I measure some bad nulls in the 125hz-200hz range. My DIY 2" thick OC703 panels have a 1/8" thick wood backing on them mounted with a 2" gap from the wall. Does this wood backing need to be removed in order to help absorb frequencies in this range, or does this low of a frequency range penetrate right through the 1/8" wood backing? I'm hoping the latter so that I don't have to deal with using up freetime having to redo these panels, I have six of them I haven't mounted yet.
Thank you so much for the advice you guys give on not only this forum, but the many others.
Well, yes and no. Pretty much any material is going to absorb, pass through and reflect some but not other frequencies and differing amounts thereof. I'm going to say that your real problem is that your panels are just 2" thick! You can go up to 8" with rigid - or so the common wisdom goes - and, really, 2" is the bare minimum and not all that much when it comes to that range and below.
As far as free time goes, I spent at least three whole months dialing in my current room. Part of me regrets it but, on the upside, I'm way more confident in my small room treating abilities. That's not including all the weeks I spent in years prior researching, building and upgrading treatment.