How much sound-absorbing material should be used indoors, and how? Korea has no explicit statutory standard, but Germany's DIN (Deutsches Institut für Normung) 18041:2016 functions as the global best practice.
DIN 18041 is a room acoustic guideline applicable to general spaces up to 5,000 m³ and sports halls up to 30,000 m³. It calculates the target reverberation time (RT60) and the required absorptive area based on the intended use of the space.
Why Refer to International Guidelines?
In domestic interior and construction projects, the selection of absorptive materials still relies heavily on experience and intuition. Because indoor noise levels are not legally mandated, owners, designers, and contractors alike find it difficult to answer the question: "how much is enough?"
"How much is enough" is calculated from volume, not guesswork.
Germany published the first edition of DIN 18041 in 1968 and has updated it for over 50 years, making it the de facto standard across the EU. The 2016 revision divides spaces into two use environments: long-range audiences (Group A) and close-range conversation (Group B).
Group A — Clear Sound for Long-Range Audiences
Group A covers spaces where the audience is positioned at a distance from the speaker. It is further divided into five use categories: music rooms (A1), lectures and presentations (A2), education (A3), education for the hearing-impaired (A4), and sports halls (A5).
The key metric is the target reverberation time (RT60 — Reverberation Time, the time for sound pressure to decay by 60 dB). RT60 increases proportionally with room volume V, and the standard specifies a recommended formula for each use category.
For example, if a music room (A1) has a volume of 1,000 m³, the recommended RT60 is approximately 1.4 s or less. A lecture or education space of the same volume requires a shorter RT60 — around 0.7 s — to achieve adequate speech intelligibility.
For Group A, the placement of absorptive materials matters as much as the total area. Absorptive surfaces must be distributed on the rear wall behind the speaker and on the ceiling to reduce reflected sound paths, ensuring the entire audience experiences uniform acoustic quality.
DIN 18041 Space Classifications at a Glance
◆ marks the shortest RT60 target. Values shown are for V=500 m³; targets increase with volume.
| 기준 | 공간 유형 | 그룹 | 주요 요건 | 목표 RT60 (500 m³) |
|---|---|---|---|---|
| Music room (A1) | Music room | Group A | Long-range audibility | ≤ 1.4 s |
| Lecture/teaching (A2/A3) | Lecture/teaching | Group A | Speech intelligibility | ≤ 0.8 s |
| Open office (RGB4) | Open office | Group B | Noise/privacy balance | ≤ 0.5 s |
| Call center/security (RGB5) | Call center/security | Group B | Minimum noise/focus | ≤ 0.4 s |
| Hospital ward (RGB3) | Hospital ward | Group B | Healing/recovery | ≤ 0.6 s |
Group B — Privacy and Focus in Close-Range Conversation
Group B applies to spaces where the audience is in close proximity to the speaker — environments such as offices, hospitals, and libraries where conversation and concentration are required simultaneously. It is subdivided into RGB (Raumakustische Gruppe B) grades 2 through 5.
The key metric for Group B is the absorptive area ratio A/V (equivalent absorptive area ÷ room volume). A/V is used instead of RT60 because in close-range spaces, total absorption is a more direct indicator of quiet than reverberation time.
RGB Grades 2–5 at a Glance
Higher RGB class demands more absorption. ◆ marks the strictest A/V requirement.
| 기준 | 등급 | 사용 시간 | 대표 공간 | A/V 권장 |
|---|---|---|---|---|
| RGB2 | RGB2 | Short stay | Reception · waiting room · changing room | Low (reference) |
| RGB3 | RGB3 | Long stay + good comm. | Hospital ward · care facility · private office | A/V ≥ 0.20 |
| RGB4 | RGB4 | Low noise + comfort | Corporate reception · lab · library · open office | A/V ≥ 0.25 |
| RGB5 | RGB5 | Special quiet/focus | Call center · security · recovery room | A/V ≥ 0.30 |
Absorptive area is not a simple geometric area — it is the equivalent absorptive area (material α value × actual surface area). For the same ceiling area, melamine foam provides approximately 1.3 to 1.5 times the equivalent absorptive area compared to PET.
How Is Reverberation Time Measured?
The international standard is ISO 3382-2:2008 (Measurement of room acoustic parameters in ordinary rooms). An omnidirectional source generates an impulse or white noise signal, and the decay curve is recorded by microphone for analysis.
