Estimated STC after soundproofing
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How soundproofing is rated: STC
The Sound Transmission Class (STC) is a single number that describes how well a wall, floor or door blocks airborne sound. Every 10 points roughly halves the perceived loudness of what comes through. A typical interior wall made of single drywall on wood studs is around STC 33 – 35, which lets normal conversation through. Building codes require about STC 50 between apartments.
| STC | What you hear through the wall |
|---|
| 25 – 30 | Normal speech easily understood |
| 35 – 40 | Loud speech heard but not easily understood |
| 45 – 50 | Loud speech barely audible; music audible |
| 55 – 60 | Loud music faint; bass still audible |
| 60 + | Most sounds inaudible – suitable for music rooms |
The four principles of soundproofing
- Mass: heavier walls vibrate less. Adding a layer of 5/8" drywall is the simplest upgrade.
- Damping: a viscoelastic compound between two drywall layers turns vibration into heat – it is especially effective at low and mid frequencies.
- Decoupling: resilient clips and hat channel, staggered studs or a separate wall stop vibration traveling through the framing.
- Sealing: airborne sound leaks through any gap. Use acoustic caulk, putty pads and door seals.
Absorption (insulation in the cavity, acoustic panels on the surface) helps a little, but it is the combination of mass, damping and decoupling that produces large STC gains.
Typical methods and costs
| Method | Typical gain | Materials / sq ft | With contractor / sq ft |
|---|
| Mass loaded vinyl + drywall | +5 – 7 | $2 – $3.5 | $5 – $7 |
| Extra drywall + damping compound | +10 – 14 | $2.5 – $3.5 | $6 – $8 |
| Resilient clips & channel + drywall | +15 – 20 | $3.5 – $5 | $9 – $12 |
| Room within a room | +25 – 30 | $8 – $12 | $18 – $25 |
Prices vary by region and project size; the calculator adds 8 % for sundries such as caulk, screws, putty pads and paint.
Doors and windows: the weak links
A wall is only as good as its weakest part. A hollow-core interior door has an STC of about 20 and gaps around it make it worse. Even a small door can drag a STC 55 wall down below 35. Replace it with a solid-core door, add perimeter seals and an automatic door bottom, or use a double-door "sound lock" for studios. Windows can be improved with laminated glass or a secondary acoustic insert.
Bass and impact noise
Low frequencies from subwoofers, drums and footsteps are the hardest to stop. STC is measured mainly from 125 Hz to 4 kHz, so a high-STC wall can still pass deep bass. For music rooms, decoupled construction with high mass is essential; for footsteps from above, the floor above (underlayment, carpet) or a decoupled ceiling matters most.
Frequently asked questions
How much does it cost to soundproof a room?
For one 12 × 8 ft wall, roughly $300 – $500 DIY with drywall and damping compound, or $700 – $1,200 with a contractor. A full room with decoupling can cost $5,000 – $20,000+.
What is the cheapest way to soundproof a wall?
Adding a layer of 5/8" drywall with damping compound and sealing all gaps gives the biggest improvement per dollar.
Do acoustic foam panels soundproof a room?
No. Foam reduces echo inside the room but blocks almost no sound from passing through walls.
What STC rating do I need?
STC 50 stops most speech; STC 55 – 60 or more is recommended for home theaters, drum rooms and music studios.
Does mass loaded vinyl work?
It adds mass, but it works best sealed between drywall layers. Hanging MLV alone gives only a small improvement.
About QuietBuild
QuietBuild is an independent, free calculator for estimating the cost and performance of soundproofing walls and ceilings in homes, studios and offices. STC values are typical laboratory figures for common assemblies; real results depend on workmanship and flanking paths. We are not a contractor or materials supplier.
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The methodology combines widely published engineering rules of thumb, manufacturer data sheets and the electrical code practices that installers use every day. We review the assumptions regularly and update the calculator when typical product specifications change.
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