Understanding STC and Ratings

What is STC?

Sound Transmission Class (STC) is a standardized measurement used to evaluate how well building materials reduce airborne sound. While STC is widely used in the USA to rate walls, ceilings, floors, windows, and doors, it is important to note that STC ratings are not a complete measure of soundproofing effectiveness.

STC focuses on frequencies between 125 Hz and 4000 Hz, which works well for speech and general sounds. However, low-frequency noises—like bass, traffic, or machinery—are often not adequately represented in STC ratings. This is why other soundproofing factors and materials must be considered alongside STC.

How Does STC Work?

STC ratings are determined by testing the Transmission Loss (TL) of a material or system across 16 standard frequencies. TL measures the reduction in sound energy as it passes through a barrier. For example:

A 100 dB sound on one side of a wall that is reduced to 75 dB on the other side has a 25 dB TL.
Walls, floors, and ceilings are tested in labs to calculate their overall STC rating, which provides a single-number summary of their soundproofing ability.

The Problem with Low Frequencies

One of the biggest drawbacks of STC ratings is their inability to account for noise below 125 Hz. This is critical because most real-world noise issues, such as heavy traffic, home theaters, and industrial equipment, generate significant low-frequency sounds. For example:

Airplane noise can fall below 125 Hz.
Drums and bass guitars produce deep frequencies.
Industrial machines, like pumps, often vibrate at low frequencies.

To effectively soundproof against these sound sources, additional measures like decoupling, mass, and damping compounds are often required.

What Do STC Ratings Mean?

Here is a general guide to interpreting STC ratings:

STC Rating	Performance	Example
25	Poor	Normal speech is easily heard and understood.
35	Mediocre	Loud speech is heard but not understood.
45	Fair	Loud speech is barely heard, but traffic noise may still be noticeable.
50	Good	Very loud sounds like music or heavy traffic are faintly heard.
60+	Excellent	Superior soundproofing; ideal for studios or theaters.

Key Elements of Effective Soundproofing

To achieve reliable soundproofing, focus on these essential components:

Decoupling: Physically separating structures to reduce sound vibration transfer.
Mass: Adding dense materials like multiple layers of drywall.
Damping Compounds: Using materials like Green Glue to absorb sound energy.
Insulation: Filling cavities with acoustic insulation to trap sound waves.

Common Myths About Soundproofing

Expensive materials guarantee better results: Not true. Basic, affordable materials often outperform "fancy" solutions.
STC ratings can be added: Misconception. You cannot simply combine STC ratings from different materials. For example, adding drywall with STC 20 to a wall with STC 33 will not create an STC 53 wall.

STC Ratings for Wall Assemblies

Here are some examples of wall assemblies and their corresponding STC ratings:

STC Rating	Assembly Build	Performance
33	Single layer of 1/2" drywall on wood studs with no insulation.	Poor
44	Double layer of 1/2" drywall on wood studs with batt insulation.	Mediocre
52	5/8" drywall on one side; double 5/8" drywall with damping compound on the other.	Good
60	Double 5/8" drywall on steel studs with insulation and Green Glue on both sides.	Excellent

Why STC Alone Isn’t Enough

Although STC is a helpful measurement, it should not be the sole factor in designing a soundproofing system. When dealing with low-frequency noise sources—such as musical instruments, industrial machinery, or heavy traffic—it’s essential to incorporate solutions that go beyond STC.

Achieving the Best Soundproofing for Your Project

For effective soundproofing, combining STC-rated materials with low-frequency solutions is the key to success. At Arrowzoom, we provide a wide range of high-quality soundproofing materials, including:

Acoustic Foam Panels
Green Glue Damping Compound
Soundproof Underlays
Insulation Clips and Brackets

Soundproofing FAQs

Frequently Asked Questions

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How do I soundproof my wall against noisy neighbours? 🤫

Soundproofing aims to prevent sound from entering or leaving a room, like blocking noise from those pesky neighbours. For more tips, check out our guide on soundproofing against noisy neighbours! 📖

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How many Acoustic Panels Do I Need?

The first step is going to be installing acoustic panels on your walls. These reduce the reverberations and echoes in the space.

Use our Free Tiles Calculator to find out

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How do you install soundproofing? 🔧

There are two main options for installing our DIY soundproofing solutions, and we're here to support you every step of the way!

DIY Installation:

All of our systems are DIY-friendly, saving you on installation costs.

80% of customers install the systems themselves because we’ve made it easy!

We provide simple, step-by-step installation guides and videos for a hassle-free experience.

Our technical team is ready to answer any questions and offer support. We're here for you! 🤗

Use a Local Contractor:

You're on your way to a noise-free home! If DIY isn’t an option, consider hiring a local tradesperson.

We simplify the process by communicating directly with your tradesperson throughout the installation.

Visit our installation page for more details! 📞

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What's the difference between impact and airborne noise? 🔊

1. Airborne Noise

This travels through the air, like conversations, TV sounds, or barking dogs. When sound waves hit a building, they cause it to vibrate, transmitting through the structure.

2. Impact Noise

This results from physical impacts on buildings, such as footsteps, slamming doors, or moving furniture. Impact noise can be harder to isolate, as these vibrations are stronger and travel further through dense materials.

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What are decibels? 📏

Decibels are measured logarithmically (not as a percentage) . This means that every increase of 10dB on the scale is a tenfold increase in sound pressure level (SPL) . Near silence is 0dB 🤫, while a sound at 10dB is ten times louder!

30-40 dB = Soft music, whisper 🎶
60-80 dB = Office noise, traffic 🚗
85-100 dB (HARMFUL) = Subway, shouted convo, chainsaw ⚠️
100-140 dB (DANGEROUS) = Chainsaw, loud concert, racing, shooting range 🚨

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Is everything in stock and ready to ship? 📦

In stock, ships in 1-2 business days! Learn More

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Where Is My Order?

Track your order: Check your email or visit our Tracking Page.

🎬 "Real Stories, Real Voices 📣"

Helped Decrease Noise by 50%
Simple, Easy, Peel & Stick Installation
Reduce Echo by 80% for my Recordings
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Understanding STC and Ratings

What is STC?

How Does STC Work?

The Problem with Low Frequencies

What Do STC Ratings Mean?

Key Elements of Effective Soundproofing

Common Myths About Soundproofing

STC Ratings for Wall Assemblies

Why STC Alone Isn’t Enough

Achieving the Best Soundproofing for Your Project

Frequently Asked Questions

How do I soundproof my wall against noisy neighbours? 🤫

How many Acoustic Panels Do I Need?

How do you install soundproofing? 🔧

What's the difference between impact and airborne noise? 🔊

What are decibels? 📏

Is everything in stock and ready to ship? 📦

Where Is My Order?

🎬 "Real Stories, Real Voices 📣"

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Arrowzoom Easy Mounting Sticky Acoustic Foam Tape - KK1207

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Understanding STC and Ratings

What is STC?

How Does STC Work?

The Problem with Low Frequencies

What Do STC Ratings Mean?

Key Elements of Effective Soundproofing

Common Myths About Soundproofing

STC Ratings for Wall Assemblies

Why STC Alone Isn’t Enough

Achieving the Best Soundproofing for Your Project

Frequently Asked Questions

How do I soundproof my wall against noisy neighbours? 🤫

How many Acoustic Panels Do I Need?

How do you install soundproofing? 🔧

What's the difference between impact and airborne noise? 🔊

What are decibels? 📏

Is everything in stock and ready to ship? 📦

Where Is My Order?

🎬 "Real Stories, Real Voices 📣"

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