Purpose of resistor in pre_amp circuit
Trying to understand this circuit. What is the resistor R1 for?

R1 biases the transistor so that it can be fed an AC signal via the capacitor C1. It also supplies some signal feedback to keep some semblance of slight quality about things but, as it stands it isn't HiFi (it's very LoFi) and impractical for most loudspeakers due to the DC current that passes through the speaker especially if you are trying to make the speaker operate at any loudness level higher than regular speech levels.