Ventilation duct muffler is a resistive sound-absorbing and noise reducing principle that has good effects on medium and high frequency broadband characteristics, a resistant sound-absorbing and noise reducing principle that has good effects on low, medium frequency and pulsation characteristics, as well as micro perforated muffler and impedance composite muffler. A muffler is a device that utilizes principles such as sound absorption, reflection, and interference to reduce airflow noise in ventilation and air conditioning systems. According to the different principles of noise reduction, it can be divided into resistive, resistant, resonant, and composite types.