Acoustic Glossary
Essential acoustic terminology for audio professionals, studio designers, and DIY enthusiasts. From RT60 to QRD diffusers, understand the language of sound treatment.
- RT60
- The time it takes for sound to decay by 60 decibels after the source stops.
- Room Modes
- Resonant frequencies where sound waves fit perfectly between room boundaries, creating standing waves.
- Schroeder Frequency
- The frequency above which room modes overlap sufficiently for statistical acoustic analysis to apply.
- Axial Mode
- A room mode that occurs between two parallel surfaces, representing the strongest type of standing wave.
- Standing Wave
- A wave pattern that appears stationary, created when waves reflect and interfere with themselves.
- Flutter Echo
- A rapid series of echoes caused by sound bouncing between parallel reflective surfaces.
- QRD Diffuser
- An acoustic diffuser using wells of mathematically calculated depths based on the quadratic residue sequence.
- PRD Diffuser
- A diffuser using primitive root sequences, offering asymmetric scattering and wider bandwidth than QRD designs.
- MLS Diffuser
- A binary amplitude diffuser using pseudorandom sequences with only two well depths.
- Diffusion
- The scattering of reflected sound in multiple directions, creating a more uniform acoustic field.
- Scattering Coefficient
- A measure (0-1) of how much reflected sound energy is scattered versus specularly reflected.
- Absorption Coefficient
- A measure (0-1) of how much sound energy a material absorbs versus reflects.
- NRC
- A single-number rating (0-1) averaging a material's absorption at 250, 500, 1000, and 2000 Hz.
- Bass Trap
- An acoustic absorber specifically designed to control low frequencies, typically placed in room corners.
- First Reflection
- The initial sound reflections from nearby surfaces that arrive within 10-30ms of the direct sound.
- Sabine Equation
- The fundamental equation relating reverberation time to room volume and total absorption.
- Wavelength
- The physical length of one complete sound wave cycle, inversely proportional to frequency.
- SPL
- A logarithmic measure of sound pressure relative to the threshold of human hearing, expressed in decibels.
- Frequency Response
- A measurement of how a system or room responds across the audible frequency spectrum.
- Impulse Response
- A recording that captures how a space or system responds to an instantaneous burst of sound.
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