EP0233390A1 - Method and apparatus for discriminating sounds due to the breakage of glass - Google Patents
Method and apparatus for discriminating sounds due to the breakage of glass Download PDFInfo
- Publication number
- EP0233390A1 EP0233390A1 EP86301025A EP86301025A EP0233390A1 EP 0233390 A1 EP0233390 A1 EP 0233390A1 EP 86301025 A EP86301025 A EP 86301025A EP 86301025 A EP86301025 A EP 86301025A EP 0233390 A1 EP0233390 A1 EP 0233390A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- low frequency
- high frequency
- sound
- glass
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/02—Mechanical actuation
- G08B13/04—Mechanical actuation by breaking of glass
Definitions
- This invention relates to a method and an apparatus for detecting sounds due to the breakage of glass.
- the sound of breaking glass is usually readily identifiable to the human ear, the physical make-up of the sound depends on such matters as the thickness and area of the glass, the manner in which it is mounted ,the height above floor level and the acoustic properties of the enclosure in which the breakage takes place. These factors make the identification of the sound from its physical characteristics, difficult and uncertain.
- the sound of breaking glass comprises an initial low frequency sound of fairly large amplitude followed by higher frequency sound as the fragments of glass collide with one another and with the floor.
- U.S. Patent 4,134,109 proposes analysing the pattern of acoustic signals in terms of signal strength of the initial sound and frequency content of subsequent sounds to discriminate between the breaking of glass and other sounds. If the amplitude of the initial sounds exceeds a given threshold and the frequency content of the later sound fits a predetermined pattern, an alarm signal is produced.
- U.S. 4,134,109 includes a complicated signal analysis circuit which is costly. Another disadvantage is the inability to discriminate between repeated large amplitude sounds containing high frequency components. It can be triggered by any sufficiently loud sound irrespective of its frequency.
- An object of the present invention is to avoid the disadvantages inherent in the prior art and to provide a method of and apparatus for detecting sounds due to the breakage of glass, which is simple and relatively inexpensive and can reliably discriminate between the sound of breaking glass and other sounds.
- a method of discriminating sounds due to the breakage of glass by converting the sounds into an electrical signal and analysing the signal, the method comprising detecting the occurrence of an initial sound, selecting only those initial sounds having components in a low frequency band and preferably exceeding a predetermined threshold level, establishing thereupon a delay followed by a time window, detecting the occurrence within the time window of a subsequent sound having frequency components in a high frequency band and generating an output signal if, and only if, the signals are detected in the required order and timing.
- apparatus for carrying out the above method comprising a transducer, a low frequency channel including a bandpass filter, a high frequency channel including a bandpass filter, first and second delay circuits, and an AND gate and alarm means , the transducer providing signals to the low frequency and high frequency channels, an output signal from the low frequency channel being applied to the first delay circuit, and the delayed output being applied to one input of the AND gate for a duration set by the second delay circuit, an output signal from a high frequency channel being applied to the second input of the AND gate, and the coincidence signal from the AND gate tripping the alarm means.
- the present inventors have discovered that the initial sound due to the breakage of glass has substantial (i.e. salient) frequency components at about 350 Hz and the subsequent sounds due to the falling pieces of glass have substantial frequency components at about 6.5 KHz. They have found that these frequencies are characteristic of breaking glass and are substantially independent of the other variable factors mentioned above such as size and thickness of glass, height and nature of mounting etc.
- the low frequency band may extend up to about 800 or 900 Hz, it is preferably centred on a frequency of substantially 350 Hz.
- a suitable value for the bandwidth of the higher frequency signal is 4 KHz to 10 KHz.
- the high frequency band is centred upon 6.5 KHz and has a bandwidth of ⁇ 2KHz.
- the time window may suitably start at 200 milliseconds after the detection of the low frequency signal and continue for a further 800 milliseconds.
- Figure 1 shows a waveform of a typical sound due to the breaking of a pane of glass. It comprises two major components, namely the transient sound generated when the pane of glass is struck (referred to herein as the "thump") followed after an interval by the sound due to the collision of the glass fragments with each other and with the surface upon which they fall (referred to herein as the "tinkle”), this being a sound of lower amplitude.
- the frequency spectra of these two components are respectively shown in Figures 2a and 2b.
- the present invention turns on the discovery that the thump has strong frequency components in the neighbourhood of 350 Hz and the tinkle has substantial frequency components in the neighbourhood of 6.5 KHz. These values being characteristic of breaking glass and substantially independent of the variable factors mentioned above.
