Why do you still hear noise after installing soundproof walls? 10 points to check



Why do you still hear noise after building soundproof walls? 10 points to inspect

: The reason why noise can still be heard after installing soundproof walls is usually not because the main wall itself is inadequate, but because sound leaks through other weak points in the system outside of the wall, collectively known as Flanking Transmission. The 10 main points to inspect include: under the door, electrical outlets, wall joints, service openings, ceilings that do not connect continuously to the structural floor, sound passing through the floor, sound passing through the building structure, overall flanking paths, non-acoustic doors, and vulnerable windows. No matter how high the STC rating of the main wall is, if there is even a single loophole, the actual functional sound insulation performance will be significantly reduced.

This is a very common scenario: investing in high-priced soundproof walls and choosing the system with the best STC rating, yet still hearing noise from the other side upon actual use. The cause is usually not the wall itself, but other overlooked points in the system. Because sound is an energy that always finds a way through the smallest gaps, this article compiles 10 points to check when your soundproof wall does not yield the expected results.

1. Sound leaking under the door

The gap left under the door leaf for opening and closing is one of the easiest paths for sound to leak through, even if it is a narrow gap of only a few millimeters. The solution is to install a door sweep or a properly sealing door threshold, which are often overlooked accessories because they seem like minor details compared to the wall.

2. Electrical outlet boxes

Electrical or switch boxes embedded back-to-back on both sides of the wall create significantly thinner wall sections. In some cases, the boxes on both sides may connect directly through wire conduits, becoming a shortcut for sound to pass through. The solution is to avoid aligning electrical outlets directly opposite each other on both sides of the wall and to thoroughly seal the gaps around the outlet boxes with acoustic sealant.

3. Wall joints

Joints between panels, wall-to-floor joints, or wall-to-ceiling joints, if not sealed with specialized acoustic sealants, become continuous gaps through which sound can flow along the entire line. Using regular adhesive tape is insufficient; specialized acoustic sealing materials such as Trandar Sealant, specifically designed for sealing joints in soundproof wall systems, must be used.

4. Service openings

Openings for plumbing pipes, air conditioning ducts, or wiring that penetrate the wall are often overlooked after MEP work is completed, as technicians typically cut holes to fit pipes snugly without considering acoustic sealing. The solution is to tightly seal the gaps around pipes with acoustic sealant and acoustic insulation every time after pipe installation is finished.

5. Discontinuous ceilings

One of the most common mistakes is building soundproof walls only up to the suspended ceiling level, allowing sound to freely travel through the plenum space above the ceiling into the next room, because standard suspended ceilings are not designed for sound insulation. A proper soundproof wall must be built continuously up to the actual structural floor above (deck-to-deck) rather than stopping at the suspended ceiling level. If this is not possible, a specialized acoustic ceiling system like Trandar Hitech Ceiling must be added in that area to block this shortcut.

6. Sound transmission through floors

Sound from upstairs rooms can transmit down through the floor structure in both impact noise forms—such as footsteps or dragging chairs—and general airborne noise. Vertical soundproof walls cannot help with this problem at all because it is a different sound transmission path. It must be resolved using a floating floor system or specialized impact-absorbing underlayment materials.

7. Sound transmission through building structures

No matter how well a soundproof wall is designed, if it is still anchored directly to building columns or beams without structural decoupling, sound and vibrations can travel along this rigid structure instead of being blocked at the wall. The solution is to use isolation clips or leave gaps at the junction points between the wall and the building structure.

8. Flanking Transmission

Flanking transmission is the collective term for sound that travels "around" via paths other than direct penetration through the wall, for which points 1-7 and 9-10 in this article are all examples. STC ratings tested in laboratories typically measure only direct transmission through the wall. However, in actual on-site situations, the practical sound insulation performance is usually lower than the lab STC rating because flanking paths occur concurrently. Inspecting and sealing all flanking paths is therefore just as important as choosing a wall with a high STC rating.

9. Doors that are not acoustic doors

Standard doors, especially hollow-core doors, have much lower sound insulation values than masonry or soundproof wall systems. Even if installed on a wall with an STC rating as high as 60, using an economical standard door will result in most sound traveling through the door, which acts as the weakest point. Doors specifically designed for sound insulation (acoustic doors) usually feature denser cores, perimeter frame gaskets, and automatic drop seals—elements that must be considered alongside the wall from the design stage.

10. Windows as weak points

Standard single-glazed windows have much lower sound insulation values than solid walls and are common weak points in areas requiring exterior noise mitigation, such as traffic noise. If the room's walls have a high STC rating but the windows are still standard single-glazed glass, most exterior noise will enter primarily through the windows. The solution is to upgrade to double-glazed or laminated glass specifically designed for sound insulation, and ensure that window frames are tightly sealed with no gaps.

A good wall alone does not mean a quiet room if there are other weak points in the system

Choosing a soundproof wall system with a high STC rating is a great starting point, but it is not the complete answer for a truly quiet room, because sound is energy that can always find its way through the smallest gaps in the system. Inspecting all 10 of these points alongside choosing quality walls is an indispensable step.

Trandar Acoustics does not view soundproof walls merely as material selection, but designs them as a system that accounts for sealing various weak points—from Trandar Sealant for joints to the Trandar Hitech Ceiling system for blocking shortcuts above the ceiling.

If you are facing issues with noise still being audible after installing soundproof walls, feel free to chat and share the details with the Trandar Acoustics team. We are happy to help inspect and recommend the most targeted solutions.