The measurement of absorption coefficients in reverberation rooms with a volume of at least 150 m³ is standardised in ISO 354 at frequencies between 100 Hz and 5 kHz. ISO 12999-2 describes the uncertainty of these measurements. It increases at both ends of the frequency range, and it  is derived from interlaboratory tests with rooms of about 200 m³ volume.  If a measurement is performed in a 50 m³ reverberation room, the frequency range of ISO 354 and the uncertainties can be assumed to be shifted upwards by two one-third octave bands. It could then be possible to reduce the uncertainty of measured absorption coefficients by combining the measurement results from a 50 m³ and a 200 m³ room in an overlapping frequency range, similar to the procedure described in ISO 10534-2:2023 (measurement in impedance tubes with different diameters). An internal round robin was conducted, where eight different absorber setups were measured by five different teams, each using a different 50 m³ room with the absorber area scaled accordingly. The absorbers had been measured beforehand in two different reverberation rooms (237 m³ and 204 m³). Against the background of the considerations described, the results were evaluated and will be reported.