Headphones 7455-kHz boost, a dip around 8 kHz, and all sorts of peaks and dips above 8 kHz. For a
natural sound balance with headphones, they should produce measurements that follow
this rough trend when tested on real ears. However, measurements carried out using
headphones on real ears or artifi cial ears (designed to mimic real ears for the purposes of
testing) reveal differing results that can only be interpreted by the experienced observer.
It is clear, though, that published response graphs of headphones should be taken with a
very large pinch of salt.
25.6 The Future
Guessing on the future is always impossible—one can only be guided by current trends,
which are unavoidably based on the past! It is very diffi cult to see how headphones will
develop. New principles of operation are unlikely to spring out of nowhere. Just about all
the likely candidates of moving air have been exploited. However, as with the high polymer
headphone, the invention of new, better materials can often turn a previously impossible
type of headphone into a reality. It is consequently unlikely that tomorrow’s headphones
will be anything other than developments of today’s (unless it becomes possible to inject the
audio signals, suitably coded by digital techniques, directly into the auditory nerve or brain).
That may be highly unlikely, not to say impractical and unnecessary, but digital technology
could play a part in equalizing the response of headphones. For instance, it is possible
to equalize the headphone signal so that the response at the ears when using headphones
more closely mimics the headphone-less characteristic. It would be possible to undertake
this equalization digitally to exactly compensate for each individual and give improved
sound quality. At present this would be fairly expensive, but with processing power falling
it should not be long before it is viable commercially. The technology already exists.
Likewise it is perfectly feasible to build digital fi lters that compensate for each
individual’s head-baffl e effect, thus converting stereo into dummy-head binaural sound
for headphone listening. This could all be done at the same time as the earphone-response
correction outlined earlier. The only question marks are the very limited market for such
equipment and the high cost of developing it. The two confl icting sides (development
costs versus economies of manufacturing scale) may not add up to a very balanced
equation now, but who knows about the future?
Finally, the diaphragm itself may be driven not by analogue but directly using digital
signals. This is not nearly so far-fetched as it sounds. With compact disc as the source,