744 Chapter 25
air, modifi es the frequency response as perceived by the ear. This situation is additionally
confused by the fact that each person’s ears are different in shape and at high frequencies
will introduce their own pattern of refl ections, causing reinforcements and cancellations
at different frequencies. Measuring headphones with artifi cial ears reveals some pretty
horrifying curves, but the results on the heads of real listeners are equally alarming.
The fact of the matter is that even if a headphone were made to measure “ fl at ” on a
person’s head as measured inside the cavity at the entrance to the ear, the headphone
would not sound right. This is quite simply because, even when listening without
headphones, the sound pressure response at this point, in the ear canal, at the eardrum, or
wherever you care to measure it, is simply not fl at. We are not dealing with an amplifi er
or an electromechanical transducer but the human ear. The ear and brain have of course
fi gured out that the normally complex pattern of refl ections and cancellations with which
it has to continually deal are perfectly natural and they sound that way.
Unfortunately, each individual’s ears make their own different imprint, but there are
some rough trends that can be observed. For instance, there is generally a 2-kHz to
Figure 25.8 : Sanyo “ turbo ” intra-aural earphones with Sanyo’s GP600D personal stereo.