Sources and devices

In this topic

• Sound power and intensity7 pages
• Electroacoustics7 pages
• Noise control5 pages
• API reference25 pages

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 sound power and intensity pages determine the central emission quantity, the sound power level: the figure that goes on a datasheet, feeds a room or outdoor prediction and is checked against noise-emission limits — including the route that reads it off the casing’s own vibration when no microphone can be placed. The electroacoustics pages turn to devices that are supposed to make sound (amplifiers, loudspeakers and microphones) and to the broadcast programme they carry, and the noise control pages hold the path measures that quiet a machine once its emission is known.

If you are here to measure a machine, start with Sound Power and let its decision guidance pick the route, which may end on an intensity probe or, when only vibration can be measured, on the radiating surface itself; 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.

Sound power and intensity

The total acoustic emission of a source, and the power flux it is built on.

• Sound Intensity (p-p): two-microphone sound intensity per IEC 61043 with the ISO 9614-1 field indicators.
• Sound Power: choosing the determination method and declaring the noise emission per ISO 4871.
• Sound Power by Pressure Methods: the enveloping surface of ISO 3744/3746 and the precision anechoic grade of ISO 3745.
• Sound Power in the Reverberation Room: the direct and comparison methods of ISO 3741.
• Sound Power by Intensity Scanning: the on-site scanning of ISO 9614-2 and the ISO 9614-3 precision grade.
• Sound power from surface vibration (ISO/TS 7849): the radiated power from the surface-averaged velocity level and the radiation factor, for the case where the machine cannot be moved, the room is not qualified and only an accelerometer is available: the Part 1 upper limit and the Part 2 engineering value.

Electroacoustics

Amplifiers, loudspeakers and microphones on the bench, and the programme signal they carry.

• Electroacoustics: distortion and frequency response: the IEC 60268-3 distortion metrics and frequency-response estimation with coherence.
• Loudspeaker Characterisation (IEC 60268-5): the sensitivity conventions, the radiating piston and the IEC 60268-5 characteristics fiche.
• Microphone Characterisation (IEC 60268-4): the sensitivity references, directional patterns and inherent noise of the IEC 60268-4 fiche.
• 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.
• Broadcast: the loudness problem solved with a measurement rather than a compressor, one gated number per programme and the range that says how much it moves.
• 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.

Noise control

Industrial noise control on the path, between the machine and whoever hears it.

• Silencers: reactive silencers by the four-pole method and the reactive-versus-dissipative choice.
• Duct-Borne Noise: Fan to Room: the end-to-end fan-to-room calculation against a room criterion, and the higher-order-mode cut-on that limits every plane-wave method.
• Room to Room: Partition, Receiving Room, Criterion: the composed source-room to receiving-room chain and the transmission loss a partition or an enclosure needs to meet a noise criterion.
• Industrial Noise Control: HVAC and Enclosures: duct attenuation, flow noise and machine-enclosure insertion loss.

What this section does not cover

• No facility is qualified here. ISO 3745’s free-field qualification of an anechoic room, ISO 3741’s reverberation-room qualification and IEC 61043’s residual-intensity test of a probe are all assumed to have been done: the library warns on the coarse advisory criteria a standard states explicitly and grades a residual index you supply, but it does not certify a room or an instrument. The same boundary runs through the electroacoustics pages, which reduce and report curves the laboratory supplies rather than telling you how to acquire them, and through ISO/TS 7849, whose clauses 5 to 7 on instrumentation, installation and measurement positions are laboratory practice this library assumes.

• Three specific absences are worth knowing before you plan a job. ISO 9614-1’s discrete fixed-point power summation is not implemented at all — only its field indicators are, reused by the scanning routes. Dissipative duct-lining silencers are not modelled from liner properties anywhere: the reactive elements are computed exactly within the no-flow plane-wave model, and the lined-elbow figure is a table lookup (Bies Table 8.11) and the plenum attenuation Wells’ closed form driven by a declared mean absorption — neither is a liner model. And no page here predicts a panel’s transmission loss: enclosure_insertion_loss combines a value you supply with the interior correction, and the prediction itself is Insulation design.

• Editions are pinned rather than current in two places: the distortion metrics follow AES17-2015 and not the 2020 revision, and the microphone rated-characteristics report follows IEC 60268-4:2014 and not the 2018 one. Object-based audio (BS.1770-5 Annex 4) is out of scope, and the library implements no spatial renderer, so an object-based programme has to be rendered to a loudspeaker layout before it can be measured.

Before and after these pages

Every emission quantity here is computed from band levels or from an intensity pair, so the calibration, weighting and filtering behind them are in Signal analysis, and Build a sound level meter runs that chain end to end on one runnable page. The derivations are split by physics rather than by topic: sound power determination is under Environment and transport, and sound intensity under Signal analysis. The electroacoustics and noise-control pages carry their derivations inline.

If you arrived here from a search and want the shape of the whole library, What do you need to measure? indexes it by the job and All guides lists every page with a line on each.