How to Specify Acoustic Panels: NRC, SAC & Fire Rating Guide

Acoustic panel specification is one of the most technically demanding parts of any commercial interior project. Get the ratings wrong and the client ends up with panels that look the part but do nothing useful. Get the fire rating wrong and you have a code compliance problem that can delay a project by months.

This guide is written for architects, specifiers, interior designers, and acoustic consultants who need a clear, working understanding of NRC, SAC, STC, and fire ratings — and what those numbers actually mean when you're comparing products and writing specifications.

Understanding Acoustic Performance Ratings

Before specifying any acoustic product, you need to understand what the rating systems measure — and what they deliberately leave out.

What Is NRC (Noise Reduction Coefficient)?

NRC is a single-number average of a material's sound absorption performance across four frequencies: 250 Hz, 500 Hz, 1,000 Hz, and 2,000 Hz. It's calculated according to ASTM C423 and expressed as a value between 0 and 1.

A panel with NRC 0.70 absorbs 70% of the sound energy that strikes it at those four frequencies. The remaining 30% is reflected back into the room.

For most commercial applications — open offices, conference rooms, restaurants, classrooms — NRC is a reliable primary specification metric. For critical listening environments like auditoriums or recording facilities, always request the full octave-band absorption coefficients rather than relying on the single-number NRC.

What Is SAC (Sound Absorption Average)?

SAC is also calculated according to ASTM C423, covering the same test data as NRC but averaged across a broader set of frequencies: 200 Hz, 250 Hz, 315 Hz, 400 Hz, 500 Hz, 630 Hz, 800 Hz, 1,000 Hz, 1,250 Hz, 1,600 Hz, 2,000 Hz, 2,500 Hz, and 3,150 Hz.

Because it accounts for more frequency bands, SAC gives a more complete picture of a material's absorption behavior than NRC alone.

In practice, SAC and NRC values for the same product are usually very close. You'll often see them listed together in technical data sheets — as AcousticMod's slat wood panel documentation shows, with NRC and SAA both at 0.45 for the slat wood panel tested to ASTM C423:2017.

NRC vs. SAC — What's the Practical Difference?

For most specification purposes, the difference is minor. NRC remains the dominant metric in U.S. commercial specification practice. SAC (also referred to as SAA — Sound Absorption Average) is gaining traction as manufacturers update their technical documentation to ASTM C423:2017 standards.

When comparing products from different manufacturers, use the same metric for both. Mixing NRC from one datasheet and SAC from another introduces a small but unnecessary comparison error.

What Is STC (Sound Transmission Class)?

STC is a completely different measurement. NRC and SAC measure how much sound a material absorbs. STC measures how much sound a construction assembly blocks from passing from one space to another.

A wall with STC 50 reduces sound transmission by approximately 50 decibels across the tested frequency range. That's a sound-blocking measurement — not absorption.

Architects specifying open-plan offices, healthcare facilities with privacy requirements, or multi-room educational buildings need to address STC at the structural level (wall construction, door specifications, ceiling plenum details) separately from acoustic panel selection.

Fire Ratings for Acoustic Panels — What You Need to Know

Fire compliance is non-negotiable in commercial specification. Most jurisdictions in the U.S. require interior finish materials in commercial occupancies to meet minimum flame spread and smoke development standards. Acoustic panels fall under interior finish materials.

Class A (ASTM E84)

ASTM E84 is the primary U.S. test standard for surface burning characteristics of building materials. Results are classified by Flame Spread Index (FSI) and Smoke Developed Index (SDI):

Class A is required in most U.S. commercial occupancies — offices, schools, healthcare facilities, assembly spaces — under the International Building Code (IBC). For high-occupancy or egress-critical spaces, verify local code requirements with the authority having jurisdiction (AHJ). Some jurisdictions are more stringent.

When specifying Class A acoustic panels, request ASTM E84 test reports from the manufacturer. Verify the report covers the specific product configuration — thickness, substrate, and finish — you're specifying, not a similar but different product.

European Standard B-s1,d0

Products manufactured or tested to European standards will carry a Euroclass fire rating rather than ASTM E84 classification. AcousticMod's felt ceiling panels and baffle systems are rated B-s1,d0, which in European classification indicates:

• B: Limited combustibility (second tier, below A1/A2)
• s1: Very limited smoke production
• d0: No flaming droplets or particles

For U.S. projects, verify whether European-rated products have been additionally tested to ASTM E84. If not, the product may require supplemental testing before specification can be confirmed for code compliance. Contact the manufacturer's technical team — this is a common and manageable specification step.

When Each Rating Applies

Always confirm with the project's AHJ. Rating requirements can vary by state, occupancy classification, and whether the building is sprinklered.