- the invention makes use of these facts by detecting the occurrence of components at these frequencies in that order, and separatedby a brief time interval.
- Figure 3 indicates schematically the response of a detection system according to the present invention.
- A the low frequency components are detected and this initiates a short time delay, shown as A in the Figure.
- B a time window is established, indicated at B in the Figure, during which the higher frequency of the tinkle components, if detected, is caused to produce a signal, for example, for setting off an alarm.
- a microphone 1 is positioned near the glass to be protected and its output is fed into two channels, a low frequency and a high frequency channel.
- the low frequency channel comprises a low frequency bandpass filter 2 with a centre frequency of 350 Hz, followed by an amplifier 3 and a voltage comparator 4 which provides an output voltage when the amplitude of the signal from the bandpass filter and amplifier exceeds a threshold value determined by the setting of potentiometer R15.
- the signal from the comparator 4 indicating that frequency components in the region of 350 Hz possibly representing the thump portion of a glass breakage signal have been detected is applied to a mono-stable 5 which, after a 200 millisecond delay triggers a timer 6. This timer produces a signal lasting for 800 milliseconds and this signal enables an AND gate 7.
- the signal from the microphone 1 is also applied to a high frequency channel.
- This comprises a high frequency bandpass filter 8 having a pass band centred on 6.5 KHz and a bandwidth of ⁇ 2 KHz, followed by a frequency to voltage converter circuit 9, the output of which is applied to a one input of a voltage comparator 10. It will not allow any signal below 4.5 KHz to generate an output. It will be understood that the high frequency band pass filter 8 merely attenuates signals at frequencies outside the bandwidth and does not exclude them altogether. This is why the frequency to voltage converter is needed. It enables discrimination to be made between noises such as caused by tapping on the window, which contains dominant low frequency components in addition to high frequency components, and the tinkle in which the dominant frequencies are high frequencies above 4.5 KHz. This further reduces the risk of false alarms.
- a signal is applied to other input of the AND gate 7.
- the reference value is set during manufacture and assembly of the detector, by means of the potential divider comprising R28 and R30. Further adjustment of the point at which the comparator 10 triggers (ie. the sound pressure threshold level) is available by varying the gain of the high band pass filter 8 and amplifier 9 circuits using variable resistor R24.
- the AND gate 7 thus receives a signal at one input during a time window extending from 200 milliseconds to one second after a 350 Hz input signal possibly representing the thump of a glass breakage, has been received and a signal at its other input indicating detection of a signal having a component at 6.5 KHz. The coincidence of these two signals within the correct time frame produces an output from the AND gate 7 indicating that breakage has taken place.
- the signal from the AND gate 7 is fed to a latch circuit 11 which operates an alarm indicator circuit 12 illuminating a light, and also to a relay circuit 13 arranged to give an audible or other warning.
- a reset circuit 14 is provided to reset the latch 11 and the timer circuits, and this may be operated from the control circuit or from a remote push button.
- the power for operating the circuit is provided by a power pack 14.
- One advantage of detecting the sound of breaking glass in accordance with the present invention is that the need for time consuming tuning of the detector circuit on site, after installation, is avoided. Tests have shown that the threshold levels against which the signals are compared in comparators 4 and 10, equivalent to a low frequency sound pressure level of about 95dB and a high frequency sound pressure level of about 75dB give satisfactory results and these threshold levels can be set in the factory during manufacture and assembly.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Burglar Alarm Systems (AREA)
Abstract
Description
- This invention relates to a method and an apparatus for detecting sounds due to the breakage of glass.
- Although the sound of breaking glass is usually readily identifiable to the human ear, the physical make-up of the sound depends on such matters as the thickness and area of the glass, the manner in which it is mounted ,the height above floor level and the acoustic properties of the enclosure in which the breakage takes place. These factors make the identification of the sound from its physical characteristics, difficult and uncertain.
- Conventional glass break detectors respond to frequencies above say, 4.5 KHz and are liable to produce false alarms upon detection of other sounds occurring in the frequency range of interest, for example telephone bells and rattling keys.
- In an attempt to reduce the occurrence of false alarms much fine tuning of the detector is necessary once it has been installed on site.
- It is known that the sound of breaking glass comprises an initial low frequency sound of fairly large amplitude followed by higher frequency sound as the fragments of glass collide with one another and with the floor. U.S. Patent 4,134,109 for example, proposes analysing the pattern of acoustic signals in terms of signal strength of the initial sound and frequency content of subsequent sounds to discriminate between the breaking of glass and other sounds. If the amplitude of the initial sounds exceeds a given threshold and the frequency content of the later sound fits a predetermined pattern, an alarm signal is produced.
