Absorption and Diffusion

Absorption removes reflected energy; diffusion scatters it. They solve different acoustic problems.

Related

AbsorptionDiffusionRoom TreatmentBass Trap

The problem

Foam everywhere makes a room dull while the bass stays uneven; a few diffusers elsewhere make it feel open. They solve different problems.

Physics or room

Absorption turns sound into heat; the coefficient runs from zero to one. Porous material works near a quarter wavelength, so thin foam absorbs mostly mids and highs. Bass needs depth, membrane traps or Helmholtz resonators. Diffusion spreads reflections without removing energy, softening comb filtering and flutter echo.

Practice and judgement

Treat reflection points and corners first: porous absorbers 5 to 10 cm at the former, bass traps at the latter. Add diffusion on the rear wall and ceiling, keeping reflection. Judge by clap, speech and bass, one change at a time.

What to listen for

Clap in the centre and listen for fast flutter. On cymbals, decide whether the tail decays naturally or is swallowed by high absorption. Play a solo voice and compare sibilance and tail.

Common misunderstandings

More foam is not better; it works above the bass. Diffusers cannot replace bass traps. Carpet and curtains change the top but barely touch 100 Hz. An over-dead room makes mixes fail.

Sources

• Everest, F. Alton，Master Handbook of Acoustics（McGraw-Hill）— 吸声与扩散章节核对，未引用
• Newell, Philip，Recording Studio Design（Focal Press）— 控制室处理章节核对，未引用

Used for fact-checking only; all prose is original.