For Apple, making their devices lighter and thinner is an obsession and the lightest of their devices have often been given the 'Air' brand – as in the iPad Air or the MacBook Air. That's a quality trait that consumers want in their mobile devices and Apple is now working on reinventing their audio speakers for a wide range of products, with the iPhone being its main focus in their latest patent filing. To make the speakers ever thinner, Apple's Acoustical Specialist Alex Salvatti invented speakers using a Halbach Array audio transducer. Salvatti worked with JBL Professional as the Principle R&D Engineer for 15 years.
Salvatti notes that portable consumer electronics devices, such as mobile phones, have continued to become more and more compact. As the form factor of such devices shrinks, system enclosures become smaller and the space available for speaker integration is reduced.
In the case of an audio speaker typically having a voicecoil suspended below a diaphragm within a gap of a magnetic return structure, precious space is occupied by the magnetic return structure that is required to direct the magnetic field produced by the magnet around the voicecoil. More particularly, since the voicecoil and the magnetic return structure extend along the axis of sound emission, they take up z-height and limit the degree to which the speaker thickness can be reduced.
As described in the patent filing, eliminating the magnetic return structure and helical voicecoil may allow for the vertical thickness of the speaker to be reduced. That is, the voicecoil may be integrated along a surface of the diaphragm and configured to interact with a magnetic field produced by a magnetic array such that the voicecoil operates within the fringe flux of the magnetic field and the thickness of the speaker is limited only by the magnetic array thickness and the excursion clearance of the diaphragm.
In one embodiment, an iPhone (mobile phone handset) is provided having a housing and a microspeaker coupled with the housing. The microspeaker may include a diaphragm configured to move along a central axis. The diaphragm may have a dielectric surface orthogonal to the central axis, and a voicecoil coupled with the dielectric surface. The voicecoil may include a conductive winding having one or more conductive paths running along the dielectric surface. The microspeaker may also include a magnetic Halbach array including at least three magnetized portions arranged side-by-side.
Each magnetized portion may extend along a respective longitudinal axis and produce respective magnetic field lines perpendicular to the respective longitudinal axis. Thus, the magnetic Halbach array may direct the magnetic field lines toward the voicecoil such that the magnetic field lines intersect the voicecoil to cause a Lorentz force to move the diaphragm along the central axis.
In an embodiment, the magnetic field lines that intersect the voicecoil run parallel to the dielectric surface and perpendicular to the conductive winding. The micro speaker may include a processor to provide an electrical audio signal to the conductive winding to move the diaphragm in response to the electrical audio signal.
Various magnetic Halbach array configurations may be incorporated in the mobile phone handset. For example, the magnetic Halbach array may include five or more magnetized portions arranged side-by-side such that each magnetized portion that is sandwiched between two adjacent magnetic portions produces respective magnetic field lines perpendicular to respective magnetic field lines produced by the adjacent magnetic portions. The magnetized portions may include magnetic rods, and a middle magnetized portion of the magnetized portions may include a rod length and a rod width.
In Apple's patent FIG. 5B noted above we're able to see a sectional view shown in perspective of a magnetic array having several Halbach arrays directing a magnetic field toward a voicecoil.
Apple patent application 20160212546 was filed in Q3 2015. The patent filing doesn't spend any time trying to present a marketing case for this new speaker in plain English. The invention is strictly technical and could only be appreciated by audio engineers that are familiar with the terminology and processes of this field. But if you like a challenging read – then check-out Apple's patent filing titled "Halbach Array Audio Transducer" here. Considering that this is a patent application, the timing of such a product to market is unknown at this time.
Apple's engineer/inventor Alex Salvatti worked on another Apple invention that came to light earlier this month that we covered in a report titled "Apple Advances their Work on Waterproof Speakers."
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