United States Patent [19]
`Franklin et al.
`
`I 1111111111111111 lllll lllll lllll lllll lllll lllll 1111111111111111111111111111
`US005388992A
`[H} Patent Number:
`[45] Date of Patent:
`
`5,388,992
`Feb. 14, 1995
`
`[75]
`
`[54] METHOD AND APPARATUS FOR TACTILE
`TRANSDUCI'ION OF ACOUSTIC SIGNALS
`FROM TELEVISION RECEIVERS
`Inventors: David Franklin; Michael Wollowitz;
`John Simpson, all of Somerville,
`Mass.
`[73] Assignee: Audiological Engineering
`Corporation, Somerville, Mass.
`[21] Appl. No.: 717,665
`[22] Filed:
`Jan. 19, 1991
`Int. CI.6 ......••••••••••.•••.. H04R 25/00; G09B 21/00
`[51]
`[52] U.S. a. .................................... 434/114; 434/112;
`340/407.1
`[58] Field of Search ............... 434/112, 113, 114, 116,
`434/185; 340/825.19, 407, 384 R, 407.1;
`341/21, 27; 381/68, 150, 151, 162, 191, 205
`References Cited
`U.S. PATENT DOCUMENTS
`4,250,637 2/1981 Scott ................................... 434/114
`4,310,315 1/1982 Frank et al .......................... 434/112
`4,581,491 4/1986 Boothroyd .......................... 434/114
`4,685,448 8/1987 Shames et al ....................... 434/185
`4,728,934 3/1988 Pfander et al ....................... 434/114
`FOREIGN PATENT DOCUMENTS
`0653197 12/1985 Switzerland ........................ 434/112
`2044977 10/1980 United Kingdom ................ 434/112
`9116694 10/1991 WIPO ................................. 434/114
`
`[56]
`
`OTHER PUBLICATIONS
`Franklin, David, "Tactileaids: What are they?" Hearing
`Journal, May 1988.
`•
`Primary Examiner-Jessica J. Harrison
`[57]
`ABSTRACT
`Inexpensive wideband transducers convert low fre(cid:173)
`quency components (i.e., approximately 50 Hz through
`800 Hz) of an audio signal to mechanical vibrations at
`the same frequencies so that the vibrations may be per(cid:173)
`ceived at the user's skin, typically at a hand or finger.
`The transducer may be a small permanent magnet mov(cid:173)
`ing coil loudspeaker with most of the diaphragm cone
`removed to minimize soundwave generation, or it may
`be a small d.c. or stepping motor arranged to have its
`drive shaft rotated in alternate directions through small
`angles corresponding to signal amplitude. Vibrations
`may be applied to the user's hand through a hand-held
`case vibrating with the motor, or to a finger via a con(cid:173)
`tactor extending outside the case from the motor or
`loudspeaker. The transducer has particular utility in
`conjunction with closed captioned in television pro(cid:173)
`grams to enhance appreciation of speech therein while
`also training the user in utilizing the transducer. One or
`more fixed frequency transducers may additionally be
`employed vibrations at a single frequency representing
`all of the higher frequency components in the audio
`signal.
`
`23 Claims, 4 Drawing Sheets
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`Valve Exhibit 1041
`Valve v. Immersion
`
`

`

`U.S. Patent
`
`Feb. 14, 1995
`
`Sheet 1 of 4
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`5,388,992
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`U.S. Patent
`
`Feb. 14, 1995
`
`Sheet 2 of 4
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`5,388,992
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`U.S. Patent
`
`Feb. 14, 1995
`
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`5,388,992
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`

`

`U.S. Patent
`U.S. Patent
`
`Feb. 14, 1995
`Feb. 14, 1995
`
`Sheet 4 of 4
`Sheet 4 of 4
`
`5,388,992
`5,388,992
`
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`

`

`1
`
`5,388,992
`
`METHOD AND APPARATUS FOR TACTILE
`TRANSDUCTION OF ACOUSTIC SIGNALS FROM
`TELEVISION RECEIVERS
`
`This invention was made with government support
`under grant awarded by the National Institute of
`Health. The government has certain rights in the inven(cid:173)
`tion.
