Q Factor

Q factor appears throughout audio and acoustics with consistent meaning: it quantifies the sharpness or selectivity of a resonant or filtering process. In parametric equalization, Q is the primary control for filter width. A Q of 1 at 1000 Hz means the filter affects frequencies from 500 Hz to 1500 Hz (bandwidth of 1000 Hz). A Q of 10 at 1000 Hz means the filter affects only 900 Hz to 1100 Hz (bandwidth of 100 Hz). The relationship between Q and bandwidth in octaves is: BW(octaves) = 2 × asinh(1/(2Q)) / ln(2). For quick reference, Q=0.7 is approximately 2 octaves wide. Q=1.4 is about 1 octave. Q=4.3 is about 1/3 octave. Q=10 is about 1/7 octave. In room acoustics, room modes have characteristic Q values that determine how audible and problematic they are. A room mode with high Q (narrow bandwidth, long decay) creates a prominent ringing at a single frequency. Low-Q modes are broader and less noticeable. The Q of a room mode is inversely related to the absorption at that frequency: more absorption means lower Q and faster decay. For feedback detection, SonaVyx's problem detector identifies feedback-prone frequencies by their high Q values. A sustained feedback tone appears as a very narrow spectral peak with Q greater than 10, distinguishing it from broader room-related response anomalies. In speaker design, a driver's resonant frequency (Fs) has an associated Q value (Qts) that determines the optimal enclosure alignment. Qts below 0.4 suits sealed boxes; Qts between 0.3 and 0.5 suits vented designs.