SE518168C2 - Method and apparatus for producing low frequency sounds and use of such apparatus - Google Patents

Abstract

In a method and a device for generating or extinguishing low frequency sound having a high sound pressure, the wave shape is divided into air pulses with variable amplitude and with considerably higher frequency than that of the wanted tone. The air pulses thereby represent instantaneous values (sampling values) of the wanted wave shape which, thus, is formed by an imaginary curve connecting the amplitude values of the discrete air pulses. The air pulses are positive during one half-cycle and negative during the other half-cycle of the wave shape. The device comprises means to pump in high frequency pulses from a chamber (1) to the surroundings during a first period of time and during a second period of time high frequency air pulses are sucked into a said chamber (2) from the surroundings. The invention also relates to use of such a device, e.g., for actively extinguishing low frequency noise.

Description

However, extinguishing such sounds encounters significant problems.

It is not particularly difficult to generate or absorb high-frequency sound energy. A common measure of the source strength of an acoustic source is the volume velocity of the air that is set in motion during the sound generation, and thus small amounts of air per oscillation are sufficient for high source strength to be achieved. For example, an oscillation of a diaphragm with an area of 1 dm * and an amplitude slightly higher than one millimeter at a frequency of 10 kHz would cause it to “pump” 100 liters of air per second, while with a corresponding area and a frequency of 20 Hz, an amplitude of about 0.5 meters would be required to achieve the same source power of 100 liters per second. This is of course very difficult to achieve, which is why hitherto known arrangements for achieving low frequency sound with high source noise are very complicated and costly.

SUMMARY OF THE INVENTION The object of the present invention is to provide a method and a device of initially defined kind, which make it possible by simple means to generate or absorb sound energy with in each context low frequency, and which also enable the achievement of relatively high source pressure.

This object is achieved with the initially stated method which is characterized in that alternating during first and second time periods only during a first time period air is pumped out from a chamber to the surroundings in a high frequency and between these shocks the chamber is supplied with air from an air tank and during a second time period abruptly with a high frequency air is sucked into a chamber and between the shocks air is supplied a said air tank from the chamber, to create an air flow with frequency components with significantly lower frequency than the frequency of the shocks. The periodicity of the generated air flow is thus given by the time for said air supply and air extraction, respectively.

This object is also achieved with the initially stated device which has the features stated in the independent claim 7. 10 15 20 25 30 35 518168 3 In this way, the high frequency with which air is pumped out or sucked into the chamber can be switched down to contain significantly lower frequency components while maintaining the source pressure, and since a high source pressure can be generated without major problems. at a high frequency, high source strength with a low frequency can be achieved in this way. In that air movements of a certain type take place during an entire mentioned period of time and then air movements of a certain other type take place during the subsequent time period, two successive time periods of the method according to the invention will correspond to a whole oscillation of a membrane of for example a loudspeaker, which oscillates with the said low frequency components.

It is pointed out here that "air tank" is to give a very broad meaning, and it is not at all necessary that the chamber adjoins directly to the air tank, but this could very well be connected to the chamber via some overhead line and thereby be located on a more or less significant distance from the chamber. It is important, however, that there is such an air tank, via which the chamber receives air during the first time period or emits air during the second time period, so that no disturbing noises occur, which would be the case if air was supplied respectively by was given from the chamber directly to the surroundings without any such air tank.

According to a preferred embodiment of the invention, the amount of air of the pump and suction shocks is varied so that the amounts of air in function of time substantially follow a given signal. In this way, it is achieved that the resulting sound source is given similar source properties as a diaphragm that oscillates with low frequency contents for generating or absorbing sound energy.

According to another preferred embodiment of the invention, air is pumped out to the surroundings and sucked in from the surroundings to a mentioned chamber by causing a membrane forming a part delimiting the chamber delimiting the chamber to be caused to vibrate with a high frequency to change the volume of the chamber at such a high frequency. By using a diaphragm in this way to produce the high-frequency pump and suction shocks, this result can be achieved with simplicity, as a diaphragm can easily be caused to vibrate at a high frequency, for example by magnetostrictive or other influence. The relatively small amount of air such a diaphragm can usually move per oscillation is thereby canceled out by the high frequency, so that a high source strength can be achieved, and this for a low frequency, which a diaphragm cannot be used for in a direct sound stringing of the diaphragm.

According to another preferred embodiment of the invention, said amount of air is varied by varying the amplitude of the membrane, which can be easily achieved by controlling the action of the membrane. It would also be possible to vary the amount of air by varying the length of the opening hours between the chamber and the surroundings at the pump and suction shocks.

It should then be implied that the invention is not limited to the use of a membrane for obtaining said air shocks, but it would be entirely conceivable for this to be done in another way, for example by connecting compressed air means and air negative pressure generating means to a said chamber. , wherein then these means can be considered as also providing said air tank.

