A normal door is lightweight and leaky
Sound finds air gaps and low-mass elements. A high-performance wall can therefore be undermined by a standard hollow-core door and untreated perimeter gaps.
Seals matter
Perimeter compression seals and an effective threshold/drop seal are crucial because small air gaps can dominate high-frequency leakage.
Mass and stiffness matter
Heavier door leaves and engineered assemblies provide better transmission loss, especially when paired with appropriate frames and seals.
Lobby arrangements can help
Where space allows, two separated doors can provide a useful airlock and reduce direct transmission — but the surrounding partitions and flanking paths must still be designed correctly.
Use acoustic theory to ask better questions about the actual room. Final treatment quantity, location and construction should be based on the project geometry and measured or modelled behaviour.