`
`BACKGROUND OF THE INVENTION
`1. Technical Field
`The present invention relates broadly to improve(cid:173)
`ments in tactile sensing of acoustic and audio signal for
`hearing impaired persons. The invention has particular, 15
`although not exclusive, utility in enhancing the ability
`of hearing impaired persons to enjoy the audio portion
`of television signals.
`2. Discussion of the Prior Art
`Tactile devices for the deaf have been studied for 20
`approximately sixty years, and within the last eight
`years have been produced as commercial items. The
`essential concept embodied in all of these devices is to
`convert sound signals into vibrations that can be felt on
`the skin via the tactile sense. Naturally enough, the 25
`greatest emphasis has been on the ability to recognize
`speech sounds, although the practical value of recogniz-
`ing various background sounds, such as bells, footsteps
`and so on, are also well appreciated. Since the tactile
`sensory system is unable to perceive vibrations much 30
`above 800 to 1000 Hz, and since significant input from
`signals to at least 4000 Hz is required to impart impor(cid:173)
`tant speech data, a significant portion of the research
`and development work in this field has addressed meth(cid:173)
`ods for processing sound signals such that information 35
`from the higher frequencies can be transmitted to a user.
`Virtually all work in the field has focused on wearable
`devices which can be used on a more or less continuous
`basis; accordingly, a further constraint has been that the
`methods chosen result in small, cosmetically acceptable 40
`designs. Using these guidelines, the kinds of systems
`that have evolved all use small skin transducers, worn
`either on the wrist, chest or around the back of the
`neck. While it is well known that placing the transduc-
`ers somewhere on a hand yields very good perceptual 45
`results, these locations are avoided for reasons relating
`to utility. Typically these transducers are resonant at a
`single frequency, usually 250 Hz as this is the most
`sensitive frequency for the tactile sense, and processing
`methods are employed that encode the desired signals at 50
`this rate. In the more advanced systems a number of
`such transducers are used, each being assigned to a
`different portion of the acoustic frequency band and
`worn at a respective position on the skin. Thus, in these
`systems, the incoming sound signal is separated by a 55
`processor into spectral segments, each segment being
`represented at a respective location on the skin as a 250
`Hz signal with a varying time envelop and intensity
`according to the spectral content of the original signal.
`The most advanced of these so-called "multiple chan- 60
`nel" tactile devices currently available use seven such
`transducers arranged side by side with channels divided
`to cover the sound frequency range from 200 Hz to
`7000 Hz, divisions being selected according to data on
`vowel frequencies commonly known in the speech dis- 65
`cipline. The processing arrangement permits no more
`than two transducers to be actuated at the same time. It
`has been found that this method is desirable both to
`
`2
`provide clarity of perception and to conserve battery
`life.
`The reason for using resonant transducers is that they
`are more efficient than wideband transducers, at least as
`5 regards presently available technology. This, in tum,
`allows compact battery supplies to provide reasonably
`long operation with attendant cosmetic acceptability,
`but only at the cost described below.
`It has been recognized that wideband transducers
`10 allow more easily perceived patterns with richer infor(cid:173)
`mation content to be applied to the skin. In particular
`there are certain sound information components, nota(cid:173)
`bly voicing data in speech and attack waveform data in
`music, that are better represented by direct presentation
`of the unprocessed signals for the lower frequency
`range of the incident sound signal. This is true for that
`portion of these signals lying between about 50 Hz to
`800 Hz; frequencies above this tend to be so dimly per(cid:173)
`ceived by the tactile sense that there is little if any infor(cid:173)
`mation communicated without some kind of encoding
`being used, such as the transducer location encoding
`described above.
`It may be that improved perception could be ob(cid:173)
`tained with a hybrid system using a similar multiple
`channel scheme wherein the lower frequency channels
`use no encoding, being excited directly by the lower
`spectral portion of the original sound signal, and only
`the upper band spectral components are encoded as
`described above. However, the technical methods for
`obtaining such a system in wearable form are not cur(cid:173)
`rently available in a configuration that also meets cos-
`metic requirements.
`On the other hand, if one relaxes the cosmetic re(cid:173)
`quirements, as would be appropriate for the intended
`uses of the present invention, then broadband transduc(cid:173)
`ers such as loudspeakers or small motors, as described
`hereinbelow, provide a means for supplying the desired
`direct
`tactile representations of lower frequency
`sounds.
