Compression driver with dome diaphragm and annular exit

A compression driver includes a dome diaphragm having a convex surface and a concave surface and a phasing plug having a base portion with a first side and an opposed second side. The base portion first side is disposed adjacent the convex surface of the diaphragm and defines a compression chamber therebetween. The base portion includes a plurality of channels that extend therethrough from the first side to the second side for sound waves to travel through the base portion, the plurality of channels converging to form an annular exit of the compression driver.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase of PCT Application No. PCT/US2019/063952 filed on Dec. 2, 2019, the disclosure of which is incorporated in its entirety by reference herein.

TECHNICAL FIELD

Embodiments relate to a compression driver for a transducer having a dome diaphragm and an annular exit to the waveguide.

BACKGROUND

Compression drivers can be divided into two groups: drivers based on dome diaphragms and drivers based on annular flexural diaphragms. Both categories of drivers have their strengths and weaknesses. Dome diaphragm drivers typically have a larger diaphragm area and therefore provide higher sound pressure level (SPL) output. Dome diaphragm-based, large-format compression drivers (with a voice coil diameter of 2 inches and larger) typically have metallic domes formed out of titanium, aluminum, magnesium, or beryllium foil. Metallic diaphragms are heavier than their polymer counterparts and may have a lower resonance, providing more efficient reproduction of lower frequencies. However, they have a lower mass-controlled velocity at high frequency and therefore lower SPL output at high frequencies. This is often compensated for by the high frequency breakups of the diaphragm. The breakups increase overall output acceleration, and therefore the in-phase components of acceleration contribute to an increased high frequency SPL output. However, the breakups are accompanied by an increase in nonlinear distortion including subharmonics and irregularity of the frequency response at high frequencies.

The majority of modern annular diaphragms are made of polymer films. The advantage of annular diaphragms is the smaller radial dimensions of the moving part of the diaphragm compared to dome diaphragms having the same diameter of the moving voice coil. Annular diaphragm-based drivers have smaller radial compression chamber dimensions, which relates to higher radial resonance frequencies. With an increase in the voice coil diameter, the dome compression chamber has resonances that start at lower frequencies, and their number increases in the audio frequency range. In contrast, annular diaphragm compression drivers may have a larger voice coil without increasing the radial dimension, with the same number of resonances in the compression chamber. However, a disadvantage of annular flexural diaphragm assemblies is that their area is smaller compared to the area of an equivalent dome diaphragm assembly.

Both types of compression drivers typically have a circular exit. The diameter of the exit is related to cross-modes that are excited at the entrance of the corresponding horn or waveguide and to the directivity control at high frequencies. In a regular, constant-directivity waveguide, control of directivity is lost when the diameter of the driver's exit (equal to the diameter of the waveguide or horn entrance) is comparable to the wavelength of the radiated signal. The same effect is observed in waveguides used in line arrays, where larger exit diameters worsen the high-frequency directivity control.

In line arrays, the entrance of the waveguide is typically circular, whereas the exit of the waveguide is rectangular with its vertical dimension significantly larger than the horizontal one. As such, wide directivity is provided in the horizontal plane and narrow directivity is provided in the vertical plane. The goal of waveguides in line arrays is to transform the circular entrance to the rectangular exit and provide a “flat” wavefront in the vertical plane, creating a cylindrical wave instead of a spherical one when a number of line arrays is stacked vertically and a single or several waveguides form a very long vertically oriented radiator. This is accomplished via the progressive time delay of sound waves towards the middle of the vertically-oriented exit in such a way that the arrival time of sound waves is equal along the vertical profile of the waveguide. In all such drivers with a circular exit and corresponding circular entrance to the waveguide, the acoustical path must narrow to reach the exit of the driver, and then start widening again in the waveguide, creating unnecessary redundancy.

SUMMARY

In one or more embodiments, a compression driver includes a dome diaphragm having a convex surface and a concave surface and a phasing plug having a base portion with a first side and an opposed second side. The base portion first side is disposed adjacent the convex surface of the diaphragm and defines a compression chamber therebetween. The base portion includes a plurality of channels that extend therethrough from the first side to the second side for sound waves to travel through the base portion, the plurality of channels converging to form an annular exit of the compression driver.

In one or more embodiments, a transducer includes a compression driver including a dome diaphragm having a convex surface and a concave surface, and a phasing plug having a base portion with a first side and an opposed second side. The base portion first side is disposed adjacent the convex surface of the diaphragm and defines a compression chamber therebetween. The phasing plug has a hub portion extending outwardly from the base portion second side along a central axis, the hub portion having a first end and a second end and an outer surface. The base portion includes a plurality of channels that extend therethrough from the first side to the second side, the plurality of channels converging to form an annular exit of the compression driver. A housing is disposed on the base portion and has a first end and a second end and an inner surface, the hub portion and the housing together forming a waveguide having an inlet adjacent the compression driver and an outlet to the ambient environment.

