What Do Acoustic Panels Do?
Updated
Acoustic panels soak up sound bouncing around inside a room, so echo dies away faster: six 2 by 4 ft panels can cut the echo time of a hard 12 by 15 ft room from 1.8 seconds to 0.8. That's what acoustic panels do. They don't stop noise coming through walls, floors or doors.
They work by friction. Sound pushes air into the "labyrinth of interconnected air spaces" in fiberglass, and as that air rubs past the fibers, sound energy turns "into heat," per Johns Manville (opens in a new tab). A 2 in. Owens Corning 703 (opens in a new tab) board rates NRC 1.00, compared with 0.05 for a gypsum board wall in Johns Manville's table.
Example: A 12 by 15 ft room with an 8 ft ceiling holds 1,440 cu ft and has 792 sq ft of surfaces. At 0.05 everywhere, you get 39.6 sq ft of absorption, and the echo time is 0.049 × 1,440 ÷ 39.6 = 1.8 seconds (Sabine formula, University of Illinois (opens in a new tab)). Six NRC 1.00 panels cover 48 sq ft and add 48 × 0.95 = 45.6: 0.049 × 1,440 ÷ 85.2 = 0.8 seconds.
Interactive
Echo time estimator
See how panels change how long a clap rings in an empty room.
Echo time (RT60) = 0.049 × room volume in cu ft ÷ total absorption in sabins (Sabine formula, University of Illinois (opens in a new tab)). In a bare 12 by 15 ft room with an 8 ft ceiling, every surface at drywall's 0.05 gives 792 × 0.05 = 39.6 sabins and an echo time of 1.8 s. Eight 2 by 4 ft panels of 2 in. fiberglass (NRC 1.00) bring it to 0.7 s; six bring it to 0.8 s.
Based on: Do Acoustic Panels Work?, What Do Acoustic Panels Do?
The catch is bass. A 2 in. panel absorbs only 15% of the sound at 125 Hz, so low notes still hang around, and you need thicker panels to deal with them.
Put panels where the sound is made in the room: home offices for clearer calls, home studios, living rooms with hard floors. For a neighbor's TV they do nothing, because blocking takes mass, decoupling and sealed gaps (that's explained in how soundproof panels work). The soundproof panels guide covers where to hang them and how many to buy, and there are more answers in the soundproof panels FAQ.