The actual use of a membrane, however, has very special advantages, which is why that embodiment is extra advantageous.

According to another preferred embodiment of the invention, air is pumped out of at least two chambers to the environment during said first time period and air is sucked into at least two chambers from the environment during said second time period, and the pumping out and the suction out of each into the chambers in question are displaced relative to each other in time, so that the time intervals between two successive pump or suction shocks are substantially removed. By synchronizing the pumping and suctioning of at least two chambers in this way, gaps in the volume flow to or from the sound generating device can be avoided and a more interference-free sound with a substantially ideal waveform is generated.

A device according to the invention has advantages which appear with all the desired clarity from the discussion above of the method according to the invention.

According to a preferred embodiment of the invention, said high frequency is more than ten times, preferably more than 30 times, higher than said low frequency. This makes it possible to generate sounds with low frequency and significantly higher source pressure than if such sound generation had taken place in a conventional manner, especially when using a diaphragm in both cases.

According to another preferred embodiment of the invention, the device comprises at least two said chambers with at least one said first and second valve for connection to the environment and a said air tank, respectively. This is advantageous, as it enables both the achievement of higher source pressures if desired and a greater flexibility of the device in terms of the possibility of generating sounds with different frequencies and source strengths.

For example, according to another preferred embodiment of the invention, said chamber was arranged to operate during said first time periods in order to pump air out to the surroundings via its first valve and another chamber to be arranged to operate during said second time periods in order to suck in air from it from the surroundings, and in this case the two chambers can be connected via their other valves to a common mentioned air tank.

This then means that the function of the two chambers can complement each other, so that a first of the chambers, which causes air to be pumped out to the surroundings, reduces the air pressure somewhat in the air tank, but this is then rebuilt via the air tank's communication with the second chamber. - 10 15 20 25 30 35 ø ø uuu »518168 6 period. This means that both the pumping out and the suction can take place under favorable air pressure conditions in the air tank.

According to another preferred embodiment of the invention, said air tank forms an airtight container adjacent to the surroundings adjacent to said chamber. This is an easy way to realize the air tank.

According to another preferred embodiment of the invention, the size of said chamber and air tank is within the micrometer range, i.e. is of typical size for a microelectromechanical structure (MEMS). This makes it possible to incorporate a device of the type according to the invention in places where a small space is available or it is judged to be important that the device is hidden. It also enables the distribution of a relatively large number of such devices over a certain surface or within a certain space in order to achieve optimal conditions for sound stringing or active noise control.

The invention also relates to a use of a device as above according to the appended use patent claims.

Additional advantages and advantageous features of the invention appear from the following description and other non-obvious patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS Exemplary preferred embodiments of the invention are described below by way of example with reference to the accompanying drawing, in which: Fig. 1 is a very schematic cross-sectional view through a device according to a first preferred embodiment of the invention, 15 20 25 30 35 o - | Fig. 2 is a diagram illustrating airflow to and from the environment over time for a device according to Fig. 1, Fig. 3 in Fig. 1 corresponding to a view of a device according to a second preferred, simplified embodiment of the invention, and Fig. 4 schematically illustrates from above a device according to a third preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 schematically illustrates the structure and function of a device according to a first preferred embodiment of the invention, and this device has two chambers 1, 2, which via a respective first valve 3, 4 are connectable to the environment and via two other valves 5, 6 and 7, 8, respectively, are connectable to an air tank 9 included in the device, which is common to the two chambers. The air tank 9 is an air with essentially the same air pressure as the ambient air pressure containing and relatively hermetically sealed container. In practice, the conditions between the volumes of the chambers and the air tank can be completely different from what is shown in Fig. 1, which is only there to explain the function of the device according to the invention.

A part of the wall of each chamber is formed by a diaphragm 10, 11, which can be influenced via a control unit 12 indicated for only one chamber to vibrate with a high frequency, for example in the range of 1 kHz - 10 kHz. The control unit 12 also controls the opening and closing of the first and second valves, but it is pointed out that these valves could also be of a passive type, i.e. affected by pressure differences between the environment and the chamber and the chamber and the air tank, respectively. In this case, the control unit is arranged to control the valves and the diaphragms in the following manner in order to produce a sound wave with a low frequency and high source pressure: During a first time period A (see Fig. 2), the control unit the fuel 10 to oscillate at a high frequency and at the same time the control unit controls the valve 3 to open when the diaphragm oscillates in Fig. 1 seen upwards and reduces the volume of the chamber while keeping the other valves 5, 6 closed, so that air is pumped out of the chamber 1. then the diaphragm 10 pivots downwards and the volume of the chamber 1 is increased, the first valve 3 is closed and the second valves 5, 6 are opened, so that air from the air tank 9 is sucked into the chamber 1. This sequence continues for a first period of time A, during which the second chamber 2 and its membrane 11 are at rest. In this case, the amount of air each pump shock contains during the time period A is varied so that these air volumes, in function of time, will substantially follow a sine curve, as illustrated in Fig. 2.

