WO2001065533A2

WO2001065533A2 - Acoustic diffuser free from resonance

Info

Publication number: WO2001065533A2
Application number: PCT/IT2001/000086
Authority: WO
Inventors: Domenico Fiorentino
Original assignee: Domenico Fiorentino
Priority date: 2000-02-28
Filing date: 2001-02-23
Publication date: 2001-09-07
Also published as: WO2001065533A3; ITRM20000102A0; IT1315850B1; ITRM20000102A1

Abstract

An acoustic diffuser free from resonance in the frequency ranges of the acoustic transducers operating at low and medium frequencies with limpid high fidelity audio response, comprising an outside container and at least a loudspeaker, characterized in that the container has a shape different from the usual parallelepiped, three side walls of said container are not parallel to one another and their inside surfaces are not even as they are formed of several curvilinear lengths connected to one another and provided with points and recesses disposed with high discontinuity both horizontally and vertically, and a front panel is applied to a front opening, thus forming the fourth side wall carrying said loudspeaker, a cap and a base being also provided.

Description

Acoustic diffuser free from resonance

The present invention relates to acoustic diffusers, commonly called acoustic boxes, and more particularly the construction of the inside walls of such boxes,

Actually, the term "acoustic box" comes from the shape of the piece of furniture housing the loudspeakers or electroacoustic transducers for transforming the electric signals modulated at acoustic frequencies and coming from the final stage of an amplifier into mechanical vibration waves which propagate to the room. Acoustic boxes of the prior art have been shaped as a parallelepiped with a quadrangular, trapezoidal, square or rectangular base and an absolutely even surface of the inside walls, such a shape being as easy as possible to be made. As known to those skilled in the art, the parallelepiped with even inside walls is the most unsuitable shape to allow a "clean" propagation of the sound because of the so-called stationary waves, i.e. waves that, once generated, are reflected many times between the opposite parallel walls like in ping-pqng, thus producing a perceivable, measurable resonance till a complete damping. Another problem of the boxes of the prior art is the resonances produced at medium frequency within the box by the woofer and midrange transducers (low and medium acoustic frequency) operating between 900 Hz and 4000 Hz, such resonances being rather troublesome. The present invention seeks therefore to overcome such problems by providing a piece of furniture containing the electroacoustic transducers, the inside walls of which do not have any even surface but, as better explained thereafter, only surfaces formed of projections and cavities connected by sharp edges having such dimensions as to operate in the above- mentioned frequency ranges The invention seeks also to provide a piece of furniture, called conveniently box in the following, which can be very easily manufactured by a method which is also an object of the present invention as the piece of furniture is made by the superimposition of different modular elements which can show any shape without limitations

The manufacturing would be certainly much more expensive if the classic construction method of pieces of furniture, l e using six flat panels glued to one another is used In fact, the manufacturing of a piece of furniture having inside and outside shapes different from the classic parallelepiped involves a cost for machines and labour which is much higher than that required by the present application The suppression of resonances in the mentioned frequency ranges provides an extremely limpid high fidelity audio response Actually, from the measurement diagrams shown in the figures one can see that the diffuser of the present invention gives a true test signal without adding anything thereto In this case, however, there are spurious frequencies m the response to the test signal but they are damped by 13 dB with respect to the conventional acoustic boxes. As specified herebelow the manufacturing method of the loudspeaker according to the invention can provide the use both of computerized numeric control (CNC) machines working by a milling cutter and still CNC machines operating by a laser cutter.

The invention will be illustrated in detail with reference to the accompanying drawings, in which:

Tables I to XI show the above-mentioned diagrams comparing the emission of a conventional box with the emission of a box according to the invention at different frequencies (between 250 Hz and 4000 Hz);

Fig. 1 is an exploded view of a possible embodiment of a box consisting of modular members, base and connecting rods;

Fig. 2 is a vertical section of the box of Fig. 1;

I

Figs, 3 and 4 show a ,box which is open along the right and left sides to show the interior;

Fig. 5 is a top view of the box with the loudspeaker removed ;

Fig. 6 is a front view of the box; Figs 7 and 8 show the outline of the inner walls of the box along horizontal parallel planes.

Figs 9A 9B are perspective views of two modules, and

Fig 10 is a similar view showing schematically the assembling steps

With particular reference to Figs 1-4 it should be noted that the acoustic diffusers according to the invention are formed each by several horizontal members 10 (A, B) with the same thickness having the same outside shape and the same size and being superimposed on one another, a base BS , a cap CP, and a front panel 13 supporting the loudspeakers ALT 1,

