This is the SONY Walkman WM-2 dynamic headphones, model MDR-4L1S. Sound from both left and right sides has been confirmed. The mute function, activated by pressing the WALKMAN button, has also been confirmed to work. - Model Name: MDR-4LIS - Brand: SONY Walkman - Type: Dynamic Stereo Headphones - Cable Length: Standard length - Design: Open-air type Released in 1981 SONY DYNAMIC STEREO HEADPHONES MDR-4(L1S) These headphones were developed for the second-generation cassette Walkman WM-2. They are lightweight and open-type, making you almost forget you're wearing them, and they offer excellent sound quality. They can be used with players and smartphones equipped with a standard 3.5mm mini-jack. Pressing the orange "WALKMAN" button on the splitter activates the mute function, allowing you to hear external sounds. *This is a vintage audio product from over 40 years ago. Some parts may have aged or show individual differences. The original performance when new is not guaranteed. Please understand and acknowledge the above before purchasing.