Technical Comparison Table — Rating Systems at a Glance

Acoustic Panel Specification by Application

Offices

Open-plan offices typically require NRC 0.70 or higher to achieve meaningful reverberation control. The combination of acoustic wall panel systems on perimeter and end walls with ceiling absorption — whether tiles or baffles — produces better results than treating walls or ceilings in isolation.

Target reverberation times (RT60) for open offices: 0.4–0.6 seconds in furnished, occupied conditions.

Schools and Educational Facilities

ANSI/ASA S12.60 sets acoustic performance standards for U.S. classrooms. Core and learning spaces should achieve background noise levels below 35 dBA and reverberation times of 0.6–0.7 seconds in smaller classrooms. Larger multipurpose spaces require individual acoustic analysis.

Felt acoustic panels are particularly common in educational settings — they absorb well, meet fire rating requirements, are durable, and tolerate the cleaning schedules typical in school environments.

Restaurants and Hospitality

Restaurant acoustic specification is genuinely difficult. The target is reducing intelligibility-destroying reverberation without creating an overly dead, uncomfortable environment. Most successful restaurant acoustic treatments target RT60 values between 0.8 and 1.2 seconds — enough absorption to reduce fatigue without killing the energy of the space.

Architectural ceiling baffles are effective in high-ceiling hospitality environments where wall panel coverage is limited by openings, glazing, or banquette layouts.

Hospitals and Healthcare

Healthcare acoustic specification carries specific regulatory requirements. FGI Guidelines for the Design and Construction of Healthcare Facilities set acoustic criteria for patient rooms, corridors, and clinical spaces. HIPAA speech privacy requirements add another specification layer in areas where patient conversations occur.

In these environments, specifiers need to confirm that acoustic panels are rated for the required fire class, are appropriate for the facility's cleaning and infection-control protocols, and carry any required VOC or antimicrobial certifications the project requires.

Auditoriums and Performance Spaces

Auditoriums require acoustic analysis beyond panel specification. The room's geometry, volume, reflective surfaces, and HVAC noise all interact with the panel treatment. For these projects, acoustic panel specification should follow a room acoustic model prepared by an acoustic consultant, rather than being determined from general guidelines.

Acoustic drop ceiling tiles and ceiling systems play a critical role in variable-absorption designs where the goal is achieving appropriate RT60 for both speech and music use cases.

What to Include in an Acoustic Panel Specification

A complete acoustic panel specification should cover the following:

Ceiling Systems vs. Wall Panels — How to Choose

For most commercial spaces, you need both. Wall panels and ceiling systems address different acoustic problems.

Wall panels reduce first-reflections — the sound that bounces off parallel walls and creates flutter echo and perceived noise. They're most effective on the wall surfaces that face primary sound sources: the wall behind a speaker in a conference room, the walls flanking an open-plan workspace.

Ceiling baffles and ceiling systems address the room's largest reflective surface. Because the ceiling is overhead and unobstructed, ceiling-mounted acoustic treatment often provides the most efficient absorption per square meter of any surface in the room. Acoustic ceiling systems are particularly effective in restaurants, schools, and offices where floor-to-ceiling height limits wall coverage.

For high-volume, high-ceiling environments — large restaurants, lobbies, gymnasiums — hanging baffles provide absorption on both faces, effectively doubling the active surface area compared to a panel mounted flat against a surface.

Common Specification Mistakes and How to Avoid Them

Specifying NRC without checking the frequency curve. An NRC of 0.70 sounds good, but if the panel performs poorly below 500 Hz, it may not address the low-frequency buildup that's making the room uncomfortable. Always request octave-band data for any specification where bass control matters.

Treating acoustic panels as soundproofing. This comes up in client discussions more than in specification documents, but specifiers need to manage expectations clearly. Panels reduce reverberation inside a space. They don't block sound from passing through walls.

Ignoring fire rating compatibility. Specifying a product that hasn't been tested to ASTM E84 for a commercial occupancy creates a compliance risk that typically surfaces during plan check or final inspection — not the best time to find it.

Not confirming that suspension hardware is included. Ceiling baffles require suspension fixings. These are frequently sold separately. Specify the complete installation system, not just the panel.

Specifying coverage area without acoustic modeling. A rough rule of thumb for offices is 15–25% wall coverage, but this varies significantly by room volume, geometry, occupancy, and target RT60. For projects where acoustic performance is a defined deliverable, use a room acoustic model.

AcousticMod Products Built for Specification

AcousticMod designs its product line for commercial specification. Each product carries documented NRC values, material specifications, and fire rating data that support the specification process.

All products are manufactured with VOC compliance and antibacterial certifications. Recycled content documentation is available for LEED credit support.

FAQ — Acoustic Panel Specification