I don't see anything to indicate that RL is \$2.2k\Omega\$. That resistor is there as part of the power supply to the microphone. If the resistor weren't there, then the output of the microphone would be shorted to the power supply, and then you'd have no output signal; the output signal would just be \$V_s\$.

RL together with the capacitor form a capacitive coupling. The signal we care about from the microphone is always changing, and mostly we care about the frequencies from 20 Hz to 20 kHz, because that's the range of human hearing. Higher frequencies can pass through capacitors, while lower frequencies can not. DC, being the lowest frequency (0 Hz) can't pass through a capacitor at all.

So, the capacitor blocks \$V_S\$ from the output. The signal from the microphone, which is AC, is less blocked by the capacitor than it is by the resistor, so most of the current goes to the output.

Negative Feedback

It gives you:

• better linearity
• lower gain
• even lower output impedance
• opportunity for frequency-dependent gain

As shown, you get DC feedback via R1+R2. But R1/C1 forms a low pass filter for signals coming from the collector and going to the base. Less negative feedback means less reduction in gain for high frerquencies. Cancel out all those double-negatives and you're left with a high-pass filter.

The transistor below corresponds to Q5 in your drawing.

^{simulate this circuit – Schematic created using CircuitLab}