it depends on the speaker. Is it a powered speaker with an amp? what is the ohm and watt rating? Is he sending the output from the Pi to an amp and then from the amp to the new speaker? What is the brand of speaker?
I reallise you might not know the answer to any of these questions but that is the kind of information that is needed tohelp you out. You can't just attach a big speaker to any device and expect it to work unless it is a powered speaker that has an amp built in.
A good test is to take your mobile phone and see if it can drive the speaker. If it can't, the pi won't either.