Infinity Alpha Junior Manual Del Usuario página 6

Line level
If your receiver has subwoofer output jacks, you may connect the Alpha Junior
Subwoofer using this method.
Note: Some receivers/amplifiers have a single (mono) subwoofer output. In this case,
it is recommended that you use a "Y"-connector (not included) to maximize the
subwoofer's performance.
6 N Alpha Junior Subwoofer – Owner's Manual