- The system of U.S. 4,134,109 includes a complicated signal analysis circuit which is costly. Another disadvantage is the inability to discriminate between repeated large amplitude sounds containing high frequency components. It can be triggered by any sufficiently loud sound irrespective of its frequency.
- An object of the present invention is to avoid the disadvantages inherent in the prior art and to provide a method of and apparatus for detecting sounds due to the breakage of glass, which is simple and relatively inexpensive and can reliably discriminate between the sound of breaking glass and other sounds.
- In accordance with the present invention, we propose a method of discriminating sounds due to the breakage of glass by converting the sounds into an electrical signal and analysing the signal, the method comprising detecting the occurrence of an initial sound, selecting only those initial sounds having components in a low frequency band and preferably exceeding a predetermined threshold level, establishing thereupon a delay followed by a time window, detecting the occurrence within the time window of a subsequent sound having frequency components in a high frequency band and generating an output signal if, and only if, the signals are detected in the required order and timing.
- Also, in accordance with the invention, we propose apparatus for carrying out the above method comprising a transducer, a low frequency channel including a bandpass filter, a high frequency channel including a bandpass filter, first and second delay circuits, and an AND gate and alarm means , the transducer providing signals to the low frequency and high frequency channels, an output signal from the low frequency channel being applied to the first delay circuit, and the delayed output being applied to one input of the AND gate for a duration set by the second delay circuit, an output signal from a high frequency channel being applied to the second input of the AND gate, and the coincidence signal from the AND gate tripping the alarm means.
- By virtue of excluding any initial sound the dominant frequency components of which fall outside the low frequency band and moreover, since the high and low bands are mutually exclusive, false alarms are far less likely to occur as compared with conventional detection systems.
- Furthermore, the present inventors have discovered that the initial sound due to the breakage of glass has substantial (i.e. salient) frequency components at about 350 Hz and the subsequent sounds due to the falling pieces of glass have substantial frequency components at about 6.5 KHz. They have found that these frequencies are characteristic of breaking glass and are substantially independent of the other variable factors mentioned above such as size and thickness of glass, height and nature of mounting etc.
- Therefore, according to the present invention although the low frequency band may extend up to about 800 or 900 Hz, it is preferably centred on a frequency of substantially 350 Hz.
- A suitable value for the bandwidth of the higher frequency signal is 4 KHz to 10 KHz. In the preferred embodiment, the high frequency band is centred upon 6.5 KHz and has a bandwidth of ± 2KHz. The time window may suitably start at 200 milliseconds after the detection of the low frequency signal and continue for a further 800 milliseconds.
- The invention will now be described with reference to the accompanying drawings in which:
- Figure 1 is a waveform of a typical sound due to breaking glass;
- Figures 2a and 2b are frequency spectrum analyses of portions of the waveform of Figure 1;
- Figure 3 is a diagram illustrating the response of the system of the invention; and
- Figure 4 is a circuit diagram showing the essential components of apparatus according to the invention and is divided into two parts designated Figures 4A and 4B, interconnected at X, Y and Z.
- Figure 1 shows a waveform of a typical sound due to the breaking of a pane of glass. It comprises two major components, namely the transient sound generated when the pane of glass is struck (referred to herein as the "thump") followed after an interval by the sound due to the collision of the glass fragments with each other and with the surface upon which they fall (referred to herein as the "tinkle"), this being a sound of lower amplitude. The frequency spectra of these two components are respectively shown in Figures 2a and 2b.
- The present invention turns on the discovery that the thump has strong frequency components in the neighbourhood of 350 Hz and the tinkle has substantial frequency components in the neighbourhood of 6.5 KHz. These values being characteristic of breaking glass and substantially independent of the variable factors mentioned above. The invention makes use of these facts by detecting the occurrence of components at these frequencies in that order, and separatedby a brief time interval.
- Figure 3 indicates schematically the response of a detection system according to the present invention. When a break occurs the low frequency components are detected and this initiates a short time delay, shown as A in the Figure. After this delay a time window is established, indicated at B in the Figure, during which the higher frequency of the tinkle components, if detected, is caused to produce a signal, for example, for setting off an alarm.
- The circuit of Figure 4 will be described in terms of functional blocks, the arrangement and connection of the individual components in each block being conventional.
- A microphone 1 is positioned near the glass to be protected and its output is fed into two channels, a low frequency and a high frequency channel.
