Patent Description:
There is an increasing demand for low-profile speaker applications. However, as the depth of a loudspeaker is decreased, the reduced distance between the low frequency driver (woofer) and the high frequency driver (tweeter) can create acoustic challenges. For example, the beamwidth of the low frequency driver can be difficult to control under these conditions. Conventional loudspeakers fail to address these challenges.

Examples of the prior art can be found in <CIT>, <CIT>, <CIT> and <CIT>.

All examples and features mentioned below can be combined in any technically possible way within the scope of the appended claims.

Various implementations include loudspeakers with a coaxial waveguide. In additional implementations, a coaxial waveguide is used to control an acoustic output of a loudspeaker.

According to one aspect of the invention, a loudspeaker includes: a high frequency, HF, driver; a low frequency LF, driver coaxially arranged with the HF driver; and a waveguide overlying a sound radiating surface of the LF driver, the waveguide having a hole pattern such that a sound radiation pattern of the LF driver matches a sound radiation pattern of the HF driver at a reference location;
a housing defining an acoustic backvolume between the LF driver and the HF driver, wherein the acoustic backvolume is configured to respond to motion of the HF driver when that driver is excited by an electrical signal; and a Helmholtz resonator coupled with the acoustic backvolume between the LF driver and the HF driver.

In an additional aspect, a method includes: providing a loudspeaker having: a high frequency, HF, driver; a low frequency, LF, driver coaxially arranged with the HF driver; and a waveguide overlying a sound radiating surface of the LF driver; and converting an electrical signal to an acoustic output at the loudspeaker, where the waveguide has a hole pattern such that the acoustic output comprises a sound radiation pattern of the LF driver that matches a sound radiation pattern of the HF driver at a reference location; a housing defining an acoustic backvolume between the LF driver and the HF driver, wherein the acoustic backvolume is configured to respond to motion of the HF driver when that driver is excited by an electrical signal; anda Helmholtz resonator coupled with the acoustic backvolume between the LF driver and the HF driver.

Implementations may include one of the following features as defined in the appended dependent claims.

In some cases, the waveguide includes an aperture through which the HF driver is exposed.

In particular aspects, the loudspeaker further includes batting located between the waveguide and the LF driver, where the batting controls cavity resonance between the LF driver and the waveguide, and where the batting is acoustically transparent at low frequencies and acts as a rigid acoustic boundary at high frequencies.

In certain implementations, the waveguide is located in front of the LF driver.

In some aspects, the waveguide includes a rigid baffle surrounding the HF driver and defining the hole pattern.

In particular cases, the hole pattern includes a plurality of holes arranged around the HF driver.

In certain aspects, energy from the LF driver is vented through holes in the hole pattern to control a beamwidth of an acoustic output.

In some cases, the waveguide includes a material for dissipating heat from the HF driver.

In particular implementations, the loudspeaker further includes: an enclosure defining an acoustic volume in front of the LF driver; and a Helmholtz resonator coupled with the acoustic volume in front of the LF driver.

In some cases, the loudspeaker includes acoustic batting in the Helmholtz resonator coupled with the acoustic volume in front of the LF driver.

In certain implementations, the loudspeaker further includes: a housing defining an acoustic backvolume between the LF driver and the HF driver; and a Helmholtz resonator coupled with the acoustic volume in front of the LF driver. The Helmholtz resonator can be located within the acoustic backvolume between the LF driver and the HF driver.

In some aspects, the loudspeaker includes acoustic batting in the acoustic backvolume between the LF driver and the HF driver.

In particular cases, energy from the LF driver is vented through holes in the hole pattern to control a beamwidth of the acoustic output, where the loudspeaker further comprises batting located between the waveguide and the LF driver, where the batting controls cavity resonance between the LF driver and the waveguide, and the batting is acoustically transparent at low frequencies and acts as a rigid acoustic boundary at high frequencies.

Other features, objects and benefits will be apparent from the description and drawings, and from the appended claims which, ultimately, define the invention.

It is noted that the drawings of the various implementations are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the implementations.

