Differences Between STC and NRC Ratings. Understanding Acoustic Measurements

When planning a soundproofing or acoustic treatment project, it’s important to understand how materials perform. In cities like New York, where noise control is essential in homes, offices, and commercial spaces, knowing the difference between STC vs NRC ratings helps choose the right solutions.

Many assume NRC vs STC ratings measure the same, but they serve different purposes. STC (Sound Transmission Class) rates how well a material blocks sound from passing through it. NRC (Noise Reduction Coefficient) measures how much sound a material absorbs within a space. A high STC rating means better soundproofing between rooms, while a high NRC rating improves acoustics by reducing echo and reverberation.

What is STC (Sound Transmission Class)?

STC measures how well walls, doors, or windows block sound. It’s important for apartments, offices, hotels, and any place where privacy matters. A material’s STC rating is determined in a lab by measuring how much sound passes through it at various frequencies. The higher the STC rating, the better the sound blocking.

Here’s a breakdown of standard STC ratings:

• STC 25-30 – Poor soundproofing; conversations are easily heard through walls.
• STC 35-40 – Moderate; loud speech is still noticeable.
• STC 45-50 – Good; most conversations are blocked.
• STC 55-60+ – Excellent; significant noise reduction, even for loud sounds.

Examples of STC-rated materials:

• Single-pane glass: STC 25-30
• Double-pane glass: STC 35-40
• Standard drywall wall: STC 35-40
• Soundproofed wall with insulation: STC 50-60+

STC has limitations. It mainly measures mid-range frequencies, so it doesn’t fully block low-frequency sounds like bass or traffic noise. Additional materials like mass-loaded vinyl and decoupling techniques are needed for better results.

What is NRC (Noise Reduction Coefficient)?

NRC measures how much sound a material absorbs inside a space. Instead of blocking noise, it helps control echo and improve speech clarity. NRC ratings range from 0 (no absorption) to 1.0 (complete absorption).

What different NRC ratings mean:

• NRC 0.0 – 0.2 – Hard surfaces like glass and concrete; sound bounces off, creating echoes.
• NRC 0.3 – 0.5 – Moderate absorption found in carpets and some ceiling tiles.
• NRC 0.6 – 0.8 – Good absorption in acoustic panels and high-quality ceiling tiles.
• NRC 0.9 – 1.0 – Excellent absorption in thick acoustic panels and soundproof foam.

Examples of NRC-rated materials:

• Painted drywall: NRC 0.05 (almost no absorption)
• Carpet with padding: NRC 0.40 – 0.60
• Acoustic ceiling tile: NRC 0.50 – 0.70
• Fabric-wrapped acoustic panels: NRC 0.80 – 1.00

NRC is crucial in offices, restaurants, and classrooms where echoes make speech difficult to understand. However, NRC ratings don’t block sound between rooms, so they should be used with STC-rated materials for complete noise control.

Key Differences: NRC vs STC Rating

NRC (Noise Reduction Coefficient) and STC (Sound Transmission Class) measure sound performance, but they focus on different aspects of noise control. While STC prevents sound from traveling between spaces, NRC reduces echo within a space. Understanding these differences helps to select the right materials for any soundproofing or acoustic treatment project.

How to Use Both Ratings in a Soundproofing Project

A well-designed acoustic space requires considering both STC and NRC ratings. High STC-rated barriers should be installed if the goal is to block sound from traveling between rooms. NRC-rated materials are needed if the issue is excessive echo or poor sound clarity.

For example, an apartment near a busy street needs STC-rated windows and walls to block external noise. However, if the living room has many hard surfaces, NRC-rated carpets and acoustic panels can improve comfort by reducing reflections. Soundproof partitions with a high STC rating in an office can prevent distractions between meeting rooms, while NRC-rated ceiling tiles and wall panels enhance speech clarity in open spaces.

By combining STC and NRC solutions, businesses and homeowners can create quiet and acoustically comfortable environments. Professional assessment ensures the right balance is achieved for each space.

Understanding the differences between STC and NRC ratings is essential for effective noise control. While STC prevents sound from traveling between spaces, NRC improves acoustics within a room. The best approach combines both—using high-STC materials for soundproofing and NRC-rated surfaces for echo reduction. Whether it’s an office, apartment, or commercial space, balancing sound blocking and absorption creates a quieter, more comfortable environment. For expert guidance on choosing the right materials, professional consultation ensures the best results.