Apple has applied for a patent (number 20180098172) for “spatial audio rendering for beaming loudspeaker array” that involves the technology in the HomePod — and perhaps future versions of the wireless speaker.
The patent filing is for a process for reproducing sound using a loudspeaker array housed in a loudspeaker cabinet and which includes the selection of a number of sound rendering modes and changing the selected sound rendering mode based on changes in one or both of sensor data and a user interface selection. The sound rendering modes include a number of mid-side modes and at least one direct-ambient mode.
In the patent filing, Apple notes that a lot of effort has been spent on developing techniques to reproduce a sound recording with improved quality, so that it sounds as natural as in the original recording environment. The approach is to create around the listener a sound field whose spatial distribution more closely approximates that of the original recording environment. Apple thinks beam forming is the answer.
As explained by MathWorks, the idea of using an array of speakers to shape sound using beamforming has been around for some time, but it’s been difficult to put into practice. Beamforming relies on different speakers responding to the same input signal in different ways—for example, by slightly delaying the signal, playing it at different volumes, or using cancellation effects. The different speaker settings allow the system to control the size, shape, and direction of the acoustic wave.
Because of the large range of sound wavelengths, there are conflicting requirements for ensuring good performance at both low frequencies (requiring a relatively large array size) and high frequencies (requiring a small distance between speakers). Fulfilling both requirements typically means that the array needs to consist of a relatively large number of speakers that have to be controlled individually. As a result, dynamically shaping the acoustic wave requires powerful real-time signal processing that until recently has been too expensive for consumer applications. With the falling cost of signal processing chips, this technology has become cheap enough to be applied in consumer products.
Of course, Apple files for — and is granted — lots of patents by the U.S. Patent & Trademark Office. Many are for inventions that never see the light of day. However, you never can tell which ones will materialize in a real product.