Do Acoustic Panels Keep Sound Out?
No, acoustic panels don't keep sound out or in. They absorb reflections inside the room and leave noise through the walls almost unchanged. Auralex's home studio guide sorts its products into "Absorb Sound to improve sound within a room" and "Block Sound to stop sound transmission," and panels are absorbers.
Absorption vs blocking
A panel soaks up sound that hits it, so less bounces back into your room. The wall behind it decides how much reaches the neighbor.
Blocking takes mass. In NRC Canada's Building Digest 239, transmission loss rises about 6 dB each time a wall's mass per unit area doubles, and a common stud wall with drywall on both sides rates about STC 33.
What to do about noise instead
For neighbors, traffic, or keeping your own sound in, you need soundproofing on the walls, doors, and windows:
Outside noise
Your studio
What panels do
Related questions
Do acoustic panels work both ways?
They don't block in either direction. A panel absorbs sound inside the room it hangs in, so it neither keeps your music in nor keeps a neighbor's noise out.
Will panels make my room quieter for me?
They cut echo, so sound made in the room dies away faster. Noise coming through the wall stays as loud as before.
What actually stops noise from neighbors?
Mass added to the walls, doors, and windows between you. Start with how to soundproof a room in an apartment.
More answers: Home recording FAQ