OMNIDIRECTIONAL SOUND SOURCE.

TECHNICAL FIELD

The present invention refers to an omnidirectional sound source. In particular, but not exclusively, the invention refers to an omnidirectional sound source for the acoustic characterization of buildings in compliance with the present ISO standards of the sector.

BACKGROUND ART In the sector of acoustics of buildings the present regulations, and in particular the UNI EN ISO 140, prescribe the methods for measuring the acoustic performance of buildings, rooms, walls or other constructions.

Two very important parameters of said performance are the reverberation time of enclosed spaces and the evaluation of the airborne sound insulation in building elements separating two adjacent rooms.

The ISO standards asserts that to perform the above and other kind of measurements a special kind of sound source is needed, called omni-directional, apt to emit isotropic sound waves, that is with the same frequency and intensity in all directions.

The standards also suggest the ways of manufacturing said instruments and define the parameters they have to satisfy in order to sufficiently approximate the above said omni-directional source.

The above produced a standardization of the sound sources that at present are provided with twelve loudspeakers in phase contained in a single box shaped as a dodecahedron.

Such box is usually mounted on a tripod about one meter and a half long and is connected, by means of proper cables, to an acoustic power amplifier of the signals to be transmitted to the loudspeakers which has to generate a sound power adequate to the measurements to perform.

The box has overall dimensions such to be inscribed in a sphere having a diameter between 32 and 45 centimetres and it has an overall weight in a range from 12 to 20 kilograms. The power amplifier is usually a parallelepiped of the weight in a range from 5 to 20 kg.

As you can easily imagine the above described instrument is not at all easy to handle and to use, both as regards the overall dimensions and the weight of its components.

You must also notice that in the specific sector of use is frequently needed to do series of measurements in locations close one to the other but anyway different. You can think, for instance, that in case the acoustic performance of a whole medium or large sized building has to be obtained the sound source, the acoustic amplifier and the tripod have to be continuously moved from a room to another and from a floor to another of the building.

Furthermore the dodecahedron shape is not the only shape on the market as are known solutions in which, still using twelve loudspeakers arranged according to the surfaces of a dodecahedron, the external surface of the box has the shape of a sphere.

In addiction it is known that, at least in theory, all regular polyhedron are apt to approximate an omni-directional sound source, that is for instance a tetrahedron, a cube, an octahedron or an icosahedron. Actually such shapes are not used due to the geometric features of the surfaces not suitable to house the speakers (triangular surfaces) and/or to the difficulty at approximating the omni-directional sound source when the number of loudspeakers is lower than twelve. A further kind of omni-directional sound source, disclosed in patent DK19940001174, provides a single loudspeaker on which is mounted a truncated-conical element having conicity in the opposite direction with respect to the speaker. Such solution works according to the principle of the diffraction to allow the sound to spread in all possible directions, in theory, when exiting from the upper base of the conical element.

However, the solutions have inevitable problems of efficiency, and also need the use of a separate amplifier. SUMMARY OF THE INVENTION

Object of the present invention is to propose an omni-directional sound source that, while providing the compliance to the present standards, is very easy and practical to handle and use. Further object of the present invention is to propose an omni- directional sound source having a very simple structure so that production costs can be greatly reduced.

The above objects are attained through a sound source, in particular for measuring the acoustic performance of buildings, comprising a box whose external surfaces house speakers, the electro-acoustic features and the layout of said speakers being able to generate a substantially isotropic propagation of the sound they emit, in the internal volume of said box being housed the amplifying means of the electric signals apt to create the sound waves produced by said speakers. Said box is, advantageously, shaped as a cube in which one vertex is chamfered and provides means for connecting a supporting tripod.

The box also comprises white and/or pink noise sound generators, means for remotely controlling said sound source, stabilized power supply means and at least a toroidal transformer placed coaxially to a tubular protrusion of said means for connecting the tripod.

The above amplifying means preferably comprise power supply means, voltage stabilizing means, a pre-amplifier stage and a

power amplifier whose components are housed on metallic parts of the surfaces of said cubic box, that act as heat spreaders. The speakers are magnetodynamic, having same performances, and they have a ratio between external diameter and height of the diaphragm greater then or equal to four.

They are also provided with a protection grid whose holes' total surface is lower then 50% of the total surface of the grid itself, which is furthermore internally provided with a truncated-conical element having the greater surface bound to the grid and the smaller surface facing the pole of the speaker.

The above outlined features make clear the advantages coming from the use of an omni-directional sound source according to the invention thanks to which separately moving the sound source and the amplifier every time a measurement in a different room had to be performed is no more needed. The advantages not only concern the easy of use but also handiness as the overall weight of the instrument is quite reduced by half with respect to omnidirectional sources of the prior art. In addiction, the cubic shape of the box allows strongly simplifying the manufacturing and assembling procedures, so reducing the production cost.

Finally, the innovatory structural features of the speakers contribute to obtain the prescribed performances for being classified as an omni-directional sound source, helping, in particular, to let choose the cubic shape of the box.

