IoT devices operate in constrained conditions, with limited supply voltage and power and, depending on the application, with set requirements also on bandwidth. On the other hand, noise is a prime concern because it puts a lower bound on the dynamic range. To balance these constraints and evaluate the most efficient front-end, the Noise Efficiency Factor (NEF) has been proposed, in effect, judging the efficiency of the amplifier based on the current consumption, bandwidth and input referred noise. Acoustic band front-ends are especially sensitive to noise because of their wide band (20Hz-22kHz) but also because of the need to sense low signal levels.