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Acoustics 101

How sound works in buildings. No physics degree required.

Sound Is Vibration

Sound is air molecules vibrating. A person talks, their vocal cords push air, the air molecules bump into each other in a wave, and that wave hits your ear. The speed, frequency, and intensity of those vibrations determine what you hear — a whisper or a shout, a bass drum or a piccolo.

How Sound Behaves in a Room

When sound waves hit a surface (wall, ceiling, floor), three things can happen:

  1. Reflection: The sound bounces off the surface like a billiard ball. Hard, smooth surfaces reflect most of the sound. Concrete, glass, drywall, and tile are reflectors.
  2. Absorption: The surface soaks up the sound energy and converts it to tiny amounts of heat. Soft, porous materials absorb sound. Carpet, fabric, acoustical ceiling tiles, and foam are absorbers.
  3. Transmission: The sound passes through the surface into the next room. Thin, lightweight walls transmit more sound. Thick, heavy walls transmit less.

Every surface in a room does all three in different proportions. A concrete wall reflects most sound, absorbs almost none, and transmits a little. A thick acoustical panel absorbs most, reflects some, and transmits very little.

Reverberation

Reverberation is what happens when sound bounces around a room multiple times before it dies out. In a room full of hard surfaces, sound reflects off the walls, ceiling, and floor over and over. You hear the original sound plus all the reflections stacked on top of each other. That's why an empty room with hard floors sounds echoey.

Reverberation time (RT60) is the time it takes for sound to drop by 60 decibels after the source stops. A typical office should have an RT60 of about 0.6–0.8 seconds. A concert hall might be 1.5–2.0 seconds. A gymnasium with no treatment might be 3–5 seconds.

Too much reverberation makes speech muddy. You hear the reflections mixing with the direct sound and can't make out words. Too little reverberation makes a room feel dead and unnatural. The goal is finding the right balance for what the room is used for.

Sound Absorption vs. Soundproofing

This is the biggest source of confusion in acoustics. They're not the same thing.

Sound absorption = reducing noise and echo inside a room. Acoustical ceiling tiles, wall panels, baffles, and carpet absorb sound. They make the room quieter for people in it. They do NOT stop sound from going through walls into the next room.

Soundproofing = blocking sound from passing through walls, floors, or ceilings into adjacent spaces. This requires mass, density, and sealed construction. Heavy walls, double drywall, mass-loaded vinyl, sealed gaps. More on soundproofing →

Putting acoustic foam on a wall makes the room quieter inside. It does almost nothing to stop your neighbor from hearing your music. That's the difference.

Key Acoustic Measurements

  • NRC (Noise Reduction Coefficient): How much sound a material absorbs. Scale of 0 to 1.0 (though some products exceed 1.0 due to testing methodology). Higher = more absorption. Deep dive on NRC →
  • STC (Sound Transmission Class): How well a wall or floor blocks sound from passing through. Higher = more blocking. A standard wall is STC 33–35. A good soundproof wall is STC 50+.
  • CAC (Ceiling Attenuation Class): Same concept as STC but specifically for ceiling systems. How well the ceiling blocks sound traveling between rooms via the plenum above.
  • RT60 (Reverberation Time): How long it takes sound to decay by 60 dB. Measured in seconds.
  • NC (Noise Criteria): Background noise level in a room, typically from HVAC. NC 30–35 is comfortable for offices. NC 25 for conference rooms.

The Six Surfaces

Every room has six surfaces: four walls, a floor, and a ceiling. Sound bounces between all of them. To control acoustics, you need to treat enough of those surfaces with absorptive material. You don't need to treat everything — treating 40-60% of the room's surface area with absorptive material is usually enough to bring reverberation under control.

The ceiling is usually the best place to start. It's the largest uninterrupted surface in most rooms, it doesn't get touched by furniture or people, and it's where acoustical tile systems live. Treating the ceiling alone solves the problem in many cases.

When to Call an Acoustical Consultant

For standard offices, schools, and retail, an experienced ceiling contractor (like us) can recommend the right products without a consultant. We've done enough projects to know what works.

For specialized spaces — performing arts centers, recording studios, cinemas, courtrooms — hire an acoustical consultant. They'll model the room, specify precise targets, and select products that meet those targets. We work with consultants on these projects regularly and are happy to coordinate.

Questions?

Acoustics don't have to be complicated. Most commercial spaces just need the right ceiling tile and maybe some wall treatment. Contact us and we'll assess your space for free.