Impedance tube laboratory
Three tube sizes covering 50 Hz to 10 kHz between them. This is the fast, low-cost route for comparing materials during development — small discs, quick turnaround, and a clear ranking of which formulation is winning.
Why three tubes and not one
A tube only gives valid results between two limits set by its diameter. Below the lower limit the tube is too short relative to the wavelength for the standing wave to be resolved; above the upper limit, cross-modes appear across the tube and the plane-wave assumption the whole method rests on stops being true. Neither limit is a quality issue — it is geometry.
That is why a single tube cannot cover the audible range and why the specimen has to be cut to match the tube being used. If your interest is low-frequency absorption you need the large tube and a 100 mm disc; if it is high-frequency behaviour you need the small one. Tell us the frequency range that matters to your product and we will tell you which discs to cut.
This is not a substitute for the reverberation room
Tube results are normal-incidence absorption. Building specifications, product declarations and green building credits are written around diffuse-field absorption from a reverberation room. The two are different physical quantities and do not convert. Use the tube to decide what to test, then test it properly.
| Tube | Diameter | Frequency range | Sample |
|---|---|---|---|
| Large | 100 mm | 50–1,600 Hz | 100 mm disc |
| Medium | 30 mm | 800–6,300 Hz | 30 mm disc |
| Small | 16 mm | 2,500–10,000 Hz | 16 mm disc |