US3631450A

US3631450A - Acoustic alarm device

Info

Publication number: US3631450A
Application number: US853295A
Authority: US
Inventors: John W Chalfant
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-08-27
Filing date: 1969-08-27
Publication date: 1971-12-28
Anticipated expiration: 1988-12-28

Abstract

A loudspeaker is adapted to be energized by an alternating current signal to provide an audible output signal of progressively increasing intensity. An alarm controlled switch applies the signal to a loudspeaker. The increase in intensity of the audible signal is facilitated by a thermistor connected in series with the loudspeaker. A high-pass filter and rectifier circuit in series with the thermistor enhance the production of harmonics of the signal frequency thereby to provide an improved audio tone and to permit said tone, or alarm signal, to be readily heard over a broad intensity range. A vibrator attached to the speaker provides a second audible signal after a predetermined audio intensity is achieved.

Description

United States Patent [72] Inventor John W. Chaliant 8325 S.W. 86th Terrace, Miami, Fla. 33143 [21] Appl. No. 853,295

[22] Filed Aug. 27, 1969 [45] Patented Dec. 28, 1971 [54] ACOUSTIC ALARM DEVICE [56] 7 References Cited UNITED STATES PATENTS 2,517,368 8/1950 Wiseley 58/19 34; .SwiiclL Primary Examiner-Richard B. Wilkinson 7 Assistant Examiner-Lawrence R. Franklin Attorney-Lloyd J. Andres ABSTRACT: A loudspeaker is adapted to be energized by an alternating current signal to provide an audible output signal of progressively increasing intensity. An alarm controlled switch applies the signal to a loudspeaker. The increase in intensity of the audible signal is facilitated by a thermistor connected in series with the loudspeaker; A high-pass filter and rectifier circuit in series with the thermistor enhance the production of harmonics of the signal frequency thereby to provide an improved audio tone and to permit said tone, or alarm signal, to be readily heard over a broad intensity range. A vibrator attached to the speaker provides a second audible signal after a predetermined audio intensity is achieved.

Patented Dec. 28, 1971 3,631,450

Switch 1? 10, COIL'ZTOL 14] l I? Power ;7 gi gg Harmonic Dual, .50 12 Network Generajor Transducer switch H CorbiroL q Bu 1" "3 5 INVENTOB 8 JOIUL WClla lfani BY v 4 Time A TTOBNE Y8 ACOUSTIC ALARM DEVICE BACKGROUND OF THE INVENTION The types of alarm clocks for various purposes available on the market today are legion. They are available with buzzers, chimes, radios, flashing lights and many other varied audible visual, and/or physical alarm mechanisms, of which many have the objective of awakening the sleeper. Most. of these alarmclocks provide a continuous audible output level usually of sufficient intensity to awaken even the deepest sleeper. Unfortunately, this high intensity or loud alarrn signal, even though in some cases it may be varied in intensity, by an adjustment knob or lever, does not meet the needs of many people. Depending upon the sleepers state of fatigue and related factors, varying intensity sounds may be required to arouse him. Stated simply, the sleepers threshold of sensitivity varies with his physical condition. Hence, too loud an alarm is often used providing in efi'ect a nerve shattering output even though in most cases such high-intensity audio signal is not necessary. In order to avoid the shock and discomfort of aloud signal the sleeper has the option of obtaining an alarm with a muffled or low-level sound or of manually setting the alarm intensity control to a lower volume level. In either case, he must take a chance that the low-level signal is not too low to awaken him. If unwilling to assume such a calculated risk, the sleeper will often tolerate too loud an alarm system with the attendant shock to his nervous system.

One US. Pat. No. 2,856,751 issued Oct. 21, I958 to Ralph H. Preiser attempts to obviate these difficulties by providing what is termed an Automatic Crescendo Alarm. The Preiser alarm utilizes a thermistor in series with abell such that the bell initially emits a relatively low-intensity sound but as the thermistor warms up due to the solenoid current passing therethrough, the bell emits a sound of increasing intensity. Hence, even though Preiser has taken a step toward eliminating the objection to most of the presently available alarm clocks, the Preiser audible signal is still a relatively harsh tone and, due to the inherent limitations of most solenoid bells, the dynamic audible range provided by the bell is limited, with a relatively high initial or minimum noise level.

