What is (NRC) Noise Reduction Coefficient and (STC) Sound Transmission Class in SoundProofing? Best 2021 Guide - Soundproof Plan : Soundproofing Tips, Product guide and How-to guide

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What is (NRC) Noise Reduction Coefficient and (STC) Sound Transmission Class in SoundProofing? Best 2021 Guide

Whenever you want to buy an acoustic or soundproof materials, you've probably seen two digits on most products, one is the noise reduction factor (NRC), and the other is the sound transmission class (STC).

Have you ever wondered what the two mean in audio engineering and why these two numbers are marked on every product?

It may be "yes" or "no", but once you've read this guide, that means you'll find it appropriate to understand both concepts, and there's one more we call impact isolation class (IIC) we'll cover the same too.

During my soundproofing research, I checked various parameters and assessed the soundproofing quality of materials everywhere. The best figures that matter are NRC and STC.

So let's go over each of them and understand what STC and NRC mean.

What is Noise Reduction Coefficient (NRC)?

In sound engineering when you talking about soundproofing of an area, you must have heard about sound absorption.

Whenever a sound wave enters your personal space due to some reflection from a hard surface such as a wall, floor or ceiling, it amplifies and creates an echo in the room.

This echo can be minimized with the help of sound absorbing materials, and the ability of each material to absorb sound frequency is determined based on a Noise reduction coefficient.

The short-term Noise reduction coefficient, also known as NRC, is the logarithmic average attenuation or attenuation level (dB / s) of sound frequencies in the 250,500, 1000 and 2000 Hz range of any sound absorbing object in the comparison area. with areas where no sound absorbing material is available.

At the simplest NRC value, state the ability of each material to absorb sound waves over the frequency range from 100 Hz to 5000 Hz.

The higher the NRC of an object or material, the better the absorption of sound waves and their reflection is reduced. Materials with 0 NRC reflect all soundwaves and are no absorption.

The largest amount for any material is approximately 1, which allows 100% of the sound waves to be absorbed. However, laboratory-tested materials have more NRC than in the real world.

All NRCs were assessed based on the size of the object, but the edges and fixings of objects also absorb more sound waves than would be estimated based on the size of the object.

Here are the NRC of different materials references: If NRC is given as 0.1 it means that the material can absorb 10% and 90% of the reflected sound waves back.

1. Brick - 0.00-0.05 NRC

2. Glass - 0.05 NRC

3. Plywood - 0.10-0.15 NRC

4. Carpet on concrete - 0.20-0.30 NRC

5. Carpet with foam pad - 0.30-0.50 NRC

NRC is calculated based on the frequency range of human speech as 100 Hz to 5000 Hz. Therefore, frequencies higher than this range may not be absorbed efficiently by these materials or be rated by the NRC.

Now that you have an idea of ​​what this noise reduction factor or NRC means, let's now go over the sound transmission class, or STC.

What is the Sound Transmission Class (STC)?

Hopefully you know the difference between sound and noise, which are the main phenomena, and wave transmission.

The sound is transmitted by vibrations of air particles coming in its path, and these vibrations cause the air particles to move and continue unless they find an obstacle in their path.

The stronger the barrier, the better the ability to blocking noise and pass through less material. Therefore, a material's ability to block sound waves is assessed using its Sound transmission class or STC score.

STC stands for sound transmission class, which is an integer assigned to each soundproof material to determine its potential to attenuate sound in the air.

If the material has a higher STC and sound waves come from the other side of the material and try to pass through it, most of its energy will be lost as it passes through the material.

It is derived from the sound attenuation value tested in the frequency range from 125 Hz to 4000 Hz and measures the sound absorption rate on a dB scale.

If the sound from the other side of the wall is 30dB, but drops to 10dB after passing through the insulation or wall, it means the wall STC value is 20.

If soundproof, the barrier material must have an STC rating greater than 50 and the STC rating assigned to each product is based on laboratory testing.

This means that it will be tested in an ideal environment, but in the real world there are many factors to consider.

So make sure to buy a product with a STC above 55-60 to meet your soundproofing requirements.

Here are some examples that explain how material output from STC can affect sound transmission.

25 - Normal speech, sound clear

30 - Normal speech, hard to hear, but strong speech is clear

35 - Strong speech, audible but unclear

60 - Very loud music almost inaudible

70 - almost inaudible power tools

75+ Most of the sounds are not heard at all

From the STC rating above, it can be seen that the higher the number the better it is at blocking sound waves. Blocking sound waves is a major requirement for soundproofing.

Two main Soundproofing techniques are used to improve STC scores on soundproof insulation.

Isolation : By making cavities in the walls, using resilient channel for double-layered drywall.

Adding Mass : By setting up, additional bulk on an existing wall which can be added with Mass loaded vinyl or MLV.

Both are ideal ways to blocking sound waves and increase the STC partition.

Difference between NRC and STC?

Noise reduction coefficient (NRC) focuses primarily on the absorption capacity of the material and is mostly rated on a scale of up to 1.

However, the sound transmission class (STC) focuses on the blocking ability of each material, which is specifically stated in the case of the isolating material used as a barrier and is rated on a scale of 100.

If you are struggled with noise from the neighbor and trying to cope with the noise than if you chose a soundproof material, then focus more on the STC results than the NRC.

However, if you want to improve the sound quality in your home or room, it is better to focus on minimizing echo by absorbing sound waves rather than focusing more on NRC than STC.

For example, NRC is especially needed for materials used in ceilings, walls, and every room in high schools to absorb as much noise as possible, such as carpet, mats, or acoustic foam.

However, the STC results are relevant for areas where you want to maintain privacy on the other side of the private area so that no other audience can hear your secret chat.

Some examples are insulating materials and drywall or green glue, which are used to make partitions.

Well, now you have a good idea of what is noise reflection coefficient, and sound transmission class are and their main differences, but now I want to give you an idea of ​​another factor which we will call the Impact insulation class.

What is Impact Insulation Class?

Generated noise may be airborne noise, which is noise generated by air transmissions, such as for example B. human chat, traffic, television noise, etc.

However, there is no noise generated from impacting other objects such as footsteps or pulling on chairs or dropping materials on the floor.

In such a case, the noise generated is caused by impact with the ground and is different from the airborne noise. To minimize this, you don't have to focus on STC or NRC.

You have to focus on the Impact Isolation Class (IIC). This will determine the ability of each material to minimize impact noise.

The IIC is also estimated based on the standard frequency range of 100 to 3150 Hz, with real steps producing, a noise frequency range of 100 Hz.

Generally it is necessary to focus on the materials used for soundproofing of the floor, such as: B. Carpet, Subfloor plywood, plywood or plinth.

My Opinion on NRC vs STC

sound absorption is a component of soundproofing. Also, to be completely soundproof in any space, you need to focus on sound absorbing materials.

To better understand STC and NRC, STC needs to focus more when looking for ways to avoid transmitting sound to the other side of your area. However, NRC will help you improve sound quality by absorbing noise.

Almost every soundproof materials has these two factors in its product, so it's better to check the reviews and, depending on your needs, don't forget to order to buy the same.

What better way to share your experience of NRC ratings in your noise zone with our readers relying on the standard and real ratings of the NRC and STC?

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