DC Sound Level Meter

Overview

The circuit is designed to measure and monitor the level of an input audio signal by displaying an on the spot reading and not the peak reading.

Terminology

• Audio or Sound Level – refers to the intensity, amount, or degree of an audio signal
• Sound Level Meter – instruments designed to react to noise much like the human ear where the measurements are compared to known standards to identify whether the noise level could have a detrimental effect on humans located near the noise source
• Full Scale Deflection – the maximum or minimum representable value that a signal represents
• Rectifier – an electrical device that converts alternating current to direct current under the process known as rectification

Circuit Explanation

There are two common emitter amplifiers used in the circuit, BC108B because they are fit for use in driver stages, low noise input stages, and signal processing circuits. For full scale deflection, an input sensitivity of 100 mV is permitted across the 100 uA meter. While the circuit possesses a fixed 20 HZ frequency response, the audio frequencies were accepted through the DC blocking capacitor.

The full wave bridge rectifier in the circuit is compsed of four diodes (electronic switches) that will convert tha input signal to a shifting DC voltage.

Application

Typical sound level meters are applied in product testing, maintenance inspections and troubleshooting, machine performance analysis, engineering control studies, audiometer analysis and calibration, frequency analysis and calibration, environmental impact studies, community noise assessment, noise ordinance enforcement, environmental noise measurement and compliance, and occupational noise measurement and compliance. Sound level meters measure real time sound and can have functions such as signal analysis, noise dose measurement, and different time and frequency weighting.