Differences between two diode balanced modulator and four diodes balanced modulator

I need to know the difference between two diode balanced modulator and four diodes balanced modulator.

where can i find that information?. Book, paper, what ever..

The two diode type is singly balanced and the four type is double balanced. This means that either one or both of the drive signals (such as audio and carrier) does not appear in the output at significant amplitudes.

In the singly balanced design it is best to allow the baseband through and suppress the carrier due to the baseband being easily filtered out and the carrier not.