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You'd be better off separating them and using them to treat different corners of your recording space.
To answer your question as you asked it, the bass trap will be unaffected in its performance. If you build your bass trap properly, the insulation sits on top of the frame, not inside it. The dimensions of your frame are the same size as your insulation sheets.
I disagree regarding the trap construction (but not in putting them together) - mine (and most traps I've seen) have an outside frame - usually 1" x X" wood (where X = nominal insulation thickness). But I'm not sure why someone would build 12" wide traps, as the insulation all comes in 24" (or 23" sometimes) widths.
That's fair enough, I got my construction from a PDF I found on the net. The explanation for it not sitting within a frame was in order that the sound waves could enter the rockwool slab via its sides along the leaves of fibre, as well as through the faces. It seemed reasonable, so that's how I've done mine.![]()
This is one method of building them. But the effect the exposed sides actually have little effect. We actually tested this exact thing - some absorption with and without a wood border in the corners of the room to see how much this actually affects bass trapping. Our tests suggests this effect is negligible, especially for bass frequencies: DIY Acoustic Panel and Bass Trap Frames -