This disclosure is based, at least in part, on the realization that a coaxial waveguide can be beneficially incorporated into a loudspeaker. For example, a loudspeaker having a coaxial waveguide can provide a desired acoustic output in flush-mounted or surface-mounted applications.

Commonly labeled components in the FIGURES are considered to be substantially equivalent components for the purposes of illustration, and redundant discussion of those components is omitted for clarity.

As described herein, low-profile speaker systems create system design challenges due to their reduced spacing between the high frequency (HF) driver (or, tweeter) and the low frequency (LF) driver (or, woofer). Because many end user applications demand flush-mounted or surface-mounted speaker designs, loudspeaker system designers must attempt to provide desired acoustic outputs with reduced spacing between the HF driver and the LF driver. Conventional approaches for addressing this issue fail to control beam width at low frequencies, exhibit cavity resonance, and/or exhibit inconsistent off-axis acoustic output.

In contrast to conventional systems, the loudspeakers disclosed according to various implementations include an LF driver that is coaxially arranged with an HF driver. The loudspeakers include a waveguide with a hole pattern for controlling the sound radiation pattern of the LF driver to match the sound radiation pattern of the HF driver at a reference location in front of the loudspeaker. In certain cases, the sound radiation pattern for the loudspeaker can be defined by its beamwidth. The loudspeakers disclosed according to various implementations can provide consistent off-axis acoustic output, for example, at various distances peripheral to the central axis of the HF and LF driver. The integrated waveguide configuration can improve consistency in the acoustic output across a wide range of frequencies (e.g., from the low-frequency cut-off of the LF driver to the crossover frequency where the HF driver controls the speaker response). Additionally, the loudspeakers disclosed according to various implementations can include acoustic batting for controlling cavity resonance between the LF and HF drivers. In some cases, the waveguide can also act as a heat sink to cool the HF driver, allowing for higher power applications with a higher sound pressure level (SPL) when compared with conventional systems.

<FIG> shows a side cross-sectional view, and <FIG> shows a plan sectional view, of a loudspeaker <NUM> according to various implementations. <FIG> and <FIG> are referred to simultaneously. According to various implementations, the loudspeaker <NUM> includes an enclosure <NUM> housing a high frequency (HF) driver <NUM> and a low frequency (LF) driver <NUM>. In some cases, the HF driver <NUM> includes a tweeter, such as a dome tweeter, cone tweeter, piezo tweeter, etc. In one particular implementation, the HF driver <NUM> is a dome tweeter. In certain implementations, the LF driver <NUM> includes a woofer.

The LF driver <NUM> is arranged coaxially with the HF driver <NUM>, such that the central axis of motion of the LF driver <NUM> coincides with the central axis of motion of the HF driver <NUM>, as indicated by axis (A) in <FIG>. However, in other unclaimed implementations, the central axis of the HF driver <NUM> can be angled/rotated with respect to axis (A), such that the output of the loudspeaker <NUM> is asymmetric.

It is understood that both the HF driver <NUM> and the LF driver <NUM> can be coupled with one or more control circuits (not depicted) for providing electrical signals to excite one or both of the drivers <NUM>, <NUM>. Each driver <NUM>, <NUM> includes a sound-radiating surface for producing an acoustic output. The control circuit(s) can include a processor and/or microcontroller, which can include decoders, DSP hardware/software, etc. for playing back (rendering) audio content at one or both of the HF driver <NUM> or the LF driver <NUM>. The control circuit(s) can also include one or more digital-to-analog (D/A) converters for converting the digital audio signal to an analog audio signal. This audio hardware can also include one or more amplifiers which provide amplified analog audio signals to the HF driver <NUM> and/or the LF driver <NUM>.

The enclosure <NUM> defines an acoustic volume <NUM> in front of the LF driver <NUM>, which responds to motion of the LF driver <NUM> when the LF driver <NUM> is excited by an electrical signal. The loudspeaker <NUM> also includes a housing <NUM> defining an acoustic backvolume <NUM> that is located between the LF driver <NUM> and the HF driver <NUM>. The acoustic backvolume <NUM> responds to motion of the HF driver <NUM> when that driver is excited by an electrical signal. In other unclaimed implementations, the HF driver <NUM> may include a separate backvolume that is sealed to its transducer, such that the HF driver <NUM> does not interact with the acoustic backvolume <NUM>. In any case, the enclosure <NUM> and the housing <NUM> can be formed of any conventional loudspeaker material, e.g., a heavy plastic, metal, composite material, etc..

