Absorption class A to E: how to choose the right acoustic panel

Two acoustic panels, both 40 mm thick, both labeled as “sound-absorbing.” One absorbs 95% of the sound, the other 35%. On the photo, you won’t see the difference, it’s often not mentioned in the quotation, and in the space, you’ll notice it immediately.

This difference is called the absorption class. It’s the only specification you need to fairly compare panels—and it’s also the specification that’s most often missing. Below, we explain what the classes mean, how to read them, and which class you need where.

What absorption class is

Sound hitting a surface is partially reflected and partially absorbed. The portion absorbed is the absorption coefficient: a number between 0 and 1. At 0, everything is reflected (think of concrete or glass), while at 1, everything is absorbed.

That coefficient varies by frequency — a panel that absorbs high tones well may do little for low tones. To make this practical, the standard EN ISO 11654 summarizes it in one number: the α_w (alpha-w), the weighted absorption value. This α_w then determines the class of the product, ranging from A to E.

The classes

Note the last row. A product with α_w 0.10 or lower falls outside the classification, but may still refer to itself as an “acoustic panel” in practice. Always ask for the class, not the description.

The question you should ask yourself

This is the most important part of this article, and the point that is often missing in almost every quote.

An absorption value always applies to a specific mounting method — more precisely: at a specific suspension height to the underside of the structural ceiling, abbreviated as a.o.p. The same panel performs significantly differently when mounted flat against the wall than when suspended with an air cavity behind it. This air layer contributes, especially at low frequencies — precisely the range where human voices lie.

The standard is clear on this: absorption values without specifying the suspension height are incomplete and cannot be used to compare products.

Practically, this means: if a supplier refers to a product as “class A” without specifying the mounting method, you still know nothing. Ask for both. Two panels that both claim to be class A can differ by two classes in your situation, simply because one was measured with a 200 mm air gap while you’re mounting it flat against the ceiling.

NRC and SAA: The American Figures

You may also encounter other values, usually for products from outside Europe. The NRC (Noise Reduction Coefficient) and the SAA (Sound Absorption Average) come from the American standard ASTM C 423. Both are averages over a frequency range — the NRC over 250 to 2000 Hz, the SAA over 200 to 2500 Hz.

They are not directly convertible to α_w. An NRC of 0.90 is not automatically class A. If you encounter NRC values, ask for the α_w along with its corresponding class, so you can compare apples with apples.

Which class do you need where necessary?

The temptation is to ask for class A everywhere. That’s expensive and not always better — a completely deadened space feels unpleasant, and people tend to speak louder unconsciously because they can’t hear their own voice.

The standard ISO 22955 for open offices takes a different approach: it links acoustic requirements to the type of activity rather than to the space itself. This is also how you should view classes.

If you have class D or E, you’re mainly buying decoration. That’s fine — acoustic panels can also be a design element — but don’t expect any acoustic effect from them.

Surface area matters just as much as class

A common misconception: choosing class A and then installing too few square meters. Four square meters of class A do less than ten square meters of class C.

The rule of thumb is that your total absorption is the sum of surface area multiplied by the absorption coefficient. This means the question ‘which class’ is never separate from ‘how many m²’ — and that a large-scale Class C solution is sometimes more cost-effective than a small Class A solution with the same result.

What you should avoid: concentrating everything on one wall. Sound comes from all directions; spreading it across ceilings and multiple surfaces makes the same area more effective.

Four things that subtly reduce performance

• Repainting. This is the most critical issue. Paint seals the pores where sound enters. Both absorption values and fire-resistant properties decrease once a panel is repainted. If you want a different color, order it that way — never paint afterward.
• Mounting flat when it is meant to hang. See above: the air gap plays a role.
• Covering with furniture. A wall panel behind a tall cabinet absorbs hardly anything.
• Add foil or coating. Every extra sealed layer over the surface costs absorption, even a thin one.

What to ask for in a quotation

Four rules, and you can compare every quote fairly:

1. The α_w-value and the absorption class according to EN ISO 11654.
2. The suspended height (a.o.p.) at which this value was measured.
3. The total surface area to be installed in m².
4. The mounting method offered — and whether it matches point 2.

If you don’t get an answer at point 2, that information in itself is telling.

How we approach this

Choosing the class is step three, not step one. First, measure what the problem is and whether it’s about echo or sound dispersion — these two issues require opposite solutions. This process is outlined in improving office acoustics: the 4-step plan.

Only then does the product choice become relevant. Our acoustic wall panels and ceiling islands come in various classes, and which you need depends on the zone. A broader overview of the options is available in the guide on acoustic panels and wall panels, and the full range on acoustic solutions.

Want to know how many square meters your space needs in which class? It’s a calculation, not an estimate. Request a quote and we’ll figure it out.

Frequently asked questions about absorption classes

What does absorption class A mean?

Absorption class A means a weighted sound absorption value (α_w) between 0.90 and 1.00 according to EN ISO 11654: the panel absorbs 90 to 100% of the incoming sound. It is the highest class and the standard choice for office landscapes, call centers, and canteens.

What is the αw value?

The _α is the weighted sound absorption coefficient according to EN ISO 11654: a single number between 0 and 1 summarizing absorption across octave bands from 250 Hz to 4000 Hz. This value determines the absorption class in which a product falls.

Why is the mounting height important for acoustic panels?

Because the air cavity behind a panel contributes to sound absorption, especially at low frequencies. The same panel performs significantly worse when mounted flat against the wall than when suspended with an air cavity. Absorption values without specifying suspension height are therefore incomplete and unusable for comparing products.

What is the difference between αw and NRC?

The _w comes from the European standard EN ISO 11654 and is linked to an absorption class from A to E. The NRC comes from the American standard ASTM C 423 and is an arithmetic average over 250 to 2000 Hz. They are not directly interchangeable: an NRC of 0.90 does not automatically mean class A.

Can you repaint acoustic panels?

Better not. Paint seals the pores, forcing sound into the material, thereby reducing both absorption values and fire-resistant properties. If you want a different color, order the panel in that color instead of painting it afterward.

Last updated on 24 October 2026 by Stijn Belmans