Why brown noise sounds lower
Brown noise gives much more weight to lower frequencies than white noise. This generated sample is a low rumble with less of the bright hiss. It shares the noise slot with white and pink; choosing another color replaces it.
This is a 20-second synthetic loop, not a heartbeat, womb recording or recording of a child.
Small speakers change the comparison
A phone may reproduce little of the lowest part of this sound. A quiet or thin result on a small speaker does not mean the volume should be raised until it sounds like a larger speaker.
The browser percentage cannot tell you the sound level reaching a child. Check the device, its position and its volume, and compare colors at a low output level.
For babies and older children
The same controls can prepare this sound for a baby or an older child; there is no age-specific signal processing. The sound does not become safer because it is labeled brown, and this site makes no claim that it improves attention or treats ADHD.
For an older child’s quiet reading time, choose a short session that ends manually or with the timer. If background sound is distracting, use Pause and keep the activity quiet.