FR3141552A1 - ACOUSTIC SPEAKER WITH OPTIMAL ACOUSTIC TRANSMISSION DEVICE, AND ASSOCIATED ACOUSTIC SPEAKER ASSEMBLY - Google Patents

Abstract

ACOUSTIC SPEAKER WITH OPTIMAL ACOUSTIC TRANSMISSION DEVICE, AND ASSOCIATED ACOUSTIC SPEAKER ASSEMBLY The present invention relates to an acoustic enclosure (1) comprising a box (2) in which at least one loudspeaker (3) is mounted, said box (2) comprising , for each speaker (3), an opening (2a) closed by the front part of the associated speaker (3) and a vent (4) opening onto the outside, the acoustic enclosure (1) further comprising , for each loudspeaker (3), an acoustic transmission device (5) extending between an input end (5a) configured to receive the sound waves emitted from the rear of the associated loudspeaker (3) and an outlet end (5b) opening into the associated vent (4), each acoustic transmission device (5) having a characteristic length and a constant characteristic cross section dimensioned such that the acoustic resistance of the acoustic transmission device (5) ) is identical to the acoustic resistance of the associated loudspeaker (3). Figure to be published with the abstract: Figure 1

Description

ACOUSTIC SPEAKER WITH OPTIMAL ACOUSTIC TRANSMISSION DEVICE, AND ASSOCIATED ACOUSTIC SPEAKER ASSEMBLY

The present invention relates to the field of acoustic speakers, and relates in particular to an acoustic speaker with an optimal acoustic transmission device and to an associated acoustic speaker assembly.

A classic speaker emits sound waves forward, but also sound waves backward. Indeed, when the speaker membrane moves forward, the air in front of the membrane is compressed, while that located behind it is rarefied, and vice versa when the speaker membrane moves backwards, the air in front of the membrane is rarefied, while that behind it is compressed. Thus, when the speaker reproduces audio content, its membrane moves forward and backward, creating unwanted pressure or depression with each forward or backward movement. A sound wave is thus created in phase opposition to that of the original signal, inducing an acoustic problem.

In order to overcome this acoustic problem, it is known to place the loudspeaker in an acoustic enclosure in order to allow the loudspeaker to more faithfully reproduce the original audio signal.

The main types of existing acoustic enclosures are:

- the closed enclosure, in which the waves emitted towards the rear of the loudspeaker are isolated in the enclosure,

- the vented enclosure, in which the waves emitted towards the rear of the loudspeaker join the waves emitted towards the front via a vent,

- the passive radiator enclosure, in which the vent is replaced by a bass speaker without a motor (coil and magnet), and

- the dual-speaker enclosure.

All of these existing loudspeaker types attempt to correct loudspeaker defects with varying degrees of effectiveness and introduce an undesired high-order frequency response.

Complex solutions also exist to try to achieve an optimal and constant level at all the frequencies required in the frequency range of the human ear (commonly accepted between 20Hz and 20kHz). However, these solutions often require several types of loudspeakers to cover the full frequency band, most of the time using bass, midrange and treble drivers at the same time but also sometimes an additional separate subwoofer for the extreme bass.

The weaknesses of these solutions which use several speakers are multiple:

- difficulty of having each speaker at the same level,

- frequency overlap between speakers almost impossible to calibrate (requires graphic or parametric equalization for approximate correction),

- very sensitive to the physical characteristics of the speaker,

- control of the phase shift according to the frequencies is complex and often impossible (introduction of unwanted high order filtering),

- very difficult overall equalization, and

- sensitive to reverberations from the room where the loudspeaker is placed.

Certain control speakers (or "monitoring"), commonly used in recording studios, can also be based on acoustic transmission line speaker technology in which the acoustic enclosure includes inside it a long conduit that acts as a guide for sound waves emitted from the back of the speaker to a port. However, these existing acoustic transmission line loudspeakers cannot cover the entire 20Hz – 20kHz frequency range and generally use multiple drivers to attempt to achieve a wider spectral range. Some are capable of reaching a minimum frequency of around 40Hz but the speaker then reaches a very high price (namely, several thousand euros).

Thus, no loudspeaker currently on the market can obtain a flat spectral response over the entire 20Hz – 20kHz frequency range, while being inexpensive.

The present invention aims to resolve the drawbacks of the prior art, by proposing an acoustic enclosure comprising an optimal acoustic transmission device which makes it possible to propagate the sound waves emitted from the rear of the loudspeaker towards a vent, and whose characteristic length and characteristic cross section are dimensioned such that the acoustic resistance of the acoustic transmission device is identical to the acoustic resistance of the loudspeaker, which makes it possible to obtain, with a single loudspeaker, a response flat spectral range over a very wide frequency band, for example over the entire frequency range 20Hz – 20kHz.

The present invention thus makes it possible to improve the audio reproduction of the acoustic speaker which can provide the most faithful sound possible with maximum efficiency in comparison with traditional speakers currently on the market.

The present invention therefore relates to an acoustic enclosure comprising a box in which at least one loudspeaker is mounted, said box comprising, for each loudspeaker, an opening closed by the front part of the associated loudspeaker and an opening vent on the exterior, the acoustic enclosure further comprising, inside the box and for each speaker, an acoustic transmission device extending between an input end configured to receive the sound waves emitted from the rear of the associated loudspeaker and an output end opening into the associated vent, said acoustic transmission device being configured to propagate the sound waves emitted from the rear of the associated loudspeaker towards the associated vent, characterized by the fact that each acoustic transmission device has a characteristic length and a constant characteristic cross section, said characteristic length and said characteristic cross section being dimensioned such that the acoustic resistance of the acoustic transmission device is identical to the acoustic resistance of the loudspeaker partner.

Thus, the dimensioning of the acoustic transmission device so that its acoustic resistance is equal to that of its loudspeaker makes it possible to obtain maximum acoustic power and maximum efficiency of the acoustic enclosure, in addition to a response flat spectral of the acoustic enclosure over a very wide frequency band (for example, over the entire frequency range 20Hz – 20kHz) due to the constancy of the cross section of the acoustic transmission device.

