STC vs NRC: which rating actually matters for your space?

These two ratings get used almost interchangeably in briefs, and they measure completely different things. Specifying the wrong one is the most common reason an acoustic fit-out doesn't solve the problem it was meant to solve.

Sound Transmission Class (STC): keeping sound out of a room

STC rates how effectively a wall, door, window, or floor/ceiling assembly blocks airborne sound from passing between two separate spaces. It's a single number derived from how the assembly performs across a range of frequencies — the higher the number, the more sound it blocks.

STC is the rating that matters when the problem is privacy between rooms: a boardroom where confidential conversations shouldn't carry into the corridor, a party wall between two tenancies, or a recording space that needs isolation from the office next door.

As a general industry reference point, a standard single-stud drywall partition typically falls in the STC 30–35 range, while assemblies built specifically for confidential meeting rooms are commonly specified at STC 50 or higher. The exact figure for any given assembly depends on its construction, and should be confirmed against tested data for the actual materials used — not assumed from a product label.

Noise Reduction Coefficient (NRC): controlling sound inside a room

NRC rates how much sound a material absorbs versus reflects, on a scale from 0 (fully reflective, like bare concrete or glass) to 1 (fully absorptive). It has nothing to do with what happens in the room next door — it's entirely about how a space sounds to the people inside it.

NRC is the rating that matters when the problem is reverberation and echo within a room: an open-plan floor where every call sounds like it's in a stairwell, a cafeteria that's uncomfortably loud, or a boardroom with a distracting echo on video calls.

Why the confusion causes real problems

A material can have an excellent NRC and a poor STC, or vice versa. A thick, soft, highly absorptive acoustic panel can do very little to stop sound from transmitting through the wall behind it if that wall itself is lightweight. Conversely, a dense masonry wall can have an excellent STC while doing nothing to reduce echo in the room it forms one side of.

Specifying only one rating when a project actually needs both is the most common gap we see in briefs that come to us after a first attempt at soundproofing hasn't worked.

Frequently asked

How do I know if I have an STC problem or an NRC problem?

If the complaint is 'I can hear what's happening in the next room,' that's an STC problem. If the complaint is 'this room itself sounds loud and echoey,' that's an NRC problem — many real briefs are actually both.

Can a material have a good NRC but a poor STC?

Yes — a thick, absorptive acoustic panel can do very little to stop sound transmission if the wall behind it is lightweight, while a dense masonry wall can block sound well without reducing echo in the room.

What STC rating does a confidential meeting room need?

As a general reference point, a standard drywall partition typically falls around STC 30-35, while assemblies built for confidential meeting rooms are commonly specified at STC 50 or higher — though the exact figure should be confirmed against tested data, not assumed from a label.

What does an NRC rating of 1 mean?

NRC is scored from 0 (fully reflective, like bare concrete or glass) to 1 (fully absorptive) — it measures how much sound a material absorbs within a room, unrelated to what happens in the room next door.

How B-Acoustics selects for both

We assess each space against its actual use case rather than defaulting to one metric — surveying existing construction, measuring baseline reverberation, and setting explicit STC and NRC targets before recommending materials. (For how these targets translate into project cost, see what drives office soundproofing cost in Singapore.)