Patent Description:
In the prior art, loudspeakers are known in a variety of different designs and for a wide range of different applications, wherein it is often the case that several loudspeakers, which emit sound waves in different frequency ranges, are used in one application. For example, in a typical car installation, it is known to use different loudspeakers, also called drivers, covering different or slightly overlapping frequency ranges. In such a typical example, a small driver for the high frequencies, e.g. over <NUM>, which is called the tweeter, a midrange driver for midrange frequencies, e.g. between <NUM> and <NUM>, a woofer for low frequencies, e.g. between <NUM> and <NUM>, and a sub-woofer for very low frequencies, e.g. below <NUM>, are used. One important objective in such a car installation is to mount the midrange driver and the tweeter as high as possible, targeting the height of a listener hears. Moreover, due to the wavelength difference between midrange frequencies and high frequencies, it is needed to keep the tweeter and the midrange loudspeakers fairly close to each other. If positioned too far apart, the phase relationship result may cause the midrange driver and the tweeter transducers to be perceived as two independent, and potentially delayed, audio sources.

Document <CIT> discloses an improved audio frequency speaker comprising: a speaker cone suspended for movement to generate air displacement; a voice coil having at least one winding attached to the cone; and a magnet having a magnetic field, the magnetic being located such that at least a portion of the coil is within the magnetic field to thereby cause the coil and the cone to move when a current from an audio frequency drive signal flows through the coil winding, wherein the improvement comprises at least one piezo-electric actuator secured to the cone and adapted to receive the audio frequency drive signal, the at least one piezo-electric actuator moving the cone at least at higher order frequencies of the audio frequency range to thereby enhance the performance range of the speaker at the higher order frequencies so that a single speaker covers the entire audio frequency range.

In view of this, it is found that a further need exists to provide a loudspeaker apparatus/system to prevent that in particular the midrange driver and the tweeter are perceived as two different audio sources.

In the view of the above, it is an object of the present invention to provide a loudspeaker apparatus/system to prevent that in particular a midrange driver and a tweeter are perceived as two different audio sources.

These and other objects, which become apparent upon reading the following description, are solved by the subject matter of the independent claims. The dependent claims refer to preferred embodiments of the invention.

According to a first aspect, a loudspeaker apparatus for emitting high and low frequency sound waves is provided, comprising the set of features defined in claim <NUM>.

In other words, the present disclosure proposes to use one membrane/diaphragm element for generating sound waves in two frequency ranges. In a first frequency range, e.g. midrange frequencies, the membrane element can be moved by the at least one voice coil/magnet assembly back-and-forth and in a second frequency range, e.g. high frequencies, the surface of the membrane can be brought into movement/vibration by the at least one piezoelectric layer or element. This allows a superimposed movement of the membrane element, which can emit sound waves in two frequency ranges. In this context, it should be noted that the term membrane or diaphragm element is to be understood in a broad manner and includes any element capable of being moved back-and-forth by a voice coil/magnet assembly on the one hand and of being set in vibration by a piezoelectric element on the other. Furthermore, the present disclosure is also not limited to a specific first and second frequency range. Rather, a wide variety of frequency ranges can be made available in different configurations/implementations. Finally, also the term piezoelectric layer or element is to be understood broadly and includes designs with separate/adhered piezoelectric layers as well as designs where the piezoelectric layer is incorporated into the membrane element. In addition, this term also includes plane designs, as well as designs with individual/separate piezoelectric elements, as long as the piezoelectric layer/element is capable of causing the membrane element to vibrate in order to emit sound in the second frequency range.

In an example, the voice coil immerse in a magnet field may drive the membrane element back-and-forth enabling sound generation in the first frequency range. In addition, the membrane element may comprise a piezoelectric element that receives an electrical pulse, and then applies directional force to an opposing membrane surface, causing it to move in the desired direction. Thus, motion may be generated when the piezoelectric element moves against the membrane surface enabling sound generation in the second frequency range.

