The receiver USB mode does not need to use a 3.5 audio cable, because it can be directly plugged into the car USB port and speaker USB port, and can be used directly after pairing with the mobile phone, but note that the car USB port and speaker USB port must support USB audio output. The receiver auxiliary mode needs 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 and the speaker 3.5 audio interface, and it can be used after pairing with the bluetooth-compatible of the mobile phone. Built-in microphone, you can use the microphone on the KN318 to make hands-free calls when talking on the phone, which is very convenient to use in the car. Item Name: bluetooth-compatible 5.1 Audio Receiver Pairing Name: KN318 Pairing: Blue LED Flashes Pairing Successfully: the Blue Light Keeps on Technology: BT5.1, A2DP, AVRCP Operating Range: up to 10m/33ft Material: ABS Features: Portable, USB Mode, Built-in Microphone, Easy to Carry Size: 3.2cm x 1.7cm x 0.9cm/1.26" x 0.67" x 0.35" (Approx.) Notes: Due to the light and screen setting difference, the item& 39;s color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement. Package Includes: 1 x bluetooth-compatible 5.1 Audio Receiver 1 x 3.5mm Auxiliary Cable 1 x User Manual