Overlying a sound radiating surface <NUM> of the LF driver <NUM> is a waveguide <NUM> for directing acoustic energy from the LF driver <NUM> to the front <NUM> of the loudspeaker enclosure <NUM>. In various implementations, the waveguide <NUM> includes at least one aperture <NUM> through which the HF driver <NUM> is exposed. That is, the waveguide <NUM> includes the aperture <NUM> to accommodate the HF driver <NUM>, such that the HF driver <NUM> is exposed at the front <NUM> of the loudspeaker enclosure <NUM>.

As shown in <FIG>, the waveguide <NUM> is located in front of the LF driver <NUM>. The waveguide <NUM> includes a hole pattern <NUM> including a plurality of holes <NUM> (shown as holes 130A, 130B, 130C, etc.) arranged around the HF driver <NUM>. This arrangement of holes <NUM> is merely one example arrangement, and it is understood that a variety of hole positions and/or sizes can be used according to the various implementations. The holes <NUM> extend through the waveguide <NUM> to allow airflow between the acoustic volume <NUM> and the front <NUM> of the enclosure <NUM>, i.e., to ambient. The hole pattern <NUM> is configured such that a sound radiation pattern of the LF driver <NUM> matches a sound radiation pattern of the HF driver <NUM> at a reference location. In some examples, this reference location includes any location approximately ten (<NUM>) meters in front of the loudspeaker within a lateral distance defined by the coverage pattern, or beamwidth of the speaker <NUM>. In certain examples, the beamwidth of the speaker <NUM> can range between approximately <NUM> degrees and approximately <NUM> degrees. That is, according to various implementations, energy from the LF driver <NUM> is vented through holes 130A, 130B, 130C, etc., in the hole pattern <NUM> of the waveguide <NUM> to control a beamwidth of an acoustic output from the loudspeaker <NUM>,.

In certain implementations, the waveguide <NUM> includes a rigid baffle that surrounds the HF driver <NUM> and defines the hole pattern <NUM>. That is, in some examples, the hole pattern <NUM> can be configured such that a center-to-center spacing between the holes <NUM> as measured by a line intersecting the central axis (A) is approximately <NUM> inches, i.e. approx. <NUM>,<NUM>, to approximately <NUM> inches , i.e. approx. <NUM>,<NUM>, (and in some particular example cases, approximately <NUM> inches i.e. approx. <NUM>,<NUM>). It is understood that various holes <NUM> in the pattern may have distinct center-to-center spacing, and that these values are merely examples of particular implementations.

In various implementations, the waveguide <NUM> is formed of a material for dissipating heat from the HF driver <NUM>. In some cases, the waveguide <NUM> includes a metal such as aluminum (or alloys of aluminum), however, in other cases, the waveguide <NUM> includes another material with sufficient thermal conductivity to aid in dissipating heat from the HF driver <NUM>.

In certain particular cases, the loudspeaker <NUM> further includes batting <NUM> located in the acoustic volume <NUM> between the waveguide <NUM> and the LF driver <NUM>. The batting <NUM> can include cotton or a synthetic fiber, and can be affixed (e.g., adhered or mounted) at the backside of the waveguide <NUM> or affixed to one or more walls of the enclosure <NUM> or the housing <NUM>. In particular example implementations, as shown in <FIG>, the batting <NUM> is affixed to the backside of the waveguide <NUM>. In various implementations, the batting <NUM> can aid in controlling cavity resonance between the LF driver <NUM> and the waveguide <NUM>. In cases where the batting <NUM> is affixed to the backside of the waveguide <NUM>, the batting <NUM> can be acoustically transparent at low frequencies (e.g., frequencies below the crossover frequency for the LF driver <NUM>), but can act as a rigid acoustic boundary at high frequencies (e.g., frequencies above the crossover frequency for the LF driver <NUM>). Additionally, when the batting <NUM> is affixed to the backside of the waveguide <NUM>, the batting <NUM> can dampen the cavity resonance in the acoustic volume <NUM> that occurs at frequencies near the crossover frequency (e.g., frequencies around <NUM> kilo Hertz (kHz)). That is, when the batting <NUM> is affixed to the backside of the waveguide <NUM>, it can provide a smoother (less reverberant) on-axis response from the HF driver <NUM>, as well as a more consistent off-axis response from the HF driver <NUM>.

