Acoustical Ceiling Glossary
40+ industry terms explained in plain language. No jargon about jargon.
If you're reading a ceiling spec sheet or sitting in a meeting with your architect and contractor, these are the terms that come up. We wrote these definitions the way we'd explain them on a job site.
Absorber
Any material that soaks up sound energy instead of reflecting it. Ceiling tiles, wall panels, and baffles are all absorbers. The more porous the material, the better it absorbs.
Acoustic Baffle
A flat panel that hangs vertically from the ceiling structure. Baffles absorb sound on both faces. Used in open-ceiling spaces where you can't install a standard grid.
Acoustic Cloud
A horizontal panel suspended below the ceiling structure. Like a baffle turned sideways. Absorbs sound from both the top and bottom surfaces.
Air Plenum
See Plenum.
ASTM E84
The standard test for surface burning characteristics of building materials. Measures flame spread and smoke development. Most ceiling tiles need to pass as Class A (flame spread ≤25, smoke ≤450).
CAC (Ceiling Attenuation Class)
Measures how well a ceiling tile blocks sound from passing through it into the plenum and down into an adjacent room. Higher CAC = better sound blocking between rooms. CAC 35+ is standard for offices. CAC 40+ for private spaces like HR offices or exam rooms.
Class A Fire Rating
The highest fire rating for interior finish materials under ASTM E84. Flame spread index ≤25 and smoke developed index ≤450. Required for most commercial ceiling installations.
Concealed Grid
A suspension system where the grid is hidden behind the ceiling tiles. Tiles interlock or clip together so you don't see any metal grid from below. Creates a seamless, monolithic look.
Cross Tee
The shorter T-shaped metal pieces that connect between main runners to complete the ceiling grid. Standard lengths are 2 feet and 4 feet. They snap into slots in the main runners — no tools needed.
Decibel (dB)
Unit of sound measurement. Normal conversation is about 60 dB. A busy open office runs 65-75 dB. Every 10 dB increase sounds roughly twice as loud to the human ear.
Direct-Mount Ceiling
A ceiling system attached directly to the structure above with no air gap or suspension system. Used where plenum space is limited. Less common than suspended systems because you lose access to what's above.
Donn Grid
Brand name for USG's suspension grid system. One of the two most common grid brands in commercial construction (the other being Armstrong Prelude). "Donn grid" is often used generically to mean any T-bar grid.
Edge Profile
The shape of a ceiling tile's edge where it meets the grid. Common profiles: square lay-in, tegular, reveal, beveled, and concealed. The edge profile determines how the tile sits in or on the grid and how visible the grid is from below.
Flanking
Sound that goes around a barrier instead of through it. In offices, the most common flanking path is over the wall partition, through the open plenum, and down into the next room. High-CAC tiles reduce flanking through the ceiling.
FRP (Fiberglass Reinforced Panel)
A rigid wall or ceiling panel made from fiberglass-reinforced polyester. Waterproof, cleanable, impact-resistant. Required by health codes in many commercial kitchen and food prep areas.
Grid System
See Suspension System.
Hanger Wire
Steel wire (usually 12-gauge) that connects the grid system to the building structure above. Hanger wires carry the weight of the entire ceiling — grid, tiles, lights, and everything else mounted in the ceiling plane.
HVAC Diffuser
The vent or register in the ceiling that distributes conditioned air into the room. Diffusers mount in the ceiling grid in place of a tile. We cut and frame openings for diffusers during grid installation.
Lay-In Tile
A ceiling tile that simply lays on top of the grid flanges. The grid face is visible from below. This is the most common and most economical tile installation method.
Light Reflectance (LR)
The percentage of light that bounces off a ceiling tile surface. Higher LR means the ceiling reflects more light back into the room, which can reduce the number of fixtures needed. Premium white tiles hit LR 0.90+.
Main Runner
The primary T-shaped metal channel that runs the length of the ceiling grid. Main runners hang from the structure above on hanger wires and support the cross tees. Standard spacing is 4 feet on center.
Mineral Fiber
The most common ceiling tile material. Made from a mix of mineral wool, clay, perlite, and recycled paper. Good balance of sound absorption, fire resistance, and cost. The white tile you see in most offices.
