Replacing IEC 60268-5: what comes next and why

Geoff Hill — chair of the AES SC-04-03 working group on loudspeaker modelling, member of IEC TC 100/TA 20/PT 60268-22, CTO of Hill Acoustics — on why the standard behind every T/S datasheet in this wiki was withdrawn, and what replaced it. Published in audioXpress; T1, because it rests on the author’s own committee work and on the standards’ contents rather than on reporting about them.

This is the spoke’s first T1 source and the first that describes the measurement regime rather than a measurement.

The standard the datasheets came from

IEC 60268-5, first issued 1972, treated a loudspeaker as “entirely passive.” By its 2003 form it specified the Thiele/Small parameters, compliance, the anechoic-chamber and IEC-baffle setups, test boxes, harmonic distortion and noise signals — four stimulus types (sine, broadband noise, narrowband noise, impulsive) across free-field and diffuse-field conditions.

That is the document thiele-small-parameters and every datasheet this wiki reads implicitly stand on.

Why it was retired

Hill’s summary is that “loudspeaker theory and practice in 2021 is much more advanced compared to the 2000 — let alone the 1980s.” The specific failures:

• It assumes a passive device. Active and digital loudspeakers — amplifier, DSP and driver sold as one unit — cannot be characterised by a standard written for a passive element. That is precisely the device camilladsp and the DSP-correction thread describe.
• The measurement techniques are dated. No chirp or multi-tone stimuli, no 3D sound-field assessment, no defect detection.
• Manufacturing QC and R&D used incompatible procedures, so a production line and a design lab could not compare numbers.

What replaced it

Three standards, not one:

• IEC 60268-21:2018 — output-based acoustical measurements.
• IEC 60268-22 — electrical and mechanical measurements on transducers (the part Hill sits on).
• IEC 63034 — micro-speakers.

The new set adds chirp and multi-tone stimuli, 3D sound-field assessment, and a Rub & Buzz test for detecting mechanical defects — a class of fault the old standard had no way to name.

What this changes here

The spoke has treated T/S parameters as the design language and asked how they are measured (ts-parameters-wikipedia answered that with the impedance-sweep method). This source adds the layer above: the measurement method belongs to a standard, that standard was written for a passive device in 1972, and it no longer exists. Two consequences worth carrying:

• A datasheet’s provenance now has a date attached. Numbers produced under 60268-5 and numbers produced under 60268-21/-22 are not guaranteed comparable, and nothing in this corpus says how a builder tells which they are holding.
• The active/DSP loudspeaker, which this spoke reached from the hobbyist side, is the same device the standards body reorganised itself around. The DSP bridge is not a niche — it is why the standard broke.

Related

thiele-small-parameters · loudspeaker-driver · ts-parameters-wikipedia · camilladsp · geoff-hill · audio-engineering-society · iec · synthesis