Good sound insulation comes from four things working together: mass (heavier or extra layers of board), decoupling (separating the two sides of the wall), absorption (insulation in the cavity) and airtightness (sealing every gap). Acoustic plasterboard helps, but on its own it won't fix a noise problem if sound is leaking through gaps, power points or the ceiling.
Whether it's the neighbour's TV through a townhouse wall, footsteps from upstairs or kids playing while you're trying to work, noise is one of the most common complaints we hear. The good news is that plasterboard walls and ceilings can be built or upgraded to block a lot more sound than a standard wall.
How sound gets through a wall
Sound travels as vibration. When it hits a wall, it makes the plasterboard vibrate, that vibration passes through the studs, and the board on the other side vibrates and passes the sound on. Sound also sneaks through any air gap, no matter how small.
It also takes indirect routes, known as flanking. Noise can travel up into a shared ceiling space, along floor joists or through ducts and come down on the other side, bypassing even a well-built wall.
Understanding acoustic ratings
Walls are rated using Rw (weighted sound reduction index). The higher the number, the more airborne sound the wall blocks. You'll also see Rw + Ctr, which adjusts the rating for low-frequency sounds like bass music, traffic and home theatre rumble. Rw + Ctr is always lower than Rw, and it's the better guide for real-world noise.
For context, the National Construction Code requires a separating wall between attached homes, such as townhouses, to achieve at least Rw + Ctr 50. A standard internal wall in a house is well below that.
The four principles of soundproofing
1. Add mass
Heavier walls are harder to vibrate. You can add mass by using thicker or denser board, such as acoustic or fire-rated plasterboard, or by adding a second layer of board. Two layers with staggered joints perform noticeably better than one.
2. Decouple the two sides
If both sides of a wall are fixed to the same studs, vibration has a direct path through. Decoupling breaks that path using:
- Resilient mounts and furring channels, which hold the board slightly away from the frame.
- Staggered studs, where each side of the wall is fixed to its own set of studs.
- Double stud walls, with two separate frames and a gap between them.
The same idea applies to ceilings. Suspending the ceiling on resilient mounts reduces footstep and impact noise from the floor above.
3. Fill the cavity
Acoustic insulation (glass wool, rock wool or polyester) in the wall or ceiling cavity absorbs sound energy and stops the cavity acting like a drum. It's one of the most cost-effective upgrades.
4. Seal every gap
Air leaks undo good work. Use acoustic sealant around the perimeter of the board, at floor and ceiling junctions, and around penetrations. Back-to-back power points are a classic weak spot, so offset them or use acoustic putty pads. Doors matter too: a hollow-core door with a gap underneath will let more sound through than the wall around it.
Common upgrades compared
| Upgrade | What it does | Best for | Disruption |
|---|---|---|---|
| Insulation in the wall cavity | Absorbs sound in the cavity | New walls, or when walls are open for renovation | Low if walls are open |
| Extra layer of plasterboard | Adds mass | Upgrading an existing wall from one side | Medium: loses about 10–15 mm of room space |
| Acoustic plasterboard | Adds denser mass | Bedrooms, home offices, media rooms | Medium |
| Resilient mounts and furring channels | Decouples board from the frame | Shared walls and ceilings under upstairs rooms | Medium to high |
| Staggered or double stud wall | Fully separates the two sides | New builds, townhouses, home theatres | High: wider wall |
| Acoustic sealant and sealing penetrations | Stops air leaks | Every job | Low |
Where people most often want soundproofing
- Bedrooms next to living areas or a neighbour's wall
- Home offices where calls need to stay private
- Home theatres and music rooms, where low-frequency sound is the challenge
- Ceilings under upstairs rooms, especially with timber floors above
- Bathrooms and laundries, where plumbing and appliance noise carries
- Offices and meeting rooms in commercial fitouts, where privacy matters
What soundproofing can't do
It's worth setting realistic expectations. A wall upgrade won't fix noise coming through windows, doors, floors or a shared roof space. If the noise is mainly low-frequency (bass, machinery), you'll usually need a decoupled system rather than just extra board. And in strata buildings, changes to shared walls may need body corporate approval.
For serious noise problems, such as a dedicated home theatre or a dispute with a neighbour, an acoustic consultant can measure the problem and recommend a system. We're happy to build to their specification.
DIY or professional?
Adding insulation or sealant can be a reasonable DIY job. But resilient mounts, multi-layer systems and party walls need to be installed exactly as the manufacturer's tested system specifies to deliver the stated rating. A single rigid fixing in a decoupled wall can short-circuit the whole system.
How we can help
Sydney Wide Plastering builds and upgrades walls and ceilings for better acoustic performance in homes and offices across Sydney. From a quieter bedroom to acoustic partitions in an office renovation, we'll recommend a practical system for your space and budget.
Want a quieter home or workplace? Contact us to talk through your options.