Soundproof Drywall Panels: QuietRock and the Alternatives

Soundproof drywall panels are gypsum boards with a damping polymer laminated inside. Unlike foam or fabric panels, they actually block sound through a wall. A 1/2 in. QuietRock 510 on one side of a 2x4 wall rates STC 49 in PABCO's published tests (opens in a new tab), where single stud walls of standard drywall test at STC 34 to 35. The main alternative is two layers of standard drywall with a damping compound in between.

How soundproof drywall panels work

Soundproof drywall works by damping. Two gypsum layers bonded with a viscoelastic polymer turn vibration into heat, a bit like a shock absorber on a car. The trade name for it is constrained-layer damping. National Gypsum's SoundBreak XP, for example, is "two layers of 5/16" high-density gypsum board bonded together with viscoelastic polymer" (National Gypsum (opens in a new tab)).

Damping adds blocking without adding much weight. QuietRock 510 weighs 2.1 lb/sq ft (PABCO (opens in a new tab)), about the same as the 2.2 lb of standard 5/8 in. Firecode X (USG (opens in a new tab)). PABCO's Sound Design Guide (opens in a new tab) says damped panels add isolation "without increasing the weight."

Soundproof drywall STC ratings

Soundproof drywall panels push a single stud wall into the high 40s and low 50s. In some builds that gets you past the STC 50 code minimum for walls between dwelling units (LADBS, IBC 1206 (opens in a new tab)).

Treat these as a rough guide, not an exact gain. The QuietRock 510 walls use studs 24 in. apart and the data sheet doesn't list their insulation, while the standard walls use studs 16 in. apart. National Gypsum also warns that "field-tested values are normally lower."

QuietRock models compared

QuietRock comes in three common thicknesses, and the thicker boards add mass on top of the damping. PABCO's submittal gives each one an STC range across its tested walls, though its assembly selector also lists a 545 wall at STC 55, the one in the chart above.

QuietRock 545 adds a steel sheet and a cement panel to the gypsum layers (PABCO (opens in a new tab)). A 4 × 8 ft sheet weighs about 200 lb (32 sq ft × 6.2 lb = 198 lb), so you'll want a panel lift.

Alternatives to QuietRock

There are four other ways to add blocking to a wall: another damped board, a damping compound between standard sheets, a dense fiberboard under the drywall, or mass loaded vinyl.

• SoundBreak XP

  STC 45 to 53

  National Gypsum's damped board on one side took its staggered stud wall from 45 to 53.

• Double drywall + Green Glue

  2 tubes per sheet

  Damping compound (opens in a new tab) between two standard sheets, screwed on within 15 minutes.

• Sonopan fiberboard

  3/4 in. board

  A wood fiber panel that screws on before the drywall. Sonopan review

• MLV under drywall

  1 lb/sq ft

  Limp vinyl sealed under a new layer. MLV soundproofing panels

Soundproof drywall vs double drywall with damping compound

Both methods use constrained-layer damping. The difference is where the sandwich gets made. QuietRock is laminated into one sheet at the factory, while double drywall with Green Glue builds the same sandwich right on the wall.

The double layer is heavier and thicker, and that helps at low frequencies, where PABCO says damped boards perform like standard gypsum. QuietRock saves 3/4 in. of wall depth and one sheet of hanging per 32 sq ft, and it's the simpler retrofit. The board is a specialty item, though, so price one sheet against two standard sheets plus two tubes before you decide.

One side of the wall or both?

One side. National Gypsum says damped board is "very effective when used on one side of a wall assembly" and that adding it to both sides "does not increase the STC value enough to warrant the additional cost." PABCO's own numbers back that up: STC 49 with QuietRock 510 on one side, 52 with it on both.

Sealing matters as much as the board does. A thin crack undoes more than you'd think. In PABCO's guide, an unsealed 1/8 in. gap 1 ft long drops a wall from STC 46 to 36, so caulk the perimeter and seal the outlet boxes. The soundproof panels guide covers decoupling and flanking paths.