Reducing one particular frequentie -Acoustics Forum-Acoustic Fields Forum

Hi Mr Foley,

I’ve experimented a lot in my attic to see where my nearfield monitor speakers are least clouded by the room modes.

I used an SPL meter and an RTA to check my sine wave generator at about 83 dB.

While the frequencies varied between ±6 and 8 dB in most places,
there was one particular frequency that was annoyingly consistent no matter where I positioned or placed the speakers “142.2 Hz ±19 dB”.
The softest tone I measured was 50 Hz and the loudest 142.2.

Got two panels of (cm) H180 W100 D9 full, I know you hate that stuff, Rockwool.
But the thing is, they helped me reduce the peak by 3dB.

It’s the best I can get with my limited knowledge, but I’ve also learned that when I’m recording vocals or guitars, especially acoustic guitars, they can sometimes benefit from a cut at 142.2 Hz.

Anyway, if I wanted to lower that specific frequency of 142.2 Hz in a concrete floor attic measuring (cm) D509 W544 H265, how would I do it?