Unmasking the Power of Active Noise Cancellation

Table of Contents

1. Introduction
2. Understanding Sound Transmission
   • Properties of Sound Waves
   • How Sound is Transmitted
   • Compression Waves and Rarefied Gas
3. Building an Enclosure to Block Sound
   • Using Heavy Metal Plates
   • Using Soft Foam Pads
   • Combining Metal Plates and Foam Pads
4. Limitations of Sound Blocking Structures
   • Reflection of Sound Energy
   • The Role of Mass, Absorption, and Stiffness
5. Active Sound Reduction
   • Phasing and Anti-Phase Noise
   • Incorporating Active Sound Reduction into an Enclosure
6. Enhancements for Sound Reduction Structures
   • Distribution of Actuators for Better Sound Reduction
   • Isolating Sound Generators from the Box
   • Future Modifications and Improvements
7. Conclusion

Building an Enclosure to Block Sound

Sound transmission can be a significant challenge when it comes to designing an auxiliary power unit for drones. The noise produced by gasoline engines can be bothersome and disruptive. To minimize this issue, it is crucial to understand how sound is transmitted and take appropriate measures to contain or block it.

Understanding Sound Transmission

Properties of Sound Waves

Sound waves are not like surface waves on Water but are compressed shells of air that move outward from a speaker. These compressed shells Create a series of sinusoidal waves that we perceive as sound. The frequency of these waves impacts the pitch, while their amplitude determines the volume.

How Sound is Transmitted

When a speaker moves forward, it compresses the air molecules in front of it, creating a compressed sheet of air that moves away from the speaker. As the speaker moves backward, it produces a region of rarefied gas behind the compressed sheet. These expanding shells of compression waves and rarefied gas represent sound. The distance between compression waves at a specific frequency determines the pitch.

Building an Enclosure to Block Sound

To reduce the transmission of sound, an effective enclosure needs to be designed. Using materials that either block or absorb sound waves can help achieve this goal.

Using Heavy Metal Plates

Using a heavy metal plate as a barrier can block sound waves by bouncing them elastically off the surface. However, the reflection of sound inside a box made solely of metal plates can result in a buildup of sound energy, reducing its effectiveness as a sound blocker.

Using Soft Foam Pads

Alternatively, using soft foam pads can absorb sound waves by distorting the surface upon impact. The energy of the sound wave is transferred to heat energy within the foam, reducing sound reflection. However, foam alone is not highly effective as it is lightweight and prone to movement, causing secondary sound waves to be significant.

Combining Metal Plates and Foam Pads

A more effective solution combines the use of both metal plates and foam pads. By bonding foam pads to the back surface of metal plates, the plate acts as a backing for the foam, increasing the sound energy absorption. The combination reduces the buildup of energy within the enclosure and allows for better sound blocking.

Limitations of Sound Blocking Structures

While the combination of metal plates and foam pads is effective in reducing sound transmission, there are limitations to consider.

Reflection of Sound Energy

Sound energy can reflect off the inside surfaces of a box, especially if the walls are made of hard, flat plates. This reflection creates a back-and-forth bounce of sound waves, intensifying the sound energy within the box. Additional measures, such as using sound-absorbing materials, can help mitigate this reflection.

The Role of Mass, Absorption, and Stiffness

When building a sound-blocking structure, the key considerations are mass, absorption, and stiffness. Achieving the right balance among these three factors is crucial. Increasing the mass or stiffness of the structure can enhance sound blocking, while increasing sound absorption through materials like foam can help reduce sound reflection.

Active Sound Reduction

In addition to passive sound reduction techniques, active sound reduction can further enhance the sound-blocking capabilities of an enclosure.

Phasing and Anti-Phase Noise

Active sound reduction involves creating an anti-phase noise to cancel out the original sound Wave. By using two speakers and adjusting their phase relationship, it is possible to decrease the overall sound amplitude. This method is effective in reducing unwanted noise transmitted outside of the enclosure.

Incorporating Active Sound Reduction into an Enclosure

By incorporating active sound reduction techniques into the design of an enclosure, it is possible to actively reduce sound amplitude within the box itself. By using microphones to sample the sound and generating anti-phase sound, it becomes possible to cancel out the noise effectively. This method does not require complex programming or structural analysis but instead relies on the properties of sound waves.

Enhancements for Sound Reduction Structures

While the combination of materials and active sound reduction offers effective sound blocking, there are ways to further enhance the performance of sound reduction enclosures.

Distribution of Actuators for Better Sound Reduction

Instead of using a single point of support for actuators, distributing smaller actuators across the surface can provide better sound reduction. Smaller actuators, when spread out, can provide more effective damping and reduce vibrations, leading to improved sound blocking.

Isolating Sound Generators from the Box

To minimize the coupling between sound generators (such as speakers) and the box itself, placing a thin-walled outer structure can act as a barrier. This isolation reduces the interference between the shakers and the microphones, allowing for better control and increased effectiveness in sound reduction.

Future Modifications and Improvements

Continual improvements can be made to sound reduction enclosures. An active circuit that adjusts amplification for each wall Based on sound pressure can be developed to enhance sound reduction capabilities. Additionally, experimenting with different materials, densities, and structures may lead to more efficient sound-blocking designs.

Conclusion

Building an effective enclosure to block sound transmission requires an understanding of sound wave properties and appropriate design choices. By combining materials such as metal plates and foam pads, it is possible to reduce sound reflection and enhance sound absorption. Incorporating active sound reduction techniques further improves the ability to block sound effectively. However, limitations and improvements can be addressed through measures such as distributing actuators and isolating sound generators. Through continuous experimentation and refinement, sound reduction enclosures can be optimized for maximum performance.

Highlights:

• Building an enclosure to block sound transmission is crucial for minimizing the noise produced by gasoline engines in drones.
• Understanding the properties of sound waves and how they are transmitted is essential in designing effective sound-blocking structures.
• Combining heavy metal plates and soft foam pads can create a more effective sound-blocking enclosure.
• Active sound reduction techniques, such as phasing and anti-phase noise, can further enhance the sound-blocking capabilities of an enclosure.
• Enhancements, such as distributing actuators and isolating sound generators, can be made to improve sound reduction structures.

FAQ

Q: What is the purpose of building an enclosure to block sound in drones? A: The enclosure helps reduce the noise produced by gasoline engines, making drones quieter.

Q: How does sound transmission work? A: Sound waves are compressed shells of air that move outward from a speaker. When the speaker moves, it creates compression waves and rarefied gas, representing sound.

Q: What materials are useful for blocking sound waves? A: Heavy metal plates and soft foam pads are commonly used. Combining both materials can be more effective than using them individually.

Q: What is active sound reduction? A: Active sound reduction involves creating anti-phase noise to cancel out the original sound wave and reduce overall sound amplitude.

Q: Can enhancements be made to sound reduction structures? A: Yes, distributing actuators, isolating sound generators, and adjusting amplification can improve the performance of sound reduction enclosures.