By means of such a loudspeaker apparatus, an exceptionally wide operating range can be provided. It may cover a range from <NUM> up to <NUM>, i.e. almost seven octaves. This extremely wide range may be achieved by the use of the two modes of sound generation, i.e. by means of a pistonic movement, where the membrane element or a driver cone moves back and forward like the piston in a car engine and by means of a modal radiation, where the vibrating piezoelectric material creates areas of excitation on the membrane surface. Thereby, a full-range sound reproduction in audio applications can be provided with a reduced number of loudspeakers needed, and widens the operational bandwidth of the loudspeaker, by virtue of a configuration that combines, in the same membrane element, the piston movement driven by a voice coil/magnet assembly and the induced vibration from a piezoelectric element.

Furthermore, the solution described in the present disclosure may enable sound from two excitation mechanisms to come from one sound source. This characteristic allows a synchronized summation of the sound sources than physically separated drivers. As well, the pattern of response is symmetric around the axis of the loudspeaker apparatus.

In an implementation, the first frequency range may be between <NUM> and <NUM> and the second frequency range is between <NUM> and <NUM>. In other words, in such an implementation the loudspeaker apparatus includes a midrange driver and a tweeter in one audio source.

In an implementation, the loudspeaker apparatus may further comprise at least one crossover circuit. In an example, the crossover frequency of the crossover circuit being at <NUM>. As the different drivers work with different frequency ranges, individual audio channels or a crossover network of filters may be used to route the different frequency ranges to the appropriate driver.

In an alternative implementation, the loudspeaker apparatus may not comprise a crossover circuit, wherein both drives of the membrane element may be caused by the same audio signal. Such an implementation is possible since the piezoelectric membrane is resistant to overloads that would normally destroy most high frequency drivers. Due to their electrical properties, piezoelectric membranes are already a capacitive load and can be used without a crossover. Therefore, a loudspeaker apparatus with the piezoelectric membrane may be driven by individual audio channels or by only one audio channel with or without an existing passive crossover network.

In an implementation, the membrane element may be arranged conically. In an alternative implementation, the membrane element may be arranged as a flat plane. In this context, it should be noted that the present disclosure is not limited to a certain geometry of the membrane element as long as it can be operated/moved in the two modes mentioned.

According to the invention, the piezoelectric layer or element is formed as a composite structure, comprising or is composed of: a top support layer; an electrode layer; a piezoelectric layer; an electrode layer; and a bottom carrier layer. According to the invention, the piezoelectric layer is formed as a composite structure, comprising at least one epoxy resin matrix and piezo-ceramic fibers embedded therein. In a further implementation, the piezoelectric layer or element may comprise piezo-ceramic fibers with two different angles of orientation, which may be arranged with an angle difference of <NUM>° DEG to one another.

In an example, a piezoelectric ceramic may be adhered to an aluminum, paper, plastic or carbon fiber membrane element. However, lighter membrane elements with higher Young's modulus with good internal loss are desired. Notably, a lightweight and stiff membrane element may increase the efficiency of the mechanical moment conversion into sound. Good internal loss or damping creates a distributed breakup with smaller peaks in the frequency response and ultimately smoother and more natural sound without harshness.

The coverage area of the piezo ceramic material according to the invention comprises a full coverage layer of piezo ceramic adhered to the membrane element. Piezoelectric sound components comprise piezoelectric membranes to amplify the sound radiation. This is a structure in which a piezoelectric ceramic is adhered to a plate made of metal, brass, nickel-alloy or any other structural material substrate. A piezoelectric loudspeaker, also known as a piezo bender due to its mode of operation, and sometimes colloquially called a "piezo", buzzer, crystal loudspeaker or beep speaker, for instance, is a loudspeaker that uses the piezoelectric effect for generating sound. The initial mechanical motion is created by applying a voltage to a piezoelectric material, and this motion is typically converted into audible sound using membranes and resonators. Compared to other loudspeaker designs piezoelectric speakers are relatively easy to drive. For example, they can be connected directly to TTL (Transistor-Transistor Logic) outputs, although more complex drivers can give greater sound intensity. Typically, they operate well in the range of <NUM> to <NUM> and up to <NUM> in ultrasound applications. In an example, the membrane/diaphragm is provided of piezoelectric fiber composites receiving an electrical pulse thought etched interlinear electrodes, and then applies directional force to the opposing host composite material plies, causing it to move in the desired direction. In such an example, motion may be generated when the piezoelectric element moves against the host composite material, thus enabling sound generation.

