US3685009A

US3685009A - Lookout assist device

Info

Publication number: US3685009A
Application number: US49438A
Authority: US
Inventors: Robert F Fleming Jr
Original assignee: Sperry Rand Corp
Current assignee: Litton Marine Systems Inc
Priority date: 1970-06-19
Filing date: 1970-06-19
Publication date: 1972-08-15
Anticipated expiration: 1989-08-15
Also published as: JPS523318B1; GB1342799A; DE2130342A1

Abstract

A hearing lookout assist device improves the contrast between meaningful marine navigation sounds and the ship''s background noise sound, such as own ship bow wake and machinery noise. The frequency response of the listening device is arranged to maximize response of the lookout''s hearing to desired navigational sounds and to minimize the masking and other deleterious effects of objectionable interfering noise sound energy.

Description

[4 Aug. 15, 1972 LOCKOUT ASSIST DEVICE United States Patent Fleming, Jr.

3,588,803 6/1971 Fleming,Jr.etal.........340/16 Primary ExaminerRichard A. Farley Attorney-S. C. Yeaton ABSTRACT A hearing lookout assist device improves the contrast June 19, 1970 [21] App]. N0.: 49,438

between meaningful marine navigation sounds and the ships background noise sound, such as own ship bow wake and machinery noise. The frequency response of the listening device is arranged to maximize response of the lookouts hearing to desired navigational sounds and to minimize the masking and other deleterious ef- R wmw 4 I i s 0 R3 4 m m W fl n m e, 2 HR 3 R w 6 WM. 1 "n W u L mt o H m k U .mF 1] 2 l8 5 55 [fll fects of objectionable interfering noise sound energy. References Cited UNITED STATES PATENTS 11 Claims,5DrawingFigures 1,987,984 1/1935 Barden.....................

PATENTEDAU: 15 m2 SHEET 1 OF 3 l G F o w c 4 w w 0 O w L H Fm w 1 2 W OH 1 m m m E MD om 9m n E H W |Aw //B/// 1 L EA RE W m 0 0 O O O O O 0 O 0 0 O O 9 8 7 6 5 4 7 6 5 4 3 2 1 250 500 FREQUENCY H b FIG.3.

ATTORNEY PA'TENTEI'J nus 15 I972 SHEET 2 [IF 3 FREQUENCY H POWER AMPLI FIE R 25x RECORDER IN VE/VTOR COMPRESSION AMPLIFIER ROBERT F FLEM/NG JR.

FILTER NETWORK RECTIFIER AMPLIFIER 19 PRE- AM PLIFIER FIG.4.

ATTORNEY LOOKOUT ASSIST DEVICE BACKGROUND OF THE INVENTION 1 Field of the Invention The invention pertains to acoustic aids to safe marine navigation and particularly relates to a hearing lookout assist device having means permitting enhanced discrimination by the ships lookout or pilot of true navigational sounds in the presence of background noise.

2. Description of the Prior Art A considerable need has been present for many years for advanced marine navigational aids, including devices for preventing collisions between ships in fog and under other conditions of poor visibility. While certain radio and radar communication systems have been provided having important anti-collision and other beneficial navigational features, reliance is still heavily placed upon sound warning devices, especially in fog and heavy rain conditions. Such sound sources as ships bells, horns, and whistles have long been recognized first in point of history as the only available warning elements, and still as principal aids on small vessels not equipped with radio systems. Even in the instances of ships fully equipped with diverse radio aids to navigation, the importance of such warning sound sources as auxiliary or stand-by devices is fully recognized, as is seen by the fact of their continued general use in the maritime industry. While there are evident in such sound warning devices certain problems connected with the propagation medium, with the inherent nature of the navigational sounds and of ambient noise, and with the character of the human car, no known attempts have been made significantly to improve their operation.

SUMMARY OF THE INVENTION The invention is a ships lookout hearing assist device for improving safety of marine vessels form damage due to collision. The listening apparatus makes beneficial use of an understanding of the phenomena of sound masking in the human ear and of the inherent properties both of noise associated with own ship and of desired navigational sounds.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are graphs showing natural properties of sound associated with marine vessels.

