What are the quietest fragrance diffusers on the market?

This plug-in waterless cold-air diffuser uses a daylight sensor and includes a night light plus 3 intensity levels. It is designed for small to medium rooms with stated coverage of 600-1,000 sq ft and automatically shuts off (including when oil runs low).

The Aroma Paradise Portable Rechargeable Mini is a USB-C rechargeable, waterless cold-air fragrance diffuser for small rooms and travel (including cars) that uses pure oil diffusion. It's designed for cordless use for up to 8 hours per charge, with coverage up to 400 sq ft. It includes auto shut-off and runs quietly (described as below 30 dB on the product page).

The Aroma Paradise Tower+ Waterless App-Enabled is a cold-air, waterless scent diffuser designed for larger rooms, using pure fragrance oil without water or heat. It supports app-based scheduling and intensity control, and it is described as whisper quiet. It is positioned for coverage up to 2000 sq ft.