Indirect transfer

Professional Definition

Indirect transmission is the transmission of sound through paths other than direct penetration through a partition separating rooms, often using installation elements or empty construction spaces.

Unlike typical side transmission (which mainly concerns the building structure, such as walls and ceilings), this term often also includes penetration through ventilation ducts (crosstalk), spaces called plenum (above suspended ceilings or below raised floors), and through leaks along cable routes. It is a critical aspect in office buildings and public utility buildings.

Acoustics in Simple Words

Imagine two completely sealed rooms, connected by a single pipe, through which you can talk like over the phone with cups. The wall between the rooms can be armored, but if the pipe (ventilation duct) is not soundproofed, the sound will pass through it unhindered. It's like a highway for noise that bypasses local, congested roads (walls). Another example is the common space above a dropped ceiling – sound can jump over the partition wall like a ball tossed over a fence.

Summary

Neglecting indirect transmission is the most common mistake when designing open space offices and conference rooms. The solution is to use silencers in ventilation, acoustic barriers in ceiling spaces, and proper sealing of service penetrations.