The Best of Acoustics1

The Myth of NRC 0.9

What is NRC 0.9 and is it really required?

NRC 0.9 is an oft-used term in the industry
Sometimes abused, sometimes misused
but

What does NRC 0.9 mean in simple terms?

It means that 90% of the sound energy, incident to the surface of the acoustical panel, is absorbed
Similarly NRC 0.7 means that 70% of the sound energy, incident to the surface of the acoustical panel, is absorbed
NRC 0.5 means that 50% of the sound energy, incident to the surface of the acoustical panel, is absorbed

NRC 0.9 is more expensive than NRC 0.7
NRC 0.7 is more expensive than NRC 0.5

NRC 0.9 – ₹ ₹ ₹ ₹ ₹
NRC 0.7 – ₹ ₹ ₹
NRC 0.5 – ₹

Here are 5 points to understand NRC 0.9

What a space needs is to bring down its Reverberation Time
and hence minimize or eliminate the echoes

NRC is the acoustical quality of a product – means to a goal
Reverberation Time (RT) is the acoustic quality of the space – the goal

2 An acoustic space may not need NRC 0.9 to bring down its Reverberation Time

3 Surface area of a space available for sound absorption.

The floor is not available because of seating and occupancy of people. So it is only the 4 walls and the ceiling.

Lets say we use NRC 0.9 ceiling tiles and leave the walls bare and reflective
Will that give good acoustics?
No, there will be a lack of clarity, muddled dialogues and a lot of echo.

Hence, it will be better to use NRC 0.5 for both walls and ceiling within the same budget as NRC 0.9 for only the ceiling to achieve the goal of lower RT

4 NRC 0.9 as tested in an acoustical laboratory,
may not be the same achieved in the project site.

5 What is NRC? 

NRC is Noise Reduction Coefficient is the arithmetic average of sound absorption coefficients at 250, 500, 1000 & 2000Hz.

What happens if we put NRC 0.9 acoustical panels in a space which has low frequencies below 500Hz?
For example: A night club, lounge, discotheque or a bar which has a lot of low frequency sounds from the subwoofers in terms of the music.

One might not achieve the results one might have expected because in that environment NRC 0.9 wont solve the issue. Low frequency sound absorbers which are membrane resonators will be required, topic for another episode of “HearYourself”.

So NRC 0.9 must be used depending on the space and its requirement

NRC 0.9 must be used judiciously. Don’t waste your money!

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