IEC 60268-5 compliant loudspeaker measurement. Frequency response, directivity pattern, and total harmonic distortion analysis powered by Rust WASM DSP engine.
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Place the microphone on-axis at 1 meter from the speaker.
Use an omnidirectional measurement mic for best accuracy.
Disable any EQ or DSP processing on the signal path.
Overlay up to 8 traces for A/B comparison.
Loudspeaker measurement is a critical discipline in audio engineering, governing everything from driver selection and crossover design to system commissioning and quality control. The international standard IEC 60268-5 (Sound system equipment - Part 5: Loudspeakers) defines the procedures for characterizing loudspeaker performance, including frequency response, sensitivity, directivity, impedance, and harmonic distortion. SonaVyx brings these professional measurements to the browser using WebAudio API signal generation, microphone capture, and a high-performance Rust WASM DSP engine for real-time spectral analysis.
The frequency response of a loudspeaker describes its sound pressure level (SPL) as a function of frequency under defined conditions. IEC 60268-5 specifies measurement on the reference axis (typically the geometric center of the radiating surface) at a distance of 1 meter in an anechoic or semi-anechoic environment. The measurement signal is typically a logarithmic sine sweep from 20 Hz to 20 kHz, chosen for its excellent signal-to-noise ratio and ability to separate linear and nonlinear components of the response. The resulting magnitude-frequency curve reveals the usable bandwidth, passband flatness, resonances, and roll-off characteristics of the loudspeaker.
Loudspeaker sensitivity is defined as the sound pressure level produced at 1 meter on-axis when driven with 1 watt of electrical power (or equivalently, 2.83 volts into an 8-ohm nominal load). This single-number rating, typically expressed in dB SPL (1W/1m), allows direct comparison between loudspeakers. Higher sensitivity means more acoustic output for a given amplifier power, which is particularly important in professional sound reinforcement where high SPL levels are required. Typical sensitivity values range from 82-86 dB for home hi-fi woofers to 95-110 dB for professional compression drivers and horn-loaded systems.
Directivity describes how a loudspeaker distributes sound energy in space as a function of angle and frequency. At low frequencies, most loudspeakers radiate omnidirectionally because the wavelength is much larger than the radiating surface. As frequency increases, the radiation pattern narrows progressively, a phenomenon called beaming. The coverage angle (or dispersion angle) is defined as the included angle where the SPL drops by 6 dB relative to the on-axis level. For constant-directivity horns used in professional audio, the coverage angle is specified as a nominal value (e.g., 90 x 60 degrees) that remains relatively constant over the designed frequency range. The directivity index (DI) quantifies the ratio of on-axis intensity to the average intensity over all directions, expressed in decibels.
THD measures the nonlinear distortion produced by a loudspeaker when reproducing a pure sine wave. The output contains not only the fundamental frequency but also integer multiples (harmonics) generated by mechanical and magnetic nonlinearities in the driver. The second harmonic (H2) is typically dominant in loudspeakers with asymmetric nonlinearities (such as non-centered voice coils), while odd-order harmonics (H3, H5) arise from symmetric nonlinearities like progressive spider stiffness. IEC 60268-5 requires THD measurement at the rated power across the specified frequency range. Professional loudspeakers typically achieve less than 1% THD in their passband at rated power, with distortion rising significantly near the low-frequency excursion limit and at very high SPL levels.
SonaVyx implements loudspeaker measurement entirely in the browser using the WebAudio API for signal generation and microphone capture, combined with a Rust-compiled WebAssembly DSP engine for spectral analysis. The log sine sweep excitation provides excellent noise immunity, and the multi-trace overlay capability (up to 8 simultaneous traces) enables direct A/B comparison of different loudspeakers, crossover settings, or measurement positions. Octave smoothing options from raw to 1/1 octave help identify trends versus fine detail, while tolerance band overlays provide instant pass/fail assessment against target specifications.
An omnidirectional measurement microphone with a flat frequency response is essential for accurate loudspeaker measurement. Popular options include the miniDSP UMIK-1 (USB, includes calibration file), Behringer ECM 8000, Dayton Audio EMM-6, and professional options like the Earthworks M30. The microphone calibration file should be loaded to compensate for any deviation from flat response. Built-in laptop microphones are unsuitable due to their non-flat response and directional characteristics.
True anechoic chambers are expensive and impractical for most users. Instead, use a ground-plane (half-space) measurement outdoors or in a large room. Place the speaker and microphone on the ground or a hard floor, with the microphone at 1 meter on-axis. The ground reflection arrives simultaneously with the direct sound, effectively doubling the measurement distance. Apply a +6 dB correction to convert to full-space. Alternatively, use windowed (quasi-anechoic) measurements with a time gate to reject room reflections.
Smoothing averages the frequency response over a bandwidth centered on each frequency point. 1/3 octave smoothing is similar to how the ear perceives frequency response and is useful for overall tonal balance assessment. 1/24 octave reveals more fine detail including narrow resonances and comb-filter effects. Raw (unsmoothed) data shows every detail but can be difficult to interpret. For loudspeaker development, start with raw or 1/24 octave to identify problems, then use 1/6 or 1/3 octave for specification and comparison.
Professional loudspeakers typically achieve less than 1% THD in their passband at rated power. Hi-fi loudspeakers may specify less than 0.5% at moderate levels. THD below 1% is generally considered inaudible for music reproduction. Distortion between 1-3% may be audible on sustained tones but is often masked by complex program material. Above 3% THD, distortion becomes clearly audible and indicates the driver is being pushed beyond its linear operating range. Low-frequency THD near the driver resonance is typically higher due to excursion limits.
Directivity index (DI) is the ratio of on-axis SPL to the spatial average SPL, expressed in decibels. A DI of 0 dB means omnidirectional radiation (equal energy in all directions). Typical values range from 3 dB (hemisphere) for a driver on an infinite baffle at low frequencies, to 15-20 dB for narrow-coverage horns at high frequencies. Smooth, gradually increasing DI with frequency indicates well-controlled directivity. Sharp peaks or dips in DI indicate diffraction effects, crossover problems, or horn mouth reflections.