FIG. 3 is a graph useful in explaining the operation of the invention.

FIG. 4 is a schematic block diagram of the invention.

FIG. 5 is a detailed circuit diagram of a portion of the system of FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENT Intelligence communicated by sound waves to a listener, such as speech communication, is relatively difficult to understand and even to hear when in a background of other relatively intense sounds. The effect is caused by a phenomenon known as masking which takes place within the listeners ear, whereby the desired sound signal is masked by background sounds. Quantitatively, sound masking is defined as the number of decibels by which a listener's hearing threshold of audibility for a given pure tone is raised in the presence of other sound waves.

A pure tone of higher frequency than the masking tone is more effectively masked than one of lower frequency. The masking tone that is substantially at the bottom of a band of frequencies to be communicated is more effective in masking because its more intense har monics spread across that frequency band; these harmonics are the aural or subjective harmonics generated within the ear because of its non-linear characteristics. In the general case, both the masking sound and the masked sound may have highly complex wave forms and spectra. A masking sound, such as noise, may vary greatly in phase and amplitude on a continuing basis, and these effects add to the problem of hearing and recognition of speech or other intelligence sound patterns.

The masking phenomenon has a degrading effect upon recognition by the ear of all kinds of sound signals, including navigational sound signals upon which the safety of marine vessels depends in an important manner. In FIG. 4, an apparatus is disclosed making beneficial use of knowledge of the character of the masking effect which takes place in the lookouts ear, of the inherent properties of desired navigational sounds, and of the inherent properties noises associated with the ship and its environment.

Before discussing the invention of FIG. 4, reference will be had to FIGS. 1 and 2 so that the novel features of the invention will be more readily apparent. FIG. 1 illustrates a graph showing the amplitude of ship s background noise plotted against frequency over the audio band from 31.5 to 4,000 Hz for an arbitrarily selected but representative ship under average environmental conditions. Sound amplitude is plotted as octave band sound pressure level in decibels referred to 2 X 10' microbars. That notation is standard in acoustics practice (one bar equals 1 dyne per centimeter squared).

It is to be observed that, in the general case, the noise spectrum plotted in FIG. 1 is due in descending order of significance to the bow wake, the ships engine, machinery, and blowers, the stern wake, the gearing of the radar scanner, and aeolian noise due to the passage of wind over sharp edges of the ship, through the ship s rigging, and across the lookouts ears. In general, it is primarily the bow wake noise that masks the lookouts hearing; next in importance are usually the ships engines and the stern wake, both of which however are noise sources normally far from the lookout s station.

Referring to FIG. 1, it is seen that a typical ships background noise amplitude varies in a fairly regular manner from 31.5 to 4,000 Hz with a relatively constant reverse or negative slope of 6 decibels per octave. In the region between 31.5 and Hz, for instance, the background noise intensity is particularly high relative to that in the remainder of the frequency band.

The navigational sounds which the lookout or ships navigator must accurately identify may be generated by any of several sources. For example, FIG. 2 illustrates the spectrum of the sounds emitted from several such sources plotted similarly to the graph of FIG. 1. The spectrum of typical ships bells appears to fall roughly in the area indicated by reference numeral 1, extending generally form 250 Hz to 800 Hz with spectral components having substantially similar amplitude. The curve 2 represents a conventional marine air horn having a spectral content lying between and 1,000 I-Iz;

another type of horn generates the relatively pure tone (250 Hz) indicated at 3. The curve 4 shows the spectrum of a typical steam horn or typhon falling between 250 and 800 Hz. The diaphone is a warbling horn whose spectrum falls with irregular amplitude between 125 Hz and 1,000 Hz, as indicated by curve 5.

Such sound sources are commonly used marine navigation and signalling devices and are particularly used in fog or other conditions of low visibility, as are also used air and steam whistles. A typical air whistle has the relatively higher frequency band of components illustrated by curve 6. Such is particularly true also of a typical steam whistle whose spectrum (curve 7) is shown to fall between 400 and 4,000 Hz.

