Researchers have determined that Americans between 25 and 64 years old hear better than their grandparents did at the same age.  Comparing research done in 1959-1962 with similar studies in 1999-2004, it appears that upper-frequency hearing is notably better than it used to be; middle-frequency hearing is roughly the same.

Researchers suspect that a combination of better treatment of childhood ear infections, fewer smokers and better health care in general, and a reduction in manufacturing jobs (as well as better hearing protection in today’s workplaces) have led to the improvement.

The reduction in upper-frequency hearing loss is especially important in speech recognition.

Women from three generations converse (NIDCD)

For more, see this NIDCD press release and this post on About.com that includes several related links.