Short answer
The most cost-effective ways to cut airborne noise between rooms are to seal all air gaps, improve the door’s acoustic seal (and upgrade to a heavier door if possible), treat electrical boxes with putty pads, and add mass to the shared wall (a second layer of drywall with acoustical sealant at the edges). Soft furnishings and bookcases help a bit, but leaks and light doors are the biggest weak points.
Why these methods work
Airborne sound rides through openings and thin materials. You’ll get the best results by:
- Stopping air movement (seal gaps and penetrations)
- Increasing mass (heavier door and/or extra drywall layer)
- Decoupling or damping if budget allows (damping compound between drywall layers)
Expect meaningful improvements with sealing and door work alone; adding drywall takes it further.
Step-by-step plan (from cheapest to bigger impact)
1) Find and seal all leaks
Time: 1–2 hours • Cost: $20–$60
Common leak points:
- Gaps around baseboards, casing, and crown
- Cracks at the wall-to-ceiling line
- The under-door gap
- Electrical boxes, cable plates, and pipe penetrations
Materials and tools:
- Acoustic sealant (sound-rated, paintable)
- Backer rod (for gaps 1/4–3/4 inch)
- Caulk gun, utility knife, rags
- Painter’s tape, drop cloth
Steps:
- With lights off on one side, shine a bright flashlight from the other; any light leaks are sound leaks. You can also use a small radio as a sound source.
- Mask adjacent finishes with tape. Fill cracks with acoustic sealant; for wider gaps, press in backer rod first, then sealant.
- Seal the seam where baseboard meets the wall. Also seal at the top plate (wall/ceiling joint) if cracked.
Tips:
- Use acoustic sealant, not standard painter’s caulk. It stays flexible and won’t crack.
- Don’t block required ventilation grilles; treat those separately (see HVAC note below).
2) Upgrade the door seal (and mass)
Time: 30–90 minutes • Cost: $15–$250 (more if replacing door)
A hollow-core interior door leaks a lot of sound. Address it in this order:
- Add a door sweep or, better, an automatic door bottom to close the undercut.
- Install quality perimeter weatherstripping (silicone bulb or compression type on the stop). Avoid flimsy foam that collapses quickly.
- If budget allows, replace a hollow-core with a solid-core door ($150–$300 slab) or add mass by laminating 1/4–1/2 inch MDF to the door face with construction adhesive and screws, then refinish. Rebalance hinges if you add weight.
Tools:
- Drill/driver, tape measure, miter saw or handsaw, screwdriver, square
Mistakes to avoid:
- Leaving even a 1/4 inch gap under the door. That small gap can defeat other upgrades.
- Over-tightening weatherstrip so the door won’t latch; aim for light, continuous contact.
3) Treat electrical boxes and plates
Time: 20–40 minutes • Cost: $10–$40
- Wrap electrical boxes on the shared wall with UL-listed acoustic putty pads.
- Add foam gasket inserts behind switch and outlet cover plates.
- If boxes are back-to-back between rooms, this is a prime leak; pads help a lot.
Safety:
- Turn off the circuit at the breaker before removing covers or devices.
4) Add mass to the shared wall (budget or upgraded option)
Time: Half to full day • Cost: $80–$450 depending on approach and size
Budget improvement:
- Add a second layer of 1/2 inch drywall directly over the existing on one or both sides of the wall. Stagger seams relative to the existing layer if possible.
- Apply acoustic sealant around the entire perimeter before fastening, and again at seams before taping/mudding.
Upgraded improvement:
- Use a damping compound between the old and new drywall layers. It costs more but can yield a larger reduction, especially for mid frequencies.
Materials and tools:
- 1/2 or 5/8 inch drywall sheets, drywall screws (1-5/8 inch coarse thread), acoustic sealant, joint compound, tape
- Stud finder, drill/driver, T-square, utility knife, drywall lift (optional), PPE
Specs and tips:
Fasteners: #6 or #7 coarse-thread drywall screws, 1-5/8 in.
Stud spacing: 16 or 24 in OC; hit studs, not just the old drywall.
Perimeter gap: 1/8 in from adjacent surfaces; fill with acoustic sealant.
Coverage: 2 tubes damping compound per 4x8 sheet (if used).
- Use a stud finder and mark studs before hanging.
- Keep a small gap at floor/ceiling and caulk it with acoustic sealant (don’t mud the perimeter).
- If you only treat one side, you’ll still get improvement; both sides is better.
Safety:
- Wear eye protection and an N95 when cutting/sanding drywall.
- Lift sheets with help to avoid back strain.
5) Soften reflections and add furnishings
Time: Immediate • Cost: Free–$200
- Place a filled bookcase against the shared wall, preferably floor-to-ceiling.
- Hang thick, densely woven curtains or a quilt over the wall or door.
- Add area rugs and upholstered pieces to reduce reverberation that “feeds” the wall.
These don’t block like mass does, but they reduce how much sound hits the wall in the first place.
Special cases and flanking paths
- HVAC transfers: Shared return grilles or door undercuts used for return air will leak sound. Consider door sweeps plus a lined transfer grille or jumper duct between rooms. If you need to maintain airflow, consult HVAC or use acoustically lined options.
- Vent or duct penetrations: Use mastic for small gaps and line short duct runs with acoustic liner if accessible.
Common pitfalls
- Relying on foam “acoustic panels” to block sound. They absorb, but don’t block transmission.
- Using standard caulk that dries rigid and cracks.
- Ignoring the door gap or electrical boxes while adding fancy wall treatments.
- Expecting bass (sub-100 Hz) to be tamed cheaply. Low frequencies require far more mass and decoupling.
When to call a pro
- Multifamily or fire-rated walls/doors that must maintain a fire rating.
- If you plan on resilient channels, significant framing changes, or moving electrical/HVAC.
- If persistent noise involves building-wide ductwork or shared chases.
Rough budget guide
- Sealing and door sweep + weatherstrip: $40–$120
- Putty pads and gaskets (4–6 boxes): $20–$60
- Solid-core door upgrade: $200–$400 installed DIY (reuse hardware where possible)
- Second drywall layer (one 12 ft wall): $150–$300 materials; add $80–$200 if using damping compound
Start with sealing and the door. Many homeowners see a noticeable reduction for under $150. Add mass to the wall for the next tier of improvement.