DESCRIPTION OF DRAWINGS

Anyway, for a better understanding of the characteristics and the advantages of the present invention, they will now be described, by way of examples, embodiment of the invention itself, with reference to the accompanying drawings, in which:

1. figure 1 shows a perspective view of an omni-directional sound source according to the invention;

2. figure 2 shows a further perspective view of the sound source of fig.1, in a in-use configuration; 3. figure 3 shows a perspective view of a portion of the internal components of the sound source of fig.1 ;

4. figure 4 shows a perspective view, in partial section, of the sound source of fig.1 ;

5. figure 5 shows a side section view of a component of the sound source of fig.1 ;

6. figure 6 shows a perspective view, like the view of fig.1 , of a different embodiment of the sound source of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to figure 1 it is pointed at as a whole with 10 a sound source comprising a cubic box 11 whose outer surfaces house six magnetodynamic speakers all having same shape, same dimensions, same bandwidth, acoustic power and efficiency. As you can see in figure the speakers 12 are housed in the middle of the outer surfaces of the cubic box 11 so that axial lines of any

adjacent two speakers intersect each other at a same angle of

90°.

A vertex of the box 11 is chamfered so that a further small flat surface, 50, is obtained, and it is provided with a central hole fitting a connecting flange, 13, whose shape is better visible in the broken view of fig.4.

Said flange 13 is bound to the box by screw means, gluing or different fastening means and it has a central hollow for housing a tripod, 14, supporting the sound source when in-use, as shown in fig.2, in a stable position on the ground.

In figures 3 and 4 are shown the electronic components arranged inside the box 11 in- order to generate and amplify the signals transmitted to the speakers 12 and transformed by these lasts into acoustic emission. A toroidal transformer, 15, apt to transform the voltage of the power supply public network or the voltage of the batteries optionally furnished with the instrument, in a voltage apt to supply the electronic components, is coaxially mounted around the tubular element of the flange 13. Such special layout is useful both to optimize the usage of the volume inside the box 11 and to balance the weights of the instruments. In fact, the transformer 15 is the heaviest component of the all sound source and such an arrangement allow, in the in-use configuration, to keep as low as possible the centre of gravity of sound source itself.

Near the transformer 15 is placed a voltage stabilizer/rectifier 16. A built-in electronic board, 18, comprises white and pink noise generators, 19, a pre-amplifier, 20, and remote control means, 21 , of the sound source, 10. Said built-in board 18, however of known technique, is bound along an edge of the internal surface of the box 11 and it makes an angle of about 45° with the two adjacent surfaces, so that the volume inside the box, for the most part occupied by the speakers 12, is optimized. The signal produced by said noise generators 19, and partially amplified by the pre-amplifier 20, is transmitted to pre-pilot transistors housed on further electronic boards 22 for increasing the signal level in order to let it useful to power transistors, 23, directly bound to the internal surface of the three faces of the cubic box shown in fig.3. The above three faces are made of metallic material, while the three more faces not shown in figure are made of wood. In fact, in this way the faces of the cubic box 11 act as heat spreaders of the heat generated by the power transistors 23. Each power transistor, 23, supply one speaker, 12, apt to emit sound waves at frequencies and intensities apt to let the user be able to perform the measurements needed to define the acoustic performances of even big buildings, in particular according to the provisions of the UNI EN ISO 140 standards. The speakers 12 used, even if belonging to the known technique, are selected, modified, and provided with special characteristics,

so that an isotropic spreading of the sound waves emitted by the sound source 10 is obtained.

As you can see in fig.5, the speaker 12 has a ratio between external diameter and height of the diaphragm, 41 , greater then or equal to four, such, that is, to reduce to overall dimensions of the speaker inside the box 11 and, most of all, to maximise the angle of emission of the sound waves.

The speaker's dust cap, 42, is made of a material that does not absorb the sound in order to improve the spreading of the heat produced by the diaphragm.

The protection grid, 43, has a low percentage of the area of the holes with respect to the global area, since it is lower than 50%. This last feature allows optimizing the diffraction of the sound waves that takes place when the wave produced by the diaphragm passes through the holes of the grid. In fact, in the middle of the grid the diffraction effect produced by adjacent holes tends to mutually compensate, so producing a quite flat wave; on the contrary, near the edge of the grid, as you can see in figure, lacking more external holes, the diffraction effect helps generating sound waves having a smaller bending radius, so encouraging a lateral diffusion of the sound. The above greater curvature of the sound wave in correspondence to the peripheral zone of the speaker allows an efficient sound propagation also in the direction of the bisecting line of the angle between the axial lines of two speakers housed in two adjacent faces of the cubic box. So, it is

also thanks to the above diffraction effect that the sound source of the invention efficiently approximates an omni-directional sound source.

To improve in an even better way the sound propagation, still using the diffraction effect, the internal surface of the protection grid 43 is provided with a diffusing element, 44, having the shape or of the lateral surface of a truncated cone either of a disc. Said diffusing element, 44, made of cardboard, wood, metal, or other rigid material, has the perimeter of the greater base bound to the 43, and the smaller base of the cone is inside the volume of the speaker 12. Differently, in case the diffusing element is a disc it can be directly bound to the grid 43. The sound waves produced by the diaphragm 41 of the speaker, crossing the diffusing element 44 are modified and their direction is changed so that a propagation towards diverging directions with respect to the axial line of the speaker itself.

