LullbeeThe most common mistake with baby sleep sound is not the sound. It is the volume and the placement. Louder is not more effective, and a machine wedged against the crib rail is doing more than anyone intends.
What the research measured
A widely cited 2014 study in the journal Pediatrics tested popular infant sound machines at maximum volume and found that many, played at full volume right next to a crib, exceeded recommended noise limits for infants. The authors' practical advice was simple. Place the sound source farther away, turn the volume down, and the same machines measured comfortably within reasonable levels.
The across-the-room rule
Keep the phone or speaker across the room, not in or beside the crib. Set the volume so an adult standing at the crib could hold a quiet conversation over it without raising their voice, about the loudness of a soft shower running behind a door. If it feels loud to an adult ear at the crib, it is too loud.
Continuous beats blasting
The goal of sleep sound is masking, smoothing over sudden noises, not overpowering the room. A moderate, steady level does that completely. Turning it up past that point adds nothing except exposure.
Lullbee ships every track loudness-matched at a gentle level, so switching sounds never produces a surprise jump, and the app is built to be played from across the room with the screen off.