherein the sound inlet opening of said one compartment and said one sound inlet opening of the other compartment communicate with a common sound inlet funnel.  
  6. The hearing aid as defined in claim 5, wherein said other sound inlet opening possesses a greater sound absorption capacity than the remaining sound inlet openings.  
  7. The hearing aid as defined in claim 6, wherein both microphones are connected via a controlled reversing switch means with a threshold value amplifier constituting said amplifier means, and said threshold value amplifier upon exceeding a predetermined signal peak controls the reversing switch means for switching to said second microphone.  
  8. The hearing aid as defined in claim 1, wherein both microphones are connected via a controlled reversing switch means with a threshold value amplifier constituting said amplifier means, said threshold value amplifier upon exceeding a predetermined signal peak controlling the reversing switch means forswitching from one of the microphones to the other of themicrophones.  
  9. The hearing aid as defined in claim 8, wherein the reversing switch means normally connects the first microphone with said threshold value amplifier and in response to said threshold value amplifier exceeding a predetermined signal peak connects the second microphone to said amplifier.  
  10. The hearing aid as defined in claim 1, wherein the hearing aid is a self-contained unit arranged for accommodation on the wearer.  
  11. The hearing aid as defined in claim 1, further comprising common housing means for accommodating at least the first and second microphones for positioning on the wearer.  
  12. The hearing aid as defined in claim 11, wherein said amplifier means is contained in said housing means.