Observing curves 1 to 7 of FIG. 2, it is seen that the significant frequencies characterizing such navigational sound sources lie above 125 Hz and actually lie mainly above 200 Hz, while, as previously noted, the more intense portions of the ships background noise shown in the typical case illustrated in FIG. 1 lie below 125 Hz. It is also observed that many of the spectral patterns of FIG. 2 which are desirable to recognize also have roughly a 6 decibel per octave reverse or negative slope generally similar to the negative slope of the curve of FIG. 1.

The inventive apparatus of FIG. 4 is designed advantageously to make use of the foregoing realizations. In FIG. 4, sound energy including ships background noise and useful navigation signals is detected by sound detector or microphone l l. Microphone 1 1 has a suitable forwardly directive sensitivity pattern, such as a cardiod pattern, its axis of major sensitivity being parallel to the fore-aft axis of the ship. The output of microphone 11 is supplied to audio preamplifier 12 having special characteristics yet to be described. The average gain, as well as other parameters, of preampli fier 12 may be fixed or manually adjustable by well known means. In particular, manually adjustable means 13 may be provided, for example, for the purpose of adjusting the slope of the gain curve of preamplifier 12.

The audio output of preamplifier 12 is coupled to a filter network 14 having relatively sharp upper and lower frequency cut-off pass band characteristics, which characteristics may be adjusted to a degree in the well known manner by manual controls such as 15 and 16. Control 15, for instance, may be used to determine the low frequency cut ofi of the filter 14, while control 16 may be used to set its high frequency cut off. Fixed filter networks may alternatively be used.

The output of filter network 14 is supplied to a compression amplifier 17 of conventional type for improving the signal-to-noise ratio of the output of band pass filter 14. Volume compression amplifier 17 is a device which reduces the relative level of a signal passing through it when the input signal is large and increases its level when the input signal is small. Thus, the gain of amplifier 17 is varied according to the reciprocal of the envelope amplitude of its input signal.

For controlling compression amplifier 17, the signal to be compressed by amplifier 17 is also supplied to an audio amplifier 19 having, like amplifier 17, a pass band substantially great as the largest pass band of filter network 14. The output of amplifier 19 is rectified in rectifier circuit 20, whose rectified output is used reciprocally to change the gain of compression amplifier 17. The rectified voltage may be used within amplifier 17 in any of several conventional ways; for example, it may be employed to vary the bias, and hence the gain of a variablemu vacuum tube amplifier stage. Compression amplifier 17, amplifier 19, and rectifier 20 are connected cooperatively to form compression amplifi- Cl means.

As a consequence of the operation of compression amplifier l7, signals coupled form it to power amplifier 22 all e a significantly reduced range of volumes; weak audio signals passed by filter network 14 are given on the order of the same amplitude as high energy audio signals passed thereby. Power amplifier 22, which may have conventional manual controls, such as symbolized by gain control 23, is employed to increase the level of signals applied to speaker or ear phone 24 or other electrical current-to-sound transducer for observation by the lookout personnel. If a record of navigation signals is desired, power amplifier 22 may also feed its output to a conventional recorder 25.

It is to be understood from the foregoing that the over all frequency response of the system of FIG. 4 is primarily determined by preamplifier 12 and filter network 14, and that the remaining elements of the system have substantially flat frequency characteristics, for example, over the 31.5 to 4,000 Hz pass band of interest.

Referring to FIG. 3, the pass band and relative response of the combined preamplifier-filter network apparatus is shown. Response is plotted as relative gain in decibels versus frequency for the 31.5 to 4,000 Hz frequency range. In the preferred adjustment of the invention, the response characteristics are represented by the curve 101 of FIG. 3. Such a response may be characterized by a low cut-off frequency of about Hz, a rising slope portion BC of about 6 decibels per octave from to 4,000 Hz, and an upper cut-off frequency of about 4,000 Hz. It is to be understood that the cut-off frequency of determined by filter network 14, while the 6 decibel slope BC is determined largely by the gain setting of the preamplifier 12.

