From simulation to a build

What the model is#

• Boxes are lumped. The driver, the air in each chamber and the air in each port are treated as single masses, springs and losses. That holds while the box and port are small next to the wavelength, which is 3.4 m at 100 Hz and shrinks as frequency rises.
• Horns are paths. Sound travels along the path as a plane wave, segment by segment, so the model follows the path’s length and area. It does not see its bends and folds.
• It is linear. Output scales with power and the shape never changes. Nothing compresses, except the voice coil temperature you can set for the Max SPL tile.
• The driver is its T/S parameters: datasheet values, as the library holds them. Real samples differ from the datasheet and from each other.

Enter the box you will build#

Volume in the enclosure panel is the net internal volume: the air the driver works against, “excluding ports, bracing, and driver displacement”. Enter the driver and the bracing under Box volume adjustments (Driver displacement and Bracing / other) and the panel’s Results show the Gross volume: the space to build inside the walls, port included.

For the vented example, 55 L net with one 100 mm port 35.6 cm long, the port itself takes 2.8 L, so the gross volume is at least 57.8 L before you add the driver’s own displacement from its datasheet.

Port model under the same Advanced is Lumped by default. Distributed treats the port as a duct, which matters when its pipe resonance comes near the band you use. Ports and end correction goes further.

The top of the response#

Above the bass, a real driver’s response is set by its cone and voice coil, which a lumped model describes only roughly. Settings › Simulation… › Non-horn upper response chooses how box designs handle it:

• Estimated · BITS frequency limit, the default, assumes a flat driver with a 24 dB/octave roll-off at the driver’s published upper frequency limit, when the library has one. The box’s own response and your EQ still apply. Impedance, excursion and phase use the physical model.
• Physical model uses the driver’s T/S parameters, including its voice coil inductance, all the way up.
• Horns always use the physical model.

Upper frequency under Settings › Display… sets how far up the solver runs. Auto is 400 Hz, or 2 kHz when the workspace has a horn.

What it leaves out#

• The room. Its modes and reflections add peaks and dips, often larger than the differences between designs. Radiation space uses idealised boundary conditions: a level offset for boxes, and a change in mouth loading for horns. It does not model a room.
• The cabinet itself: panel resonances and standing waves inside a box. A lumped box has the same pressure everywhere inside it.
• Where the sound goes. The model gives one level at the listening distance, not how the sound spreads with angle.
• Behaviour at the limits: a softening suspension and motor near Xmax, a port that compresses and chuffs, a coil that heats up. Limits: travel, heat and air shows where each one starts.
• Your driver. Measured T/S parameters of your own sample beat the datasheet; enter them with Edit params on the T/S Parameters tile.

The full list, with how the solver is checked against other tools, is in Model and limits and on the validation page.

Measure the build and compare#

1. 1

   Measure

   Measure the finished box with a measurement microphone and a tool such as REW. An impedance sweep is worth taking too: it shows the real tuning without any room in it. Note the distance and where the box stood.
2. 2

   Import

   Drop a REW export, an .frd or a .zma file on a graph, or paste a table. Or open Measured traces, below the enclosure panel on the left, and choose Add measured trace.
3. 3

   Link it

   In the trace’s details set Linked to to the enclosure it measures, then fill in Distance and Space. A linked trace takes a shade of the enclosure’s colour and hides with it.
4. 4

   Line up the level

   Align… matches the trace’s average level to the design over a band you choose. Only the offset changes, and Residual after aligning says how far the shapes still differ.
5. 5

   Read the difference

   Compare the impedance first: on a vented box the dip between its two peaks is the real tuning, and it tells you whether the port and volume came out as modelled. Then compare the SPL shape, remembering the room.

Measured traces and notes covers the import formats, smoothing and display options.

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