bass traps for home acoustic treatment

so here's my situation the acoustics in my apartment are poor and bothering my neighbor in the adjacent apartment. i've taken some sound level measurements and i have problem area's such as the corner of the wall between the apartments. i'm looking for tried-and-true methods for creating a bass trap. I've measured at least a 6db gain in the corner. so who has built them and has advice?

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Prove your connections, use a meter!
I promise, I'll behave!

Any foam supply shop will have what your looking for. it's foam sheets that have an egg carton look. it will deaden the sound in prblem areas. I used it in my basement across the celing and it made a huge difference.