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In the field of washing machine noise reduction, as washing machine speeds increase and functions diversify, the noise spectrum generated during operation becomes more complex. A single sound-absorbing material can no longer meet users' increasing demands for quiet performance. Furthermore, washing machines generate noise with varying characteristics during different operating phases (such as washing, spinning, and drying), making a fixed noise reduction structure incapable of achieving optimal noise reduction results.
Gree Electric Appliances recently disclosed a patent titled "Noise Reduction Device and Clothing Processing Equipment" (CN119615572A). To address the long-standing noise problem of clothing processing equipment such as washing machines, it proposed a noise reduction solution based on micro-perforated plates and active noise reduction technology.
Noise reduction solution design ideas
The core of this patent is to achieve noise reduction through a rotatable micro-perforated plate and a sound-absorbing cavity. The micro-perforated plate has several micro-perforations, which form a sound-absorbing cavity with the inner wall of the box. One end of the micro-perforated plate is rotatably connected to the box, and its rotation is controlled by a drive mechanism. The noise collector in the noise reduction adjustment module collects noise signals. The control module controls the drive mechanism based on the signals, adjusts the angle of the micro-perforated plate, and changes the depth of the sound-absorbing cavity, thereby effectively reducing noise according to different noises.
Schematic diagram of the principle of Helmholtz resonator
Key structural design
In terms of specific technical solutions, the noise reduction device includes several key structures. The box serves as the basic structure and provides a mounting carrier for other components.
Schematic diagram of the noise reduction device's enclosure (2-enclosure; 21-side panel)
The microperforated panels have a thickness of 0.2-0.5 mm and a perforation rate of 1%-2%. The microperforations are 0.2-0.5 mm in diameter and are mostly circular, with square panels having specific side length and width ranges. Made of the same material as the enclosure, these parameters optimize sound absorption performance. The drive mechanism 's rotating drive element directly or indirectly rotates the microperforated panels around the bottom end of the enclosure's height.
Schematic diagram of the structure of a micro-perforated plate (1-micro-perforated plate, 11-micro-perforated plate)
The noise reduction and adjustment module consists of a noise collector and a control module. The noise collector is used to collect noise signals in real time and can use a MEMS microphone. The control module is electrically connected to the noise collector and the drive mechanism, controlling the drive mechanism based on the noise signal and performing operations such as spectrum analysis on the noise signal.
Schematic diagram of the connection between the noise collector, control module, speaker, and rotating drive in the noise reduction device
Auxiliary noise reduction design
To further enhance the noise reduction effect, the device also features a noise absorption layer within the anechoic cavity. The layer contains several acoustic black hole structures arranged in multiple rows and columns.
Schematic cross-sectional view 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 principle of a Helmholtz resonator with an acoustic black hole structure
The acoustic black hole structure is a specially designed structure that efficiently absorbs sound wave energy, similar to how black holes in astronomy absorb matter and light. It is connected to the microperforated plate and the enclosure at both ends along the thickness of the microperforated plate. It is made of a flexible material such as rubber or foam.
When the micro-perforated plate rotates, the acoustic black hole structure can stretch 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 into the washing machine casing. The micro-perforated plate is connected to the bottom end of the casing through a rotating shaft and is initially installed parallel to the casing sidewall. This arrangement maximizes the use of the internal space of the washing machine without obstructing normal maintenance access.
Schematic diagram of the microperforated plates at different positions in the noise reduction device (1-microperforated plate; 6-acoustic black hole structure; 7-first limit mechanism; 8-speaker)
When the system is operating, the noise collector first captures the noise signals from the washing machine. The control module then performs real-time spectrum analysis on these signals to identify the "target frequency band" where the main noise components reside. 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, primarily from motor and mechanical vibrations), the control module activates a dual noise reduction mechanism: first, it drives the micro-perforated plate to rotate outward to its maximum angle, increasing the depth of the anechoic cavity and enhancing the physical noise reduction effect; second, 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 expands as the micro-perforated plate rotates, increasing the spacing between its internal rings, which 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 according to the specific frequency: for lower mid-to-high frequencies (such as 300-1500Hz, mainly from water flow and clothing flapping), 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 band.
The patent highlights an innovative detail: a dedicated speaker located at the bottom of the microperforated plate, near the rotating shaft. This arrangement cleverly addresses the difficulty of addressing low-frequency noise from the bottom of conventional washing machines. As the microperforated plate rotates outward, the depth of the bottom cavity increases, and the anti-phase sound waves emitted by the speaker effectively cancel out the low-frequency noise propagating from the bottom.
Limit protection mechanism
The device is equipped with a limit mechanism, which is connected to the box and located on both sides of the micro-perforated plate in a specific direction. By telescoping the limiters and drive components, the micro-perforated plate is prevented from shifting due to vibration, ensuring stable operation of the noise reduction device.
Patented technology advantages
Adaptability is the core advantage of this technology. The noise characteristics of a washing machine vary with different operating modes (gentle wash, powerful wash, spin, 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 optimal noise reduction at all times. This adaptive feature ensures that the washing machine's acoustic performance remains 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 lightweight (only 0.2-0.5mm thick), occupying virtually no space inside the washing machine. Compared to traditional sound-absorbing cotton, the micro-perforated panel, made of metal or high-density plastic, offers advantages such as high temperature resistance (up to 100°C), moisture resistance, and airflow resistance, significantly extending its service life. Furthermore, the all-metal/plastic structure is easier to recycle, in line with current environmental trends in the home appliance industry.
Conclusion
Gree Electric's patented noise reduction technology, utilizing intelligent adjustment, an acoustic black hole structure, and active speaker noise reduction, has opened up new avenues for physical noise reduction. It's not just applicable to washing machines; its core technology can also be applied to the noise reduction designs of other home appliances, including air conditioners, refrigerators, and range hoods.
Note: This article is reprinted from 21dB Acoustics