This is preferably achieved by changing the amplitude of the oscillations of the diaphragm 10 with time, but it is also possible to control the opening hours of the first valve 3 or to combine both of these measures.

When the first period A has come to an end, period B begins, during which air is sucked in abruptly from the surroundings of the chamber by causing the diaphragm 11 to oscillate at a high frequency. When the diaphragm 11 pivots downwards (see Fig. 1), the valve 4 is opened, while the other valves 7, 8 are kept closed and an air shock is sucked into the chamber 2. When then the diaphragm 11 pivots in Fig. 1 seen upwards again and thereby the volume of the chamber decreases, the first valve 4 is kept closed and the second valves 7, 8 are opened, so that air from the chamber can be pumped out into the air tank, and the latter it is possible to cause an air pressure in the chamber 2 again when the downward swing of the diaphragm relative to the surroundings to again suck in air into the chamber. This procedure is performed in the same way as the procedure during period A.

In this way a sound wave is produced with a frequency which is half the frequency of the frequency of the shifts between said time periods. For optimal operation of the device, it is important that the air pressure in the respective chamber does not change significantly during a mentioned period of time, and it is therefore advantageous that the volume of the air tank is dimensioned to ensure that the maximum pressure the difference therein does not exceed 50%. In this case, it is advantageous to let one chamber operate at a time and to let these two chambers have a common air tank in the manner shown in Fig. 1, as this will mean that a much smaller air tank is required in terms of volume than if two different chambers with each air tank would be used.

However, in practice it is quite possible that the device has only one chamber 1 with an air tank 9, as shown in Fig. 3, and then the diaphragm 10 and the valves 3, 5, 6 will be controlled on it for a first period of time. The method shown at A in Fig. 2 and for a second period of time is controlled in the manner shown at B in Fig. 2. In this figure there is also shown a safety valve 13, which is used to connect the air tank to the surroundings if the air pressure in it should become too high or too low.

It is further illustrated in Fig. 4 that it is possible to arrange more than two chambers of a device of this kind, and there four chambers are connected to the same air tank 9, and two chambers 1, 1 'are arranged to operate during the first time period. and two chambers 2, 2 'to operate during the second time period. In this case, the action of the chambers operating during the same period of time is preferably shifted in the manner described higher up, so that the gaps between the airflow stacks shown in Fig. 2 are substantially filled and there is essentially no distance between them on the following subsequent airflow stacks. so that the sound wave obtains an almost ideal appearance of a certain time signal.

The invention is of course not in any way limited to the preferred embodiment described above, but a number of possibilities for modifications thereof should be obvious to a person skilled in the art, without this for that reason deviating from name c. 518 168 The basic idea of the invention, as defined in the claims.

For example, more than two chambers could operate during the same time period to achieve an optimal curve shape of the generated Uudwave.

It would also be possible for each chamber to have its own air tank.

It is further pointed out that it is possible to allow a small amount of air to flow into the idea in Fig. 1 as seen from the left chamber 1 before the first valve 3 closes during the downward oscillation of the diaphragm, nor is it necessary to open the first valve 3 directly when the diaphragm begins to generate an overpressure in the chamber when the diaphragm is swung upwards, but the opening can take place from a certain level of the overpressure.

Claims (1)