`In order to provide a frame of reference, it is desir(cid:173)
`able to note the specifics of the narrowband transducers
`currently used in the tactile field. A typical unit is ap(cid:173)
`proximately one inch long by 0.5 inch thick by 0. 7 inch
`wide and weighs about seven grams. Its low weight and
`flat configuration is appropriate for the usual methods
`of mounting. Since all signals applied to such a trans-
`ducer are encoded at a single frequency, typically 250
`Hz, requirements for bandwidth are only related to the
`required response time. A well designed unit follows
`waveform changes at better than a 20 msec rate, ade(cid:173)
`quate for virtually all speech sounds and all environ-
`mental sounds of interest. For such a device a typical
`peak driving energy to obtain maximum perceptual feel
`is on the order of 350 mw. It has been found over a
`period of years of actual use that the average duty cycle
`for these kinds of systems is on the order of 0.2. Accord-
`ingly, for a wearable system using one such transducer,
`the expended energy/hour is on the average about 70
`mwatt-hours. A typical rechargeable battery pack used
`to power these devices, constrained in size according to
`the usual cosmetic considerations, stores about 1600
`mwatt-hours. Hence, as is verified in many thousands of
`hours of actual use, a system using one such transducer
`will operate, on the average, for about twenty-three
`hours between charges. Generally, the decrease in
`hours of operation between charges does not follow
`linearly with an increasing number of transducers be(cid:173)
`cause, depending on design parameters, it is not true
`
`

`

`5,388,992
`
`5
`
`3
`that all transducers in a system have the same duty
`cycle. For the seven channel device mentioned previ(cid:173)
`ously, where only two transducers at most are activated
`simultaneously, the time of operation between charges
`is approximately 15 hours.
`In contrast, a typical mass-produced small motor
`requires about 1.5 watts in the application mode de(cid:173)
`scribed herein to elicit the same perceptual intensity; it
`weighs about forty grams and has a cylindrical configu(cid:173)
`ration typically on the order of one inch in diameter and 10
`one inch in length. It is clear that neither the configura(cid:173)
`tion nor the power requirements lend themselves to
`application in a wearable form and that the· weight also
`mitigates against this use. However, for a hand-held or
`hand-contact application in which larger size is allow- 15
`able and hence a larger space can be allocated for the
`battery pack, the use of such small motors is not pre(cid:173)
`cluded. If loudspeakers are utilized, they require only
`350 mw to achieve the same level drive for the applica(cid:173)
`tions described herein; however the loudspeakers are 20
`typically even larger and heavier than the small motors.
`Again, for hand-held or hand-contact applications this
`larger size and weight is not objectionable.
`From the foregoing it will be appreciated that the
`present invention is intended to teach the use of small 25
`mass-produced motors or loudspeakers in tactile trans(cid:173)
`ducers for the deaf and hearing impaired in those appli(cid:173)
`cations where large size and low efficiencies, as com(cid:173)
`pared to the usual tactile transducers, are not serious
`detriments. In particular, but not exclusively, this 30
`would apply to transducing television audio signals
`whether or not accompanied by captioning.
`The present invention has particular, but not exclu(cid:173)
`sive, utility in conjunction with television programming
`incorporating closed captioning or similar techniques 35
`employed to provide titling on the video screen to rep(cid:173)
`resent spoken words in the audio signal. The closed
`captioning titling technique is described and defined in
`Report No. E-7709-C, revised May 1980, by the Public
`Broadcasting Service. The disclosure in that report is 40
`expressly incorporated herein. Typically, a closed cap(cid:173)
`tioning decoder processes the closed captioning signal
`that is included in line twenty-one of the NTSC video
`signal. Decoding results in titling that is overlayed on
`the television screen, the titling content corresponding 45
`to speech in the audio portion of the received television
`signal. The present invention, by providing a low cost
`wideband transducer that can be used in conjunction
`with closed captioning, not only enhances appreciation
`of television programs for hearing impaired persons; it 50
`also permits such persons to be trained in the use of the
`transducers since the speech signals being tactually
`transduced are simultaneously viewed as titling on the
`television screen.