The cross section of the sound transmitting device must remain constant over the entire length of the sound transmitting device to ensure constant acoustic resistance of the sound transmitting device, regardless of the frequency above the low cutoff frequency of the sound transmitting device. acoustic transmission. Below the latter, the acoustic resistance of the acoustic transmission device collapses.

The acoustic transmission device thus ensures a constant acoustic power whatever the frequency above the low cutoff frequency of the acoustic transmission device.

The acoustic transmission device allows optimal control of the movement of the loudspeaker membrane, allowing a reduction in physical constraints on it, and therefore makes it possible to guarantee greater longevity of the loudspeaker as well as an increase in the admissible power thereof.

The acoustic transmission device allows an increase in the total efficiency of the acoustic enclosure and therefore a reduction in the return to the audio amplifier of reactive power which is harmful to digital amplifiers (Class D), particularly at low frequencies.

The use of small speakers can ensure a maximum bandwidth of up to 20 kHz. Larger speakers will not be able to reach 20 kHz. Using small speakers will not affect the low cutoff frequency of the sound transmission device. Only the power will be reduced, so it will be enough to add several loudspeakers to achieve the desired power.

With the present invention, unlike traditional speakers, all edge effects are corrected.

The present invention is based on acoustic transmission line technology which allows, in the acoustic field, strict control of the frequency spectrum of the acoustic enclosure. It can provide a flat spectral response from the highest to the lowest frequencies, where the latter are defined by the length of the acoustic transmission line following a simple linear relationship.

The acoustic enclosure according to the invention is independent of the resonant frequency of the at least one speaker. Even if the speaker has a resonant frequency of 80 Hz or even 120 Hz, this will not prevent the loudspeaker from reaching lower frequencies like 20 Hz or even lower only depending on the length of the sound transmission device .

Since the acoustic transmission line architecture has no limit in high frequencies, the highest frequency of the loudspeaker will be limited by the maximum frequency that the at least one loudspeaker can provide.

The present invention makes it possible, with a single loudspeaker, to cover at least the entire frequency range 20Hz – 20kHz. Furthermore, with the present invention, there is no management of frequency overlap, nor uncontrolled phase shift, which makes it possible to reduce unwanted resonance/rejection behavior.

Practically no equalization is necessary with the acoustic enclosure according to the invention, which allows a frequency response made flat by acoustic transmission line technology, self-compensation for loudspeaker defects, and lower sensitivity to the reverberations of the room.

The acoustic resistance of the acoustic transmission device being much higher than the acoustic resistance of a room (having a large volume compared to that of the acoustic transmission device and therefore no constraint on variations in air pressure), this makes the frequency response of the acoustic enclosure of the present invention almost independent of its location as well as the size and furnishings of the room in which it is installed. On the contrary, classic loudspeakers generally have low acoustic resistance and not constant frequency, which makes them very dependent on the configuration of the rooms.

The acoustic enclosure according to the invention has significant power efficiency (acoustic power / electrical power) for all frequencies: use of both the front and rear acoustic power of the speaker (the rear acoustic power being restored through the vent with the same frequency response as the front acoustic power by simply adding a fixed phase shift (same as reverberation from a wall)), high dynamic range, ability to obtain a full range in a small volume (e.g. , 20Hz – 20kHz with a 2 liter enclosure for 20 Watts RMS in equivalent acoustic power), the minimum response frequency does not depend on the resonant frequency of the loudspeaker (for example, 20Hz can be reached with a loudspeaker having a resonant frequency of 80Hz or even 120Hz), there is no need for a separate subwoofer.

The overall cost of the solution is reduced: a low-end loudspeaker is sufficient to obtain a high-level acoustic result (the solution can be used for professional acoustic solutions), compatibility with class D amplifiers even at low frequencies ( low return in reactive power), fully scalable in power by association of several acoustic speakers without impact on the frequency response or on the phase shift.

According to a particular characteristic of the invention, the characteristic length Lo _LT (in meters) of the acoustic transmission device is defined according to the following equation:

,

where c is the speed of sound in air (in m/s), and F _C is the desired low cutoff frequency of the acoustic transmission device (in Hz).

Thus, the choice of the low cutoff frequency of the acoustic transmission device makes it possible to define the characteristic length of the latter.

According to a particular characteristic of the invention, the surface Su _LT (in m²) of the characteristic cross section of the acoustic transmission device is defined according to the following equation:

,

where P0 is the atmospheric pressure (in Pa), Pr _HP is the maximum pressure (in Pa) exerted on the air by the membrane of the associated loudspeaker, Vo _HP is the maximum volume of air (in m ³ ) displaced by the membrane of the associated loudspeaker, and Lo _LT is the characteristic length (in m) of the acoustic transmission device.

Thus, once the characteristic length Lo _LT of the acoustic transmission device is defined, knowledge of the values Pr _HP and Vo _HP associated with the loudspeaker makes it possible to define the value Su _LT of the acoustic transmission device making it possible to obtain a resistance acoustics of the acoustic transmission device identical to that of the loudspeaker.

According to a particular characteristic of the invention, the characteristic cross section of the acoustic transmission device is one of circular, oval, rectangular, and polygonal.

It should be noted that any other shape is possible for the characteristic cross section of the acoustic transmission device, the essential being that the value of the surface of the characteristic cross section is constant over the entire length Lo _LT .

The shape of the cross section of the acoustic transmission device may, for example, be circular, so that the acoustic transmission device constitutes a tubular conduit. The shape of the cross section can also be rectangular to optimize the size of the acoustic enclosure.

According to a particular characteristic of the invention, the acoustic enclosure comprises a plurality of identical and adjacent speakers, a common opening for the plurality of speakers, a common vent for the plurality of speakers and a transmission device common acoustic for the plurality of speakers, said common acoustic transmission device having a length corresponding to the characteristic length and a cross section corresponding to the characteristic cross section multiplied by the number of speakers.

Thus, the plurality of loudspeakers mounted adjacent in the same box are associated with the same acoustic transmission device, this increases the surface area of displaced air and therefore the volume of air displaced, which has the effect of consequence of increasing the surface of the cross section of the common acoustic transmission device and therefore the volume of the acoustic enclosure. Thus, for example, a speaker with two speakers is equivalent in terms of volume and admissible power to two speakers each coupled with a single speaker.

