•   Acoustic resistance, r_a

Represents

• transformation of the acoustic energy to the other form of energy or
• radiation of the acoustic energy from the system

Acoustic resistance can be realized either by a tube or a slit where energy is lost because of viscous dissipation:

In the case of viscous losses:

Laminar flow conditions

• Acoustic resistance of a tube (see figure a)
  
  
  
• Acoustic resistance of a slit (see figure b)
  
  
  
  where μ is viscosity of gas