The report states that several devices, final or prototypes, make several rounds to the lab for audio tests. Here they are tested, tuned and retested until the team is satisfied with the results.
Also mentioned is that Apple has built its own anechoic chamber, which specifically exists to test Homepod speakers. This room is echo-free and non-reflective and is built into another room, letting no noise make its way inside. The anechoic chamber is also the largest one built in the US, says the report.
Apple has another chamber built where it tests the voice detection for its AI – Siri. “We went out to hundreds of employees rooms and took thousands of measurements in each room,” said Geaves. “That allowed us to characterize each of those acoustic spaces and come up with an average for all of those rooms in terms of reverberation.”
Furthermore, there is a different chamber specifically to listen for electronic noise. This means the small buzz noise that comes out from speakers when they are plugged in but are not playing any audio. This particular chamber has one foot thick panels along with 80 isolating mounts. It is designed to be -2 dBA, which is well below what we can hear.