Brown noise (also called red noise) has a power spectral density of 1/f^2, dropping 6 dB per octave. It sounds deep and rumbling. No peer-reviewed study has specifically tested brown noise with ADHD participants. The Nigg et al. (2024) meta-analysis explicitly states: "effects of other types of colored noise, including brown noise, in ADHD have not yet been empirically assessed."
The strongest indirect evidence comes from Lu et al. (2020), who tested "red noise" (mathematically identical to brown noise) in a general-population sample. Red noise outperformed pink and white noise on psychomotor speed, executive function, and working memory, and was rated the most subjectively pleasant of all noise colors tested.
Brown noise is included in Ebbi based on this indirect evidence, the theoretical plausibility that the stochastic resonance mechanism applies across noise colors, and strong demand from the ADHD community on social media.