`OBJECTSANDSUMMARYOFTHE
`INVENTION
`It is therefore, a primary object of the present inven(cid:173)
`tion to enhance a deaf or hearing impaired person's
`appreciation and enjoyment of television by means of a 60
`hand-held or hand-contact tactile device imparting a
`vibratory signal containing broadband television signal
`audio information over a bandwidth from about 50 Hz
`to about 800 Hz in direct form without any frequency
`translation. It is another object of the present invention 65
`to provide such device in the form of a small inexpen(cid:173)
`sive mass-produced electric motor or loudspeaker
`driven directly by the sound signal via an appropriate
`
`4
`electronic driving circuit. It is also an object of the
`invention to encode only the higher frequencies in the
`sound signal in order to provide tactile vibrations with
`a fixed carrier frequency such as 250 Hz.
`According to the present invention, the tactile signals
`supplement other sources of sound information avail(cid:173)
`able from a television set, such as text captioning ap(cid:173)
`pearing on the screen, speech reading from the visual
`image and residual hearing assisted by hearing aids or
`some other means. Coupling to the tactile device from
`the sound output of the television set may be via: direct
`coupling to an output jack contained on the television
`set; an infrared or frequency modulated signal coupled
`from the television set via an appropriate transmitter/(cid:173)
`receiver pair, either as part of the tactile system or
`coupled to the tactile system; or an internal microphone
`provided as part of or plugged into the tactile system.
`A further primary object of this invention is to enable
`a deaf or hearing impaired person to learn to recognize
`speech and other sounds cutaneously through the tactile
`modality during such periods as he might use the de(cid:173)
`scribed tactile device while watching television and
`using the device. Specifically, use of such a device
`while watching television not only improves apprecia(cid:173)
`tion of the television programming material, but also
`improves skill with the tactile modality; it thereby
`serves as a training method for deaf and hearing im(cid:173)
`paired individuals whose daily use of tactile devices is a
`primary means for obtaining information about the
`world of sound, both as regards speech information and
`environmental sound information.
`It is a further object of this invention to provide a
`cutaneously tactile device for use as a means of appreci(cid:173)
`ating both speech and non-speech sounds generated
`from sources other than television sets, whereby the
`device serves as a communication device and an envi(cid:173)
`ronmental sound awareness device in contexts other
`than as an adjunct to its use with television sets.
`A still further object of the present invention is to
`provide an inexpensive and effective means for enabling
`a deaf or hearing impaired person to cutaneously per(cid:173)
`ceive vibrations in the frequency band between 50 and
`800 Hz in such a manner as to assist his appreciation of
`television programming materials and other sound in(cid:173)
`formation while holding a tactile transducer or trans-
`ducers in his hand or against some other portion of his
`body, wherein low frequency vibrations in the range of
`approximately 50 to 800 Hz are provided by a small
`inexpensive mass-produced electric motor or loud(cid:173)
`speaker.
`In accordance with the present invention, tactual
`vibratory signals in the frequency range between about
`50 Hz and 800 Hz are provided by a loudspeaker or
`55 small inexpensive mass-produced electric d.c. or step(cid:173)
`ping motor responsive to an audio signal derived from
`sound events in the aforesaid frequency range. Driving
`signals for d.c. and stepping motors are usually of one
`polarity only, resulting in motor rotation in one direc(cid:173)
`tion (i.e., continuously in the case d.c. motor, step-wise
`in the case of stepping motors). In the present invention
`the alternating audio input signal instead causes the
`motor to reverse its direction and magnitude of rotation
`in accordance with the polarity and magnitude of the
`input driving signal. As a consequence, the motor rotor
`rocks back and forth around a more or less fixed angular
`position with a rate and magnitude proportional to the
`frequency and magnitude of the said sound signal.
`
`

`

`5,388,992
`
`20
`
`25
`
`30
`
`6
`tion to function as a low frequency wideband trans(cid:173)
`ducer;
`FIG. 9 is a side view in section of another embodi(cid:173)
`ment of the present invention wherein a small motor is
`5 employed to reciprocate a contact pad or platform to
`provide tactile vibration;
`FIG. 10 is a side view in section similar to FIG. 9 but
`showing the motor mounted on a soft mounting pad;
`FIG. 11 is a view in perspective of a small loud(cid:173)
`speaker modified for use as a transducer in accordance
`with the present invention;
`FIG. 12 is a view in transverse section of a loud(cid:173)
`speaker similar that shown in FIG. 11 but modified to
`enhance its low frequency response; and
`FIG. 13 is a view in section of a loudspeaker trans(cid:173)
`ducer mounted in a housing in accordance with the
`present invention.
