Gree's noise reduction patent: Adjustable micro-perforated plate + acoustic black hole achieves intelligent noise reduction in washing machines.

In the field of washing machine noise reduction, as washing machine speeds increase and functions become more diversified, the noise spectrum generated during operation becomes more complex. Single sound-absorbing materials are no longer sufficient to meet users' ever-increasing demands for quiet performance. In addition, washing machines generate noise with different characteristics at different working stages (such as washing, spin-drying, and drying), and a fixed noise reduction structure cannot achieve the optimal noise reduction effect.

Gree Electric Appliances recently published a patent titled "Noise Reduction Device and Clothing Processing Equipment" (CN119615572A), which proposes a noise reduction solution based on micro-perforated plates and active noise reduction technology to address the long-standing noise problem of clothing processing equipment such as washing machines.

Noise Reduction Solution Design Ideas

The core of this patent lies in achieving noise reduction through a rotatable micro-perforated plate and a sound-absorbing cavity. The micro-perforated plate has several micro-perforations, forming a sound-absorbing cavity with the inner wall of the enclosure. One end of the plate is rotatably connected to the enclosure, and its rotation is controlled by a drive mechanism. A noise acquisition unit in the noise reduction adjustment module collects noise signals, and the control module controls the drive mechanism based on these signals to adjust the angle of the micro-perforated plate and change the depth of the sound-absorbing cavity, thereby effectively reducing noise for different types of noise.

Schematic diagram of the Helmholtz resonator

Key structural design

In terms of specific technical solutions, this noise reduction device includes several key structures. The enclosure serves as the basic structure, providing a mounting platform for other components.

Schematic diagram of the enclosure in the noise reduction device (2-Enclosure; 21-Side panel)

The micro-perforated panels are 0.2-0.5 mm thick with a perforation rate of 1%-2%. The micro-perforations are 0.2-0.5 mm in diameter and are mostly circular in shape, while the panels themselves are square with specific ranges for side length and width. The material is the same as the enclosure. These design parameters optimize sound absorption performance. The drive mechanism 's rotating components can directly or indirectly rotate the micro-perforated panels around the bottom of the enclosure along its height.

Schematic diagram of the microperforated plate (1-microperforated plate, 11-microperforation)

The noise reduction and adjustment module includes a noise acquisition unit and a control module. The noise acquisition unit is used to acquire noise signals in real time and can use a MEMS microphone. The control module is electrically connected to the noise acquisition unit and the drive mechanism, controls the drive mechanism according to the noise signal, and can also perform operations such as spectrum analysis on the noise signal.

Connection diagram of noise collector, control module, speaker, and rotation drive in the noise reduction device

auxiliary noise reduction design

To further enhance the noise reduction effect, the device also incorporates a noise absorption layer located within the anechoic cavity. This noise absorption layer contains several acoustic black hole structures arranged in multiple rows and columns at intervals.

Cross-sectional schematic diagram of the acoustic black hole structure in the noise reduction device (6-acoustic black hole structure, 61-tubular shell, 62-ring).

Schematic diagram of the Helmholtz resonator with acoustic black hole structure

An acoustic black hole structure is a specially designed structure that can efficiently absorb sound wave energy, similar to how black holes in astronomy absorb matter and light. Its two ends, along the thickness direction of the micro-perforated plate, are connected to the micro-perforated plate and the housing, respectively, and are made of a stretchable material such as rubber or foam.

When the micro-perforated plate rotates, the acoustic black hole structure elongates accordingly, effectively absorbing low-frequency sound waves and improving the noise reduction effect of the entire noise reduction device on low-frequency noise.

Patent Examples

The patent provides several specific embodiments. In the basic embodiment, the noise reduction device is directly integrated inside the washing machine cabinet. The micro-perforated plate is connected at the bottom along the height of the cabinet via a pivot, and is initially installed parallel to the side wall of the cabinet. This arrangement maximizes the use of the internal space of the washing machine without obstructing normal maintenance access.

Schematic diagram of the structure of micro-perforated plates in different positions in the noise reduction device (1-micro-perforated plate; 6-acoustic black hole structure; 7-first limiting mechanism; 8-speaker)

When the system is working, the noise acquisition unit first obtains the noise signal from the washing machine during operation. The control module then performs real-time spectrum analysis on these signals to identify the "target frequency band" where the main noise components are located. Based on the analysis results, the system will adopt different noise reduction strategies:

When the target frequency band is in the low-frequency range (e.g., 50-300Hz, mainly from motor and mechanical vibration), the control module activates a dual noise reduction mechanism: on the one hand, it drives the micro-perforated plate to rotate outward to its maximum angle, increasing the depth of the sound-absorbing cavity and enhancing the physical noise reduction effect; on the other hand, it activates the speaker to emit anti-phase sound waves, further eliminating low-frequency noise through active noise reduction technology. At this time, the acoustic black hole structure extends as the micro-perforated plate rotates, increasing the spacing between its internal rings, which particularly optimizes the absorption of low-frequency sound energy.

When the target frequency band is in the mid-to-high frequency range , the system further subdivides the processing based on the specific frequency: for lower mid-to-high frequencies (such as 300-1500Hz, mainly from water flow and clothing splashing), the micro-perforated plate will maintain a moderate tilt; for higher mid-to-high frequencies (such as above 1500Hz, mainly from mechanical friction and airflow), the micro-perforated plate will return to a vertical position to minimize the depth of the anechoic cavity. This fine adjustment ensures optimal noise reduction across the entire audible frequency range.

The patent highlights an innovative detail: a dedicated speaker is placed at the bottom of the micro-perforated plate near the pivot. This arrangement cleverly solves the problem of low-frequency noise from the bottom of traditional washing machines. As the micro-perforated plate rotates outward, the depth of the bottom cavity increases, and the anti-phase sound waves emitted by the speaker can effectively cancel out the low-frequency noise propagating from the bottom.

Limiting protection mechanism

The device is equipped with a limiting mechanism connected to the housing and located on both sides of the micro-perforated plate in a specific direction. Through telescopic limiting components and driving components, the micro-perforated plate is prevented from shifting due to vibration, ensuring the stable operation of the noise reduction device.

Patent technology advantages

Adaptability is the core advantage of this technology. The noise characteristics of a washing machine change with different operating modes (gentle wash, intensive wash, spin dry, etc.), and traditional static noise reduction structures cannot adapt to these changes. Gree's intelligent adjustment system can identify the noise spectrum characteristics in real time and automatically adjust the angle of the micro-perforated plate to ensure it is always in the optimal noise reduction state. This adaptive characteristic allows the washing machine's acoustic performance to remain stable under various operating conditions.

This patented technology also excels in space utilization and environmental protection . The micro-perforated panel structure is extremely thin and light (only 0.2-0.5mm thick), taking up almost no usable space inside the washing machine. Compared to traditional sound-absorbing cotton, the micro-perforated panel uses metal or high-density plastic materials, offering advantages such as high temperature resistance (up to 100℃ or higher), moisture resistance, and resistance to airflow impact, significantly extending its service life. Furthermore, the all-metal/plastic structure is easier to recycle, aligning with current environmental trends in the home appliance industry.

Conclusion

Gree Electric's noise reduction patent, through intelligent adjustment, an acoustic black hole structure, and active noise cancellation by speakers, has opened up new avenues for physical noise reduction technology. It is not only applicable to washing machines, but its core technology can also be extended to the noise reduction design of other home appliances such as air conditioners, refrigerators, and range hoods.

Note: This article is reprinted from 21dB Acoustics.