Horns · Guide

Damp a horn with stuffing

The figure fills 50 % of H1 in the tapped horn example, from the closed end, at 10,000 Pa·s/m². Inside the working band, 25–120 Hz, the response changes by at most 1.0 dB. Above 200 Hz the fill does more: the highest peak moves from 119 dB at 243 Hz to 116 dB at 301 Hz. That is the usual reason to stuff a horn: to calm the path’s resonances above the band while keeping the band itself.

Set it

In the Horn Editor

• Hover a span and click its stuffing toggle to fill the whole span. Click the lit toggle again to empty it.
• Drag a flag on the bottom edge to resize the fill. Drag it past a station to carry the fill into the next span.
• Drag the stipple to slide the fill along the path.
• Click the resistivity chip to type a value, or drag it up or down. Denser dots mean a higher resistivity.
• Hover the fill for its extent, its resistivity and the band the material model fits.

In the horn card

Each span has a Stuffing choice: None or Fibrous fill. Fibrous fill adds Resistivity · Pa·s/m², Start · % and End · %. A new fill starts at 10,000 Pa·s/m² across the whole span.

Airflow resistivity

100 to 100,000 Pa·s/m². Use the value measured for your material, or the supplier’s figure.

Start and End

Percentages of the span, measured from where it starts. The fill occupies the whole cross-section between them.

Which spans

Every path: main, rear, stub and the Paraflex auxiliary path and adapter.

Mode spacing

Becomes Unfilled mode spacing once a path has fill. Filled air is dispersive, so read its resonances from the response instead.

What the model assumes

Fill uses the equivalent-fluid model from Yasushi Miki’s 1990 paper, Acoustical properties of porous materials: modifications of Delany-Bazley models. Its absorption depends on frequency and on the material’s airflow resistivity.

• The material fills the whole cross-section over its length. A lining on the walls is a different thing and is not modelled.
• Compression of the fill and turbulent flow are not modelled.
• Density is not a substitute for airflow resistivity, and there are no material presets. Measure it, or ask the supplier.
• The model fits from 1/100 of the resistivity to the resistivity itself, in hertz: 10,000 Pa·s/m² fits from 100 to 10,000 Hz. Results outside that band are extrapolated.
• Start and End follow the span, so resizing a span changes the physical length of its fill.

Check what it did

Compare SPL, impedance and the horn diagnostics before and after. Pressure and particle velocity along the path show where the fill is working. Reading the horn diagnostics.

Stuffing and folding

The Fold tile cannot carry stuffing onto the folded passage yet. A stuffed horn gets no folded line on the graphs, and its fold cannot be written back into the horn. Folding.

Stuffing and Hornresp

The Hornresp export writes the fill’s resistivity and occupied length to Hornresp’s own fields, with a warning: Hornresp uses a different material model, so its response can differ. It refuses stuffing on a Paraflex auxiliary path and on a multiple-entry horn. The regression tests track stuffed cases against Hornresp without claiming agreement. Exporting to Hornresp.