In one or more embodiments a transducer includes a compression driver including a dome diaphragm having a convex surface and a concave surface and a magnet assembly disposed adjacent the concave surface of the diaphragm. The compression driver further includes a phasing plug having a base portion with a first side and an opposed second side, the base portion first side disposed adjacent the convex surface of the diaphragm and defining a compression chamber therebetween. The phasing plug has a hub portion extending outwardly from the base portion second side along a central axis. The base portion includes a plurality of channels that extend therethrough from the first side to the second side, the plurality of channels including concentric annular passages converging to form an annular exit of the compression driver. A housing is disposed on the base portion, the hub portion and the housing together forming a waveguide, where the waveguide has an annular inlet adjacent the compression driver and a rectangular outlet to the ambient environment.

DETAILED DESCRIPTION

Embodiments of a transducer disclosed herein include a dome diaphragm-based compression driver with an annular driver exit and a waveguide with a corresponding annular inlet. With reference first toFIGS.1and4, cross-sectional views of a transducer100are shown which includes a compression driver102and a waveguide104. In one or more embodiments, the compression driver102includes a magnet assembly106which may comprise an annular permanent magnet108disposed between an annular top plate110and a back plate112. The magnet assembly106provides a permanent magnetic field for electrodynamic coupling with a voice coil114. The voice coil114is mechanically coupled to a diaphragm116and produces movement thereof to convert received electrical signals into sound waves which are propagated from the compression driver102toward the waveguide104. In one or more embodiments, the diaphragm116has a dome configuration and is disposed coaxially with a central axis118above the magnet assembly106.

As shown inFIGS.1-6, the compression driver102further includes a phasing plug120having a base portion122and a hub portion124extending outwardly or upwardly from the base portion122, both of which are coaxially disposed about the central axis118. The hub portion124has a first end126disposed proximate to the base portion122and a second end128disposed at a distance from the base portion122. The hub portion124may be integrally formed with the base portion122or may be attached to the base portion122by any suitable means. As an alternative to the solid hub portion124depicted herein, an interior of the hub portion124could alternatively be hollowed out to decrease weight and/or cost. The base portion122of the phasing plug120may be generally circular or may have any other suitable geometry. The phasing plug120may include a circumferential flange130for coupling or mounting (e.g., via bolts as shown inFIGS.1,4, and7-10) the phasing plug120to the back plate112of the magnet assembly106.

With reference toFIGS.1,3-4and6, the dome diaphragm116has a lower, concave surface132and an upper, convex surface134. Contrary to typical compression drivers with dome diaphragms where the acoustic signal is directed by the phasing plug adjacent the concave surface of the dome, in one or more embodiments disclosed herein the acoustic signal may enter the phasing plug120from the convex surface134of the dome diaphragm116. The base portion122of the phasing plug120includes a first side136facing the convex surface134of the diaphragm116and an opposing second side138facing the waveguide104. The first side136may be generally concave, complementary to the convex surface134of the diaphragm116, whereas the second side138may be generally planar. It is understood that any directional terms as used herein are merely to indicate the relative placement of various components of the transducer100, and are not intended to be limiting.

As shown inFIGS.1-6, the base portion122of the phasing plug120further includes at least one channel140that extends as a passage through the base portion122from the first side136to the second side138through which sound waves created by the diaphragm116may travel. A compression chamber is defined in a space between the convex surface134of the diaphragm116and the first side136of the phasing plug base portion122. In practice, the height of the compression chamber may be quite small (e.g., approximately 0.5 mm or less) such that the volume of the compression chamber is also small. The actuation of the diaphragm116generates high sound pressure acoustical signals within the compression chamber, and the signals travel as sound waves through the base portion122of the phasing plug120via the channels140. In a non-limiting embodiment, sound-absorbing material may be disposed under the concave surface132of the diaphragm116to mitigate any air resonances in this cavity.

As depicted herein, a plurality of channels140may be provided as annular passages arranged circumferentially about the central axis118, forming concentric circles adjacent the convex surface134of the diaphragm116. The channels140may be positioned at concentric radii in order to provide blocking of radial acoustical modes excited in the compression chamber. The channels140serve to carry sound waves from all areas of the convex surface134of the diaphragm116through the phasing plug120and into the waveguide104. The channels140each have a first end142adjacent the convex surface134of the diaphragm116and in communication with the compression chamber, and a second end144at the second side138of the base portion122. The channels140may each have substantially similar lengths from their first ends142to their second ends144, where the second ends144of the channels140all converge to form an annular exit146to the compression driver102, such that each pulse of sound reaches the waveguide104as one coherent wavefront.