In other cases, as noted herein, the batting <NUM> is affixed to one or more walls of the enclosure <NUM> and/or the housing <NUM>, either with or without batting <NUM> affixed to the backside of the waveguide <NUM>. Batting in these additional locations can dampen resonances in the loudspeaker <NUM>, but may not act as the rigid acoustic boundary at high frequencies.

In operation, the control circuit in loudspeaker <NUM> is configured to convert an electrical signal to an acoustic output at the HF driver <NUM> and the LF driver <NUM>. As noted herein, the hole pattern <NUM> in the waveguide <NUM> is configured such that the acoustic output has a sound radiation pattern of the LF driver <NUM> that matches a sound radiation pattern of the HF driver <NUM> at the reference location. That is, energy from the LF driver <NUM> is vented through holes <NUM> in the hole pattern <NUM> to control a beamwidth of the acoustic output. In certain cases, the batting <NUM> is used to control cavity resonance in the acoustic volume <NUM> between the LF driver <NUM> and the waveguide <NUM>, such that the batting <NUM> is acoustically transparent at low frequencies and acts as a rigid acoustic boundary at high frequencies.

<FIG> shows a cross-sectional depiction of an additional unclaimed implementation of a loudspeaker <NUM>. As shown in <FIG>, loudspeaker <NUM> can include a Helmholtz resonator <NUM> coupled with the acoustic volume <NUM> in front of the LF driver <NUM>. In certain cases, the Helmholtz resonator <NUM> is located within the wall of the enclosure <NUM> proximate the LF driver <NUM>. During operation of the loudspeaker <NUM>, the Helmholtz resonator <NUM> can dampen cavity resonance in the acoustic cavity <NUM>. In some implementations, the Helmholtz resonator <NUM> includes a pocket <NUM> of gas (e.g., air) that is coupled with the acoustic volume <NUM> by a narrowed neck section <NUM>. In other example implementations, a portion of the pocket of the Helmholtz resonator <NUM> is filled with acoustic batting <NUM>, which can control the Q factor of that Helmholtz resonator <NUM>. The Q factor is a dimensionless parameter that indicates energy losses within a resonant element. The batting <NUM> can be affixed to an inner surface of the Helmholtz resonator <NUM> and can be used to match the Q factor of the Helmholtz resonator <NUM> with the Q factor for the acoustic volume <NUM> to which it is coupled.

<FIG> shows a cross-sectional depiction of an additional implementation of a loudspeaker <NUM>. As shown in <FIG>, the loudspeaker <NUM> can include a Helmholtz resonator <NUM> coupled with the acoustic volume <NUM> between the LF driver <NUM> and the HF driver <NUM>. In certain cases, the Helmholtz resonator <NUM> is located within the wall of the housing <NUM> behind the HF driver <NUM>. According to some implementations, the Helmholtz resonator <NUM> is located within the wall of the housing <NUM> in a location between the LF driver <NUM> and the HF driver <NUM>, e.g., extending into the acoustic backvolume <NUM> between the LF driver <NUM> and the HF driver <NUM>. The Helmholtz resonator <NUM>, in some cases in combination with the acoustic batting <NUM>, can be used to dampen cavity resonance in the acoustic volume <NUM>. In some implementations, the Helmholtz resonator <NUM> includes a pocket of gas (e.g., air) that is coupled with the acoustic backvolume <NUM> by a narrowed neck section (not labeled in <FIG>). In certain implementations, as discussed with reference to the Helmholtz resonator <NUM> in <FIG>, a portion of the acoustic backvolume <NUM> is filled with acoustic batting <NUM>.

