As others have asked, what do you want to accomplish. You would need to understand the result would be a monoaural signel - exactly the same thing emanating from both speakers. The major issue is that the impedance load on the amplifier would be cut in half. That means the speakers would draw more current from the amplifier which could be a problem for the amp, the speakers or both. As others have said above, it is doable with the right equipment. But you need to understand that two channel input would become monaural. It is an unusual thing to want to do.
