What Is a Good Sound Absorption Coefficient? DASM - Leading Acoustic Testing Unit in Vietnam

Sound absorption coefficient (symbol: α) is an index representing the sound absorption capacity of a material when sound waves impact its surface.

What is the sound absorption coefficient?

The sound absorption coefficient, also known as the sound absorption coefficient – symbol: α. This is an index representing the sound absorption capacity of a material when sound waves impact its surface. This index ranges from 0 to 1, in which:

• α = 0: The material does not absorb, all sound is reflected back
• α = 1: The material absorbs completely, ideal in acoustic treatment

In summary, the higher the measured sound absorption coefficient result, the better the material is classified into the group of sound absorption materials. Sound absorption materials will absorb sound well and the space will reduce reverberation, resonant sound, and noise interference. Thus, the sound quality is better, the sound is clearer, more faithful, and more pleasant.

DASM Institute – Sound Absorption Coefficient Measurement Service in Reverberation Room According to ISO 354 & ASTM C423

DASM is certified for acoustic testing operation registration

Sound absorption level testing for Vinh Hung perforated barrier acoustic panels

What sound absorption coefficient is considered “good”?

Below is the classification table of the sound absorption capacity of materials according to the α value:

α value	Evaluation	Typical materials
0.00 – 0.30	Poor (strong reflection)	Brick, glass, concrete
0.30 – 0.50	Medium	Thin carpet, vulcanized rubber, simple perforated ceiling
0.50 – 0.70	Fair
0.70 – 0.90	Good	Sonic panels, fiberglass, acoustic wood panels, mineral wool for acoustics, acoustic foam
≥ 0.90	Very good	Acoustic wood, acoustic mineral wool, bass traps, high-end composite systems, etc.

In practice, good sound absorption materials usually have an α of 0.7 or higher and should be combined correctly with other sound insulation and sound absorption materials to achieve the highest efficiency for the project.

Combining with which type of material appropriately depends on the function and purpose of the project as well as the design and budget of the investor.

What is NRC? Is it important?

NRC (Noise Reduction Coefficient) is the average index of the sound absorption coefficient at 4 important frequency bands (250Hz – 500Hz – 1000Hz – 2000Hz).

The sound absorption coefficient NRC is a familiar index in technical documents of civil, industrial projects, conference rooms, studios, etc.

NRC	Evaluation
NRC < 0.50	Low efficiency
NRC ≥ 0.70	Good – meets design standards

In summary: NRC ≥ 0.70 is considered a good standard to ensure the space absorbs sound effectively, limits reverberation, interference, and echoes; helping the space achieve more professional sound quality.

Recommended sound absorption coefficient by project type

Project type	Recommended α value
Office, classroom	≥ 0.50
Meeting room, auditorium	≥ 0.60
Studio, cinema	≥ 0.75
Factory, corridor	≥ 0.40

Choosing sound absorption materials and sound insulation materials for noise reduction correctly according to the standard α level helps ensure sound quality and compliance with construction and interior design regulations, bringing you a better sound experience.

DASM – Testing sound absorption coefficient according to international standards

At the VILAS standard laboratory – where acoustic measurements and material testing of the DASM institute are specialized, we perform measurements of the sound absorption coefficient according to two popular international standards: ISO 354 and ASTM C423

International standard equipment:

• Standard reverberation room
• Calibrated Class 1 microphone
• Automatic sound absorption coefficient measurement system, accurate and transparent results

Test results can be used for:

• Technical dossiers, project bidding
• Sound absorption material certification
• Product export according to ISO standards

When should you measure the sound absorption coefficient?

You should perform sound absorption coefficient measurements at DASM when:

• When you are a manufacturer of sound absorption materials needing technical certification
• When you are a design and construction unit needing to verify material efficiency
• When you need to compare and select materials suitable for each type of project
• When preparing bidding documents or projects requiring in-depth acoustic testing

Contact DASM today if you need to measure the sound absorption coefficient? Want to know if your materials meet the standards?

DASM is currently a trusted partner in sound absorption coefficient measurement and acoustic material certification in Vietnam. Our experienced technical team and acoustic experts will consult – design architectural acoustics to meet specific practical needs and your dossier.