Apple wants to improve the speakers in its various devices with a special coating

Apple has been granted a patent (number US 11606640 B2) for “coating for improving loudspeaker sound quality.” The goal is to improve the speakers in the company’s various products. 

About the patent

The patent relates generally to audio speakers and, in particular, but not exclusively, to a coating that improves loudspeaker sound quality and to audio speakers that use the coating in their back volumes to improve loudspeaker performance.

Speakers typically include a back volume and a membrane or diaphragm that oscillates and emits sound when driven by an electromagnetic transducer. A variety of different forces act on the membrane while it’s being moved, distorting its intended acceleration by the electromagnet and thus distorting the sound waves it emits. Reduction of these additional membrane forces leads to improved sound quality.

One of the forces acting on the membrane results from pressure fluctuations in the back volume due to compression and decompression by the moving membrane of air in the back volume. These pressure fluctuations can be reduced by increasing the space of the back volume—e.g., by making it larger. 

However, in hand-held devices such as cell phones, increasing the size of the back volume is possible only to a minor degree because these devices should be kept conveniently small. Apple’s solution is a special coating to improve sound quality.

Summary of the patent

Here’s Apple’s abstract of the patent: “Aspects are disclosed of an acoustically active coating. The coating is a porous coating having a thickness and including between 2% and 30% by mass of a binder and between 70% and 98% by mass of a zeolite. The coating comprises a plurality of convex shapes connected by concave connectors and has a distribution of pore sizes. Other embodiments are disclosed and claimed.”