
Shape indicator (L, M, H)
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Nyquist Team
When choosing acoustic panels, we usually look at one number indicating their effectiveness. However, this is a trap – two materials with the same 'average' can behave completely differently. The symbols L, M, and H are signposts that warn or inform about the exceptional properties of the material in specific sound ranges.
Professional Definition
The shape indicators (L, M, H) are letter designations according to the PN-EN ISO 11654 standard, added to the weighted sound absorption coefficient (αw), indicating that in a certain frequency band, the material demonstrates significantly higher effectiveness (by 0.25 or more) than one would expect from the reference curve.
The symbols represent the respective bands: L (Low) – low frequencies (250 Hz), M (Medium) – mid frequencies (500 Hz, 1000 Hz) and H (High) – high frequencies (2000 Hz, 4000 Hz). This is information for the designer that the given acoustic structure is specialized and performs better in a specific range than its averaged class would suggest.
Acoustics in Simple Words
This can be compared to a graphic equalizer in audio equipment. The main absorption indicator tells us about the overall
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