Released in 1991, the ER4 was the world’s first noise-isolating high-fidelity in-ear earphone that became the basis of all subsequent in-ear earphones and in-ear monitors worldwide, creating an entire category of consumer electronics. 30 years later, the ER4 is still produced and while it’s changed over the years, it is still channel-balanced to within 1 dB by Etymotic.
If any earphone was to be considered the most significant in earphone history, it would be the ER4, the one that started it all. So I thought it would be interesting to see how it has evolved over the years.
