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Flanking Transmission

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Acoustic Flanking Transmission

Acoustic flanking transmission refers to the indirect path through which sound travels between different spaces or structures, bypassing conventional soundproofing measures. This phenomenon can occur through two main channels: flanking airborne sound and flanking impact noise. Understanding these types of flanking transmission is crucial for effective acoustic design and noise control in buildings and other structures. In this website segment, we will explore each of these subjects in detail, providing insights into their characteristics, causes, and potential mitigation strategies.

Flanking Airborne Sound

Flanking airborne sound refers to the propagation of sound waves through non-structural elements such as ducts, voids, cavities, or other interconnected pathways within a building. These pathways act as conduits for sound, allowing it to bypass barriers and transfer from one space to another. Flanking airborne sound can significantly reduce the effectiveness of sound insulation measures and compromise the desired acoustic environment.

Common causes of flanking airborne sound include:

  1. Ductwork and Ventilation Systems: Inadequate sound insulation in ducts and ventilation systems can allow sound to travel freely between spaces.
  2. Electrical and Plumbing Penetrations: Holes or gaps around electrical conduits, plumbing pipes, or other service penetrations can create pathways for sound transmission.
  3. Shared Structural Elements: Thin walls, ceilings, or floors between adjacent spaces can easily transmit sound due to their insufficient mass or lack of proper soundproofing materials.
  4. Stiff acoustic coupling of structural separations, where acoustic energy can freely travel through the structure and into adjacent enclosures.

Flanking transmission of airborne sound energy is an issue that can occur with stiff acoustic coupling of separations such as walls, floors and facades. The dominant sound transmission path is amplified with all the other flanking paths and in turn, increases the sound in the adjacent room.

To mitigate flanking airborne sound, several strategies can be employed:

  1. Seal Openings and Gaps: Ensure that all openings and gaps in walls, floors, ceilings, and service penetrations are properly sealed with acoustic sealants or gaskets.
  2. Insulate Ductwork: Install sound-absorbing materials in ducts and ventilation systems to minimize sound transmission.
  3. Increase Mass and Isolation: Enhance the mass of shared structural elements by adding additional layers of drywall, mass-loaded vinyl, or other dense materials.
  4. Introduce decoupling techniques, such as resilient channels, floating floors or wall linings such as staggered stud walls separated from the structure with flanking transmission, to reduce direct vibration transfer.

A common way to mitigate airborne flanking transmission is to construct wall linings such as stud walls separated from the flanking element. The same can be done for the dominant sound transmission. In the case shown in the animation, the ceiling is constructed as a suspended ceiling to reduce the dominant transmission pat and the walls are lined with stud walls separated by an airgap.

Flanking Impact Noise

Flanking impact noise refers to the transmission of structure-borne vibrations and resulting noise through interconnected building elements. It occurs when an impact, such as footsteps or the movement of heavy objects, creates vibrations that travel through walls, floors, ceilings, or other structural components and radiate sound in adjacent spaces. Flanking impact noise can be particularly problematic in multi-story buildings or areas where impact activities are common, such as gyms or entertainment venues.

Key causes of flanking impact noise include:

  1. Insufficient Floor-Ceiling Isolation: Inadequate soundproofing between floors can allow impact vibrations to transfer easily, generating noise in adjacent spaces.
  2. Inadequate Wall Construction: Thin or poorly constructed walls may lack the necessary mass or decoupling to prevent the transmission of impact vibrations.
  3. Structural Connections: Inefficient isolation of structural elements, such as beams or columns, can facilitate the propagation of vibrations and impact noise.

Impact noise can find many ways to adjacent room. In the animation, a horizontal flanking path is shown through the floor and wall.

To minimize flanking impact noise, the following strategies can be implemented:

  1. Floor-Ceiling Isolation: Enhance the isolation between floors by using resilient underlayment, sound isolation clips, or floating floor systems.
  2. Decouple Walls: Implement methods such as staggered stud walls, double walls with an air gap, or resilient channel systems to reduce direct vibration transmission.
  3. Vibration Dampening: Apply vibration-damping materials or resilient mounts to structural elements to absorb and dissipate impact vibrations.

A common way to reduce impact noise and its flanking transmission paths, is to completely separate the floor with the use of a floating floor system. In the animation a screen on compressed mineral wool is shown. In this case the floating floor is also separated from the separating wall between the enclosures, this is to avoid further flanking transmission up through the wall.

By addressing both flanking airborne sound and flanking impact noise, architects, engineers, and building professionals can create acoustically efficient environments that minimize the transmission of unwanted noise and enhance occupant comfort and well-being.