NRC (Noise Reduction Coefficient)
Measures how much sound a material absorbs, on a scale of 0 to 1. NRC 0 means the surface reflects all sound. NRC 1.0 means it absorbs all sound. Most ceiling tiles range from NRC 0.50 (basic) to NRC 0.95+ (premium). For open offices, target 0.70+.
Open Plenum
A ceiling design where the plenum space is left exposed — no ceiling tiles. You see the ductwork, pipes, structure, and wiring. Popular in modern offices, restaurants, and breweries. Creates acoustic challenges because all those hard surfaces reflect sound.
PET Felt
Acoustic material made from compressed polyester fibers, typically 50-60% recycled plastic bottles. Used for baffles, wall panels, and ceiling tiles. Lightweight, colorful, doesn't shed fibers like fiberglass.
Plenum
The space between the ceiling tiles and the structural deck above. Houses HVAC ducts, electrical conduit, plumbing, fire sprinkler pipes, and data cables. In a standard office, the plenum is 2-4 feet deep.
Plenum-Rated
Materials and cables approved for use in the plenum space. Plenum-rated products produce less smoke and toxic fumes if they catch fire. Required by code for anything installed above the ceiling tiles.
Prelude Grid
Brand name for Armstrong's suspension grid system. The most widely installed grid system in North America. Available in 15/16" and 9/16" face widths.
Reveal Edge
A tile edge profile where the tile sits recessed below the grid flange, leaving a visible shadow gap between the tile surface and the grid. Creates a defined, geometric look. Different from tegular, which steps down below the grid.
RT60 (Reverberation Time)
The time it takes for sound to decay by 60 dB after the source stops. Long RT60 = echoey room. For offices, target 0.5-0.8 seconds. For conference rooms, 0.4-0.6 seconds. Measured in seconds.
Seismic Bracing
Diagonal wires or rigid braces that prevent the ceiling grid from swaying during an earthquake. Required by California building code on virtually every suspended ceiling installation. We install seismic bracing on every job.
Snap-In Tile
A ceiling tile that clips or snaps into a concealed carrier system. The grid is hidden from below. More expensive than lay-in but creates a cleaner look.
Sound Masking
A system that adds low-level background noise (typically "pink noise") to a space to cover up distracting conversations. Often installed above the ceiling tiles. Works alongside acoustic ceiling tiles — the tiles absorb sound, masking covers what's left.
STC (Sound Transmission Class)
Measures how well a wall, floor, or ceiling assembly blocks sound from one side to the other. Higher STC = better sound blocking. STC 50 is the minimum for office walls. STC 60+ for conference rooms. Note: STC rates the full assembly, not just the tile.
Suspension System
The metal framework that hangs from the building structure and holds ceiling tiles in place. Consists of main runners, cross tees, wall angles, and hanger wires. Also called a grid system or T-bar system.
T-Bar
The T-shaped metal channel that forms the visible grid of a suspended ceiling. Called T-bar because the cross-section looks like an upside-down letter T. The flat bottom flange supports the ceiling tiles.
Tegular Edge
A stepped tile edge where the tile drops below the grid line, creating a shadow reveal. Gives a more refined, three-dimensional look compared to flat lay-in tiles. Available in 15/16" and 9/16" versions to match grid face width.
Thermal Resistance (R-Value)
Measures how well a ceiling tile insulates against heat transfer. Higher R-value = better insulation. Most ceiling tiles have R-values between R-1 and R-7. Helps reduce heating and cooling costs by keeping conditioned air in the room.
Tile Size
The two standard ceiling tile sizes are 2'×2' (24"×24") and 2'×4' (24"×48"). 2×4 is the traditional commercial standard. 2×2 gives a more modern, symmetrical look and is easier to handle. Grid layout is built around these two sizes.
VOC (Volatile Organic Compound)
Chemical compounds that off-gas from building materials. Low-VOC ceiling tiles are important for indoor air quality and are required for LEED and WELL certification. All major manufacturers now offer low-VOC product lines.
Wall Angle
The L-shaped metal trim piece installed around the perimeter of a room at ceiling height. Wall angle supports the edges of the grid where it meets the walls. It's the first piece of the grid system we install and sets the ceiling height.
Wall Panel (Acoustical)
Panels mounted to walls to absorb sound and reduce reflections. Types include fabric-wrapped fiberglass, stretch fabric systems, PET felt panels, and perforated wood panels. Used in offices, conference rooms, restaurants, and anywhere walls are causing echo.
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