DIY parametric speaker

by Jessie Wong / Friday, 21 April 2023 / Published in Ultrasonic Technology

Parametric speakers are a fascinating technology that utilizes ultrasonic waves to produce highly directional sound beams, enabling sound to be targeted to specific areas without spilling into the surrounding environment. Building your own DIY parametric speaker can be a rewarding project for audio enthusiasts, providing an opportunity to explore the science of sound, experiment with ultrasonic transducers, and create a unique audio device. This article will guide you through the concepts, components, and steps necessary to construct your own parametric speaker.

1. Understanding the Basics of Parametric Speakers

Parametric speakers operate on the principle of amplitude modulation of ultrasonic waves. Unlike conventional speakers that emit sound in all directions, parametric speakers utilize ultrasonic frequencies (typically above 20 kHz) that are inaudible to humans. These ultrasonic waves interact with the air, demodulating into audible frequencies within a highly focused beam. This technology is ideal for applications requiring sound targeting, such as museum exhibits, public announcements, and personal audio systems.

The key components of a parametric speaker include:

Ultrasonic transducers: These generate the ultrasonic waves.
Signal generator: Produces the audio signal to be modulated.
Modulation circuit: Combines the audio signal with the ultrasonic carrier wave.
Amplifier: Boosts the signal for the transducers.

2. Components Needed for a DIY Parametric Speaker

To build your own parametric speaker, you’ll need the following materials and tools:

Component	Description
Ultrasonic transducers	Use high-quality ultrasonic transducers; Beijing Ultrasonic offers reliable options.
Signal generator module	A simple function generator to create the desired carrier wave, typically above 40 kHz.
Modulation circuit	A circuit to modulate the ultrasonic carrier wave with your audio signal.
Power amplifier	A class-D amplifier to drive the ultrasonic transducers efficiently.
Microcontroller (optional)	If you want to add advanced functionalities like programmable modulation.
Power supply	Ensure it meets the voltage and current requirements of your components.
Audio source	Any device with an audio output, such as a smartphone or MP3 player.
Soldering tools	For assembling the circuit components.
Enclosure	To house the components and secure the transducers for optimal sound directionality.

3. Circuit Design and Assembly

The heart of the parametric speaker lies in its modulation and amplification circuits. The steps below outline the basic process:

Signal generation: Use the signal generator to produce a carrier wave with a frequency of 40 kHz or higher. This frequency should match the resonance frequency of your ultrasonic transducers.
Amplitude modulation: Build a modulation circuit to combine the audio signal with the ultrasonic carrier wave. This can be achieved using op-amps or an analog multiplier IC.
Amplification: Connect the modulated signal to a class-D amplifier. Class-D amplifiers are preferred because of their high efficiency, which is critical when driving ultrasonic transducers.
Transducer array: Arrange your ultrasonic transducers in a grid or circular pattern. The alignment and spacing of the transducers significantly affect the directionality and intensity of the sound beam.
Assembly: Solder the components onto a circuit board, ensuring proper connections. Place the board and transducers in an enclosure to protect the components and focus the sound beam.

4. Testing and Calibration

Once your parametric speaker is assembled, testing and calibration are essential to ensure optimal performance.

Initial testing: Connect an audio source to the modulation circuit and power on the system. Aim the parametric speaker at a reflective surface and listen for the demodulated sound.
Beam focus: Adjust the position and spacing of the ultrasonic transducers to maximize the focus and clarity of the sound beam. A well-aligned array will produce a highly directional audio output.
Audio quality: Experiment with different modulation techniques, such as single-sideband (SSB) modulation, to improve the clarity and fidelity of the demodulated sound.
Power levels: Ensure the amplifier is providing sufficient power to the transducers without exceeding their rated capacity.

5. Troubleshooting Common Issues

Building a DIY parametric speaker can present several challenges. Here are some common issues and solutions:

Problem	Solution
Low audio output or clarity	Check the modulation circuit for proper operation and ensure the transducers are correctly aligned.
Overheating components	Verify the power amplifier’s heat dissipation capabilities and ensure adequate ventilation.
Distorted sound	Experiment with different modulation techniques and refine the transducer placement.
Uneven sound beam	Reconfigure the transducer array to improve uniformity and directionality.

6. Applications and Benefits

DIY parametric speakers have a wide range of applications, from hobby projects to practical uses in daily life. Some potential applications include:

Private listening zones: Create a personal audio experience without disturbing others in the room.
Interactive displays: Use focused sound beams in museums or exhibitions to provide audio guides.
Public announcements: Deliver targeted messages in crowded areas without broadcasting to the entire space.

The benefits of parametric speakers are equally impressive. They offer unmatched directional sound control, reduced noise pollution, and the ability to create unique audio experiences.

7. Conclusion

Building a DIY parametric speaker allows you to delve into the exciting world of ultrasonic audio technology. By understanding the principles of operation, sourcing high-quality components such as those from Beijing Ultrasonic, and carefully assembling and calibrating your speaker, you can create a device capable of producing highly directional sound beams. Whether used for private listening or innovative audio applications, a DIY parametric speaker is a testament to the versatility and potential of ultrasonic sound.