Accordingly, it is an object of this invention to provide an improved acoustic alarm device which produces an audible signal having a relatively pleasant tone.

Another object of this invention is to provide an improved acoustic alarm device which produces an audible output signal of high intensity and having a relatively large dynamic range.

A further object of the invention is the provision of a dynamic loudspeaker in which the voice coil thereof is adapted to move in an oscillatory amplitude sufficient to cyclic impact against a rigid member for producing audible shock waveemission from the diaphragm of the loudspeaker.

BRIEF DESCRIPTION OF THE INVENTION In a preferred embodiment of this invention an alarm device is constructed to have a sound transducing means, a switch means for applying-a low-frequency alternating current voltage signal to the sound transducing means thereby to produce an audible oscillating signal varying in content and intensity with the frequency and amplitude of the voltage signal applied thereto, an impedancemeans coupled in circuit with the transducing means and the switch means for increasing the amplitude of the voltage signal that is applied to the transducing means as a function of time. Finally, harmonic generating means are coupled in circuit with the transducing means for generating harmonics of the voltage signal for application to the transducer, thereby improving the quality of the audible alann signal, and the ease with which it, together with corresponding intensity changes, may be heard.

In one form of vthe invention, a vibrator or member arm is attached to the loudspeaker so that the axial movement of the voice coil interacts with the end of the vibrator arm to cause impact vibration thereof. This additional vibrationproduces a simultaneous audible signal in the core or diaphragm of the loudspeaker to provide an output signal of increased audio intensity and increased dynamic frequency range.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features that are considered characteristics of this invention are set forth with particularity in the appended claims. The invention, itself, however, both as to its apparatus and method as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIG. 1 is a block diagram of an acoustic alarm system constructed in accordance with this invention;

FIG. 2 is a schematic circuit diagram of an acoustic alarm device constructed in accordance with a preferred embodiment of this invention;

FIG. 3 is an enlarged partial sectional view of a loudspeaker illustrating the preferred manner in which the vibrator arm is attached thereto;

FIG. 4 is an enlarged partial cross-sectional view of the speaker cone illustrating an alternative manner in which the vibrator arm may be attached to the loudspeaker; and

FIG. 5 is a graphical illustration of the alarm devices response in which the sound intensity produced by the vibrator arm and loudspeaker is plotted as the ordinant and time is plotted as the abscissa.

A may be a conventional source of line voltage, is connected through a switch 12 to an amplitude control network illustrated by the block 14 thence to a harmonic generator illustrated by the block 16 to energize a dual transducer denoted by the block 18. The switch 12 may be actuated by a switch control device denoted by the block 34. The switch control device in practice may be a conventional clock mechanism or some other type of actuator (electrical or mechanical) controlled as by the opening of a door or the passage of a person past a photocell, etc. In its preferred embodiment, the form of the switch control device 34 is a clock mechanism which operates through a suitable mechanical linkage denoted by the dashed line 36 to close the switch 12.

The amplitude control network 14 may include a thermistor or other circuit element having a negative temperature coefficient of resistance so that the electrical signal allowed to pass therethrough progressively and gradually increases in amplitude as a function of time as the circuit element, in this case a thermistor, begins to heat up and thereby its resistance value decreases. Alternatively, other timing circuits such as those with an RC voltage level control of current flow or other timing circuits both electrical and mechanical which control or vary current flow as a function of time may be used.

The signal after passage through the amplitude control network 14 then passes to a harmonic generator 16 whose function is to modify the hannonic content of the voltage signal passing therethrough as by clipping or similar known techniques. By increasing the harmonic content of this signal, which is then applied to the dual transducer 18, a richer, more pleasing audible tone results. The dual transducer 18, may in a preferred embodiment of this-invention, comprise a conventional miniature permanent magnet dynamic loudspeaker. In alternative embodiments any type of sound transducer may be used. This electrical signal having a high harmonic content, is reproduced by the transducer to provide the audible alarm signal which increases in intensity with time.

