Initial Impressions of Yamaha EPH-100: EPH-100's bass is strong, deep, tight and punchy as compared to the Eterna Rev.1, it remains controlled as compared to the eterna Rev. 1. Mid-range is neither recessed nor forward but it is slightly forward than the eterna Rev. 1. Clarity, details and note presentation is excellent. EPH-100's treble is more extended than the Eterna Rev. 1 but still remains smooth(NOTE: My ears are more prone to harshness in the treble region). I like the treble of EPH-100 a lot. Instrument separation is obviously better than the Eterna Rev. 1. Before EPH-100, Eterna lacks air but it is not the case with the EPH-100 at all. EPH-100 doesn't lack air at all.
EDIT: After listening them for few more hours, I can say that Eterna has slight recessed mid-range next to the EPH-100. Eterna has more mid-bass which leads to sound them thicker and lacks clarity before Yamaha EPH-100. Next to EPH-100, Eterna's bass is little bit boomy. EPH-100 has better instrument separation, airier sound, not as thick as eterna.
EPH-100 and Eterna both have very good bass quantity but EPH-100 is better in terms of quality bass.