Design and analysis of watch speaker to enhance waterproof performance by using liquid silicone rubber side diaphragm

Abstract

Smartwatches provide many useful functions to users, such as texting messages, receiving social media updates, and playing music. The microspeaker used in a smartwatch needs to be smaller than that used in a smartphone, and it also requires high-quality acoustic and good waterproof performance. This study proposes a watch speaker with improved low-frequency acoustic performance by using the electromagnetic-mechanical-acoustic (E-M-A) coupling analysis method. Experimental results obtained using a prototype were used to validate the analysis method. Based on the same method, a novel type of watch speaker with smaller airgaps demonstrated an improved sound pressure level (SPL) at low frequencies when using a 60 A shore-hardness liquid silicone rubber (LSR) side diaphragm (SDP). The novel type using 60 A hardness SDP is named novel type #1. At the same time, novel type #2 and novel type #3 were analyzed for comparison with novel type #1. The analysis SPL results show that the novel type #2 shows a better low-frequency SPL and a minor drop in the mid-frequency. The watch-speaker samples were manufactured and subjected to SPL measurements. Furthermore, the novel type #2 with LSR has lower von Mises stress on the SDP, excellent waterproof performance that can withstand 10 ATM, and similar total harmonic distortion (THD) to prototype.