Help please with Tone4 tutorial

i built the circuit exactly as shown in the arduino tutorial:

however, the speakers are not loud enough for my uses (i need about double the volume), any easy fixes? i am new to arduino so please use simple language

ps i am using the arduino uno

Look at this post, using mosfet;topic=157647.0;attach=39938

A single loudspeaker can double the volume with the toneAC() library, Arduino Playground - toneAC Library

Perhaps with another loudspeaker, or placing the loudspeaker in a box, already will make it twice as loud.