1. 0 15 20 25 30 35 518 168: šßf fi fï fi šš- 11 PATENTKRAV:. A method for generating low frequency sound, 334119_- t_e_c_k_n_a_t thereof, that alternately during first and second time periods only during a first period of time air is pumped out from a chamber (1) intermittently with a high frequency to the surroundings and between these shocks the chamber is supplied air from an air tank (9) and during a second period of time abruptly with a high frequency air is sucked into a chamber (1, 2) and between the shocks air is supplied to said air tank from the chamber, to create an air flow with frequency components with significantly lower frequency than the frequency of the shocks. . Method according to claim 1, in that the amount of air of the pump and suction shocks is varied so that the amounts of air substantially follow a given signal as a function of time. . Method according to claim 1 or 2, in that the air is pumped out to the surroundings and sucked in from the surroundings to a said chamber (1, 2) by causing a membrane (10, 11) forming a part delimiting the chamber to be formed. vibrate at a high frequency to change the volume of the chamber at such a high frequency. . Method according to claims 2 and 3, in that said amount of air is varied by varying the amplitude of the membrane (10, 11). . Method according to claim 2 or claims 2 and 3 or 4, characterized in that said amount of air is varied by varying the length of the opening hours between the chamber (1, 2) and the environment at the pump and suction shocks. . Method according to any one of the preceding claims, in that air is pumped out of at least two chambers (1, 1 ') to the environment during said first time period and air is now sucked in at least two chamber (2, 2 ') from the environment during said second time period, and that the pumping and the suction from the respective into the respective chamber are displaced in time relative to each other, so that the time intermediate spaces between two successive pumping or suction shocks from a of the chambers in a group of at least two chambers are filled by pump or suction shocks from the other chamber or chambers in the same group. . Device for generating low frequency sound, [Law of which it comprises at least one chamber (1) containing air and connectable to the environment via a first valve (3) and to an air tank (9) included in the device via a second valve (5, 6), a first means (10) arranged to pump air out of said chamber to the environment via said first valve, a second means (11) arranged to suck in air to a chamber (2) from the environment via a first valve (4) and a unit (12) arranged to control said means to operate alternately during each of the first and second time periods, respectively, so that the first means during a first time period (A) bursts out with a high frequency air from a said chamber to the surroundings and between the shocks that chamber air is supplied from said air tank via an associated second valve (5, 6) and the second means during a second period of time (B) intermittently sucks in air from a high frequency the surroundings in a mentioned chamber and between the air tank of the shocks is supplied with air from this chamber via an associated second valve (7, 8), in order to create an air flow with frequency components with a substantially lower frequency than the frequency of the shocks. . Device according to claim 7, in that said high frequency is more than 10 times, preferably more than 30 times, higher than said low frequency. . Device according to claim 7 or 8, in that the control unit (12) is arranged to coordinate the control of said means (10, 11) and first valves (3, 4) to vary the amount of air 518 168 '. 13 of said pump and suction shocks, respectively, so that said air volumes in function of time substantially follow a given signal. Device according to any one of claims 7-9, wherein each of said first and second means is formed by a separate membrane (10, 11) forming part of the respective chamber (1, 2). delimiting the wall, and that the control unit (12) is arranged to control the diaphragm to vibrate at a high frequency in order to change the volume of the chamber at such a high frequency. Device according to claims 9 and 10, in that the control unit (12) is arranged to vary said amount of air by controlling the amplitude of the membrane (10, 11) to vary. Device according to claim 9 or claims 9 and 10 or 11, characterized in that the control unit (12) is arranged to control the variation of said air volume by controlling the length of the opening hours of said first valve (3, 4) to the environment to vary. Device according to any one of claims 7-12, in that one or more of said first and second valves are passive, i.e. they are arranged to be controlled by pressure differences between the chamber (1, 2) and the environment respectively the chamber and the air tank ( 9). Device according to any one of claims 7-12, in that one or more of said first and second valves are active, i.e. a control unit (12) is arranged to control opening and closing thereof. Device according to any one of claims 7-12, in that it comprises at least two said chambers (1, 2) with at least each said first (3, 4) and second valve (5, 6, 10). '' 0 o un v 518 168 14 7, 8) for connection to the surroundings and a said air tank (9). Device according to claim 15, in that it comprises a said chamber (1) arranged to operate during said first time periods for pumping out air to the surroundings via its first valve (3) and a second chamber (2) arranged to operate during said second time periods to draw air therein from the environment. Device according to claim 15 or 16, in that it has at least two chambers (1, 2) connectable via its second valves to a common said air tank (9). Device according to claim 15 or 16, in that it comprises at least two said air tanks (9) and at least two said chambers are connectable to different air tanks. Device according to any one of claims 15-18, in that the control unit (12) is arranged to control at least two said means (10; 11) of the same kind, first or second, arranged in separate chambers (1, 1 ', 2, 2 ') to act alternately during the first or second time period in question so that the time interval between two consecutive pump or suction shocks from one of the chambers in a group of at least two chambers with means of the same kind is filled by pump or suction shocks from one or the other chambers in the same group. Device according to any one of claims 7-19, in that it comprises more than two said chambers (1, 1 ', 2, 2') connectable via first and second valves to the environment or an air tank. Device according to any one of claims 7-20, in that said air tank (9) forms a container airtight against the surroundings adjacent to said chamber (1, 2). Device according to claim 21, in that the dimensions of the air tank (9) are adapted to the amount of air said means are arranged to pump out of the respective suction into said chamber (1). , 2) during a said time period so that the air pressure in the air tank does not change significantly during a said time period. Device according to claim 22, in that the volume of the air tank (9) is dimensioned to ensure that the maximum pressure difference therein does not exceed 50% of the ambient pressure. Device according to any one of claims 7-23, in that the size of said chamber (1, 2) and valves (3, 4) is within the micrometer range, i.e. is of typical size for a microelectromechanical structure (MEMS). Use of a device according to any one of claims 7-24 for generating sound with low frequency and high sound pressure. Use according to claim 25, in that it is for active quenching of low frequency noise.