In an example, the membrane element may also be made of Macro Fiber Composite (MFC). The MFC can also be applied, normally bonded, as a thin, surface-conformable sheet to various types of membrane elements, or embedded in a composite structure membrane element. The MFC may consist of rectangular piezo ceramic rods sandwiched between layers of adhesive, electrodes, and polyimide film. The electrodes are attached to the film in an interdigitated pattern, which transfers the applied voltage MFC-structure directly to and from the ribbon-shaped rods. Such an example enables in-plane poling, actuation, and sensing in a sealed and durable, ready-to-use package. The MFC can also be applied as a thin, surface-conformable sheet to various types of structures, or embedded in a composite structure.

In an implementation, the membrane element may be provided from carbon fibers (Kevlar). In a further implementation, the membrane element may be provided from a composite material comprising: at least one carbon fiber (Kevlar) layer and a damping layer. In a further implementation, the membrane element may be provided of a material having piezoelectric properties, for example, comprising nanotubes of boron nitride.

According to a further aspect, a vehicle door is provided, comprising at least one loudspeaker apparatus described above. In an example, the loudspeaker apparatus may be a combined midrange and tweeter loudspeaker. In a car installation, the large diaphragm and long excursion woofers, e.g. about <NUM> to <NUM> in diameter, are typically placed in lower areas, e.g. lower door corners, where there is more space for larger drivers. The size of the membrane for tweeters, e.g. about <NUM> diameter, and midrange drivers, e.g. about <NUM> to <NUM> diameter, allows higher mounting positions in a car installation, e.g. upper door corner, instrument panel, etc., targeting the height of the listener hears, to avoid obstructions and to better define the sound stage. As described in the present disclosure, an important issue in a car installation is to mount the midrange and twitters drivers as high as possible, targeting the height of the listener hears. Due to the wavelength difference between mid and high frequencies, every attempt should be made to keep the tweeter and the mid-range speakers fairly close to each other. If positioned too far apart, the phase relationship result may cause the mid-range and the tweeter transducers to be perceived as two independent, and potentially delayed, audio sources. In case of limited space or design constrains in a car installation, the most direct, but typically least acoustically effective approach is to use coaxial type speakers. Such coaxial speakers are usually <NUM>- or <NUM>-way loudspeakers in which the tweeter, or the tweeter and a midrange driver, are mounted in front of the woofer, partially obscuring it. The advantage of such a design is the ability to use a smaller area, hence their popularity in car audio. However, according to the present disclosure, there is no need for a tweeter in front of the woofer membrane, which may eliminate any obstruction of the membrane and prevents a phase-misalignment between high and low frequencies, further improving the acoustic performance of the loudspeaker apparatus.

A further aspect relates to a use of a piezoelectric layer or element and/or a membrane element comprising such a piezoelectric layer in a loudspeaker apparatus described above. According to a further aspect, a vehicle is provided, comprising at least one loudspeaker apparatus described above. In an example, the loudspeaker apparatus is a combined midrange and tweeter loudspeaker. However, the disclosed loudspeaker apparatus is not limited to a use in a door panel of a vehicle. In fact, potential applications range from automotive and aerospace industry to consumer electronic products.

In the following, the disclosure is described exemplarily with reference to the enclosed figure, in which.

Notably, the figures are merely schematic representations and serve only to illustrate an embodiment of the present disclosure.

<FIG> and <FIG> show a schematic view of a loudspeaker apparatus <NUM> according to an embodiment of the present disclosure, wherein <FIG> shows a partially cut view of the loudspeaker apparatus <NUM>. <FIG> shows a cross-sectional view of the loudspeaker apparatus <NUM>, although in order to make it easier to understand the function of the loudspeaker apparatus, several parts are not shown in <FIG>.

