Each method below states the standard, the specimen we need, what the report contains and the current lead time. The specimen requirement is the part worth reading twice — it is what delays most programmes.
The specimen is laid out in the reverberation room and the decay rate of the room is measured with and without it. The difference gives the equivalent absorption area, from which the absorption coefficient αs follows per third-octave band. Single-number ratings αw, NRC and SAA are derived under ISO 11654 and ASTM C423.
Third-octave αs from 100 Hz to 5 kHz, the practical coefficient αp, the single-number rating with shape indicators (L, M, H), room conditions, and the measurement uncertainty. Lead time two weeks from specimen arrival.
The specimen is built into the aperture between the two coupled reverberation rooms. Sound is generated in one room and the level difference measured, corrected for the receiving room's absorption, giving the sound reduction index R per third octave and the weighted single number Rw with spectrum adaptation terms C and Ctr.
The single most common surprise: a partition that performs to specification in the laboratory can lose 8–10 dB on site through flanking transmission around it. A laboratory Rw describes the element, not the building.
Lead time three weeks, including build.
A standard tapping machine runs on the test floor and the level in the room below is measured. For floor coverings and underlays, the reported value is the improvement ΔLw relative to the bare reference floor.
Sound power is what a machine emits; sound pressure is what someone hears at a distance. Confusing the two is the most frequent error in tender documents we are sent. We measure power by the enveloping surface method in the semi-anechoic chamber (grade 2, ISO 3744) or, where the accuracy justifies it, in the anechoic configuration (grade 1, ISO 3745).
Lead time ten working days.
Turning measured values into the declared emission figures that go in the product manual and the technical file. The declaration is a two-part statement: the measured value and the uncertainty K. Declarations that quote a single number without K are incomplete, and are one of the things market surveillance authorities look for.
Comparative work during design: three prototypes ranked against each other, a panel measured in four mounting conditions, a machine measured before and after a modification. Same chambers, same instruments, faster and cheaper because we are not producing an accredited report.
These results are clearly marked as non-accredited and must not be used in a CE file. Nearly every accredited test we run began as a development test six months earlier.
| Stage | Who | Typical time |
|---|---|---|
| Enquiry and method confirmation | You and our engineer | 2–3 days |
| Quotation and chamber slot booked | Us | 1 day |
| Specimen delivered | You | — |
| Build and measurement | Us | 1–3 days |
| Report drafted, checked, signed | Two engineers | 5 working days |
Reports are checked and signed by a second engineer who did not run the measurement. That is an accreditation requirement and it is also why we will not issue a report the same afternoon, however urgent the deadline.