On August 14, 2014, the US Patent & Trademark Office published a patent application from Apple titled "Long-Throw Acoustic Transducer." Apple's invention generally relates to the field of audio speakers that use a moving magnetic piston as the sound producing element. The invention will be able to produce more vibrant audio for music and alerts with vibrations for future iDevices. Apple notes that their invention may be advantageous for acoustic transducers that are used in "thin" devices where the height of the acoustic transducer must be small to fit within the device. Theoretically that could mean that this was designed for the iPhone 6 and/or other future iDevices like the iPad mini and beyond. As far as the iPhone goes, we'll know if this was used or not the minute that iFixit does their teardown of the iPhone 6 in September.
Apple's Patent Background
Audio speakers use electrical signals to produce air pressure waves which are perceived as sounds. Many audio speakers use a diaphragm that is movably suspended in a frame. The diaphragm is coupled to a voice coil that is suspended in a magnetic field. The electrical signals representing the sound flow through the voice coil and interact with the magnetic field. This causes the voice coil and the coupled diaphragm to oscillate in response to the electrical signal. The oscillation of the diaphragm produces air pressure waves.
It is necessary for the audio speakers to displace a volume of air to produce sound pressure waves that are perceptible to a listener. A speaker diaphragm is limited in the distance it can move, and this limit become smaller as the speaker is reduced in size. This limits the volume of sound that can be produced by a small speaker, particularly in lower frequency range.
It would be desirable to provide an audio speaker that can displace a larger volume of air from a more compact structure suitable for use in portable devices.
Apple invents a new Audio System for Thin Devices
Apple's invention generally relates to the field of audio speakers that use a moving magnetic piston as the sound producing element. This will produce more vibrant audio for music and alerts with vibrations for iDevices. Apple notes that their invention may be advantageous for acoustic transducers that are used in "thin" devices where the height of the acoustic transducer must be small to fit within the device.
More specifically, Apple's invention covers an acoustic transducer which includes a housing, which may be a circular cylinder or may have a rectangular cross-section. Two permanent magnets that closely fit the inside of the housing are joined by a linkage having a high magnetic permeability to form a piston that is inserted into the housing. Two pole coils surround the housing with each coil adjacent one of the permanent magnets. The coils are arranged to cause the piston to oscillate within the housing and emit sound waves when coupled to an electrical signal. One end of the housing may be closed except for a barometric leak. A third permanent magnet or a spring may provide a restoring force that centers the piston between the coils when the piston is not subjected to other forces. One of the permanent magnets on the piston may include a vent passage.
About the Acoustic Transducer
In Apple's patent FIG. 1 noted below we technically see a view of an acoustic transducer #100. The acoustic transducer shown includes a cylindrical housing #110 having a circular cross-section, which is shown with a front portion of the housing cut away along a diameter to allow the internal components to be seen.
The acoustic transducer further includes a piston #120. A first permanent magnet #122 and a second permanent magnet #126 are coupled to a linkage #124 having a high magnetic permeability to form the piston. One of the permanent magnets provides a north magnetic pole for the piston structure and the other permanent magnet provides a south magnetic pole. Each of the permanent magnets closely fit to the inside of the housing. A ferromagnetic liquid may be used between the first and second permanent magnets and the housing to provide lubrication and a seal between the magnets and the housing.
Oscillations of the piston at audible frequencies will cause an audible sound to be emitted from the two open ends noted as #112 and #114 of the housing. The pressure waves coming out of each of the two open ends will be out-of-phase and could cancel in far field. However, if the acoustic transducer is situated such that one end #114 is opened to the exterior of a device casing and the other end #112 radiates into the inside of the device casing, essentially putting it in a wraparound baffle, the concern of phase cancellation can be mitigated.
Oscillations of the piston at lower frequencies, perhaps between 100 HZ and 250 Hz or perhaps even into sub-audible ranges, may produce a sufficiently strong vibration that the acoustic transducer can be used to produce a tactile alert.
For example, in a cellular telephone application it may be possible to use the acoustic transducer as both a speaker and an alerting vibrator. By configuring the subsystem that delivers the electrical signal to the acoustic transducer to provide either a signal suitable to produce an audio output or a signal suitable to produce tactile alert, which may also result in an audible audio output, the acoustic transducer may selectively perform the functions of both an audio speaker and an alerting vibrator.
The separation of the first and second permanent magnets and the first pole coil and the second pole coil allows the piston to achieve larger displacements with a lower piston mass than would be possible with a single permanent magnet and/or a single coil. This in turn allow a larger volume of air to be displaced by the piston which creates a louder sound.
In Apple's patent FIG. 3 noted above we're able to see a pictorial view of another version of the acoustic transducer.
Acoustic Transducer for Thin Devices
In Apple's patent FIG. 5 below we're able to see a pictorial view of a third kind of acoustic transducer that has a housing that is a cylinder with a cross-section of a rectangle with filleted corners. The use of a rectangular cylinder #510 for the housing allows the acoustic transducer to have a larger cross-section and thus, a larger volume of air displacement than a circular cylindrical housing with a diameter equal to the smaller side of the rectangle. This may be advantageous for acoustic transducers that are used in "thin" devices where the height of the acoustic transducer must be small to fit within the device.
Apple credits Scott Porter, Christopher Wilk and Ruchir Dave as the inventors of patent application 20140226849 which was originally filed in Q1 2013. Considering that this is a patent application, the timing of such a product to market is unknown at this time.
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