ETYMOTIC research ER4XR. I purchased it from Soundhouse about two years ago. I'm putting it up for sale. Please comment if you have a desired purchase price. While the "ER4SR" offers a flat sound faithful to the original sound, the "ER4XR" emphasizes the low frequencies while maintaining high resolution, achieving a powerful and dynamic sound that you wouldn't expect from a balanced armature type. The mid-high frequencies are not buried by the low frequencies, allowing for clear music playback befitting a flagship model. I used it in conjunction with other earphones, so the total usage time is probably less than 100 hours. I will also include the genuine 2.5mm balanced cable. Please check the photos for other accessories. It is also for sale on other sites, so please forgive me if it sells out.