Research on Noise Reduction of Variable-Frequency Compressors Using Basalt Fiber-Felt Composite  

I. Research Background and Significance  
Environmental noise pollution has become a critical issue affecting human health and quality of life, with industrial equipment (e.g., variable-frequency compressors) being a major contributor. Traditional noise-absorbing materials (e.g., cotton fiber felt) exhibit limited performance in high-frequency ranges and are susceptible to environmental factors like temperature. Basalt fiber, a high-performance inorganic material with a porous structure and superior acoustic properties, has emerged as an ideal alternative for noise control applications.  

II. Characteristics and Fabrication of Basalt Fiber 
1. Material Advantages  
   Basalt fiber, one of China’s four key high-performance fibers, enhances sound absorption by converting air vibrations within its pores into thermal energy. Its optimized density and structure make it more effective than cotton fiber for broadband noise absorption.  

2. Fabrication Process  
   Researchers from Qingdao University developed a composite felt by blending basalt fibers with cotton fibers. By optimizing ratios and processing parameters, the composite achieved high flexibility and acoustic performance. Experiments demonstrated its superior noise reduction at high frequencies (85 Hz) compared to low frequencies (45 Hz), with enhanced efficacy in low-temperature environments.  

III. Experimental Design and Noise Reduction Analysis 
1. Testing Conditions  
   Experiments evaluated noise levels under varying operating conditions (temperature, frequency) of a variable-frequency compressor, covering low (45 Hz), mid (65 Hz), and high (85 Hz) frequency bands. Performance comparisons were made between basalt fiber felt and conventional cotton felt.  

2. Key Results  
   High-Frequency Superiority: The basalt fiber felt achieved a sound absorption coefficient of 0.85–0.95 at high frequencies, nearing the performance of phenolic glass fiber felt.  
   Temperature Dependency: Its noise suppression capability improved at lower temperatures, whereas traditional materials degraded under high temperatures.  
   Overall Performance: The basalt composite improved noise reduction by ~20% compared to cotton felt at the same frequency, effectively mitigating broadband noise from compressor vibrations and airflow.  

IV. Comparison with Traditional Noise Reduction Technologies  
1. Material Performance  
   While conventional materials (e.g., glass wool) exhibit high absorption coefficients (0.90–0.99), they suffer from aging and environmental concerns. Basalt fiber felt matches their acoustic performance while offering superior heat resistance and eco-friendliness.  

2. Application Scenarios  
   Unlike passive solutions (e.g., enclosures, mufflers), basalt fiber felt can be directly wrapped around compressors or integrated into soundproof structures, simplifying retrofitting. For example, in HVAC systems, it reduces low-frequency noise transmission via copper pipes into indoor spaces.  

V. Prospects and Challenges  
1. Industrial and Household Applications 
   Basalt fiber felt holds promise for industrial compressors, air conditioner units, and more. Combined with enclosures, it can reduce factory boundary noise to below 45 dB, meeting environmental standards.  

2. Technical Optimization 
   Low-Frequency Enhancement: Hybrid designs (e.g., sandwich structures) could improve low-frequency absorption.  
   Cost Reduction: Scaling up production is critical to lowering costs, as basalt fiber remains expensive.  

VI. Conclusion  
Basalt fiber-felt composites, with optimized structures and fabrication processes, demonstrate significant potential for high-frequency noise control in variable-frequency compressors. Future research should focus on stability under complex operating conditions and synergies with other noise reduction technologies to broaden applicability.