Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
  • H04R1/2807—Enclosures comprising vibrating or resonating arrangements
  • H04R1/283—Enclosures comprising vibrating or resonating arrangements using a passive diaphragm
  • H04R1/2834—Enclosures comprising vibrating or resonating arrangements using a passive diaphragm for loudspeaker transducers

Definitions

• the present invention refers to a wave-guide acoustic transformer.
• the wave-guide acoustic transformer is an acoustic box for loudspeakers. With this system, it is possible to make single-way or multi-way diffusers with one or two anisotropic wave guides for every loudspeaker.
• the acoustic box is used as support for loudspeakers. These are heavy transducers: therefore, in order to stably support them, it is necessary to use suitably sturdy structures which prevent the use of very light-weight materials. Using an acoustically inert structure to support the loudspeaker, it is possible to design extremely light-weight systems with original acoustic solutions.
• the loudspeaker sends the sound waves inside wave guides made of cylindrical membranes.
• the elastic constant of the side wall of the cylinders is anisotropic and characterized by high values along the cylinder axis and by much lower values for the circumference of the cross section. In their path, the wave fronts apply a perpendicular pressure on the side surface of the cylinders, deform their section and generate a sound wave front with radial symmetry which is diffuse in the listening environment .
• Object of the present invention is solving the above prior art problems by providing a wave-guide acoustic transformer that allows making single-way or multi-way diffusers with one or two anisotropic wave guides for every loudspeaker, providing an acoustically inert structure for supporting the loudspeaker, so that it is possible to design extremely light-weight systems with original acoustic solutions.
• Figure 1 shows a preferred, but not limiting, embodiment of the acoustic transformer according to the present invention
• Figure 2 shows a wave guide made of a diaphragm with a cylindrical coil
• Figure 3 shows a wave guide made of a very light-weight diaphragm with a single sheet
• Figure 4 shows a wave guide whose length is different for right and left channels in order to make an asymmetrical stereophony wherein the negative interference of a channel is partially compensated by the other channel;
• Figure 5 shows an upper guide adapted to create a positive resonance which brings about a partial compensation
• Figure 6 shows a panel (10) of the sizes of the loudspeaker fastened at 45 degrees
• Figure 7 shows a loudspeaker (3) with the wave guide (4) fastened thereover.
• a preferred embodiment of the wave-guide acoustic transformer according to the present invention is shown and described .
• the prototype of the wave-guide acoustic transformer has a single wide-band loudspeaker and uses two cylindrical anisotropic deformable membranes with sound waves.
• a plastic gasket (6) is fastened through screws to the bracket of a supporting rod (2) and operates as support for the loudspeaker (3) .
• the wave guide for medium and low frequencies is fastened, made of a spirally-wound sheet of paper ( Figure 2) .
• the side wall of the cylinder (diameter 10 cm, height about 80 cm) is the diaphragm (4) with suitable stiffness to operate as sound wave guide, but yieldable enough to allow small distortions causes by internal wave fronts (7).
• the closed base of the cylinder (5) has the same loudspeaker surfaces and reflects the internal wave fronts upwards, preventing the acoustic pressure from directly propagating towards the listening environment.
• the sound emitted by the upper side (8) of the loudspeaker (3) is sent partially to the listening environment and partially inside the upper wave guide (9) obtained by folding a sheet of paper as shown in Figure 3 and open on both sides.
• the bigger fold (3.1) is used for fastening the guide to the supporting rod.
• the smaller fold (3.2) makes the cylinder sufficiently yieldable to be deformed along the circumference also at high frequencies.
• the wave guide is suitably spaced to allow the direct emission of parte of medium frequencies.
• the loudspeaker membrane is accelerated upwards, creating a pressure increase above and simultaneously a pressure decrease below, inside the sound wave guide.
• the internal wave front directed downwards has traveled for about 3.5 cm below the loudspeaker membrane and interacts in a complex way with the side wall of the wave guide and the structure of the loudspeaker itself. The result of these interactions at high frequency is not relevant for listening.
• the wave front After 200 microseconds, the wave front has traveled for about 7 cm and passed the loudspeaker magnet. From that time on, the wave front orthogonal to the wave guide moves downwards, interacting only with the side diaphragm on which the pressure, previously generated by the loudspeaker membrane, is applied.
