This requires a different technique from more usual sound level measurements. If you tried to measure the sound level from earphones with an ordinary sound level meter, you could get very different answers depending on exactly where you put the microphone and very likely none of them would be right!To measure an earphone properly, you have to put it on or in, an ear! Real ears vary between individuals, so in practice we use a standard artificial ear, called a coupler. This incorporates a microphone, which measures the sound level in a position corresponding to the eardrum in a real ear.