Acoustics – Wave generation
Patent
1991-02-06
1992-05-05
Eldred, J. W.
Acoustics
Wave generation
116137R, 116140, 331155, G10K 500
Patent
active
051099489
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a frequency controlled, motor driven, low frequency sound generator.
A low frequency sound generator with a positive feedback system is described in SE, B, 446 157 (corresponding to EP, B1, 0 006 833). It consists of an open resonator arranged as a sound emitter for generating standing gas-borne sound waves, which produce a varying gas pressure in the resonator, and; a feeder unit with a pipe for supplying pressurized gas into the resonator and, a back and forth springing movable valve slide, the position of which remains unaffected by the pressurized gas. The valve slide regulates the gas flow from the pipe while supplying a modulated flow of pressurized gas into the resonator. The valve slide is constructed as a sleeve, which is axially displaceable inside or outside the pipe and controls an opening arranged in the pipe wall for the supply of pressurized gas from the source.
In SE, A, 8701461-9 (publication No. 457 240, corresponding to PCT/SE88/00172) a low frequency sound generator is described which is a further development of the above mentioned generator. The slide valve, in this case, is designed as a piston movable inside a pipe/cylinder, said piston being arranged in order to regulate a connecting opening between an air surge tank and the inside of the cylinder at one of the end surfaces of the piston. The air surge tank surrounds the cylinder and the feeder unit and is also connected to the pressurized gas source. One end of the cylinder is open towards the interior of the resonator and the connecting opening may communicate with the interior of the resonator depending on the position of the piston.
The basic principle for the operation of both these low frequency sound generators is: when the sound pressure in the resonator is higher than the surrounding atmospheric pressure, the valve slide will move in such a direction as to free the opening, and then air having a higher pressure than the sound pressure will be forced into the resonator.
When the sound pressure in the resonator is lower than the surrounding atmospheric pressure, the valve slide will be forced to move in the opposite direction with the result that the opening is closed completely.
The above described low frequency sound generators are both air driven. In a feeder unit forming a part of the sound generator, working according to the above described principle, it is essential to supply a large volume of air through the opening during a very short period of time and with a minimum loss of pressure during the passage of the air into the resonator. The supplied pressurized gas has so far been generated by a blower, which is both space demanding and expensive as well as having the disadvantage of the supplied air being relatively hot. The purpose of the present invention is to generate sound pressure pulses in the resonator without the use of a blower.
The low frequency sound generators according to above mentioned documents have a positive feedback system which means that the movement of the valve slide and the subsequently generated pressure gas pulses are automatically adjusted to one of the natural frequencies of the air column inside the resonator. This way, adjustments can be made according to variations in the frequency depending on e.g. changes in the temperature. The apparatus, according to the present invention, is equipped with a control system which is normally used in such a way that a maximum sound pressure is obtained in the resonance unit in the same way as when using a positive feedback system as described above, but it can also be adjusted in such a way that a lower sound pressure may be obtained.
The invention, with examples of embodiments, will now be explained in detail with reference to enclosed drawings, in which:
FIG. 1 is a side view of the entire low frequency sound generator including resonator
FIG. 2 shows the driving part of the feeder unit in enlargement
FIG. 3 shows the air pulse generating part of the feeder unit in enlargement
FIG. 4 shows a block diagram of the control syste
REFERENCES:
patent: 1173708 (1916-02-01), Chance
patent: 4307964 (1981-12-01), Dudgeon et al.
patent: 4359962 (1982-11-01), Olsson et al.
patent: 4801897 (1989-01-01), Flecken
Eldred J. W.
Infrasonik AB
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