The versatility of the invention is enhanced by the fact that a fair latitude of tolerance in the adjustment of the apparatus is permitted. For example, the concept calls for sharply attenuating lower audio frequencies, say below 200 Hz, and amplifying signals above 200 Hz. The slope of the portion AB of the curve of FIG. 3 in the low frequency range may be about 50 decibels per octave; however, it is to be understood that a slope as low as 30 decibels per octave or as high as 100 or more decibels per octave may be used. The corner frequency at B where the slope sharply changes can be as low as 100 Hz or as high as 200 Hz. The slope of the BC portion of the curve may vary, for example, form 4 to 8 decibels per octave.

The high corner frequency at C may be chosen at 4,000 Hz; the presence of frequencies above 4,000 Hz adds little to the lookouts ability to discern desired navigation signals. Experience has shown that the high corner frequency may also be selected as low as 2,000 Hz (point E in FIG. 3) with some small loss of useful frequency spectrum. A cut-off point no higher than 4,000 Hz would generally be selected to avoid the presence of hiss due to the self-noise of the preamplifier 12. The upper cut-off slope CD of 50 decibels or more is chosen also to attenuate the same hiss. In summary, while the curve 101 represents a preferred characteristic adjustment for the invention, it is seen that other curves bounded by

curves

100 and 102 may be satisfactorily used. For example, the slope of portion AB of curve 101 may be adjusted in several ways so that portion AB falls within the low frequency boundaries of

curves

100 and 102. Variation of the 6 db. portion BC of the curve 101 may similarly be accomplished between the

curves

100 and 102. Similarly, latitude is allowed at the high frequency cut off portion CD of curve 101 so that it may have a slope falling between

curves

100 and 102.

Observing simultaneously FIGS. 1,2, and 3, it is seen that the intense potion of the ship s background noise is substantially reduced, while the band of frequencies in which intelligence data lies is accentuated While the positive slope of the BC portion of the FIG. 3 graph is selected at substantially 6 decibels per octave, this slope may be varied within the scope of the invention. This positive slope is chosen because representative ships background noise and navigational sounds both have reverse or negative slopes in the region of 6 decibels per octave. With an increasing gain of substantially 6 decibels per octave and with adequate volume compression, all sounds are heard by the lookout at about the same sound level, without excessive amplification of low frequency sounds which would produce serious masking effects. The 6 to 8 decibel rising portion of the characteristic curve also is beneficial in detecting navigational sounds emitted by distant sources, since relatively high frequency sounds sufier relatively greater attenuation when propagated over large distances.

One circuit found to be particularly suitable for use in the preamplifier-filter network apparatus of FIG. 4 is illustrated in FIG. 5. The major parts of preamplifier 12 are indicated in FIG. 5 at 12 a and 12 b Circuit 12 is a modified type of operational amplifier in supply on the market in integrated semiconductor microcircuit form, as is also the conventional amplifier, emitter-follower circuit 12 b.

In FIG. 5, the output of microphone 11 is applied to the input winding 30 of audio step-up transformer 31, whose output winding is grounded at one side and is coupled to the input of circuit 12 a. Transformer 31 functions to match the impedance of microphone 11 to circuit 12 a and also furnishes required direct current and electrostatic isolation.

Winding 32 feeds, through the trimming resistor 33, the base of n-p-n transistor 34, associated in a conventional low current, high impedance input circuit with a second n-p-n input transistor 35 whose purpose will become apparent later.

Transistors

34 and 35 have respective collector resistors 36 and 37 couple to a V voltage source at terminal 38, while the emitters of the transistors are coupled in common through resistor 39 to a V voltage source at terminal 40.

Diode networks

70 and 71 serve respectively to provide V for

transistors

34 and 35 and provide a constant voltage for current generators 48 and 49.