• the front arrives at the closed base of the wave guide which it reflects upwards.
• the result of this reflection can interact with the loudspeaker membrane only after having traveled the wave guide along an opposite direction in other 2.5 milliseconds. Not all the reflected energy arrives at the membrane for two reasons: the front is partially reflected downwards by the loudspeaker magnet and is dampened by interacting with the side diaphragm.
• the box geometry makes that, for about 5 milliseconds, the loudspeaker membrane does not interact with the internal reflections generated by the box itself and afterwards interacts only with dampened wave fronts, obtaining a strong reduction of the distortion. Also outside, the box interacts in a very reduced way with the reproduced sound. Acoustically, an exceptionally clear response to transients is obtained.
• the acoustic behavior changes when the frequency changes,; in particular, 10,000, 1,000, 100 Hz allow explaining the operation for high, medium and low frequencies.
• the wavelength is 3.4 cm, lower than the diameter of about 10 cm of the loudspeaker which behaves in a directive way, mainly sending the acoustic waves upwards.
• This frequency already attenuated by the presence of the loudspeaker, deforms in a neglected way the side diaphragm of the lower wave guide.
• the sound waves (8) sent upwards apply a described pressure from half-waves of about 1.7 cm which, for about 50 microseconds, internally or externally deform the side surface of the diaphragm (9) creating undulations which slide upwards.
• the passive radiator (9) re-addresses high frequencies at 360 degrees in the listening environment.
• the wavelength is 34 cm, greater than the loudspeaker diameter whose emission can be deemed spherical and with reduced effects on the upper wave guide.
• the pressure is directed inwards or outwards for times long enough to modify the side surfaces of the diaphragm, generating an undulation which slides vertically and is able to create a series of secondary fronts.
• the secondary fronts have a perfectly radial symmetry with respect to the cylinder axis and facilitate the space localization of the origin of sounds in the sound image. This effect has a relevance increasing when the frequency decreases.
• the wavelength is 340 cm, greater than the cylinder height (80 cm) of the lower wave guide.
• the difference in acoustic load makes that, already at few cm from the loudspeaker membrane, the external sound front has a pressure lower than the internal sound front.
• the internal pressure for the majority of time exerts on the side surface of the wave guide an outward or inward directed pressure on the whole length of the diaphragm.
• the acoustic signal coming from the side diaphragm of the wave guide is more important than the upward directed signal from the loudspeaker.
• the loudspeaker membrane is the primary of an acoustic transformer, while the side diaphragm of the wave guide is the secondary.
• the pressure of the wave front generated by a stationary sinusoidal signal applied to the loudspeaker can be considered uniform in a disk whose thickness is infinitesimal and which moves downwards.
• the pressure can be represented with a sinusoidal function:
• the total force F(t) is a sinusoidal function which changes in time and is applied orthogonally on the surface of the side diaphragm of the wave guide.
• the system is linear within the linearity of the speed of sound and of the box geometry.
• the force is not uniform on the whole diaphragm since there is a gradient which is modified in time. This gradient does not disturb the listening, since the human ear is accustomed to listen to sounds emitted by bodies on which stationary and non-stationary sound vibrations pass.
• a wave guide is suitable, which is made of a diaphragm with cylindrical coil, as shown in Figure 2, sturdy enough to resist to strong stresses generated by low frequencies. It is better that it is closed on both sides to minimize the distortion generated by the deformation of the side wall.
• a wave guide is suitable, which is made of a very lightweight diaphragm with single sheet, as shown in Figure 3. It is better that it is open on both sides in order to also send upwards part of the sound energy.
• the shape is an indication: the passive radiator operates provided that there is at least one inflection which allows the rest of the circumference to be dilated or compressed.
• the geometry of the wave-guide acoustic transformer has as further advantages a strong reduction of internal reflections and a uniform load distribution on the loudspeaker membrane. If correctly made, it is suitable as optimum acoustic box for systems with single-way and multi-way sound reproduction.