The specific circuit details of one system that has been successfully built and operated are shown in the schematic drawing of FIG. 2. Thus, the power source 10, which in this instance is illustrated by the conventional generator symbol, provides an alternating 60 Hertz (Hz.) voltage signal such as that derived from a normal wall outlet of most houses. The voltage signal is connected through a step down transformer 11 so as to provide a lower voltage. This reduced voltage signal from the transformer 11 is passed through the switch 12, actuated by the linkage 36 from the switch control device 34, as described, to a thermistor 38. A unidirectional conducting device, such as a diode 40, and a capacitor 42 are connected in series between the thermistor 38 and one end of the voice coil of a loudspeaker 44. in turn the other end of the voice coil 43 is returned to the transformer 11 to complete this circuit. The diode 40 has a variable resistor 50 connected in parallel. The capacitor 42 may be a conventional low voltage, high-capacity element such as is provided by an electrolytic capacitor. A neon lamp 26 or other indicator may be connected in the load circuit to indicate when power is on, i.e., when the switch 12 is closed.

With the circuit arrangement shown, it may be assumed that the switch control device 34 operates through the linkage 36 to close the switch 12. With the closing of the switch 12, the low-voltage alternating current signal from the step down transformer 11 energizes the neon lamp 26 indicating the alarm is on and passes a current through the thermistor 38. The initial high resistance of the thermistor 38 limits the current to a relatively low value. This current signal in turn has its negative going excursions clipped by the diode 40. The variable resistor 50 is maintained at a relatively high-resistance level to control the degree of clipping. if its value is reduced, the clipping is decreased. In any event, this low current, clipped signal is passed through the capacitor 42 which is selected to have a value that presents a relatively high impedance to the fundamental 60 Hertz frequency component but yet presents a significantly lower impedance to the passage of higher frequency components. This has the effect of amplifying" the higher frequency components with respect to the 60 Hz. fundamental frequency component. The clipping function performed by the diode 40 causes the generation, predicted according to Fourier analysis, of plural odd harmonics of the fundamental frequency. These odd harmonics freely pass-through the capacitor 42, to the voice coil 43 of the loudspeaker 44 while the fundamental component is attenuated. Thus, the initial audible signal produced by the loudspeaker 44 is one of low-audio intensity complete with many harmonics of the fundamental frequency thereby producing a more pleasing tone to the car than is normally available from the pure 60 Hertz hum.

As the thermistor 38 begins to heat with the current passing therethrough its resistance decreases such that the speaker 44 produces an audible signal of progressively increasing intensity. This operation is illustrated in the graphical representation of FIG. in which the audio output signal produced by the speaker is illustrated by the line 60. It may be noted that at zero time (the time the switch control 34 closed the switch 12,) the output signal sound intensity is relatively low. This intensity progressively increases until the maximum is reached, this maximum being represented either by the maximum signal applied from the source or from the point at which the speaker becomes overloaded and does not produce a greater intensity signal. This maximum intensity point is represented by the upper portion of the line 60 designated by the numeral 92.

In accordance with a preferred embodiment of this invention a small loudspeaker 44 is provided, as may be seen most clearly in FIG. 3, with a rigid or substantially rigid vibrator arm 62-. ln the illustration of FIG. 3, the speaker itself is illustrated as having a cone portion 64, the voice coil 66, which moves vertically back and forth in the drawing and a speaker rim portion 68 which is mounted by conventional means to a housing or cabinet 70. The vibrator arm, secured as by a suitable screw or other fastening mechanism 72 to the cabinet, or for that matter directly to the rim 68 of the speaker, extends downwardly (in the drawing) generally parallel to the cone face and has a bent lower portion, the vibrator impact end 74 which is adapted to be just above the voice coil 66 of the speaker. The voice coil 66 may be provided with a small contactor 76 which with the axial motion of the voice coil, tends to strike the impact end 74 of the vibrator arm 62. Each time the vibrator end 74, of a nonrigid type, is struck, the vibrator arm tends to vibrate at its own resonant frequency, which may be selected to be of a relatively high audio range, say in the order of 2 to 3 kilohertz. The vibration of the vibrator arm tends to cause the cabinet 70 to resonate thereby amplifying the vibrational energy to produce an audio sound of buzz of increasing intensity as the signal to the voice coil increases in intensity.

