TL;DR: The common acoustic specification mistakes are predictable: confusing soundproofing with treatment, ignoring bass, over-damping the room, forgetting the height axis, treating the two sides unequally, specifying treatment too deep for the space, and overlooking the fire rating of the finished surface. Avoiding them is mostly about matching the right tool to each problem.
1. Confusing soundproofing with treatment
Panels improve sound inside a room; they don't stop sound passing through walls. If the brief is "stop the neighbours hearing it," that's isolation, not treatment.
2. Ignoring bass
Most treatment targets mid/high frequencies and leaves room modes untouched, so the room still booms. Low frequencies need dedicated, corner-loaded resonance control.
3. Over-damping
Lining every surface with absorption makes a room sound dead and fatiguing. The target is the right reverberation time (see RT60), not the shortest.
4. Forgetting the height axis
Length and width get attention; the floor-to-ceiling axis is often neglected, leaving the room inconsistent. Acoustics should be balanced on all three axes.
5. Treating the sides unequally
Asymmetric treatment pulls the stereo image off-centre. The left and right of the room should mirror each other.
6. Specifying treatment too deep
Deep traps eat floor area — expensive in a prime room and often impossible in a retrofit. A slim system avoids it. (See the cost of lost space.)
7. Overlooking the finish's fire rating
If panels sit behind a fabric or feature wall, that finish has its own fire rating. Specify the whole build-up. (See fire ratings.)
Specify it properly
A measured design, the right tools for each of the three problems, and verification at the end. Start a project or read The System.
FAQ
What's the most common acoustic mistake?
Confusing soundproofing with treatment — buying panels expecting quiet neighbours, or building an isolated box expecting great sound. They're different disciplines.
Why does my treated room still boom?
Bass was ignored. Mid/high absorption doesn't fix low-frequency room modes; you need corner-loaded resonance control.
Can you have too much treatment?
Yes — over-damping leaves a room sounding dead. Aim for the correct, even reverberation time.