The manufacturer of EM is Future Sonics (hereinafter referred to as FS) of the United States, with the slogan "FS products can better protect your hearing and further your career". As one of the few top manufacturers (the other is known as Senhai) that adhere to the dynamic circle at present, its product line is extremely short, and in the early years, it did not provide customization to individual users. On average, it changed units every six and a half years. As a customized ear model headset, Ear Monitor fits comfortably and its price is the same as the flagship level of non customized headphones. As the king of customized dynamic circle, the overall performance is calm and natural, and the triple frequency connection is smooth. There was a strong sense of presence. When Faye Wong sang "To Youth", it seemed that she was crooning in the open place.