The Five differences between speech and music in hearing aids..

Also....

Typical outputs for normal intensity speech can range from 53 dB SPL for the [th] as in 'think' to about 77 dB SPL for the [a] in 'father'.
Shouted speech can reach 83 dB SPL.
This 24 dB range (+/- 12 dB) is related to the characteristics of the human vocal tract and vocal chords.

http://www.audiologyonline.com/articles/article_detail.asp?article_id=477

Sound Therapy options.... Tinnitus..

http://www.audiologyonline.com/articles/article_detail.asp?article_id=1687

Age related voice changes.. Men higher pitched..
Women lower pitched..

http://www.sciencedaily.com/releases/1999/11/991124070453.htm