The shown embodiment of the loudspeaker apparatus <NUM> comprises a frame or basket <NUM>, a membrane or diaphragm element <NUM> suspended by a surround gasket <NUM>, a voice coil <NUM> which is arranged in a magnet field of magnet element <NUM>. The loudspeaker apparatus <NUM> further comprises an elastic structure <NUM>, also called Spider <NUM>, for elastically supporting the movement of the voice coil <NUM> within the magnet field, e.g. between a center pole piece and a top plate of the magnet element <NUM>. In the shown embodiment, the membrane element <NUM>, e.g. provided by aluminum, paper, plastic or carbon fiber, comprises a piezoelectric ceramic layer <NUM>, which is adhered to the membrane element <NUM>. The shown embodiment of the loudspeaker apparatus <NUM> does not comprise a crossover circuit, both drives of the membrane element <NUM> are caused by the same audio signal <NUM>. Such an implementation is possible since the piezoelectric layer/membrane <NUM> is resistant to overloads that would normally destroy most high frequency drivers. Due to their electrical properties, piezoelectric layers/membranes <NUM> are already a capacitive load and may be used without a crossover. Therefore, the loudspeaker apparatus <NUM> with the piezoelectric layer/membrane <NUM> may be driven by only one audio channel <NUM>.

The voice coil <NUM> immerse in the magnet field of the magnet element <NUM> driving the membrane element <NUM> back-and-forth enabling sound generation in a first frequency range, e.g. between <NUM> and <NUM>. The back-and-forth movement for a sound generation in the first frequency range is indicated in <FIG> by the arrows <NUM>.

In addition, the membrane element <NUM> with the piezoelectric layer/membrane <NUM> may receive an electrical pulse, and then applies directional force to the opposing surface of the membrane element <NUM>, causing it to move in the desired direction. This movement for a sound generation in the second frequency range is indicated in <FIG> by the dotted line <NUM>. Thus, motion is generated when the piezoelectric layer/membrane <NUM> moves against the membrane element <NUM> enabling sound generation in the second frequency range, e.g. between <NUM> and <NUM>. In other words, in the shown embodiment, the loudspeaker apparatus <NUM> includes a midrange driver and a tweeter in one audio source. However, the present disclosure is not limited to such an arrangement.

<FIG> shows a vehicle door <NUM> comprising one loudspeaker apparatus <NUM> shown in <FIG> and <FIG>. As can be taken from <FIG>, the loudspeaker apparatus <NUM> can be mounted at a high position targeting the height of the listener hears. Moreover, in the shown embodiment, the loudspeaker apparatus is a combined midrange and tweeter loudspeaker. Thus, the midrange and tweeter frequencies are provided by one sound source and a listener does not perceive both as two different audio sources.

Claim 1:
Loudspeaker apparatus (<NUM>) for emitting high and low frequency sound waves, comprising:
at least one membrane element (<NUM>) for generating sound waves, said membrane element (<NUM>) being adapted to simultaneously generate sound waves in a first frequency range and in a second frequency range;
at least one voice coil/magnet assembly (<NUM>, <NUM>) adapted for operatively engaging with the membrane element (<NUM>) such that the membrane element (<NUM>) is drivable by the voice coil/magnet assembly (<NUM>, <NUM>) in the first frequency range to generate sound waves in the first frequency range; and
at least one piezoelectric layer or element (<NUM>) being arranged at the membrane element (<NUM>) in such a way that the membrane element (<NUM>) is drivable by the piezoelectric layer or element (<NUM>) in the second frequency range in order to generate sound waves in the second frequency range, and
the piezoelectric layer or element (<NUM>) being formed as a composite structure, comprising at least one epoxy resin matrix and piezo-ceramic fibers embedded therein,
characterised in that the piezoelectric layer or element is a full coverage layer of piezo-ceramic adhered to the membrane element.