A field measurement simultaneously yields three metrics: EDT (Early Decay Time, initial 10 dB decay × 6), T20 (5–25 dB range × 3), and T30 (5–35 dB range × 2). EDT most closely corresponds to perceived listening impression; T30 is the most stable.
Lab numbers alone always underdeliver — apply a 1.2 ~ 1.5 safety factor.
Which Category Does My Space Belong To?
Lecture/meeting (V ≈ 100 ~ 500 m³)
"Slides visible, speech unclear"
Open office (V ≈ 300 ~ 1,500 m³)
"Neighbor calls break focus"
Call center/security
"Call quality inconsistent"
Music room/performance
"Instrument attacks muddy"
Hospital ward / library
"Patient struggles to sleep"
Gym / pool
"Whistles echo, instructions lost"
Tornex Free 5-Step Absorption Simulation
Tornex provides a free analysis of acoustic material type, area, and quantity based on DIN 18041. The process takes five steps, starting from drawings, photographs, and the intended use of the space received before construction.
Step 1. Space type classification — confirm whether the space falls under Group A1–A5 or RGB2–5.
Step 2. Estimate current reverberation time — calculate drawing surface areas × current material α values (or measure on-site).
Step 3. Determine target RT60 — apply the DIN 18041 formula based on volume V.
Step 4. Simulate required absorptive area — calculate αw × area needed to reach the target RT60.
Step 5. Tornex product matching — recommend from PET, melamine foam, or wood-wool based on the spatial tone, budget, and installation conditions.
Frequently Asked Questions
Q1Is DIN 18041 legally mandatory in Korea?
Q2Key difference between Group A and B?
Q3How is reverberation time measured?
Q4Why do lab αw and field values differ?
Q5What if A/V target is not met?
Glossary
DIN 18041 — Deutsches Institut für Normung 18041. German room acoustics standard. The 2016 revision is the current edition.
RT60 — Reverberation Time 60. Time in seconds (s) for sound pressure to decay by 60 dB. Determined by room volume and absorption.
EDT — Early Decay Time. Initial 10 dB decay time × 6. The reverberation metric most closely related to perceived listening impression.
T20 / T30 — Reverberation time measurement intervals. T20 = 5–25 dB range × 3; T30 = 5–35 dB range × 2.
A/V — Equivalent absorptive area ÷ room volume. Unit: m²/m³. Key metric for Group B.
RGB — Raumakustische Gruppe B. DIN 18041 Group B grade (RGB2–RGB5).
αw — Weighted Sound Absorption Coefficient. Single absorption metric defined by ISO 11654. Range 0.00–1.00.
STI — Speech Transmission Index. Speech intelligibility index. Range 0.00–1.00; 0.60+ is considered good.
ISO 354 — Standard for measuring sound absorption coefficient in a reverberation chamber. Foundation data for αw calculation.
References
[1] DIN 18041:2016 — Acoustic quality in rooms · DIN Media. https://www.dinmedia.de/en/standard/din-18041/245356770
[2] Nocke C. (2016) "The new standard DIN 18041 — Acoustic quality in rooms" · ICA 2016 Proceedings. http://www.ica2016.org.ar/ica2016proceedings/ica2016/ICA2016-0716.pdf
[3] Nocke C. (2018) "DIN 18041 — a German view" · Euronoise 2018. https://www.euronoise2018.eu/docs/papers/176_Euronoise2018.pdf
[4] Vital-Office "DIN 18041 audibility in rooms — requirements, recommendations and advice" · English commentary.
https://www.vital-office.net/din-18041-audibility-in-rooms-%E2%80%93-requirements-recommendations-and-advice-for-the-planning-of-offices-conference-rooms-and-classrooms
[5] ISO 3382-2:2008 "Measurement of room acoustic parameters — Part 2: Reverberation time in ordinary rooms" · ISO. https://www.iso.org/standard/36201.html
[6] ISO 11654:1997 "Sound absorbers for use in buildings — Rating of sound absorption" · EN ISO copy PDF.
https://nobelcert.com/DataFiles/FreeUpload/EN%20ISO%2011654-1997%20(2000).pdf
[7] NTi Audio "Reverberation Time Measurement (RT60) Application Note" · Measurement procedure guide. https://www.nti-audio.com/Portals/0/data/en/NTi-Audio-AppNote-Reverberation-Time.pdf