Nothing, not even a full-sized headphone, comes close to ER-4B in terms of tonal accuracy(diffuse-field). How accurate is it? Its target response is almost same as the one from the most up-to date study on the eardrum response in a diffuse-field. Although this product is advertised for binaural recordings only, it is basically same as ER-4S with the lack of room attenuation at the high frequencies. ER-4B should be little too bright for normal recordings, but once you figure out how to utilize this with a binaural simulator, you'll see ER-4B is not in the league of headphones anymore, rather in the league of hi-fi speakers.