WoodHighly absorbent

Physikalisch-Technische Bundesanstalt

Source: H. Lenz, Marktübersicht schallabsorbierende Anordnungen, Ruhr Universität Bochum, 1981, Seite 159

Value from the PTB table, not verified

Wilhelmi acoustic panel Variantex-Rupfen

Wilhelmi acoustic panel – Variantex-Rupfen (1981)

PTB reference data

Original description

Material properties

Manufacturer: Wilhelmi Werke AG

Thickness: approx. 0.7 in

Wall distance: 2 in, 12 in

Surface: coated with acoustic non-woven and natural fiber burlap

Reverberation chamber (ASTM C423 / ISO 354)· 2 variants

NRC

0.60

α_p per octave band

f (Hz)	125	250	500	1k	2k	4k
α_p	0.30	0.25	0.45	0.85	0.75	0.65

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Compare		Value
	2 in	NRC0.60
	12 in	NRC0.55

NRC: 0.60 (derived from ISO 354 lab data)

Weight / density: 6 - 7 kg / m²

Measured values as a table (2 measurements)

Wilhelmi acoustic panel Variantex-Rupfen: sound absorption coefficient αs per ISO 354 by frequency and test build-up
Build-up	NRC	100 Hz	125 Hz	160 Hz	200 Hz	250 Hz	315 Hz	400 Hz	500 Hz	630 Hz	800 Hz	1000 Hz	1250 Hz	1600 Hz	2000 Hz	2500 Hz	3150 Hz	4000 Hz
ca. 18 mm · 6 - 7 kg / m² · 50 mm · acoustic fleece and Naturfaser-Rupfen	0.60	0.24	0.36	0.35	0.33	0.18	0.19	0.37	0.39	0.60	0.80	0.90	0.83	0.83	0.83	0.65	0.63	0.64
ca. 18 mm · 6 - 7 kg / m² · 300 mm · acoustic fleece and Naturfaser-Rupfen	0.55	0.32	0.30	0.25	0.16	0.17	0.19	0.36	0.42	0.70	0.79	0.86	0.86	0.80	0.77	0.65	0.66	0.67

Measured values as a table (2 measurements)

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Last updated: 09/02/2026