After prototyping numerous sound systems for automobiles, it is often frustrating for the design engineer to gather a number of listeners and each turns out to have their own perception of the system performance. Some people are sensitive to localization problems in the car yet are unaware of reflection induced frequency response problems. The converse holds true for other listeners that notice small anomalies in frequency but are oblivious to localization difficulties. A trained listener can often balance the frequency and imaging issues though by tilting their head or mentally biasing the acoustical data.The reasons for these differences in listeners is often due to the pinna, which is the visible part of the outer ear. In-The-Ear™ microphones, recently developed by Etymotic Research , are placed in the ear canals of several listeners to measure these influences in hope of understanding why these contrasting opinions exist.