• a very inexpensive version, to be coupled with a PC and consumer electronics, can be made by removing the supporting rod and using the lower plug (5) as base, the side diaphragm (4) as support for gasket (6) and loudspeaker (3). Highs can be re-addressed towards the listener with a panel (10) with the same sizes of the loudspeaker fastened at 45 degrees, as shown in Figure 6.
• the loudspeaker (3) can be fastened as base, and itself as base, and the wave guide (4) can be fastened over it, as shown in Figure 7.
• the acoustic transformer has the majority of its surface which can be made of paper, transparent films or other material which can be easily molded and can be used as sound photograph-carrier, to send information or a furniture complement.
• the wave-guide acoustic transformer comprises:
• a membrane (4) having a cylindrical shape open at its sides, used as sound wave guide and omnidirectional acoustic passive radiator,
• a loudspeaker (3) adapted to send sound waves (7) inside the cylindrical membrane (4)
• the cylindrical membrane (4) receives energy only from the sound wave fronts traveling in the internal air volume and has a strongly anisotropic modulus of elasticity in parallel with the cylinder axis and along the circumference of the cylinder itself, the internal sound waves (7) not modifying the length of the cylinder since, along the axis, the elastic constant is very high, the internal sound waves (7) themselves being adapted to modify the circumference of the cylindrical membrane (4) since, along the circumference, the elastic constant is much lower.
• the cylindrical membrane (4) is made by winding in a cylindrical coil a single sheet of paper tightened with a force of few grams, in order to leave a layer of air between the overlapped surfaces of the turns, the layer of air remaining in communication both with the internal volume, and with the external volume of the cylindrical membrane ( 4 ) .
• the layer of air present between the overlapped surfaces has a medium thickness on the order of the tenth of a millimeter, the layer of air operating as viscous and elastic fluid which uniformly distributes the pressure on the overlapped surfaces, the layer of air keeping low the friction between the turns, decreasing the number of contact points, and facilitating the sliding of the overlapped surfaces one over the other in the direction of the circumference inside the cylindrical membrane (4).
• the plane and circular wave front (7) which propagates itself inside the wave guide is adapted to exert on the single annular section of the cylindrical membrane (4) a uniform radially oriented pressure which modifies the diameter of the affected section, the sum of the effect of the single sections generating outside the cylindrical membrane (4) a wave front with radial symmetry with respect to the cylinder axis.
• the gasket (6) is made of a plastic material with the housings for the screws for fastening to an external bracket and with an edge able to be overlapped to the flange of the loudspeaker (3) for fastening the gasket (6) to the flange of the loudspeaker (3) with an airtight seal.
• An edge of the gasket (6) is fastened to an edge of the cylindrical membrane (4) with an airtight seal.
• the circular plug (5) is fastened to an edge of the cylindrical membrane (4) with an airtight seal and reflects the internal sound waves (7) .
• the fraction of reflected sound energy of the circular plug (5) is decreased by applying sound- absorbing material on the internal side of the circular plug (5) or by making the circular plug (5) with material with a higher transmission point or by completely removing it.
• the cylindrical coil is made by winding sheets of materials different from paper with surfaces able to slide one over the other.
• the cylindrical coil is replaced by a single layer of film with a strongly anisotropic modulus of elasticity, so that such modulus along the cylinder axis is much greater with respect to the modulus along the circumference.
• the film is fastened to a support shaped as a cylindrical sector and emits sound waves on a circular sector lower than 360 degrees.
• the cylindrical membrane ( 4 ) is adapted to support the weight of the loudspeaker (3) .
• the circular plug (5) is adapted to perform the function of bearing base for placing the diffuser on the floor or on the shelf of a piece of furniture .
• An anisotropic cylindrical membrane (9) open on both sides is adapted to be assembled separate with suitable spacers on the front side of the loudspeaker (3) .
• the cylindrical membranes (4, 9) are adapted to be pre-molded and/or decorated before being assembled in the acoustic transformer.

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• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

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• 2013
  • 2013-07-15 IT IT000007A patent/ITSS20130007A1/it unknown
• 2014
  • 2014-05-13 WO PCT/IT2014/000128 patent/WO2015008306A1/en active Application Filing
  • 2014-05-13 EP EP14739964.6A patent/EP3022945A1/de not_active Withdrawn

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