According to a particular characteristic of the invention, each acoustic transmission device comprises one of an acoustic transmission line arranged between its input end and its output end, and several parallel acoustic transmission lines arranged between its end of inlet and its outlet end.

Thus, the acoustic transmission device comprises either a single acoustic transmission line having the characteristic cross section, or several parallel acoustic transmission lines whose sum of the cross sections is equal to the characteristic cross section.

Each acoustic transmission line may include one or more bends (to be, for example, serpentine-shaped) so as to reduce the volume of the acoustic enclosure box. However, for the sake of design simplicity, it is preferable to have as few elbows as possible.

According to a particular characteristic of the invention, the acoustic enclosure further comprises, for each acoustic transmission device, an anti-resonance device configured to attenuate the resonances of the structural elements of the acoustic enclosure.

Thus, the anti-resonance device makes it possible to attenuate the resonances of the structural elements of the acoustic enclosure due to the shape of the acoustic transmission device.

According to a particular characteristic of the invention, the acoustic enclosure comprises a single acoustic transmission device, the acoustic enclosure further comprising internal separation walls arranged in a parallel manner inside the box to form a path between the rear of the at least one loudspeaker and the vent, constituting a serpentine-shaped acoustic transmission line between the input end and the output end of the acoustic transmission device.

Thus, the staggered arrangement of the internal parallel separation walls in the box makes it possible to create a path serving as an acoustic transmission line between the rear of the speaker and the port.

According to a particular characteristic of the invention, the acoustic transmission device comprises a single acoustic transmission line consisting of a sealed conduit having the characteristic length and the characteristic cross section, the acoustic enclosure further comprising, as an anti-resonance device , a plurality of anti-resonance axes arranged inside the box, each anti-resonance axis passing through all of the parallel internal separation walls.

Thus, the anti-resonance axes make it possible to greatly reduce the internal resonances of the acoustic enclosure. However, they do not allow them to be completely canceled when used at high power.

According to a particular characteristic of the invention, each acoustic transmission device comprises a plurality of superimposed acoustic transmission lines, each acoustic transmission line consisting of a sealed conduit having the characteristic length, the sum of the cross sections of the plurality of conduits corresponding to the characteristic cross section of the acoustic transmission device.

Thus, for reasons of canceling any internal resonance of the acoustic enclosure, the characteristic cross section can be divided into several distinct cross sections. This configuration ensures the absence of internal resonances which can seriously harm the quality of sound reproduction. Unlike anti-resonance axes, the solution by multiplication of sections ensures total cancellation of internal resonances. It is therefore a preferred solution, especially when the loudspeaker is subjected to high acoustic power.

The present invention also relates to a loudspeaker assembly comprising a plurality of loudspeakers as described above, the speakers of the plurality of loudspeakers being electrically connected together in at least one manner among series and in parallel.

Thus, the combination of several acoustic speakers according to the invention makes it possible to increase the acoustic power, while maintaining maximum bandwidth.

The plurality of loudspeakers will affect neither the total frequency response nor the phase of the acoustic signal but will multiply the total admissible power accordingly.

According to a particular characteristic of the invention, the plurality of acoustic speakers are distributed into a plurality of groups of acoustic speakers, each group of acoustic speakers comprising an even number of acoustic speakers connected electrically in parallel, the groups of acoustic speakers being electrically connected in series, so that the electrical impedance of the acoustic speaker assembly is compatible with an audio amplifier.

The most commonly used electrical impedance in audio amplifiers is 8 Ohms. Thus, in the case where the acoustic speaker assembly is connected to an audio amplifier having an electrical impedance of 8 Ohms, the acoustic speakers will be connected together so as to also have an electrical impedance of 8 Ohms.

To better illustrate the object of the present invention, preferred embodiments will be described below, by way of illustration and not limitation, with reference to the appended drawings.

In these drawings:

is a schematic sectional view of an acoustic enclosure according to a first embodiment of the present invention;

is a schematic sectional view of an acoustic enclosure according to a second embodiment of the present invention;

is a schematic sectional view of an acoustic enclosure according to a third embodiment of the present invention;

represents the curve of evolution of the acoustic impedance of an acoustic transmission line as a function of frequency;

is a schematic diagram in the field of acoustics of an acoustic enclosure according to the present invention;

represents the curve of evolution of the acoustic power of an acoustic transmission line as a function of its acoustic resistance;

is a horizontal sectional view of an acoustic enclosure as an example according to the first embodiment of the invention;

is a perspective view of an acoustic enclosure assembly according to one embodiment of the invention;

is a perspective view of an acoustic enclosure assembly according to another embodiment of the invention;

is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

is a schematic diagram of an acoustic enclosure assembly according to a particular embodiment of the invention;

is a block diagram of an acoustic enclosure assembly according to another particular embodiment of the invention;

is a block diagram of an acoustic enclosure assembly according to yet another particular embodiment of the invention;

is a diagram representing a loudspeaker with its acoustic transmission line;

is a diagram representing an acoustic transmission line;

is a vertical sectional view of an acoustic enclosure according to a first variant of the first embodiment of the invention; And

is a vertical sectional view of an acoustic enclosure according to a second variant of the first embodiment of the invention.

If we refer to the , we can see that there is shown an acoustic enclosure 1 according to a first embodiment of the present invention.

The acoustic enclosure 1 comprises a box 2 in which a loudspeaker 3 is mounted.

Box 2 includes an opening 2a closed by the front part of speaker 3 and a vent 4 opening to the outside.

The acoustic enclosure 1 further comprises, inside the box 2, an acoustic transmission device 5 in the form of an acoustic transmission line extending between an input end 5a, formed in a chamber 6 in which the speaker 3 is arranged and configured to receive the sound waves emitted from the rear of the speaker 3, and an output end 5b opening into the vent 4.

Since the opening 2a and the vent 4 are formed on the same side of the box 2, the acoustic transmission device 5 is bent. However, the acoustic transmission device 5 could also be rectilinear in the case where the opening 2a and the vent 4 are formed on two opposite sides of the box 2, without departing from the scope of the present invention.

The acoustic transmission device 5 is configured to propagate the sound waves emitted from the rear of the speaker 3 towards the vent 4.

