This figure seems to indicate an upper limit of 8,000 Hz for the sound energy in speech. In fact, the spectrum does extend to higher frequencies, especially for the “s” sound.8 But the ability to hear these higher frequencies, though it may be important for such things as sound localization, makes little contribution to speech intelligibility. This is one of the reasons that pure-tone audiometry does not normally include frequencies higher than 8,000 Hz.