- The low frequency channel comprises a low
frequency bandpass filter 2 with a centre frequency of 350 Hz, followed by anamplifier 3 and avoltage comparator 4 which provides an output voltage when the amplitude of the signal from the bandpass filter and amplifier exceeds a threshold value determined by the setting of potentiometer R15. - The signal from the
comparator 4 indicating that frequency components in the region of 350 Hz possibly representing the thump portion of a glass breakage signal have been detected is applied to a mono-stable 5 which, after a 200 millisecond delay triggers atimer 6. This timer produces a signal lasting for 800 milliseconds and this signal enables an AND gate 7. - The signal from the microphone 1 is also applied to a high frequency channel. This comprises a high
frequency bandpass filter 8 having a pass band centred on 6.5 KHz and a bandwidth of ± 2 KHz, followed by a frequency to voltage converter circuit 9, the output of which is applied to a one input of avoltage comparator 10. It will not allow any signal below 4.5 KHz to generate an output. It will be understood that the high frequencyband pass filter 8 merely attenuates signals at frequencies outside the bandwidth and does not exclude them altogether. This is why the frequency to voltage converter is needed. It enables discrimination to be made between noises such as caused by tapping on the window, which contains dominant low frequency components in addition to high frequency components, and the tinkle in which the dominant frequencies are high frequencies above 4.5 KHz. This further reduces the risk of false alarms. - If the output of the converter 9 drops below a reference value applied to the other input of the comparator a signal is applied to other input of the AND gate 7. The reference value is set during manufacture and assembly of the detector, by means of the potential divider comprising R28 and R30. Further adjustment of the point at which the
comparator 10 triggers (ie. the sound pressure threshold level) is available by varying the gain of the highband pass filter 8 and amplifier 9 circuits using variable resistor R24. - The AND gate 7 thus receives a signal at one input during a time window extending from 200 milliseconds to one second after a 350 Hz input signal possibly representing the thump of a glass breakage, has been received and a signal at its other input indicating detection of a signal having a component at 6.5 KHz. The coincidence of these two signals within the correct time frame produces an output from the AND gate 7 indicating that breakage has taken place.
- The signal from the AND gate 7 is fed to a
latch circuit 11 which operates analarm indicator circuit 12 illuminating a light, and also to arelay circuit 13 arranged to give an audible or other warning. - A
reset circuit 14 is provided to reset thelatch 11 and the timer circuits, and this may be operated from the control circuit or from a remote push button. - The power for operating the circuit is provided by a
power pack 14. - One advantage of detecting the sound of breaking glass in accordance with the present invention is that the need for time consuming tuning of the detector circuit on site, after installation, is avoided. Tests have shown that the threshold levels against which the signals are compared in
comparators
Claims (7)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP86301025A EP0233390A1 (en) | 1986-02-14 | 1986-02-14 | Method and apparatus for discriminating sounds due to the breakage of glass |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP86301025A EP0233390A1 (en) | 1986-02-14 | 1986-02-14 | Method and apparatus for discriminating sounds due to the breakage of glass |
Publications (1)
Publication Number | Publication Date |
---|---|
EP0233390A1 true EP0233390A1 (en) | 1987-08-26 |
Family
ID=8195888
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP86301025A Withdrawn EP0233390A1 (en) | 1986-02-14 | 1986-02-14 | Method and apparatus for discriminating sounds due to the breakage of glass |
Country Status (1)
Country | Link |
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EP (1) | EP0233390A1 (en) |
Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0499148A1 (en) * | 1991-02-11 | 1992-08-19 | Pittway Corporation | Glass breakage detector |