The acoustic transmission device 5 has a characteristic length and a constant characteristic cross section, said characteristic length and said characteristic cross section being dimensioned such that the acoustic resistance of the acoustic transmission device 5 is identical to the acoustic resistance of the loudspeaker 3.

Thus, sizing the acoustic transmission device so that its acoustic resistance is equal to that of its loudspeaker makes it possible to obtain maximum acoustic power and efficiency with a flat spectral response of the acoustic enclosure on the entire frequency range 20Hz – 20kHz. The cross section of the acoustic transmission device 5 must remain constant along its length in order to guarantee constant acoustic resistance of the acoustic transmission device 5, regardless of the frequency above the frequency low cutoff of the acoustic transmission device 5. Below the latter, the acoustic resistance of the acoustic transmission device 5 collapses.

The acoustic transmission device 5 allows optimal control of the movement of the membrane of the speaker 3, allowing a reduction in the physical constraints on it, and therefore makes it possible to guarantee greater longevity of the speaker 3 as well as a increase in its admissible power.

The acoustic transmission device 5 allows an increase in the total efficiency of the acoustic enclosure 1 and therefore a reduction in the return to the audio amplifier of reactive power which is harmful to digital amplifiers (Class D), particularly at low frequencies.

The acoustic enclosure 1 according to the invention is independent of the resonant frequency of the speaker 3. Even if the speaker 3 has a resonant frequency of 80 Hz or even 120 Hz, this will not prevent the enclosure acoustic 1 to reach lower frequencies like 20 Hz or even less, the low frequency being solely dependent on the length of the acoustic transmission device 5.

Since the acoustic transmission line has no limit at high frequencies, the highest frequency of loudspeaker 1 will be limited by the maximum frequency that loudspeaker 3 can provide.

The overall cost of the solution is thus reduced, given that a low-end speaker 3 is sufficient to obtain a high-level acoustic result.

The characteristic cross section of the acoustic transmission device 5 may, for example, have a circular, oval, rectangular or polygonal shape. It should be noted that any other shape is possible, the main thing being that the value of the surface of the characteristic cross-section is constant over its entire length.

For example, the shape of the cross section of the acoustic transmission device 5 can be circular, so that the acoustic transmission device 5 constitutes a tubular conduit. The shape of the cross section can also be rectangular to optimize the size of the acoustic enclosure 1.

The characteristic length Lo _LT (in meters) of the acoustic transmission device 5 is defined according to the following equation:

,

where c is the speed of sound in air (in m/s), and F _C is the desired low cutoff frequency of the acoustic transmission device 5 (in Hz).

In addition, the surface Su _LT (in m²) of the characteristic cross section of the acoustic transmission device 5 is defined according to the following equation:

,

where P0 is the atmospheric pressure (in Pa), Pr _HP is the maximum pressure (in Pa) exerted on the air by the membrane of speaker 3, Vo _HP is the maximum volume of air (in m ³ ) displaced by the membrane of the loudspeaker 3, and Lo _LT is the characteristic length (in m) of the acoustic transmission device 5.

If we refer to the , we can see that there is shown an acoustic enclosure 7 according to a second embodiment of the present invention.

The common elements between the first embodiment of the invention on the and this second embodiment of the invention bear the same reference number, and will not be described in more detail here when they are of identical structures.

The acoustic enclosure 7 according to the second embodiment is identical to the acoustic enclosure 1 according to the first embodiment, with the exception of the fact that it further comprises:

- a second speaker 8 placed in a second chamber 9 of the box 2 and the front part of which closes a second opening 2b formed in the box 2;

- a second vent 10 opening to the outside; And

- a second acoustic transmission device 11 in the form of an acoustic transmission line extending between an input end 11a, formed in the second chamber 9 and configured to receive the sound waves emitted from the rear of the second top -speaker 8, and an output end 11b opening into the second vent 10.

The second acoustic transmission device 11 is configured to propagate the sound waves emitted from the rear of the second speaker 8 towards the second vent 10. The second acoustic transmission device 11 has a characteristic length and a constant characteristic cross section, said characteristic length and said characteristic cross section being dimensioned such that the acoustic resistance of the second acoustic transmission device 11 is identical to the acoustic resistance of the second loudspeaker 8.

It should be noted that the acoustic enclosure 7 could also include any number of speakers, each associated with a separate vent and a separate acoustic transmission device, without departing from the scope of the present invention.

If we refer to the , we can see that there is shown an acoustic enclosure 12 according to a third embodiment of the present invention.

The common elements between the second embodiment of the invention on the and this third embodiment of the invention bear the same reference number, and will not be described in more detail here when they are of identical structures.

The acoustic enclosure 12 according to the third embodiment is identical to the acoustic enclosure 7 according to the second embodiment, with the exception of the fact that:

- the two speakers 3 and 8 are identical, adjacent and arranged in a common chamber 6 of the box 2;

- the acoustic enclosure 12 has a common opening 2a for the two speakers 3 and 8;

- the acoustic enclosure 12 has a common vent 13 for the two speakers 3 and 8; And

- the acoustic enclosure 12 has a common acoustic transmission device 14 for the two speakers 3 and 8, in the form of an acoustic transmission line extending between an input end 14a, formed in the common chamber 6 and configured to receive the sound waves emitted from the rear of the two speakers 3 and 8, and an output end 14b opening into the common vent 13.

The common acoustic transmission device 14 has a length corresponding to the characteristic length (that is to say, the length of the acoustic transmission device 5 according to the first embodiment) and a cross section corresponding to the characteristic cross section multiplied by the number of speakers (that is to say, to the cross section of the acoustic transmission device 5 according to the first embodiment multiplied by two).

It should be noted that the acoustic enclosure 12 could also include any number of adjacent speakers, with a common vent 13 and a common acoustic transmission device 14, without departing from the scope of the present invention.

As indicated above, for each of the acoustic transmission devices 5, 11 and 14 of the three acoustic enclosures 1, 7 and 12, the parameters to be taken into account to obtain a flat spectral response are its length and its cross section (or its diameter in the case of a tubular conduit type transmission line).

As the cross section of the acoustic transmission line impacts the spectral response, it must be constant over the entire length of the acoustic transmission line to achieve a flat response.

