Frequency Response
Definition
Frequency Response
Frequency response describes how an audio system amplifies or attenuates signals at each frequency across the audible spectrum, typically displayed as magnitude in decibels versus frequency in hertz on a logarithmic scale. A flat frequency response (within ±3 dB) indicates accurate signal reproduction. SonaVyx measures frequency response using both single-channel RTA and dual-channel transfer function analysis.
|H(f)| dB = 20 × log₁₀(output amplitude / input amplitude) at each frequency f
How Frequency Response Is Measured
Frequency response can be measured via single-channel RTA (playing pink noise and analyzing the microphone spectrum) or dual-channel transfer function (comparing microphone input to electrical reference). Transfer function provides more accurate results by removing the stimulus spectrum from the measurement. SonaVyx supports both methods, with transfer function preferred for diagnostic accuracy and RTA preferred for quick visual monitoring.
Practical Example
A PA speaker measures flat ±2 dB from 80 Hz to 16 kHz in an anechoic environment. When installed in a venue, SonaVyx reveals a +8 dB room mode at 125 Hz and a -6 dB dip at 2 kHz from ceiling reflection comb filtering. The engineer applies a -8 dB parametric cut at 125 Hz (Q=2) and notes the 2 kHz dip has low coherence, indicating it cannot be corrected with EQ.
Interpreting Frequency Response
A flat frequency response means every frequency is reproduced at the same level — the system adds no coloration. In practice, perfectly flat response is neither achievable nor always desirable. Studio monitors target ±1.5 dB flatness. PA systems in rooms typically achieve ±3 to ±6 dB after EQ. House curves for live sound intentionally roll off high frequencies by 3 to 6 dB above 4 kHz for listener comfort at sustained high SPL.
Smoothing
Raw FFT frequency response data shows every fine detail including comb filter nulls and room modes. Octave smoothing averages adjacent frequency data to reveal broader trends. 1/3 octave smoothing approximates human frequency discrimination and is used for system tuning. 1/6 octave reveals more detail for diagnostic purposes. SonaVyx supports smoothing from 1/1 to 1/24 octave, letting users choose the level of detail appropriate for their task.
On-Axis vs Off-Axis
Speaker frequency response varies with measurement angle. On-axis response (directly in front) typically shows the flattest and widest bandwidth. Off-axis response rolls off at high frequencies where the speaker becomes increasingly directional. The coverage angle — the angle at which response drops 6 dB — narrows with increasing frequency. Measuring frequency response at multiple angles characterizes the speaker's directivity pattern.
Speaker Specifications
Manufacturers specify frequency response as a range (e.g., 55 Hz to 20 kHz ±3 dB). The tolerance window (±3 dB) significantly affects the claimed range — the same speaker might specify 55 Hz to 20 kHz at ±3 dB but only 80 Hz to 18 kHz at ±1.5 dB. SonaVyx helps verify manufacturer claims by measuring the actual installed response in the deployment environment.
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