Normal-incidence transmission loss simulation

What is simulated

In the ASTM E2611 configuration, the sample sits between an upstream and a downstream tube section, with two microphone positions on each side. From the sound field on both sides, the sample's 2×2 transfer matrix is obtained, and from it the transmission coefficient τ. Transmission loss is then

As with absorption, the result is for plane waves at normal incidence, within the same tube-diameter frequency limits.

Deliverables

• Normal-incidence transmission loss TL(f) in dB.
• Absorption α(f) and reflection R(f) for the same sample.
• CSV data, plots and a short report.

Typical uses

• Comparing panel, lattice or metamaterial designs that must block sound as well as absorb it.
• Checking how transmission loss changes with thickness, perforation or cell geometry before building prototypes.

Pricing

Transmission loss is an add-on of +$90 per design on top of the design price ($190 per design, or $158 and $139 each in 5- and 10-design packs). Select "Absorption + transmission loss" on the quote form.

Accepted files and required inputs

• Geometry: STL, STEP, IGES, 3MF, OBJ, or a ZIP of these. Up to 95 MB per file and 10 files per request.
• Either the full sample as it would sit in the tube, or one periodic unit cell plus the sample thickness and diameter.
• Units of the CAD file (for example millimetres), so the geometry is scaled correctly.
• Backing condition: rigid backing, or the depth of any air gap behind the sample.
• Tube diameter and frequency range: Ø29 mm (about 500–6300 Hz), Ø100 mm (about 50–1600 Hz), or both stitched into one curve.
• Whether you also need transmission loss.

What normal-incidence TL is not

Normal-incidence transmission loss from a tube is not the same quantity as sound reduction measured between reverberant rooms for building elements, and it should not be quoted as a building-acoustics rating.