Sources and devices

Every prediction elsewhere in this documentation starts from a source descriptor, and this section is where those descriptors are measured. Its common thread is emission: numbers that belong to the device rather than to the room or the distance it is heard at.

The central quantity is the sound power: the total acoustic energy per second a source radiates. Expressed in decibels as the sound power level, it is the figure that goes on a datasheet, feeds a room or outdoor prediction and is checked against noise-emission limits. Sound Power covers the five standardised routes to it, from the enveloping pressure surface of ISO 3744/3746 to the reverberation room of ISO 3741, the on-site intensity scanning of ISO 9614-2 and the precision grades of ISO 3745 and ISO 9614-3. Behind the intensity-based routes sits sound intensity itself: the signed power flux that can localise sources and separate them from background noise, measured with a two-microphone probe per IEC 61043 and qualified by the ISO 9614-1 field indicators, covered in Sound Intensity (p-p).

Electroacoustics turns to devices that are supposed to make sound: amplifiers, loudspeakers and microphones. It covers the IEC 60268-3 distortion set (THD, THD+N and SINAD, intermodulation and DIM), the H1/H2 frequency-response estimators with coherence, and the sensitivity conventions of IEC 60268-4/-5 where datasheet comparisons usually go wrong. Swept-sine distortion and phase utilities extends the bench with the one-sweep alternative: the Farina / Novak harmonic separation that turns a single exponential sweep into the full set of harmonic frequency responses and a THD measured as a function of the excitation frequency, plus the minimum-phase, group-delay and excess-phase utilities that dissect what the measured response’s phase is made of.

Programme loudness covers the signal the devices carry: the ITU-R BS.1770-5 loudness of a broadcast or streaming programme in LUFS, the EBU R 128 normalisation to -23 LUFS, the EBU Mode momentary/short-term/integrated meters, the loudness range and the oversampled true-peak level in dBTP.

If you are here to measure a machine, start with Sound Power and let its decision guidance pick the route; read Sound Intensity (p-p) when that route involves an intensity probe. If you are here to bench-test audio gear, go straight to Electroacoustics; if you are here to level a programme, go to Programme loudness.

Pages in this section

• Sound Intensity (p-p): two-microphone sound intensity per IEC 61043 with the ISO 9614-1 field indicators.
• Sound Power: the sound power level by enveloping surface, reverberation room, intensity scanning and the precision anechoic and intensity methods.
• Electroacoustics: distortion and frequency response: the IEC 60268-3 distortion metrics, frequency-response estimation with coherence, and microphone and loudspeaker sensitivity conventions.
• Swept-sine distortion and phase utilities: harmonic separation and THD(f) from one exponential sweep (Farina / Novak synchronized swept-sine), and minimum phase, group delay and excess phase from a measured response.
• Programme loudness and true peak: the ITU-R BS.1770-5 programme loudness and true-peak level with the EBU R 128 normalisation practice, EBU Mode metering and loudness range.