The Patent behind the Six-Speaker Sound System with Force-Cancelling Woofers for the 2021 iMac was published today
Today the US Patent & Trademark Office published a patent application from Apple that relates to the new iMac six-speaker sound system as Apple promotes in their marketing as noted in our cover graphic above. Apple's patent point #0011 states that electronic device comprises a speaker enclosure that includes a six-sided box.
Apple new iMac marketing further states that "The sound system on iMac brings incredible, room-filling audio to any space. Two pairs of force-cancelling woofers create rich, deep bass without unwanted vibrations."
Apple's patent application point #0052 states in-part: "The force cancelation can reduce potential rattle or interference of various components in proximity with the speaker module, thereby improving sound quality. It will be understood that alternative force cancellation configurations can be implemented. For instance, a primary woofer can be positioned between and adjacent to two smaller woofers. The force generated by the two smaller woofers can be substantially equal and opposite to the force generated by the primary woofer. Thus, when acoustically in phase, the primary woofer and the two smaller woofers have the effect of substantially canceling the generated forces."
In the bigger picture, Apple notes that due to the increasing demand for electronic device components with reduced dimensions, yet high performance, integrated speaker assemblies can be designed with limited space available for a back volume.
Back volume, also referred to as speaker volume, is the empty air space in communication with the speaker that can provide air to push against to prevent the speaker from being overdriven. One purpose of the back volume is to contain the back wave or negative wave emitted from the speaker so that the back wave cannot radiate into the ambient atmosphere and interfere with the positive sound waves, thereby allowing for desired levels of acoustic performance.
The acoustic performance in the low frequency audio range can be dependent on the back volume size. The back volume can further influence the stiffness of the diaphragm of a speaker. For instance, the larger the diaphragm and the smaller the back volume, the stiffer the diaphragm becomes. A stiff diaphragm can require more power to produce a desired output as compared to a more flexible diaphragm. Accordingly, it can be desirable to increase the back volume of a speaker assembly to achieve desired levels of performance, while reducing the amount of space within the internal volume of an electronic device occupied by a speaker assembly.
Apple's patent FIG. 1 below represents the new thin iMac illustrating speaker vents; FIG. 4 shows an exploded perspective view of the iMac of FIG. 1 illustrating speaker modules.
Apple's patent figures below represent the various configuration considerations that the engineers presented for the new thin-line iMac speakers.
As one example, Apple notes that the iMac in FIG. 9 can include a housing (#704) which contains one or more speaker assemblies (#718) in an internal volume at least partially defined by the housing. Each speaker assembly can include a speaker enclosure (#724) connected to a speaker module (#720) by one or more tunnels (#730a & #730b). The speaker modules can each include a first woofer (#734a) and a second woofer (#734b). In some examples, the speaker enclosure can define a speaker volume (#740). The speaker enclosure can also include support ribs (#742) positioned within the speaker volume. In some examples, a flexible portion (#746) of the speaker enclosure can have mechanical properties such that it can function as a suspension spring or passive radiator.
The positioning of the support ribs can define the flexible portion and a rigid portion (#748) of one or more of the walls of the speaker enclosure. In some examples, the flexible portion can oscillate or vibrate in a desired manner in response to acoustic waves emitted from the speaker module.
The rigid portion can be held secure and stiffened by the ribs and/or the material of the speaker enclosure itself. In other words, the flexible portion can function as a passive radiator that uses the sound otherwise trapped in the speaker enclosure to excite a resonance on the flexible portion.
In some examples, the material and/or thickness of the wall or walls of the enclosure provides the stiffness and strength in the rigid portion, and the flexibility and tolerance in the flexible portion. In other words, the support ribs may not be necessary to create a passive radiator within the speaker enclosure.
In some examples, the entirety of the wall of the speaker enclosure can vibrate as the passive radiator. That is, the entire wall surface can vibrate or oscillate in response to the acoustic waves emitted from the speaker module.
If you're interesting in diving into the finer details behind the new iMac's speaker system, then review Apple's patent application number 20210176547. Today's patent could be considered a patent fulfilled with the release of the new 2021 iMac.