As illustrated inFIGS.1-10, the hub portion124is disposed within a housing150having a first end152disposed on or attached to the phasing plug120(e.g., at the second side138of the base portion122), and a second end154disposed at a distance from the base portion122. The hub portion124and the housing150together form the waveguide104. More particularly, an outer surface156of the hub portion124and an inner surface158of the housing150may cooperatively define the waveguide104and provide a path for the propagation of sound waves from an inlet160of the waveguide104to an outlet or exit aperture162of the waveguide104. In the assembled waveguide104, the exit aperture162may be generally aligned with the hub portion124. The waveguide104may function to control directivity of sound waves (i.e., coverage of sound pressure over a particular listening area) that propagate out of the transducer100into the ambient environment and to increase reproduced SPL over a certain frequency range. The housing150may include a generally planar flange164surrounding the outlet162, which may be generally circular as depicted herein, which can be used to couple the transducer100to a transducer housing or other component of a loudspeaker system.

The waveguide inlet160may be a continuous, annular ring formed by the outer surface156of the hub portion124at its first end126and the inner surface158of the housing150at its first end152. The waveguide outlet162may be embodied as a rectangular exit aperture provided at the second end154of the housing150, with a smaller dimension in a horizontal plane and a larger dimension in a vertical plane. This configuration provides wide directivity response (wider dispersion) in the horizontal plane and narrower dispersion in the vertical plane, which typically satisfies requirements for the directivity of horn drivers in practical applications. The requirement for narrow directivity in the vertical plane is especially important in line array applications where the overall array includes numerous separate systems which form a vertical wavefront close to that of a cylindrical sound wave to avoid undesirable dispersion of sound energy in the vertical plane and increase coverage distance.

The contour of the outer surface156of the hub portion124and the inner surface158of the housing150may “shape” and improve the wavefront, making it flatter at the exit of the transducer100(exit aperture162). The shape of the hub portion124has different profiles in the vertical and horizontal planes that may provide time alignment and, correspondingly, a flat wavefront in the vertical plane at the exit aperture162. In modern waveguides that are typically used in line arrays, the vertical directivity is controlled by the phase and time relationships of the acoustical signals radiated at different vertical points within the waveguide104. The typical goal is equal time arrival and in-phase radiation across the vertical dimension of the rectangular exit aperture162that provides a “flat” wavefront in the vertical plane.

As illustrated inFIGS.1-6, the shape of the inner surface158of the housing150and the outer surface156of the hub portion124are continuous, smooth, undulating surfaces that provide an uninterrupted pathway from the waveguide inlet160to the waveguide outlet162. The transformation of the air path from the annular exit146of the compression driver102and the corresponding annular waveguide inlet160to the rectangular exit aperture162may be provided by a customized shape of the hub portion124that starts with a generally circular cross-section at the first end126and then transitions into a blade-like shape at the second end128. The waveguide104is symmetric with respect to both a vertical plane (FIGS.1-3and7-8) and a horizontal plane (FIGS.4-6and9-10).

Regions of the hub portion124below a transition point166along the vertical dimension of the waveguide104may follow one curvature and regions of the hub portion124above the transition point166may follow another curvature. As such, the hub portion outer surface156and the housing inner surface158may protrude outward farther from the central axis118adjacent the transition point166compared with below or above the transition point166, wherein the transition point166can have any suitable location between the waveguide inlet160and the waveguide outlet162. For example, with reference toFIGS.4-6which depicts cross-sectional views along a horizontal plane, the outer surface156of the hub portion124may be substantially linear from the waveguide inlet160to the transition point166. The outer surface156may then curve inward until terminating in the blade-like shape at the hub portion second end128. The inner surface158of the housing150may curve slightly outward from the waveguide inlet160to the transition point166, then may curve slightly inward until reaching the waveguide outlet162. The inward curvature of the inner surface158is less than the inward curvature of the outer surface156, thereby increasing the cross-section or width of the annular waveguide pathway170.

Accordingly, the waveguide104provides an annular pathway170for sound waves to travel from the annular waveguide inlet160to the rectangular exit aperture162. The internal cross-sectional area or width of the annular pathway170generally increases from the inlet160to the outlet162of the waveguide104. The waveguide104controls the propagation of sound waves by providing substantially equal sound path lengths from the exit146of the compression driver102, providing a controlled cross-sectional area expansion rate from the inlet160to the outlet162of the waveguide104.

In the embodiments disclosed herein, using a dome diaphragm provides an effective area greater than that of an annular diaphragm, increasing the maximum SPL output of the compression driver. In addition, the dome diaphragm has a comparatively low resonance frequency, and the combination of these properties makes the transducer well suited for two-way line arrays. Still further, the smaller cross-sectional dimensions of the acoustical paths, compared to a driver with a circular exit, improves directivity control at high frequencies. Lastly, the annular interface of the compression driver and the waveguide has a significant advantage of a much shorter driver-waveguide assembly. In a driver with a circular exit, the acoustical path narrows to reach the exit, and then starts widening again in the waveguide. However, in the transducer disclosed herein, the acoustical path widens gradually from the phasing plug through the waveguide, thereby omitting the redundant stage of “narrowing-widening” is omitted and allowing the assembly to be much shorter.