Apple wants the speakers on its iPhones to sound even better. The tech giant has filed for a patent (number 20210337304) for a “coating for improving loudspeaker sound quality.”
About the patent filing
In the patent filing, Apple notes that loudspeakers typically include a back volume and a membrane or diaphragm that oscillates and emits sound when driven by an electromagnetic transducer. However, a variety of different forces act on the membrane while it is 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, Apple says that 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. The solution? An acoustically active coating.
Per Apple’s patent filing, 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.