The respective collectors of

transistors

34 and 35 are directly couple to the bases of transistors 41 and 42, which transistors are associated in a second stage of the preamplifier functioning in a conventional manner to provide amplification, level shifting, and conversion from double-ended operation to single-ended output upon lead 45. Transistors 41 and 42 are connected through resistor 43 to the V voltage terminal 40. The collectors of the respective transistors 41 and 42 are connected directly and through resistor 44 to the V voltage terminal 38. Transistors 48 and 49 respectively cooperate in the usual manner in the first and second stages of the circuit in determining current flow levels.

Lead 45 is connected to the base of transistor 46 which, together with transistor 47, forms a conventional Class AB low standby power output amplification stage whose output appears on lead 50. It is seen that circuit 12 a is a substantially conventional one of the several multi-purpose types of operational amplifiers available on the market. Specifically, the amplifier 12 a is one half of an integrated circuit amplifier produced by Fairchild Semiconductor as its p.A739 dual low-noise operational amplifier and is also readily available on the market.

The output lead 50 of circuit 12 a is applied to coupling capacitor 51 which is connected, in turn, to circuit 12 b which, as previously noted, is a conventional emitter-follower amplifier circuit. The latter is used to load coupling capacitor 51 and to drive the coupling and blocking capacitor 52. Capacitor 52 is connected through a resistor 43 to filter network 14, resistor 53 serving to match the characteristic impedance of filter network 14 to the relatively low impedance of emitter-follower circuit 12 b.

Other circuit elements attached to the conventional circuit 12 a are important in the operation of the invention. For example, a conventional damping network 60 is coupled to the second stage of the preamplifier circuit 12 a. Network 60 comprises a series resistorcapacitor circuit, including condenser 61 and resistor 63 couple between the bases of transistors 41 and 42. Coupled between the bases of transistors 41 and 46 is a capacitor 62. These operate to provide loop stabilization by preventing high frequency oscillations as is the common practice. The damping network 60 is preferably adjusted according to the present invention so as to limit the open loop high frequency response of circuit 12 a, thus preventing high frequency oscillations. If preferred, elements of the damping network such as 61, 62, and 63 may be made manually adjustable.

Of fundamental interest in the operation of the invention is the circuit for controlling the positive gain slope of preamplifier 12. For this purpose, the output lead of circuit 12 a is coupled via feed back network elements to transistor 35 of the input stage of circuit 12 a. The feed back path includes a resistor-condenser network comprising variable resistor 54 in series connection between lead 50 and input transistor 35 and shunted by capacitor 55. Between resistor 54 and input transistor 35 is coupled a variable resistor 56, one end of which is grounded.

In operation, it is the coupling capacitor 51 and feed back capacitor 55 which are adjusted to give the desired 6decibel per octave increase in gain with increase in frequency. It is seen that the gain slope characteristic of preamplifier 12 may be altered from the preferred 6 decibel choice, if desired, by resetting capacitor 51 by manipulation of calibrated knop 13c. The same effect may be achieved by changing the value of capacitor 55 by cooperative manipulation of calibrated knob 13 b. The variable resistors 54 and 56 in the feed back network are over all gain-determining resistors, so that such may be altered by operating the calibrated knob 13 a. Resistors 54 and 56 evidently may be separately adjusted or gang controlled in the well known manner.

It is seen that the invention provides the ships lookout or pilot with means for greatly improved discrimination between useful navigational sounds and noise sounds generated by own ship and by the ambient condition in which the ship finds itself. The common navigational and fog sound warning devices used by ships in the vicinity of own ship are much more readily detected by the lookout, and the deleterious effects of sound noise energy which would, if present induce masking harmonic sounds in the lookouts ear, are markedly reduced. The lookout is not subjected to adverse weather conditions, as the desired sound signals are available in the shelter of the pilot house.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

1 claim:

1. A hearing assist means for processing a first frequency band of intelligence sound energy in the presence of noise energy which noise energy varies in amplitude over a band encompassing said first frequency band substantially as a first function of increasing frequency having a first characteristic slope, comprismg:

sound detector means,

amplifier means connected amplifier said sound detector means said amplifier means having a gain characteristic over a frequency band including said first frequency band varying as a second function of increasing frequency having a second characteristic slope opposite in polarity to said first slope,

band pass means connected to the said amplifier means adapted substantially to pass only said first frequency band, and

utilization means connected to said band pass means.