ALT 2 in a conventional manner

As can better be seen in Figs 5, 7, 8, the outline of the inside walls of each member is anything but conventional and neither is the geometrical shape of the solid formed by the same member, the latter forming a truncated prism with a substantially t trapezoidal base instead of the conventional parallelepiped with square or rectangular base shown in the example As it is apparent the inside wall of each member 10 (A B) , which is here referred to as module consists of an assembly of curvilinear wall members formed by recesses RZ and points PT disposed discontmuously and fully at random the length of the points and the depth of the recesses being particularly important It should be appreciated that there is discontinuity in the inside walls PIA-PIB of the acoustic diffuser according to the invention also in the vertical direction since the vertically contiguous superimposed modules (10A, 10B) have inside walls with different outlines As a result discontinuity steps are formed vertically between overlying and underlying modules of walls PIA-PIB, thus avoiding stationary waves along the latter to be formed with the consequence of a resonance reduction to a minimum

Another advantageous feature of the acoustic diffusers according to the invention is that their modular construction allows automatic fast production methods to be used In fact the presently preferred material, i.e. the composite material called MDF (Medium Density Fiberboard), has been selected for its mechanical, physical characteristics of hardness, strength, workability, and density Such material allows computerized numeric control (CNC) machines to be used for the production of the single modules as well as their assembling by gluing them by the use of a reduced number of ancillary equipment In addition, CNC machines for cutting by laser can also be used with the material mentioned above

However, the selection of such a material does not exclude the use of other suitable materials such as resins of different types, aluminium, etc The modules forming the box of the acoustic transducer are shown more in detail in the plan views of Figs 5, 7 and 8 and in the perspective views of Figs 9A and 9B, and the production method is illustrated in Fig 10 Such method provides as mentioned above, the shaping of several modules 10A and 10B (Figs 10A, 10B) with the illustrated inside configuration and in the necessary number to form the box with the requested volume as well as base BS and "cap" CP with the same outside profile as modules 10A 10B, and three preferably wooden connecting rods AS1 AS2 , AS3 As can be clearly seen, three holes FI , F2 , F3 with a diameter corresponding to that of rods AS(1,2,3) are formed through the thickness of the walls of each module 10A, 10B in vertically aligned positions as well as through cap CP and base BS With the use of the described components, the assembling of the box can be easily and quickly carried out by superimposing alternatively modules 10A, 10B to base BS, applying a glue between the modules, inserting rods AS(1.2,3) into respective holes F(l,2.3) gluing the same, and superimposing cap CP Once the box is assembled in the described way, front panel 13 provided with holes for receiving and fastening loudspeakers ALT1 , ALT2 is glued to the front opening APF The application of any deadening panels (not shown) to the inside face of base BS and/or cap CP is also provided Front panel 13 is of the absolutely conventional type

A tuning tube TDA to be used in case bass-reflex loudspeakers are used is shown in the drawings As known, it is not necessary in case of pneumatically suspended loudspeakers .

Claims

1. An acoustic diffuser free from resonance in the frequency ranges of the acoustic transducers operating at low and medium frequencies with limpid high fidelity audio response, comprising an outside container and at least a loudspeaker (ALT) , characterized in that three side walls of said container are not parallel to one another and their inside surfaces (PIA, PIB) are not even as they are formed of several curvilinear lengths connected to one another and provided with points (PT) and recesses (RZ) disposed discontinuously , and a front panel (13) is applied to a front opening (APF) , thus forming the fourth side wall carrying said loudspeaker (ALT) , a cap (CP) and a base (BS) being also provided.

2. The acoustic diffuser free from resonance according to claim 1, wherein said front panel (13) supports a woofer loudspeaker (ALT1) and a middle range loudspeaker (ALT2).

3. The acoustic diffuser free from resonance according to claim 1, wherein said container consists of a modular construction comprising several modules shaped substantially as a horse-shoe of two different types (10A, 10B) with the same height and the same outside profile but with differently outlined inside walls so that discontinuity steps are formed vertically in the inside walls (PIA, PIB) of said container formed of several modules (10A, 10B) superimposed to one another, thus providing a further obstacle to the stationary waves

4 The acoustic diffuser free from resonance according to claim 1, wherein a deadening panel lines the inside surface of said cap ( CP ) and/or said base (BS)

5 The acoustic diffuser free from resonance according to .claim 3, wherein said modules (10A, 10B) are superimposed alternatively and glued on one another along their even separation surfaces

6 The acoustic diffuser free from resonance according to claims 3 and 5, wherein said modules (10A, 10B) are preferably composed of MDF (Medium Density Fiberboard) material having optimum mechanical. physical characteristics of hardness, strength, density, and workability, said modules being manufactured by computerized numeric control (CNC) machines

7 The acoustic diffuser free from resonance according to claims 3 and 6 wherein said modules (10A, 10B) , said base (BS) and said cap ( CP ) have through holes (FI, F2 , F3 ) vertically aligned in corresponding positions and forming continuous vertical passages, and wherein a rod (AS1 AS2 AS3) is inserted and glued in each vertical passage thus forming a sturdy connecting stiffening member for said superimposed glued components (BS CP , 10A, 10B)

8. The acoustic diffuser free from resonance according to claims 1 to 7 , wherein a tuning tube (TDA) is provided in said container, in case bass-reflex loudspeakers (ALTl, ALT2 ) are used.