USB mode does not require a 3.5 audio cable. Plug it directly into the car's USB interface or the speaker's USB interface, and it can be used directly after pairing with the mobile phone's Bluetooth. Noticed : USB playback mode can only be used when the car USB interface or speaker USB interface supports USB audio output. In AUX mode, you need to connect one end of the 3.5 audio cable to the kn318 audio interface, and the other end to the car 3.5 audio interface or the top 3.5 audio interface -speaker, then it can be used after pairing with the mobile phone's Bluetooth. Built-in microphone, when the mobile phone speaks, you can make hands-free calls through the product microphone, which is very convenient to use in the car. It adopts the appearance of piano baking varnish and the compact and mini body design, the total length of the body is only 3.2cm. The USB interface of the audio equipment has the function of audio transmission, which can be directly plugged into the USB; the USB of a small number of devices may be incompatible or delayed, so it should be used in conjunction with AUX! Built-in Bluetooth 5.1 chip, wired to wireless, away from clutter and the constraint of various threads, which changes cumbersome life