Topakustik 28/4 M grooved and perforated fiber absorber

Topakustik – 28/4 M

PTB reference data

Original description

Material properties

Manufacturer: n'H Akustik + Design AG

Wall distance: 7.9 in

Reverberation chamber (ASTM C423 / ISO 354)

NRC

0.75

derived from ISO 354 lab data

α_p nach ISO 11654

f (Hz)	125	250	500	1k	2k	4k
α_p	0.65	0.95	0.95	0.70	0.50	0.45

Create a permanent free account — Access frequency bands, variants and export.

Free. No password required.

Value from the PTB table, not verified

NRC: 0.75 (derived from ISO 354 lab data)

Measured values as a table (1 measurement)

Topakustik 28/4 M grooved and perforated fiber absorber: sound absorption coefficient αs per ISO 354 by frequency and test build-up
Build-up	NRC	125 Hz	250 Hz	500 Hz	1000 Hz	2000 Hz	4000 Hz
200 mm	0.75	0.65	0.93	0.93	0.72	0.50	0.43

Measured values as a table (1 measurement)

Access frequency bands, variants and export. Create a permanent free account

Last updated: 08/28/2026