How to determine whether a speech segment is voiced/unvoiced?
The reason I asked about the environment of the recording is because if you have a well controlled situation (e.g. a talk-show, an interview that takes place in a studio, a discussion in a relatively quiet room and other similar situations), you can take your power estimates from every frame, create a histogram of those values and use that to find the threshold value that would then discriminate your frames between voiced and un-voiced.

This is similar to Otsu's method and it is important to have a well controlled situation for the assumption of "...a bimodal histogram..." to be valid.

Hope this helps.