Frequency

Frequency is the number of complete vibration cycles per second, measured in hertz (Hz). In acoustics, frequency determines the pitch of sound: low frequencies (20–250 Hz) are perceived as bass, mid frequencies (250–2000 Hz) carry speech intelligibility, and high frequencies (2000–20000 Hz) provide clarity and sibilance. The human hearing range extends from approximately 20 Hz to 20 kHz. Room acoustic design must address the full frequency range because absorption materials, insulation systems, and room resonances are all frequency-dependent. Building regulations typically specify limits across six octave bands from 125 Hz to 4000 Hz. Low-frequency control is often the most challenging and costly aspect of acoustic treatment, requiring thicker absorbers or tuned resonant systems.