`
`5
`Whether a motor or a loudspeaker is employed to
`transduce the audio signals, the transducer effectively
`converts audio signals in the 50 Hz to 800 Hz range to
`cutaneously perceived vibrations at those same frequen(cid:173)
`cies.
`In one preferred embodiment of this invention a
`hand-held housing includes the transducer assemblies,
`the electronics, the interconnect jack, the batteries and
`possibly a microphone, although in order to eliminate
`the possibility of feedback, the microphone, if used, is 10
`best implemented via a remote unit plugged into the
`interconnect jack.
`In an alternative preferred embodiment the housing is
`not hand-held but is placed instead on a surface and the
`hand of the person using the device is placed on it. In 15
`either of these embodiments the transducers may be
`isolated from the mass of the housing, or from the massy
`parts of the housing and contents, in order to improve
`DESCRIPTION OF THE PREFERRED
`coupling efficiency and increase the amount of motion
`EMBODIMENTS
`of the transducer assemblies.
`Referring specifically to FIG.1 of the accompanying
`In use, the transducer is plugged into a reception
`drawings, a preferred embodiment of the invention is
`mechanism such as a remote microphone, the output
`shown in the context of supplementing the appreciation
`jack from an infrared or frequency modulated receiver
`of sound accompanying a received television signal.
`receiving the sound channel from the television set, or
`What is shown is a television set 1 providing two audio
`directly into an audio output jack on the television set.
`output signals and having an audio output jack 3 and a
`An appropriate interconnect cord of suitable length is
`loudspeaker 2, either of which can be used as a sound
`employed as necessary. The deaf or hearing impaired
`source for a hand-held tactile unit 19 having an input
`user thus tactually receives information about the sound
`audio jack 17. Depending on the particular application,
`events in the television program being watched.
`the audio input jack 17 of tactile unit 19 may receive the
`television audio signal from: a microphone 11 for pick-
`BRIEF DESCRIPTION OF THE ORA WINGS
`ing up the acoustic signals from speak.er 2 and coupled
`.
`.
`by cable 12 to jack 17; a direct audio cable 10 between
`The above and still ~rther _obJe<:ts, features and ad-
`jacks 3 and 17; FM Receiver 14 via its output cable 16;
`vantages ~fthe present mventioi_i will ~ome ap~ar~nt
`upon c~ns1derat10~ of the followmg de~ed descnption 35 or infrared (IR) Receiver 13 via its output cable 15. In
`the case where either IR Receiver 13 or FM Receiver
`of specific embodunents thereof, especially when taken
`14 is employed, it receives input signal from IR Trans-
`in co~jui_iction with the acco~panying_ drawings,
`mitter 7 or FM Transmitter 9, respectively, which in
`wher~11_1 like refe~ence n~erals tn the vanous figW:es
`are utilized_ to des1~te like components, ~d wherem:
`turn receives its audio input signal from either a respec-
`FIG. 1 1s a fu_nct10nal system block. dmgr~ of a 40 rive microphone 6 or 4 via loudspeaker 2 or, altema-
`tively, directly from audio cable 10, if the receiver is
`preferred embodiment of_ the pr~nt mvent1on. ~m-
`ploy_ed to transduce sound mformation from a televis10n
`equipped to receive direct electrical signals as is often
`receiver; .
`.
`. .
`the case. Regardless of the means of coupling, the tele-
`FIG. 2 1s a block diagram of the hand-held umt m the
`vision audio signal is delivered from the television set to
`system of ~IG. _1;
`45 the input electronics of the hand-held or hand-con-
`.
`.
`.
`tacted tactile unit 19 for the purpose of enhancing the
`FIG. 3 1s a circwt block diagram of the electrorucs
`processor employed in the unit of FIG. 2;
`user's appreciation of the auditory program material.
`FIG. 4A is a top view in plan showing one hand-held
`Any variations in the coupling methods as may be af-
`embodiment of the present invention and the hand of a
`forded by different technologies or coupling mecha-
`user thereof;
`50 nisms are considered to fall within the scope of the
`FIG. 4B is a partially diagrammatic side view in sec-
`present invention.
