This dataset contains Room EQ Wizard (REW) measurement data supporting the article “Optimized Soft-Enclosure Particle Dampers for Audio Equipment and Loudspeakers: Design, Filling Strategy, and Experimental Performance”. The measurements were used to evaluate optimized soft-enclosure particle dampers for audio equipment and active loudspeakers under controlled real-world listening-room conditions. The experiments compared damped and non-damped configurations using a Mac Pro (Late 2013), an RME ADI-2/4 Pro SE audio interface, active Gradient Revolution loudspeakers, and a Sennheiser MKH 40 (P48) measurement microphone. The dataset consists of one REW measurement file: - `kuulavaimennintesti202050914_nimetty.mdat` The article analyzes twelve measurements from this file. Six are impulse/sweep measurements acquired at 48 kHz with a frequency-grid length of 54,613 points. Six are stepped-sine distortion measurements acquired at 96 kHz and evaluated at 31 discrete frequency points from approximately 20.5 Hz to 20 kHz. The available measurement groups include: - `digi_vaimennin_*`: damped reference condition- `digi_ei_vaimenninta_*`: DAC without dampers- `kaiuttimet_ei_vaiment_*`: loudspeakers without dampers The data support comparisons of frequency response, SPL differences, phase/group-delay behaviour, THD+N, impulse-response-derived descriptors, clarity C80, reverberation-time descriptors, energy-time curves, and related acoustic metrics. The `.mdat` file can be opened with Room EQ Wizard (REW).