• The inside of the wooden frame is brush-treated, which gives the frame
  itself a sound absorbing function without the need to install expensive,
  sound absorbing materials on the interior of the frame.
• By organizing irregularities one after another on the interior surface of the
  sound absorbing path inside the frame, the noise contact area is increased,
  which subsequently enhances sound absorption.
• The U-shaped sound absorbing material is added to the noise path of the
  left-side frame to absorb and reduce noise over a larger area.
• The use of carbonized wood stained with vegetable oil allows for excellent
  preservation, waterproofing, insect repelling, water repellency, and
  resistance to deformation.

1 Perforated aluminum sound absorbing material, 2 Transparent plate,
3 Carbonized wooden frame, 4 Sound absorbing rod, 5 Noise inducing path