2. Apparatus as described in claim 1 wherein said first and second characteristic slopes are substantially equal but opposite in polarity.

3. Apparatus as described in claim 1 wherein said second characteristic slope is substantially 6 decibels per octave.

4. Apparatus as described in claim 1 wherein said second characteristic slope lies between 4 and 8 decibels per octave.

5. Apparatus as described in claim 1 wherein the lower cut-off frequency of said band pass means is determined substantially by the lower frequency present in said intelligence sound energy for the purpose of excluding low frequency components of said noise energy from masking intelligence sounds in the ears f the listener.

6. Apparatus as described in claim 1, wherein said utilization means includes compression amplifier means.

7. Apparatus as described in claim 6, wherein said utilization means comprises electric current-to-sound transducer means connected to said compression amplifier means.

8. Apparatus as described in claim 6, wherein said utilization means comprises recorder means connected to said compression amplifier means.

9. Apparatus as described in claim 1 wherein said first frequency band and the pass band of said band pass means extend from substantially Hz to substantially 4,000 Hz.

10. The method of enhancing the detection of marine navigational sound signals with respect to marine acoustic noise, the method comprising:

converting said navigational and noise signals to electrical signals,

amplifying said electrical signals by an amplifier having a gain versus frequency characteristic adjusted to have a slope opposite but substantially equal to the slope of the amplitude versus frequency characteristic of said noise signal,

rejecting said electrical noise signals of frequencies lower than substantially the lowest frequency of said navigational signals, and

generating sound waves according to the remaining amplified electrical signals.

11. The method as described in claim 10 including the step of volume compression of said remaining amplified electrical signals.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 685, 009 Dated Aug. 15, 1972 It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:

In line 38 of column 7 Claim 1 should read: "amplifier means connected to said sound de- Signed and sealed this 22nd day of May 1973 (SEAL) Attest:

ROBERT GOTTSCHALK =Commissioner of Patents EDWARD M.FLETCHER,JR. Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 685, 009 Dated Aug. 15, 1972 It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:

Claim 1 should read:

In line 38 of column '7, "amplifier means connected to said sound de Signed and sealed this 22nd day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOT'ISCHAIK Attesting Officer Commissioner of Patents

Claims

1. A hearing assist means for processing a first frequency band of intelligence sound energy in the presence of noise energy which noise energy varies in amplitude over a band encompassing said first frequency band substantially as a first function of increasing frequency having a first characteristic slope, comprising: sound detector means, amplifier means connected amplifier said sound detector means said amplifier means having a gain characteristic over a frequency band including said first frequency band varying as a second function of increasing frequency having a second characteristic slope opposite in polarity to said first slope, band pass means connected to the said amplifier means adapted substantially to pass only said first frequency band, and utilization means connected to said band pass means.

5. Apparatus as described in claim 1 wherein the lower cut-off frequency of said band pass means is determined substantially by the lower frequency present in said intelligence sound energy for the purpose of excluding low frequency components of said noise energy from masking intelligence sounds in the ears of the listener.

9. Apparatus as described in claim 1 wherein said first frequency band and the pass band of said band pass means extend from substantially 125 Hz to substantially 4,000 Hz.

10. The method of enhancing the detection of marine navigational sound signals with respect to marine acoustic noise, the method comprising: converting said navigational and noise signals to electrical signals, amplifying said electrical signals by an amplifier having a gain versus frequency characteristic adjusted to have a slope opposite but substantially equal to the slope of the amplitude versus frequency characteristic of said noise signal, rejecting said electrical noise signals of frequencies lower than substantially the lowest frequency of said navigational signals, and generating sound waves according to the remaining amplified electrical signals.