Noise pollution from urban indoor substations has become increasingly prominent.This study addresses the excessive noise levels at a 110 kV indoor substation by analyzing sound source characteristics and simulating noise propagation

systematically investigating the current noise status and distribution patterns.Taking into account the low-frequency noise reduction requirements at the main transformer room fan outlet

a novel impedance-composite muffler structure was proposed.Initial structural parameters were determined through theoretical derivation and calculation

and finite element numerical simulation was employed to analyze the sound field and flow field distribution characteristics.The results indicate that

compared with conventional resistive plate-type mufflers

the proposed impedance-composite muffler significantly improves insertion loss in the 450 Hz~750 Hz frequency range

while maintaining similar flow field distribution and pressure loss.This new muffler structure effectively meets low-frequency noise reduction requirements for indoor substations and provides a reference for muffler design in substation noise control projects.