Spectrum of the gravitational waves. Pop II, Pop III.2, and Pop III.1 stars are denoted by blue, red, and black lines, respectively. Case A (f_{∗ ,III} = 0.01,f_esc = 0.21), case B (f_{∗ ,III} = 0.004,f_esc = 0.45), and case C (f_{∗ ,III} = 0.002,f_esc = 0.75) are denoted by dashed, solid and dotted lines, respectively. The sensitivity curves of the advanced LIGO H1L1, LISA, and BBO detectors are denoted by green, orange, and purple, respectively (Thrane & Romano 2013), assuming T = 1 yr of observations.