Apple really wants you to implement a multi-HomePod speaker set-up and has ideas for making such an audio system offer superb sound. The company has filed for a patent (number)20200107121) for a self-equalizing loudspeaker system.
In the patent filing, Apple notes that the sound quality of loudspeakers (as perceived by a listener) is affected by the room or other acoustic space or environment (e.g., vehicle cabin) in which they’re placed. A reverberant room will cause the level of a certain frequency band (depending on the acoustic characteristics of the room) to increase in such a way that timbral character is deteriorated.
Apple wants to change this for those using multiple HomePod set-ups. The solution: digital signal processing systems for audio signals produced by microphones in acoustic environments. More specifically, to processing systems designed to adjust the tonal balance of a loudspeaker in a room or other acoustic space it is placed in, to improve a listeners experience
Here’s the summary of the patent filing: “An impulse response is computed between i) an audio signal that is being output as sound by a loudspeaker that is integrated in a loudspeaker enclosure, and ii) a microphone signal from a microphone that is recording the output by the loudspeaker and that is also integrated in the loudspeaker enclosure. A reverberation spectrum is extracted from the impulse response. Sound power spectrum at the listening distance is computed, based on the reverberation spectrum, and an equalization filter is determined based on i) the estimated sound power spectrum and ii) a desired frequency response at the listening distance. Other aspects are also described and claimed.”