The vibrator arm 62 is provided with an adjusting screw 80 threaded through the vibrator arm. The screw 80 engages a shim 82 attached to the cabinet 70. By adjustment of the screw 80, the spacing'between the vibrator end 74 and the striker 76 may be varied. Thus as the spacing is adjusted the characteristic of the buzz or humming tone will be changed as is illustrated by the two

characteristic lines

81 and 82 in the graph of FIG. 5. ln both cases, the vibrator signal starts at some finite level. This finite level is determined by the amplitude necessary for the striker 76 to actually contact the vibrator end 74. Once contact is made and the vibrator arm emits a very low-level buzzing signal, this signal like that of the speaker generated signal, increases in intensity as the amplitude of the signal applied to the voice coil increases, until a maximum value is achieved. In general, smaller spacings of the vibrator end 74 from the contactor 76 provide louder audio intensities, i.e., the curve 81 represents the smaller spacing. The total audio output from the device of this invention is the sum of the two signals, i.e., tone from the loudspeaker plus the buzz of the vibrator arm.

The purpose of increasing the harmonic content of the power signal prior to application to the loudspeaker, or dual transducer 18, is to provide a richer, more pleasing audible tone; to produce a signal containing frequencies in the sensitive human hearing range where changes in intensity are the most easily discernible; and to permit the use of a conventional miniature permanent magnet dynamic loudspeaker, in an illustrative case, one having a 2-inch diameter cone.

Although such a small loudspeaker will not sufficiently radiate a 60 Hz. driving signal, the axial movement of its voice coil will follow the 60 Hz. driving voltage. Therefore, a unique feature of this invention is the use of the fundamental component of the 60 Hz. voltage to drive the voice coil of said miniature loudspeaker through the mechanical motions necessary to actuate the vibrator (transducer No. 2). The 60 Hz. sound radiated by said miniature loudspeaker will be of relatively low apparent intensity; while, simultaneously, harmonics produced by the harmonic generator undergo less attenuation by capacitor 42 than the 60 Hz. fundamental frequency.

Loudspeakers of the electrodynamic-type are designed to normally operate with cone amplitudes that fall within predetermined limits well within the low-impedance portion of their suspension means in order to transfer electric oscillatory energy to corresponding acoustical energy with reasonable high fidelity.

When the cone of the speaker is energized beyond the above mentioned range, it gradually encounters increasing high-mechanical impedance of the suspension and thus requires a greater electrical energy input. When this increased amplitude is suddenly arrested by impact with a relatively rigid body, the energy stored in the cone is released with an excessive burst of acoustical energy which will produce complex shock waves of sound with a considerably greater increase in sound energy of short duration, which waves are superposed on the normal acoustical output from the normal free cone output of the oscillatory signal.

Whereas a persons hearing is generally relatively insensitive to volume or sound level changes at 60 Hz. because of loss of hearing efficiency at that low frequency, it is well known that hearing efficiency and sensitivity to sound intensity changes increase with frequency until a certain upper frequency limit, varying with the individual, has been reached, at which point efficiency and sensitivity again begin to taper. The

frequency of maximum sensitivity and efficiency also varies with the individual.

Accordingly, an objective of the harmonic generator is to produce harmonics over such an audible frequency range that any person whose hearing is reasonably good, regardless of his frequency of maximum efficiency and sensitivity, will be able to hear the harmonic generator produced portion of the alarm signal throughout its low to high audio intensity range. Thus, this portion of the alarm system may be stated to be individual to the users particular frequency of maximum sensitivity and efficiency.

