4. Technical Resources for Improving Room Acoustics 01: Absorption and Diffusion

Now that you have hopefully been able to gain some insight into which factors may negatively affect your room acoustics, I want to introduce some technical resources to you which may will help you overcome the problems decribed above. There are two fundamental ways of keeping interfering reflections in check: Absorption and Diffusion.

Absorption

Absorption means depriving a sound wave of some or all of its energy when it hits a reflecting surface. The reflection is thus attenuated and has less capacity to interfere.

Reflection from absorbing wall
Time-level chart
Absorption is suitable for
  • diminishing comb filter effects
  • minimising flutter echoes
  • reducing room resonance
  • optimising decay times which are imbalanced or too long.
Diffusion

Diffusion, in contrast, reflects the sound wave not just in one direction, as a hard, smooth wall would do, but disperses the sound wave in many different directions. This, too, reduces the interfering effect of a single mirror reflection, since its direction is not focussed in one way but rather dispersed throughout the space. The overall sound energy remains unchanged, however. Diffusion thus makes sense if your decay time is already quite short and you do not want to shorten it further. This is often the case in higher frequency ranges.
Reflection dispersed by diffuser
Comb filter effect hardly noticeable
Time-level chart

Diffusion is furthermore suitable for

  • diminishing comb filter effects
  • elminiating flutter echoes
  • increasing diffusivity in the room, making it seem larger acoustically.

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