The circuit outputs line level audio to drive a headphone or amplifier. If you wish to drive a speaker, then you need to use an amp circuit (there are several on the circuits page). Or you could be very crude and just use a single transistor to drive a speaker by connecting the base to the audio out through a lowish value resistor (value unimportant...1K) and 0.1uf capacitor, collector to V+ and emitter to ground with speaker in series. You'll likely need a few hundred ohm resistor in series with the speaker to prevent heating the transistor. 2N2222 or equivalent.