Not sure if this is a known issue, but I recently got some APMs and was very disappointed with the tuning. The bass was extremely loud and muddy, as if it were a parody of what people make fun of Beats users for. I went through the spatial audio settings and turned on/off personalized spatial audio to no avail, and had resigned myself to thinking I was a sucker for not just sticking with wired monitors.
Today, I finally tried toggling Headphone Accommodations on and back off and it fixed the issue entirely! The tuning sounds much more reasonable, and sounds great with Headphone Accommodations on or off.
My theory is that either the APM’s DSP profile was bad or my phones internal audio configuration was corrupted carrying it over from my AirPods Pros, and toggling things caused it to reset.
Searching online, I’ve seen some conflicting reviews where it seems like others may have had a similar problem with the low end- if this is you, give it a shot! Now, I just wish Apple would give us a proper EQ instead of burying things in Accessibility settings…