"earphones may be preferred by those who want to hear the slight high-frequency boost which is standard practice in CD and vinyl recordings (5 dB at 10 kHz). ER-4B earphones were originally designed to provide an eardrum-pressure frequency response closely mimicking that of the open ear in a diffuse sound field, making them ideal for any material that has not been equalized for loudspeaker playback, such as properly equalized binaural recordings. Many early listeners found the 4B earphones a bit bright, which led to the introduction of the ER-4S."
Que significa exactamente esto?
Gráfica de la respuesta:

MI inglés es un poco precario, y usando el traductor la explicación me queda un poco grande.
Saludos!