The greater the cross section of the acoustic transmission line, the more air movement will occur. On the other hand, the higher the cross section of the acoustic transmission line, the less the air will be compressed and the less it will correct the defects of the loudspeaker. This is the reason why the section of the acoustic transmission line must be chosen optimally to maximize the acoustic power. This is due to the volume of air movement which must be transformed into compression by the acoustic transmission line to transmit the acoustic power acting as acoustic resistance.

The length of the acoustic transmission line defines the minimum admissible frequency, i.e. the low cutoff frequency of the acoustic transmission device.

The low cutoff frequency of the acoustic transmission device is defined according to the equation:

,

where F _c is the low cutoff frequency of the acoustic transmission line (in Hz), c is the speed of sound in air (approximately equal to 300 m/s), Lo _LT is the characteristic length of the line acoustic transmission (in meters), and the coefficient 4 is due to the fact that a quarter of the signal period needs to be taken into account.

For example, for an acoustic transmission line of four meters, the minimum admissible frequency will be:

.

There represents the curve of evolution of the acoustic impedance of an acoustic transmission line as a function of frequency (logarithmic scale).

We see that below F _c , the frequencies are acoustically short-circuited (the acoustic impedance will tend towards zero) and that the efficiency collapses very violently.

On the contrary, above F _c , the acoustic impedance is constant and equal to the acoustic resistance Rac of the acoustic transmission line.

The sound power Pac is defined by the air pressure multiplied by the air flow:

.

The air compression capacity of the acoustic transmission line is inversely proportional to the section of the acoustic transmission line. The air displacement capacity of the acoustic transmission line is proportional to the section of the acoustic transmission line. Thus, the optimal section of the acoustic transmission line must be defined to obtain maximum transmission of acoustic power.

The speaker's ability to move air depends linearly on the speaker cone diameter and the speaker cone travel, defined by the voltage (V _coil ) applied to the speaker coil. The speaker's ability to compress air depends linearly on the force applied to the cone, defined by the current (I _coil ) applied to the speaker coil.

It should be noted that the K _HP parameter can be compared to the KV parameter (turns per volt ratio) for a brushless motor (magnetic motor) which allows efficiency up to 98%. For a loudspeaker, the K _HP parameter depends on its physical characteristics (diameter of the cone, elasticity of the damper, weight of the moving part, etc.). By analogy, an acoustic enclosure according to the present invention makes it possible to optimally reproduce the acoustic power using a magnetic loudspeaker.

Furthermore, it should be noted that the acoustic transmission line makes it possible to transmit the acoustic power from the rear of the loudspeaker to the port without changing the spectrum but only with a fixed phase shift:

In this way, the acoustic power at the port makes it possible to double the acoustic power at the front of the speaker, which ensures very high power efficiency.

Based on this definition, the acoustic impedance of the acoustic transmission line in the admissible frequency range can be introduced.

Using the analogy of loudspeaker electrical equations:

,

,

and by the definition of acoustic power, the acoustic impedance of an acoustic transmission line in the admissible frequency domain can be defined by:

It should be noted that, for a large section of the acoustic transmission line, the air pressure will tend towards zero, Rac _LT will then be close to zero. On the contrary, for a zero section of the acoustic transmission line (closed enclosure), the air movement will be zero and Rac _LT will tend towards infinity.

For the acoustic impedance of a loudspeaker, we obtain the following equations:

The acoustic enclosure according to the present invention can thus be modeled in the field of acoustics by the equivalent in the field of electricity. There represents a voltage divider bridge in the field of acoustics, which includes a loudspeaker acoustic model 15 and an acoustic transmission line acoustic model 16.

The use of the equivalent of the voltage divider bridge in the acoustic field makes it possible to obtain:

,

where Ap _LT is the air pressure of the acoustic transmission line, Ap _HP is the air pressure of the loudspeaker, Rac _HP is the acoustic resistance of the loudspeaker, and Rac _LT is the acoustic resistance of the line acoustic transmission.

And the equivalent of Ohm's law in the acoustic domain gives:

,

where Ad is the air flow.

Using the definition of sound power for an acoustic transmission line:

By combining the last three equations, we obtain:

By taking the derivative of this equation using Rac _LT as a variable, we see that the maximum power is found at:

Maximum power is thus obtained when the acoustic resistance of the acoustic transmission line and the acoustic resistance of the loudspeaker are identical.

There represents the acoustic power curve of the acoustic transmission line Pac _LT as a function of Rac _LT .

Given that Rac _LT evolves inversely proportional to the section of the acoustic transmission line, there is a direct link between the maximum power of the loudspeaker and the size of the acoustic transmission line and therefore the size of the enclosure acoustic. Consequently, at a given loudspeaker power, the maximum power restitution of a transmission line loudspeaker depends linearly only on its volume.

The dimensioning of the section of the acoustic transmission line will now be described below.

The definition of loudspeaker acoustic power is as follows:

(N/m² * m ³ /s).

where Pac _HP is the acoustic power of the loudspeaker, Pr _HP is the maximum pressure produced by the loudspeaker membrane, and De _HP is the maximum air flow produced by the loudspeaker membrane.

The force exerted on the speaker membrane is defined as follows:

where Fo _HP is the force exerted by the loudspeaker coil on the membrane, B _HP is the magnetic field in the air gap of the permanent magnet of the loudspeaker, L _{coil HP} is the length of the coil wire of the loudspeaker speaker, and I _HP is the electric current passing through the coil.

Since it is often difficult to obtain the value of the magnetic field in the air gap as well as the length of the coil wire, a simple method for determining the force exerted by the coil is described below.

You must first lay the speaker alone (not mounted in an enclosure) flat, with the membrane facing up.

It is then necessary to add a weight to move the membrane at the maximum displacement of the speaker within the manufacturer's linearity limit. This displacement will be reused in the calculation below, and will be noted Cu _HP .

The force Fo _HP will therefore be the weight (in kg) added to the membrane multiplied by 9.81 N/kg.

The pressure exerted by the speaker membrane on the air is defined as follows:

,

where Pr _HP is the maximum pressure exerted on the air by the speaker diaphragm, Fo _HP is the force exerted by the speaker coil on the diaphragm, and Su _HP is the surface area of the speaker diaphragm .

The surface of the loudspeaker diaphragm is defined as follows:

,

where Su _HP is the surface area of the membrane, and D _HP is the diameter of the membrane.

