It should be related to Interaural Intensity Difference. Your brain is programmed to compare the sound perceived by both of ears. Usually your brain uses this data to determine the direction of sound. In case of single-ear IEM the pressure difference between both ears will be at max. One ear hears everything and the other ear is dead silent. So it comes down to perception.
Try single ear IEM in a crowded coffee shop. It wont sound that high then. The pressure difference will be lesser.
Latest Answers