Returning to <FIG>, it is understood that the loudspeaker <NUM> can also include a Helmholtz resonator <NUM> in one of the locations shown and described with reference to <FIG> and <FIG>. These example implementations are illustrated in phantom, with a Helmholtz resonator <NUM> coupled to the acoustic volume <NUM> and located either in the wall of the enclosure <NUM> (similarly to the loudspeaker <NUM> in <FIG>), or in the wall of the housing <NUM> (similarly to the loudspeaker <NUM> in <FIG>).

<FIG> shows an example frequency response graph illustrating sound pressure level (SPL) versus frequency for a loudspeaker according to various implementations (e.g., loudspeaker <NUM>, <NUM> or <NUM>) and a conventional loudspeaker without the waveguide(s) described herein (e.g., waveguide <NUM> or waveguide <NUM>). <FIG> illustrates that the frequency response of a loudspeaker according to various implementations (e.g., loudspeaker <NUM>, <NUM> or <NUM>) has significantly less variation over a range of frequencies (i.e., the response is smoother) as compared with a conventional loudspeaker without the waveguides described herein.

<FIG> shows example beamwidth graphs for: (a) a conventional loudspeaker without the waveguide(s) described herein; and (b) the loudspeaker(s) described according to various implementations (e.g., loudspeaker <NUM>, <NUM> or <NUM>). These graphs illustrate the variation in beamwidth versus frequency for each of the corresponding loudspeakers. As can be seen in this comparison with the conventional loudspeaker in graph (a), the beamwidth between the high frequency and the low frequency is significantly more consistent in graph (b), representing the response for a loudspeaker according to various implementations (e.g., loudspeaker <NUM>, <NUM> or <NUM>).

In contrast to conventional loudspeakers, loudspeakers <NUM>, <NUM>, and <NUM> can provide a low-profile (e.g., flush-mounted or surface-mounted) speaker configuration with a consistent off-axis response and a smooth on-axis high-frequency response. For example, in some cases, the loudspeakers described herein can provide an acoustic output comparable to loudspeakers with significantly greater depth.

It is understood that the relative proportions, sizes and shapes of the loudspeakers <NUM>, <NUM>, <NUM> and components and features thereof as shown in the FIGURES included herein can be merely illustrative of such physical attributes of these components. That is, these proportions, shapes and sizes can be modified according to various implementations to fit a variety of products. For example, while a substantially rectangular-shaped loudspeaker may be shown according to particular implementations, it is understood that the loudspeaker could also take on other three-dimensional shapes in order to provide acoustic functions described herein.

In various implementations, components described as being "coupled" to one another can be joined along one or more interfaces. In some implementations, these interfaces can include junctions between distinct components, and in other cases, these interfaces can include a solidly and/or integrally formed interconnection. That is, in some cases, components that are "coupled" to one another can be simultaneously formed to define a single continuous member. However, in other implementations, these coupled components can be formed as separate members and be subsequently joined through known processes (e.g., soldering, fastening, ultrasonic welding, bonding). In various implementations, electronic components described as being "coupled" can be linked via conventional hard-wired and/or wireless means such that these electronic components can communicate data with one another. Additionally, sub-components within a given component can be considered to be linked via conventional pathways, which may not necessarily be illustrated.

Claim 1:
A loudspeaker (<NUM>, <NUM>, <NUM>) comprising:
a high frequency (HF) driver (<NUM>);
a low frequency (LF) driver (<NUM>) coaxially arranged with the HF driver (<NUM>); and
a waveguide (<NUM>, <NUM>) overlying a sound radiating surface of the LF driver (<NUM>), the waveguide having a hole pattern (<NUM>) such that a sound radiation pattern of the LF driver (<NUM>) matches a sound radiation pattern of the HF driver (<NUM>) at a reference location;
a housing (<NUM>) defining an acoustic backvolume (<NUM>) between the LF driver (<NUM>) and the HF driver (<NUM>), wherein the acoustic backvolume (<NUM>) is configured to respond to motion of the HF driver (<NUM>) when that driver is excited by an electrical signal; and
a Helmholtz resonator (<NUM>) coupled with the acoustic backvolume (<NUM>) between the LF driver (<NUM>) and the HF driver (<NUM>).