How to play music from multiple speakers?

So I'm having a new years party and i need to have loud music of course! So I'm going to be using a beats by dre beatbox speaker but i don't think that it will be loud enough so I'm also using a friends speakers ( ) So how can i make my phone play to both at the same time? I think they are NOT wireless… Also is there a way that i could plug my iPhone in to one and my macbook in to another but have them play the same music symutaniously?

If you want to be able to play music from multiple speakers you will probably need to use a jack splitter like this:

Protronix%C2%AE Stereo Headphone Splitter Adapter

Just plug the jack splitter into the headphone jack in your iPhone and plug each Speaker into one of the audio jacks on the splitter.