Microphones and Buzzers

Experiment: Transduction of Sound Waves

1. Aim

To study the conversion of electrical energy into sound energy using a piezoelectric buzzer and the conversion of sound energy back into electrical energy using a condenser microphone.

2. Apparatus / Components Required

• SEELab3 or ExpEYES-17 unit
• One Piezoelectric Buzzer
• One Electret Condenser Microphone
• Connecting wires
• A whistle or tuning fork (optional)
• PC or Smartphone with SEELab3 software

3. Theory & Principle

Sound is a mechanical wave that requires a medium to travel. The devices that convert energy from one form to another (like electrical to mechanical) are called Transducers.

• Piezoelectric Buzzer (Output Transducer): Works on the Inverse Piezoelectric Effect. When an AC voltage is applied to a piezoelectric material, it deforms mechanically, vibrating the air and creating sound waves at the same frequency as the electrical input.
• Condenser Microphone (Input Transducer): Contains a thin diaphragm that acts as one plate of a capacitor. Sound waves cause the diaphragm to vibrate, changing the capacitance and generating a small varying electrical signal that mimics the sound wave’s pressure variations.

4. Circuit Diagram / Setup

1. Microphone: Connect the electret condenser microphone between the MIC terminal and GND. (Note: The MIC terminal provides the necessary DC bias for the microphone).
2. Buzzer: Connect the piezoelectric buzzer between WG and GND.
3. Placement: Align the microphone and buzzer so they face each other at a distance of about $5\text{ cm} - 10\text{ cm}$.

5. Procedure

1. Open the SEELab3 software and select the “Oscilloscope” or “Sound” tool.
2. Testing the Microphone: Enable the trace for the MIC channel. Speak into the microphone or whistle near it. Observe the complex electrical waveforms generated by your voice.
3. Generating Sound: Set WG to a sine wave. Adjust the frequency to find the buzzer’s resonant point (usually around $3000\text{ Hz} - 4000\text{ Hz}$). At this frequency, the sound will be loudest and the trace on the oscilloscope will be most stable.
4. Signal Capture: Observe the waveform on the MIC channel while the buzzer is sounding. Compare its frequency with the WG frequency.
5. Distance Study: Move the buzzer further away and observe the decrease in the amplitude of the captured electrical signal.

6. Observation Table

7. Results and Discussion

• The piezoelectric buzzer successfully converted the AC electrical signal from WG into an audible sound wave.
• The condenser microphone converted the sound waves back into electrical signals, which were visualized on the oscilloscope.
• It was observed that the amplitude of the captured signal is highly dependent on the frequency and the distance between the source and the receiver.

8. Precautions

1. Microphone Polarity: Electret microphones have polarity. Ensure the terminal connected to the casing is grounded.
2. Avoid Clipping: If you shout too loudly into the microphone, the signal may “clip” (flatten at the top), leading to distortion.
3. Buzzer Resonance: Piezo buzzers are very quiet outside their resonant frequency. Always check the datasheet or sweep the frequency to find the peak performance point.

9. Troubleshooting