Eased (edge) - An acoustical panel edge detail also known as a quarter-inch (¼") bevel.

Early reflection - Reflected energy that occurs in close proximity to the source but is slightly out of synchronization (time / phase) with the source information.

E400 Test - See Mounting.

Drywall - A dense architectural wall construction material applied to wood or metal studs, A/K/A Sheet Rock or Gypsum Wall Board (GWB), useful primarily as a sound barrier but is low frequency absorber in some applications.

Doppler effect - The apparent shift in frequency when the sound source, or the observer, is in motion.

Diffusor - See Diffuser.

Direct sound
- Sound Wavesarriving at the listening location directly from the source. Differing from reflected sound, which arrives at the listening location after bouncing off the surrounding surfaces.

Diffusion - The scattering or random distribution of a sound wave after striking a surface.

Diffuser

Diffuse sound - Sound that is completely random in phase. Sound which appears to have no single source/