Before buying pads or replacing a HomePod because the low end carries into an adjoining room, try the Reduce Bass setting with a repeatable listening comparison.
Use two listening positions
Apple documents Reduce Bass in HomePod audio settings. Play the same track at a comfortable fixed volume, first with the setting off and then on. Listen at your regular seat and from the adjacent room, with the door in the same position. A track with a repeating bass line gives you a stable point of comparison.
Test placement separately if needed
If the setting helps in both places, leave new hardware out of the initial budget. If the issue persists, compare a second stable location on a suitable surface and keep the audio setting unchanged for that trial. This is a listening check, not proof of sound isolation or a guarantee about what neighbors hear.
See the manufacturer’s guidance for current requirements. Related: homepod stereo pair used matching model.