The volume of air displaced by the speaker is defined as follows:

,

where Vo _HP is the maximum volume of air displaced by the speaker diaphragm, Su _HP is the surface area of the speaker diaphragm, and Cu _HP is the maximum stroke of the diaphragm.

There represents these different parameters.

Given that the acoustic resistance of the loudspeaker is:

,

and that the acoustic resistance of the acoustic transmission line is:

,

as the two acoustic resistances must be identical ( ), we obtain :

.

And, knowing that the power is conserved in the system:

The last two equations imply that:

To define the relationships between pressures and volumes of air, the following thermodynamic equation is used:

,

where P is the pressure (in Pa), V is the volume (in m ³ ), n is the quantity of matter (in mol), R is the universal constant of ideal gases (≈8.314 JK ^-1 .mol ^-1 ) , and T is the absolute temperature (in K).

Given that in the present case, the quantity of material as well as the temperature remain constant, they will be replaced by the constant K:

Knowing that the volume of air to be taken into account in the system is the volume of the acoustic transmission line because above the minimum frequency defined by the length of the acoustic transmission line, the conduit of the acoustic transmission line can be considered closed, given that below this frequency the air pressure will no longer have any effect on the system. This also explains the collapse of acoustic resistance below this frequency.

where K is a constant, Vo _LT is the volume of the acoustic transmission line, and P0 is the atmospheric pressure (subsequently assumed to be 101000 Pa).

In the initial equation of thermodynamics, K can be replaced by its value:

Thus, in the general case, the relationship between the volume V and the pressure P is:

The variables P and V are defined as follows:

,

where P is the system pressure, P0 is the atmospheric pressure, and Pr _LT is the pressure exerted in the acoustic transmission line.

,

where V is the system volume, Vo _LT is the volume of the acoustic transmission line, and dV is the volume change in the acoustic transmission line.

There represents these different parameters.

Thus, by combining the last three equations, we obtain:

SO :

Therefore, factoring Vo _LT and putting everything on the same denominator, we obtain:

Knowing that the pressures of the loudspeaker and the acoustic transmission line must be the same, we obtain:

Knowing that the variation in volume is the volume of air displaced by the speaker membrane:

,

and that the volume of the acoustic transmission line is:

,

where Vo _LT is the volume of the acoustic transmission line, Su _LT is the cross-sectional area of the acoustic transmission line, and Lo _LT is the length of the acoustic transmission line,

we therefore obtain:

,

or the surface of the section of the acoustic transmission line:

.

Knowing that the pressure exerted by the loudspeaker is negligible compared to the atmospheric pressure P0, we finally obtain:

If we refer to the , we can see that there is shown an implementation by way of example of the acoustic enclosure 1 according to the first embodiment.

The acoustic enclosure 1 shown on the has dimensions of 60 x 220 x 150mm with an acoustic transmission device 5 of four meters making it possible to obtain a bandwidth of 20Hz-20kHz.

It should be noted that the use of an acoustic transmission device having a length greater than four meters makes it possible to reach frequencies lower than 20Hz. For example, a length of eight meters allows you to go down to 10Hz, which can be useful for certain acoustic installations. Thus, the acoustic transmission device of the present invention keeps all its qualities and characteristics below 20Hz with an appropriate length, when this is useful for, for example, physically feeling very low frequencies even if the latter remain inaudible to the human ear.

The acoustic transmission device 5 is bent several times between its input end 5a and its output end 5b so as to reduce the size of the box 2 and therefore of the acoustic enclosure 1.

In particular, the acoustic enclosure 1 comprises internal vertical separation walls 17 arranged in a parallel and staggered manner inside the box 2 to form a path between the rear of the speaker 3 and the vent 4, constituting a serpentine-shaped acoustic transmission line between the input end 5a and the output end 5b of the acoustic transmission device 5.

The acoustic enclosure 1 further comprises, as an anti-resonance device, a plurality of anti-resonance axes 18 arranged horizontally inside the box 2, each anti-resonance axis 18 passing through all of the vertical internal separation walls 17 .

The anti-resonance axes 18 thus make it possible to greatly reduce the resonances of the structural elements of the acoustic enclosure 1. However, they do not make it possible to completely cancel them in the event of use at high power.

The acoustic enclosure 1 further has a lateral conduit 19 allowing the passage of a connecting wire through it, so as to electrically connect the loudspeaker 3 to a connector 20 disposed at the rear of the enclosure acoustic 1.

As there should be no air leaks with the exception of vent 4, it is preferable to use silicone at the end (speaker side 3) of conduit 19 provided for the passage of the electrical wire of speaker 3. For the same reason, it is preferable to use a seal between opening 2a of box 2 and the front face of speaker 3.

The volume of the box 2 of the acoustic enclosure 1 is thus composed of the volume of the acoustic transmission device 5 and the volume of the structural material required (namely, the internal partition walls 17) to construct the acoustic transmission device 5 rigidly and stablely.

Advantageously, the structural volume could range from 1/2 to 1 time the volume of the acoustic transmission device 5, depending on the material used for the acoustic enclosure 1.

Like: Structural volume = (½ to 1) * Vo _LT

We therefore obtain:

Speaker volume = Vo _LT + (½ to 1) * Vo _LT = (3/2 to 2) * Vo _LT

If we refer to Figures 8 to 13, we can see that different speaker assemblies 21, 22, 23, 24, 25 and 26 are shown according to particular embodiments of the present invention.

Each acoustic enclosure assembly 21, 22, 23, 24, 25 and 26 comprises a plurality of acoustic enclosures 1 as described above, the speakers 3 of the plurality of acoustic enclosures 1 being electrically connected together in at least one way among series and parallel.

Thus, the combination of several acoustic enclosures 1 makes it possible to increase the acoustic power of the acoustic enclosure assembly 21, 22, 23, 24, 25 and 26, while maintaining maximum bandwidth.

The plurality of acoustic speakers 1 will affect neither the total frequency response nor the phase of the acoustic signal but will multiply the total admissible power accordingly.

Given that the size of a speaker 3 defines its maximum power, the relationship between the power and the size of an acoustic enclosure 1 according to the invention is constant and evaluated for a speaker 3 of 10 Watts RMS at approximately 10 Watts RMS/dm ³ or 10 Watts RMS/liter. This value can be reduced by increasing the acoustic impedance of the acoustic transmission device 5 and therefore by increasing the acoustic impedance of the speaker 3.