In summary, a 60 Hz. fundamental voltage is'used to drive a miniature loudspeaker voice coil so that the striker 76 will strike the buzzer vibrator end 74 when the driving signal has reached a predetermined level. With relatively low efficiency, a 60 Hz. sound is radiated by the loudspeaker cone. Simultaneously, harmonics of the 60 Hz. fundamental frequency are more efficiently radiated, giving tone richness to the loudspeaker output, and permitting the listener to hear distinct signal intensity changes ranging from nearly inaudible to a relatively high-intensity level at which point the buzzer (transducer No. 2) is activated. A dual signal results, consisting of the buzzer signal and the harmonic generator signal, both increasing in intensity until their respective saturation or cutoff points have been reached.

The acoustical alarm device described has many advantages over those of the prior art. Due to the operation of the harmonic generator 16, the tone of the alarm device is far richer and more pleasing tothe car than that available from the ordinary alarrn. A major advantage lies in the dynamic range of the alarm system. When the system is turned on," the signal reproduced by the loudspeaker is nearly inaudible, The output signal, complete with its harmonics, increases with time until a point is reached at which the vibrator arm is also actuated to add a mechanical buzz occurring at a separate and different frequency from the speaker's audible signal, to the total audible signals from the device. When the vibrator first begins to operate, it produces a very low-level signal which builds to an output level or intensity equal to that of a conventional alarm clock. Thus, the alarm system begins operation with a single, nearly inaudible, pleasing hum, and gradually advances its output to a maximum which contains two basic signals: one from the loudspeaker emitting a 60 Hz. sound and strong amplified" harmonics and a second stronger signal from the buzzer, which produces a fundamental frequency (its actual resonant frequency) substantially higher than 60 Hz. Typically, this buzz from the vibrator is a harsher signal and is utilized and operates only if the alarm is not disengaged prior to its beginning operation. This permits the light sleeper who is awakened immediately by the low intensity, rich tonal signal to shut off the alarm and thereby not be bothered by the harsher buzz. For the heavier sleeper, the operation by of the buzzer may be required before his awaking. Thus, the alarm may be stated to be individual to the users particular threshold of sensitivity.

In an alternative embodiment of this invention, the vibrator mechanism illustrated in FIG. 3 may be modified to that illustrated in FIG. 4. In the illustration of FIG. 4, the same loudspeaker is illustrated as having the cone 64, rim portion 68 and voice coil 66 as previously described. In this instance, however, the vibrator arm 62 is attached directly to the upper portion of the cone 64 as by a suitable adhesive. In this manner, the vibrator arm 62, which may be no more than a small metal strip, is energized by the vibratory mechanical energy of the cone to cause the free end 74 of the vibrator arm 62 to oscillate. Thus the vibrator end 74 engages the striker 76 of the voice coil. Since there is a phase difference between the voice coil vibrations and the vibrations of the cone, several modes of vibrations are induced into the vibrator 62 to produce a still different tonal quality.

It is now apparent that the oscillatory acoustical output of a flexible diaphragm electromagnetic transducer which is rigidly secured to a frame about the outer margin thereof and having a substantially rigid vibrator member positioned for oscillatory impingement at the center portion of the diaphragm will be responsive to a relatively high-input signal and will produce high-energy audible shock waves considerably greater than that produced by the normal free operation of the cone, which may include frequencies related to the resonant character of the vibrator member. The complex high-energy shock waves may also be superposed on the predetermined relatively normal low oscillatory energy applied to the diaphragm.

Whatever the particular loudspeaker-vibrator mechanism or other sound transducer-vibrator mechanism employed, the invention provides a relatively simple transducer alarm.

It will be obvious that various modifications may be made in the apparatus and in the manner of operation it. It is intended to over such modifications and changes as would occur to those skilled in the art, as far as the following claims permit and as far as consistent with the state of the prior art.

What is claimed is: 1. An acoustic alarm device comprising in combination a sound transducing means,

switch means for applying a low-frequency alternating current voltage signal to said sound transducing means thereby to produce an audible signal varying in content with the frequency and amplitude of said voltage signal,

impedance means coupled in circuit with said transducing means and said switch means for increasing as a function of time the amplitude of said voltage signal that is applied to said transducing means whereby the loudness of said audible signal progressively increases with time,

harmonic generating means coupled in circuit with said transducing means for generating harmonics of said voltage signal for application to said transducing means thereby producing an audible alarm signal improved in tonal quality and containing frequencies in the sensitive human hearing range where changes in alarm intensity are the most easily discernible,

a vibrator means adapted to be mechanically energized by said transducer means thereby to produce a second audible signal.

