Where Does the Sound Come From?
The following explanation can be found on Soundproof Guide:
"Humans can really only process noises that go from about 20 Hz to 20,000 Hz. Most of the time, the electricity going through a charger can be up to 30,000 Hz or more. (Source)
One of the biggest culprits when actual noise is heard by humans is when the power adapter converts AC power to DC power.
It uses an electromagnetic coil as a transformer, instead of inductor. This makes the lower voltage power convert DC in a diode bridge rectifier. Power goes through the capacitor, which keeps the flow going before sending it through the power cable.
Every step of the process can create a little bit of noise. A high-pitched noise is usually going to be originating from a transformer, as it will make a noise when electricity is passed into the coil.
This causes the component to start to vibrate, and there is a resonance frequency associated with it. In fact, it happens so commonly that there is a term called coil whine, which has affected the chargers to an old television."
How Loud Should Spruce Be?
Our testing results indicate that Spruce should be a little louder when nothing is plugged into it. You can expect noise levels of 11.7-17.6 decibels, which is between the sound level of breathing and leaves rustling.
When Spruce is charging something, sound levels are expected to be between 3.9-6.3 decibels, which is quieter than breathing.
In the event your Spruce makes noises louder than leaves rustling, our support team at email@example.com will happily assist you!