There is some debate about where, exactly, the vocal range for each voice lies. Roughly speaking, however, the alto range is considered to be just under two octaves, going from G3, or the G below middle C, up to E5, or the E 10 notes above middle C. Tenors, on the other hand, have a range roughly from C3, or the C one octave below middle C, up to C5, or the C one octave above middle C.
Although tenors tend to sing somewhat lower than altos overall, there is significant overlap between the two ranges. In addition, women who sing both alto and tenor parts typically have deeper, richer tones than those who sing soprano or mezzo soprano. This is because they are singing from their "chest voices," which resonate deeper and lower in their bodies than the voices of those in the higher ranges, who typically sing from their "head voices."
Some argue that women should never sing the tenor part in choral settings, especially if the group is a mixture of men and women. They may feel this way simply because they prefer the more traditional divisions. Others insist that female and male tenor voices do not blend well. Finally, some vocal instructors believe it is harmful to women's long-term vocal health for them to sing regularly in such a low register.
Although many people believe female and male tenor voices have intrinsically different sounds, a 2010 study analyzed the vocal characteristics of both groups and found "there was more variance between the individuals than between groups of male and female singers" and that there were "no significant differences" between the voices of the two genders. In addition, the lack of male singers in many choral groups has caused music directors to use female tenors out of necessity.