`tion of the hand-held embodiment of FIG. 4A;
`As described above, television set 1 may be equipped
`FIG. SA is a side view in elevation of another em-
`with a closed captioning decoder that produces titling
`bodiment of the present invention, adapted to be placed
`on the television screen corresponding to speech in the
`on a surface, and showing the hand of a user thereof; 55 audio portion of the received television signal. A hear-
`FIG. SB is a partially diagrammatic side view in sec-
`ing impaired person can thusly view the speech being
`simultaneously transduced to tactile signals at unit 19.
`tion of the embodiment of FIG. SA;
`FIG. 6 is a view in plan of a d.c. motor employed as
`The person is thereby able to see the words represented
`a low frequency wideband transducer in accordance
`by the sensed tactile sensations and become familiar
`with one embodiment of the present invention;
`60 with the meanings of those sensations. Once the person
`is trained in using unit 19, the unit may be used indepen-
`FIG. 7A is a top view in section of a conventional
`variable reluctance tactile transducer of the type used
`dently of closed captioning to enhance appreciation of
`for a high frequency channel in the transducer embodi-
`television audio signals as well as general speech.
`FIG. 2 illustrates details of tactile 19 unit shown in
`ments of the present invention;
`FIG. 7B is a side view in section of the transducer of 65 FIG. I. A housing 21 has at one end the audio input jack
`17. The shape of housing 21 is chosen to be conve-
`FIG. 7A;
`FIG. 8 is a view in perspective of another small
`niently held in one hand with, in the preferred method,
`motor modified in accordance with the present inven-
`the end having audio input jack 17 nearest the wrist. At
`
`

`

`7
`this end is a compartment to hold batteries 20, prefera-
`bly of the rechargeable type, and a circuit board 23 on
`which is assembled electronic processor 24, a low fre(cid:173)
`quency power driver 25 and a high frequency power
`driver 26. The output signal from the low frequency 5
`power driver 25 is coupled to a small motor 30, and the
`output signal of the high frequency power driver 26 is
`coupled to a high frequency transducer 35, via suitable
`wiring. As shown, the high frequency transducer 35 is
`suspended away from housing 21 by means of a gasket 10
`37 acting to isolate transducer vibrations from those of
`the housing. In contrast, the small motor 30 is rigidly
`attached to housing 21 such that its vibrations are di(cid:173)
`rectly coupled to the housing and thence to the tactile
`sense via the skin on the user's hand. In the preferred 15
`method of use, the palm of the user's hand is wrapped
`around housing 21 with the finger tips placed on the
`surface of high frequency transducer 35. Tangential
`rotary low frequency vibrations are coupled to housing
`21 from small motor 30 while the high frequency trans- 20
`ducer 35 vibrates normal to the surface of housing 21,
`but isolated from it by suspension gasket-37. The user is
`able to differentiate between the two vibration sources
`on his skin because the high frequency vibrations are
`near his finger tips while the low frequency vibrations 25
`are applied over the entire front of his hand. Addition(cid:173)
`ally, the perceptual experiences from the two channels
`differ because the low frequency vibrations from small
`motor 30 have a complex waveform consisting of all
`low frequencies while the vibrations from transducer 35 30
`are at a fixed frequency with a nearly constant ampli(cid:173)
`tude. These differences in signal content between the
`two transducers 30 and 35 are illustrated more clearly in
`FIG. 3.
`Referring to FIG. 3, the circuitry on circuit board 23 35
`(FIG. 2) receives an audio input signal through input
`jack 17 to be amplified by preamplifier 40. The ampli(cid:173)
`fied signal is divided into two channels, one consisting
`of only low frequency components (e.g., below 1 KHz)
`separated by a low pass filter 41 while the high fre- 40
`quency channel is established by a bandpass filter 47
`having a typical passband of 2000-:-7000 Hz. In the low
`frequency channel a variable attenuator 42 permits ad(cid:173)
`justment of the signal intensity, after which a band(cid:173)
`shaped highpass filter 45 provides pre-emphasis to take 45
`into account the relatively low efficiency of the small
`motor 30 as a transducer at higher frequencies. The
`shape of the amplitude versus frequency characteristic
`of filter 45 depends on the characteristics of both motor
`30 and the user's skin characteristics. The output signal 50
`from filter 45 is fed to low frequency driver 25 and
`thence to small motor 30. Thus, it is seen that the small
`motor is driven directly by the low frequency compo(cid:173)
`nents of the audio signal.