2. An acoustic alarm device comprising in combination a sound transducing means,

switch means for applying a low-frequency alternating current voltage signal to said sound transducing means thereby to produce an audible signal varying in content with the frequency and amplitude of said voltage signal, impedance means coupled in circuit with said transducing means and said switch means for increasing as a function of time the amplitude of said voltage signal that is applied to said transducing means whereby the loudness of said audible signal progressively increases with time, harmonic generating means coupled in circuit with said transducing means for generating harmonics of said voltage signal for application to said transducing means thereby producing an audible alarm signal improved in tonal quality and containing frequencies in the sensitive human hearing range where changes in alarm intensity are the most easily discernible, wherein said transducer means is a loudspeaker having a voice coil and a vibrator secured at one end to said loudspeaker and adapted to be struck at the other end by the movement of said voice coil thereby to produce vibratory energy in an audible range.

3. An acoustic alarm device comprising in combination a sound transducing means,

switch means for applying a low-frequency alternating current voltage signal to said sound transducing means thereby to produce an audible signal varying in content with the frequency and amplitude of said voltage signal, impedance means coupled in circuit with saidtransducing means and said switch means for increasing as a function of time the amplitude of said voltage signal that is applied audible signal progressively increases with time,

are the most-easily discernible wherein'said transducer means is a loudspeaker having a voice coil and a vibrator secured to one end to the cone of saidloudspeaker whereby movement of said cone produces vibratory energy in said vibrator in an audible range.

Claims

1. An acoustic alarm device comprising in combination a sound transducing means, switch means for applying a low-frequency alternating current voltage signal to said sound transducing means thereby to produce an audible signal varying in content with the frequency and amplitude of said voltage signal, impedance means coupled in circuit with said transducing means and said switch means for increasing as a function of time the amplitude of said voltage signal that is applied to said transducing means whereby the loudness of said audible sigNal progressively increases with time, harmonic generating means coupled in circuit with said transducing means for generating harmonics of said voltage signal for application to said transducing means thereby producing an audible alarm signal improved in tonal quality and containing frequencies in the sensitive human hearing range where changes in alarm intensity are the most easily discernible, a vibrator means adapted to be mechanically energized by said transducer means thereby to produce a second audible signal.

2. An acoustic alarm device comprising in combination a sound transducing means, switch means for applying a low-frequency alternating current voltage signal to said sound transducing means thereby to produce an audible signal varying in content with the frequency and amplitude of said voltage signal, impedance means coupled in circuit with said transducing means and said switch means for increasing as a function of time the amplitude of said voltage signal that is applied to said transducing means whereby the loudness of said audible signal progressively increases with time, harmonic generating means coupled in circuit with said transducing means for generating harmonics of said voltage signal for application to said transducing means thereby producing an audible alarm signal improved in tonal quality and containing frequencies in the sensitive human hearing range where changes in alarm intensity are the most easily discernible, wherein said transducer means is a loudspeaker having a voice coil and a vibrator secured at one end to said loudspeaker and adapted to be struck at the other end by the movement of said voice coil thereby to produce vibratory energy in an audible range.

3. An acoustic alarm device comprising in combination a sound transducing means, switch means for applying a low-frequency alternating current voltage signal to said sound transducing means thereby to produce an audible signal varying in content with the frequency and amplitude of said voltage signal, impedance means coupled in circuit with said transducing means and said switch means for increasing as a function of time the amplitude of said voltage signal that is applied to said transducing means whereby the loudness of said audible signal progressively increases with time, harmonic generating means coupled in circuit with said transducing means for generating harmonics of said voltage signal for application to said transducing means thereby producing an audible alarm signal improved in tonal quality and containing frequencies in the sensitive human hearing range where changes in alarm intensity are the most easily discernible wherein said transducer means is a loudspeaker having a voice coil and a vibrator secured to one end to the cone of said loudspeaker whereby movement of said cone produces vibratory energy in said vibrator in an audible range.