WO1993019385A1 (en) * | 1992-03-24 | 1993-09-30 | Rover Group Limited | A device for and method of surveillance of a space |
EP0592191A1 (en) * | 1992-10-07 | 1994-04-13 | Guardall Limited | Activation circuit |
EP0605993A2 (en) * | 1993-01-07 | 1994-07-13 | Ford Motor Company | Motor vehicle security sensor system |
DE19521194A1 (en) * | 1995-06-10 | 1996-12-12 | Telefunken Microelectron | Monitoring method for openings, covered by glass panes, in closed and locked cabinets or cars |
US5608377A (en) * | 1995-10-20 | 1997-03-04 | Visonic Ltd. | Acoustic anti-tampering detector |
WO1997009701A1 (en) * | 1995-09-01 | 1997-03-13 | Digital Security Controls Ltd. | Glass break sensor |
GB2284668B (en) * | 1993-12-01 | 1998-04-01 | Visonic Ltd | Glass breakage detector |
GB2434876A (en) * | 2006-02-01 | 2007-08-08 | Thales Holdings Uk Plc | Frequency and time audio signal discriminator |
JP2014016725A (en) * | 2012-07-06 | 2014-01-30 | Panasonic Corp | Intrusion detection device |
US9188487B2 (en) | 2011-11-16 | 2015-11-17 | Tyco Fire & Security Gmbh | Motion detection systems and methodologies |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4091660A (en) * | 1977-03-16 | 1978-05-30 | Matsushita Electric Industrial Co., Ltd. | Apparatus for detecting the breaking of a glass plate |
US4134109A (en) * | 1977-05-16 | 1979-01-09 | Omni Spectra, Inc. | Alarm system responsive to the breaking of glass |
GB1577941A (en) * | 1977-08-19 | 1980-10-29 | Rca Corp | Glass break defectors |
GB2080592A (en) * | 1980-07-03 | 1982-02-03 | Rca Security Systems Ltd | Vibration and/or impact detection system |
-
1986
- 1986-02-14 EP EP86301025A patent/EP0233390A1/en not_active Withdrawn
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4091660A (en) * | 1977-03-16 | 1978-05-30 | Matsushita Electric Industrial Co., Ltd. | Apparatus for detecting the breaking of a glass plate |
US4134109A (en) * | 1977-05-16 | 1979-01-09 | Omni Spectra, Inc. | Alarm system responsive to the breaking of glass |
GB1577941A (en) * | 1977-08-19 | 1980-10-29 | Rca Corp | Glass break defectors |
GB2080592A (en) * | 1980-07-03 | 1982-02-03 | Rca Security Systems Ltd | Vibration and/or impact detection system |
Cited By (20)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0499148A1 (en) * | 1991-02-11 | 1992-08-19 | Pittway Corporation | Glass breakage detector |
GB2279748A (en) * | 1992-03-24 | 1995-01-11 | Rover Group | A device for and method of surveillance of a space |
WO1993019385A1 (en) * | 1992-03-24 | 1993-09-30 | Rover Group Limited | A device for and method of surveillance of a space |
GB2279748B (en) * | 1992-03-24 | 1996-07-24 | Rover Group | A device for and method of surveillance of a space |
EP0592191A1 (en) * | 1992-10-07 | 1994-04-13 | Guardall Limited | Activation circuit |
EP0720938A3 (en) * | 1993-01-07 | 1996-12-18 | Ford Motor Co | Motor vehicle security sensor system |
EP0720938A2 (en) * | 1993-01-07 | 1996-07-10 | Ford Motor Company | Motor vehicle security sensor system |
EP0605993A3 (en) * | 1993-01-07 | 1994-08-31 | Ford Motor Co | |
EP0605993A2 (en) * | 1993-01-07 | 1994-07-13 | Ford Motor Company | Motor vehicle security sensor system |
US5510765A (en) * | 1993-01-07 | 1996-04-23 | Ford Motor Company | Motor vehicle security sensor system |
GB2284668B (en) * | 1993-12-01 | 1998-04-01 | Visonic Ltd | Glass breakage detector |
US5917410A (en) * | 1995-03-03 | 1999-06-29 | Digital Security Controls Ltd. | Glass break sensor |
DE19521194A1 (en) * | 1995-06-10 | 1996-12-12 | Telefunken Microelectron | Monitoring method for openings, covered by glass panes, in closed and locked cabinets or cars |
WO1997009701A1 (en) * | 1995-09-01 | 1997-03-13 | Digital Security Controls Ltd. | Glass break sensor |
AU708497B2 (en) * | 1995-09-01 | 1999-08-05 | Tyco Safety Products Canada Ltd | Glass break sensor |
US5608377A (en) * | 1995-10-20 | 1997-03-04 | Visonic Ltd. | Acoustic anti-tampering detector |
GB2434876A (en) * | 2006-02-01 | 2007-08-08 | Thales Holdings Uk Plc | Frequency and time audio signal discriminator |
GB2434876B (en) * | 2006-02-01 | 2010-10-27 | Thales Holdings Uk Plc | Audio signal discriminator |
US9188487B2 (en) | 2011-11-16 | 2015-11-17 | Tyco Fire & Security Gmbh | Motion detection systems and methodologies |
JP2014016725A (en) * | 2012-07-06 | 2014-01-30 | Panasonic Corp | Intrusion detection device |
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