`In contrast, the high frequency signal components are 55
`detected by detector 49 after filter 47 and then low pass
`filtered by filter 50 to recover the signal amplitude
`without regard to the detected frequency components,
`other than that these components must be 2000 Hz or
`greater. This amplitude function is multiplied in multi- 60
`plier 61 by a 250 Hz signal from oscillator 56. The am(cid:173)
`plitude of the 250 Hz signal may be adjusted by attenua-
`tor 60. The modulated output signal from multiplier 61
`is applied to a signal amplifier or driver 26 to excite the
`high frequency transducer 35.
`It will be appreciated that, while the low frequency
`motor 30 receives low frequency signals from the origi-
`nal sound source modified only linearly by filtering, the
`
`65
`
`5,388,992
`
`8
`high frequency transducer 35 receives only a 250 Hz
`signal whose amplitude is related to the average ampli(cid:173)
`tude of the original sound signal components between
`approximately 2000 Hz and 7000 Hz. The purpose of
`leaving a frequency gap between the top of the low
`channel and the bottom of the high channel is to better
`define the differences between the signals. It has been
`found in practice that this technique gives rise to the
`best use of the upper channel if only one transducer is
`used to represent that channel. While not a critical
`requirement, in the preferred embodiment this approach
`is utilized.
`FIG. 4A illustrates a hand 62 holding tactile unit 19,
`the tip of a forefmger 63 being in contact with the high
`frequency transducer 35 while the remainder of the
`front of the hand grasps the unit. The interior of unit 19
`is illustrated in FIG. 4B wherein the batteries 20 are
`shown mechanically isolated from the housing structure
`or case 21 by means of a suspension 22, or the like, while
`the small motor 30 is rigidly attached to the housing. By
`isolating the heavy batteries from the housing, the ex(cid:173)
`cursion magnitude of the housing in response to vibra(cid:173)
`tions of motor 30 may be increased. The high frequency
`transducer 35 has a suspension 37 for the purpose of
`isolating the transducer vibrations from those of hous(cid:173)
`ing 21. Also illustrated in FIG. 4B is the electronics
`assembly 24, 25 and 26.
`FIGS. SA and SB illustrate an embodiment of the
`invention not designed to be hand-held but instead
`placed on a surface during use. In this design the user's
`hand 62 is placed on housing 22 which, in turn, rests on
`a support surface. Small motor 30 is isolated from the
`housing 22 by a suspension 32, and high frequency
`transducer 35 is likewise isolated by its suspension 37. In
`this embodiment the batteries 20 need not be isolated
`from the case 21.
`FIG. 6 is a diagram of the low frequency transducer
`realized as a permanent magnet direct current motor
`having magnets 71 and 72 mounted on its case 73 with
`a three-pole rotor and windings 76, 77 and 78 to receive
`an input driving signal at terminals 80. This signal is
`coupled to the windings 76, 77 and 78 via brushes 74
`and 75 through commutator 82. Unlike the usual opera(cid:173)
`tion mode of a direct current motor, the alternating
`phases of the signal cause the rotor to vibrate about its
`center axis in a rotational motion wherein the average
`angular position remains constant, and wherein the rate
`and amplitude are proportional to the driving signal •
`frequency and amplitude, respectively. The total mass
`of the rotor assembly 76, 77, 78 and 82 is comparable to
`that of the stationary case assembly 71, 72, 73, 74 and 75;
`therefore, the desired vibration of the latter is signifi(cid:173)
`cant. Although a three-pole motor is shown, in general,
`for the rocking motion inherent to this kind of motor
`operation, the greater the number of poles, the more
`efficient the operation. In the preferred embodiment,
`cost is an important consideration and the least expen(cid:173)
`sive motors tend to have no more than three poles. In
`alternate configurations, however, where efficiency is a
`more important parameter, trade-offs of cost against
`efficiency are appropriate.
`FIG. 7A and 7B illustrate a conventional variable