The sound source of the invention works, as can be easily understood from what above disclosed, in a way that is quite analogous to the omni-directional sources of the prior art used to define the acoustic performances of buildings.

The sound source 10 and the tripod 14 thereof are carried, in a special bag, where the measurements have to be performed. It has to be noticed that, since the sound source has a built-in amplifier, there is no need to carry heavy and bulky external amplifying means.

The tripod 14 is firmly placed in the desired location and the sound source is mounted on it by using the supporting flange 13. The specific arrangement of the transformer 15 assures a great stableness to the sound source 10. The cable 24 is connected to the connector 25 on the box 11 , and to or an electric socket to provide power supply from the power supply network either a rechargeable battery pack. Switching on and adjusting the various parameters can be done both from its remote control and from the control panel on one face of the box 11 , as you can see in fig.1. Said control panel comprises a potentiometer 26 for adjusting the global volume, a commutator 27 for selecting the emission of white or pink noise, a commutator 28 for enabling the input of the signal from an external source, a connector 29 for the input of the signal from an external source, a connector 30 for the output of the signal towards an external source, a potentiometer 31 for adjusting the volume of input of the external source and a switch 32 for powering on and off the sound source. Once selected, for instance, the emission of white noise and adjusted the output volume, the sound source is switched one and measurements of the sound insulating performances of a wall or of the reverberation time of a room are carried out. Then, new measurements could be required to be carried out in different rooms, may be at different floors of the same building.

The sound source is so switched off, removed from the tripod and carried to the following place of measuring. During these procedures are particularly useful the advantages of the sound source of the invention as it is not necessary to move bulky amplifiers and, thanks to the new shape and structural features, the sound source is very light and easy to handle with respect to the sound sources of the prior art. Obviously any modification or change can be introduced to the above disclosed sound source, still remaining safe the advantages and characteristics of the invention.

In particular, in fig. 6 is shown a sound source, 10' in which the edges of the cubic box 11' are chamfered in order to house twelve little tweeters, 33, that, together with the speakers 12', assure the optimal emission of the highest frequencies in the direction of the bisecting line of the angle between the axial lines of two speakers housed in two adjacent faces of the cubic box, Also in this case the tweeters 33 are arranged so that the axial lines of nay two adjacent tweeters 33 intersect with a same angle, so creating a spherical symmetry. Moreover, in this last embodiment, all the faces of the cubic box are made of wood but they provide metallic elements, 34, in correspondence to the areas where, inside the box, are bound the power transistors 23. Obviously the box, 11 or 11 ', could be made of different materials with respect to the ones described, the heat spreading being

obtained to specific different components housed inside the box. The metallic elements 34 could have any shape and dimensions, or they could be not structural but simple covering elements. The batteries supplying electric power to the sound source could be fastened to the external surface of the tripod or they could be sized and shaped to fit the internal cavity of the tripod itself. Handling means could also be bound to the external surface of the box in order to facilitate lifting and moving the sound source. The box could have different shapes with respect to the cubic shape above disclosed, mainly as ύ function of the number of speakers to be housed or even just for design reasons. The kind, number and layout of the speakers may vary, always looking for the most isotropic sound propagation. In particular the diffusing element 44 could be bound to the grid at the perimeter of its smaller base, with inverse conicity with respect to that shown in fig.5, so that a different diffraction effect is obtained. In addiction, more diffusing element 44 could be bound to a same grid 43, being arranged in various ways on the internal surface of the grid 43 itself. The noise generators 19, the pre-amplifier 20 and the remote control means 21 could be housed in separate electronic boards and differently arranged inside the box 11 , as well as the other electronic components could be differently arranged even auxiliary transformers or other components not mentioned in the above description.

The components apt to amplify the signal could be different with respect to those described, only part of them being housed inside the box, some amplifying operations being carried out of the box itself. In fact, a different embodiment could provide the housing of just the transformer 15 and, in case, the voltage stabilizer 16 inside the box, the pre-pilot transistors and the power transistors, lighter but more heating components, being housed in specific external boxes. An especially advantageous embodiment of the invention provides the housing, inside the box, of digital amplifiers, such as the so called T class amplifiers. The use of this last kind of amplifiers brings relevant advantages from many points of view. First of all, they have high power efficiency, more than 90%, so that they do not need great heat conductive surfaces for heat spreading. That, in particular, allows building the box of the sound source entirely in wood or other materials, without the need of providing surfaces made of heat conductive materials. In addiction, the above said digital amplifiers are much lighter then standard analog amplifiers so they help increasing the handiness of the sound source. Last, but not less important, advantage deriving from the use of digital amplifiers concerns the great simplification of the apparatus that leads to a relevant reduction of the production costs.

These and more changes or modifications can be brought to the sound source according to the invention, still remaining in the ambit of protection defined by the following claims.