For a given speaker 3, given that the power of an acoustic enclosure 1 according to the invention depends linearly only on its size, the stacking of several acoustic enclosures 1 will linearly multiply the overall power of the system.

There represents an acoustic speaker assembly 21 in a sound bar using two 20W acoustic speakers 1 (60 x 300 x 110mm) making it possible to obtain an overall power of 40W.

Figures 9 to 11 represent acoustic enclosure assemblies 22, 23 and 24 of shelves using acoustic enclosures 1 of 20W (60 x 150 x 220mm).

The acoustic enclosure assembly 22 of the comprises two acoustic speakers 1 spaced from one another (namely, one acoustic speaker 1 of 20W per channel), to obtain two small ambient (or “surround”) speakers.

The acoustic speaker assembly 23 of the includes two 20W acoustic speakers 1 joined together, to obtain a 40W central speaker (with a total size of 60 x 300x 220mm).

The acoustic speaker assembly 24 of the includes two groups of four 20W acoustic speakers 1 superimposed (i.e. one group per channel), to obtain main speakers of 80W per channel (with a total size of 240 x 150 x 220mm or 120 x 300 x 220mm).

Figures 12 and 13 represent high-power speaker assemblies 25 and 26 using 20W (60 x 75 x 440mm) speakers 1.

In the , 4*8 = 32 acoustic speakers 1 of 20W are used to obtain an overall acoustic power of 640W (with a total size of 480 x 300 x 440mm or 240 x 600 x 440mm).

In the , 16*8 = 128 20W acoustic speakers 1 are used to obtain an overall acoustic power of 2560W (with a total size of 960 x 600 x 440mm).

It should be noted that all speaker assemblies 21, 22, 23, 24, 25 and 26 will have the same bandwidth (for example, 20Hz to 20kHz).

The combination of several identical loudspeakers also allows, if each of them is individually controlled very precisely by digital processing, a very precise spatialization of the sound. This method is very commonly used to simulate rear speakers from a single soundbar at the front, including a large number of speakers (around ten to several dozen) each controlled individually using the effect laser of light wave propagation, but applied here to sound waves. In the specific case of the present invention, this method is particularly interesting because the greater the number of speakers, the more the spatialization precision will be increased.

If we refer to Figures 14 to 16, we can see that there are shown different examples of connections of acoustic enclosures 1 in acoustic enclosure assemblies 27, 28 and 29.

The plurality of loudspeakers 1 are distributed into a plurality of groups of loudspeakers 30, each group of loudspeakers 30 comprising an even number of loudspeakers 1 electrically connected in parallel, the groups of loudspeakers 30 being connected electrically in series, so that the electrical impedance of the acoustic enclosure assembly 27, 28 or 29 is compatible with an audio amplifier (not shown in the Figures).

The most commonly used electrical impedance in audio amplifiers is 8 Ohms. Thus, in the case where the acoustic enclosure assembly 27, 28 or 29 is connected to an audio amplifier having an electrical impedance of 8 Ohms, the acoustic enclosures 1 will be connected together so that the acoustic enclosure assembly 27, 28 or 29 also has an electrical impedance of 8 Ohms.

The interconnection of several loudspeakers 1 has no impact on the overall spectrum and the phase shift to the extent that all the loudspeakers 1 remain identical and powered by the same electrical signal.

For example, ten 10 Watts RMS acoustic speakers 1 with a volume of 10 liters will restore 100 Watts RMS of acoustic power at all frequency ranges.

There represents the connections of an acoustic enclosure assembly 27 by way of example comprising two groups 30 of two acoustic enclosures 1 (each with a speaker 3 of 8 Ohms).

There represents the connections of an acoustic enclosure assembly 28 by way of example comprising four groups 30 of four acoustic enclosures 1 (each with an 8 Ohm speaker 3).

There represents the connections of an acoustic enclosure assembly 29 as an example comprising eight groups 30 of four acoustic enclosures 1 (each with a 4 Ohm speaker 3).

Thus, each of the acoustic speaker assemblies 26, 27 and 28 of Figures 14 to 16 has an electrical impedance of 8 Ohms.

If we refer to the , we can see that there is shown a partial vertical sectional view of the acoustic enclosure 1 shown in .

It can be seen that the cross section of the acoustic transmission device 5 formed by the internal vertical separation walls 17 has a rectangular shape.

Since the structure of the acoustic transmission device 5 is created from rectangular surfaces (internal partition walls 17 constituting the conduit of the acoustic transmission device 5), certain reinforcements must be integrated into the design to avoid unexpected internal resonances.

An acoustic transmission device 5 for a complete frequency range can be made up of 10 to 20 internal separation walls 17 which are almost all the same size and therefore all have the same internal resonance frequency. This can cause the speaker 1 to vibrate and therefore strongly affect the frequency response.

To avoid this, a first solution is to add anti-resonance axes 18 passing through each internal separation wall 17, over the entire width of the acoustic enclosure 1. The diameter of the anti-resonance axes 18 must remain small so as not to have an impact on the section of the conduit of the acoustic transmission device 5.

If we refer to the , we can see that there is shown a partial vertical sectional view of the acoustic enclosure 1 according to a variant of the invention.

In this variant of the invention, the anti-resonance axes are removed and replaced by a multiplication of conduits placed in parallel. For example, instead of having a single four-meter conduit, three horizontal separations can be created which will form four superimposed four-meter conduits with a section four times smaller than the initial conduit. Given that the impedance of a duct is linked to its section, the sum of the four sections of the four ducts will give the same total section and therefore the same acoustic impedance. The thickness of the horizontal separations must remain low so as not to have too much impact on the sum of the sections.

This variant thus makes it possible to guarantee the absence of internal resonances which can seriously harm the quality of sound reproduction. Unlike the anti-resonance axes 18, the solution by multiplication of sections ensures total cancellation of internal resonances. This is therefore a preferred solution, especially when loudspeaker 1 is subjected to high acoustic power.

This variant thus has two advantages:

- it reduces the possibilities of internal resonance even more than the anti-resonance axes 18, and

- it allows the construction of the acoustic enclosure 1 per layer (construction by molding then assembly).

In the , the acoustic enclosure 1 has four identical and stacked stages 31, and an upper closing cover 32, which makes it possible to create four superimposed conduits 33 having the same length and the same cross section, the total section 34 of the four cross sections of the four conduits 33 being equal to the cross section of the conduit of the , so that the cross section of each conduit 33 is equal to a quarter of the cross section of the conduit of the .

In practice, the four stages 31 and the upper closing cover 32 are injection molded or manufactured by 3D printing, then the four stages 31 are superimposed and fixed together (for example, by gluing or screwing), then the upper cover of closure 32 is fixed on the last floor 31 (for example, by gluing or screwing), the different elements being assembled to present an airtight seal, in particular by means of joints and/or directly by means of the glue. Advantageously, we will use a polyurethane-based glue.

It is of course understood that the particular embodiments which have just been described have been given for informational and non-limiting purposes, and that modifications can be made without departing from the present invention.

Claims (12)

Acoustic enclosure (1; 7; 12) comprising a box (2) in which at least one loudspeaker (3, 8) is mounted, said box (2) comprising, for each loudspeaker (3, 8), a opening (2a, 2b) closed by the front part of the associated loudspeaker (3, 8) and a vent (4, 10; 13) opening onto the outside, the acoustic enclosure (1; 7; 12) comprising in furthermore, inside the box (2) and for each loudspeaker (3, 8), an acoustic transmission device (5, 11; 14) extending between an input end (5a, 11a; 14a) configured to receive the sound waves emitted from the rear of the associated loudspeaker (3, 8) and an output end (5b, 11b; 14b) opening into the associated vent (4, 10; 13), said acoustic transmission device (5, 11; 14) being configured to propagate the sound waves emitted from the rear of the associated loudspeaker (3, 8) towards the associated vent (4, 10; 13), characterized by the fact that each acoustic transmission device (5, 11; 14) has a characteristic length and a constant characteristic cross section, said characteristic length and said characteristic cross section being dimensioned such that the acoustic resistance of the acoustic transmission device (5, 11; 14) is identical to the acoustic resistance of the top -associated speaker (3, 8). Acoustic enclosure (1; 7; 12) according to claim 1, characterized in that the characteristic length Lo _LT of the acoustic transmission device (5, 11; 14) is defined according to the following equation: ,
where c is the speed of sound in air, and F _C is the desired low cutoff frequency of the acoustic transmission device (5, 11; 14). Acoustic enclosure (1; 7; 12) according to claim 2, characterized in that the surface Su _LT of the characteristic cross section of the acoustic transmission device (5, 11; 14) is defined according to the following equation: ,
where P0 is the atmospheric pressure, Pr _HP is the maximum pressure exerted on the air by the membrane of the associated loudspeaker (3, 8), Vo _HP is the maximum volume of air displaced by the membrane of the loudspeaker ( 3, 8) associated, and Lo _LT is the characteristic length of the acoustic transmission device (5, 11; 14). Acoustic enclosure (1; 7; 12) according to one of claims 1 to 3, characterized in that the characteristic cross section of the acoustic transmission device (5, 11; 14) is one of circular, oval, rectangular , and polygonal. Acoustic enclosure (12) according to one of claims 1 to 4, characterized in that it comprises a plurality of identical and adjacent loudspeakers (3, 8), a common opening (2a) for the plurality of loudspeakers speakers (3, 8), a common port (13) for the plurality of speakers (3, 8) and a common acoustic transmission device (14) for the plurality of speakers (3, 8), said device common acoustic transmission (14) having a length corresponding to the characteristic length and a cross section corresponding to the characteristic cross section multiplied by the number of loudspeakers (3, 8). Acoustic enclosure (1; 7; 12) according to one of claims 1 to 5, characterized in that each acoustic transmission device (5, 11; 14) comprises one of an acoustic transmission line arranged between its end input end (5a, 11a; 14a) and its output end (5b, 11b; 14b), and several parallel acoustic transmission lines arranged between its input end (5a, 11a; 14a) and its output end ( 5b, 11b; Acoustic enclosure (1; 7; 12) according to one of claims 1 to 6, characterized in that the acoustic enclosure (1; 7; 12) further comprises, for each acoustic transmission device (5, 11; 14), an anti-resonance device configured to attenuate the resonances of the structural elements of the acoustic enclosure (1; 7; 12). Acoustic enclosure (1) according to one of claims 6 and 7, characterized in that it comprises a single acoustic transmission device (5), the acoustic enclosure (1) further comprising internal separation walls (17 ) arranged in parallel inside the box (2) to form a path between the rear of the at least one speaker (3) and the vent (4), constituting an acoustic transmission line in serpentine shape between the input end (5a) and the output end (5b) of the acoustic transmission device (5). Acoustic enclosure (1) according to claim 8 in dependence on claim 7, characterized in that the acoustic transmission device (5) comprises a single acoustic transmission line consisting of a sealed conduit having the characteristic length and the cross section characteristic, the acoustic enclosure (1) further comprising, as an anti-resonance device, a plurality of anti-resonance axes (18) arranged inside the box (2), each anti-resonance axis (18) passing through the assembly parallel internal separation walls (17). Acoustic enclosure (1; 7; 12) according to one of claims 1 to 6, characterized in that each acoustic transmission device (5, 11; 14) comprises a plurality of superimposed acoustic transmission lines, each transmission line acoustic being constituted by a sealed conduit (33) having the characteristic length, the sum of the cross sections of the plurality of conduits (33) corresponding to the characteristic cross section of the acoustic transmission device (5, 11; 14). Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) comprising a plurality of acoustic enclosures (1; 7; 12) according to one of claims 1 to 10, the speakers (3, 8) of the plurality of acoustic enclosures (1; 7; 12) being electrically connected together in at least one of series and parallel. Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to claim 11, characterized in that the plurality of acoustic enclosures (1; 7; 12) are distributed in a plurality groups of loudspeakers (30), each group of loudspeakers (30) comprising an even number of loudspeakers (1; 7; 12) electrically connected in parallel, the groups of loudspeakers (30) being connected electrically in series, so that the electrical impedance of the acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) is compatible with an audio amplifier.