Practical tools for measured work
Speaker Driver Displacement Calculator
Estimate the internal enclosure volume displaced by a driver's basket and motor assembly.
Rear-of-baffle basket envelope diameter, not the outer mounting flange.
Envelope diameter where the basket meets the motor.
From the rear face of the baffle to the motor assembly.
Editable estimate of how much of the tapered basket envelope is solid material.
Subtract total displacement from gross internal enclosure volume before port tuning. Prefer a manufacturer's published displacement or a measured volume when available.
How it works
Direct answer. Measure the part of each loudspeaker driver that sits behind the baffle. This tool estimates how much internal box volume the basket material and motor assembly occupy, then totals identical drivers for the enclosure-volume workflow.
Method. The basket envelope is a circular frustum, V = pi h (R^2 + Rr + r^2) / 3. Because a ventilated basket is not a solid frustum, only the entered solid fraction is counted. The motor is approximated as a cylinder, V = pi r^2 h. These two estimates are added per driver and multiplied by driver count.
Worked example. A 260-to-150 mm basket envelope 100 mm deep, estimated 15% solid, plus a 150 x 50 mm motor gives about 1.39 L per driver. Two identical drivers would displace about 2.78 L.
Using the result. Feed the total displacement into the speaker-box calculator along with bracing and port displacement. Use the resulting net volume, not the gross shell volume, for port tuning.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Measurement units
- Millimetres
- Identical driver count
- 1
- Basket front diameter
- 260 mm or in
- Basket rear diameter
- 150 mm or in
- Basket depth
- 100 mm or in
- Estimated basket solid fraction
- 15 %
- Motor / magnet diameter
- 150 mm or in
- Motor / magnet depth
- 50 mm or in
Primary result: Total displacement: 1.39 L.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
This is a measurement-based geometric approximation, not manufacturer data. It excludes irregular frame ribs not represented by the solid fraction, terminal blocks, wires, cooling fins, rear covers, gaskets behind the baffle, attached hardware and any geometry overlap between the simplified solids. Basket fill percentage is an explicit user estimate, not a universal property. Prefer the driver maker's published displacement or a safe physical displacement measurement when accuracy matters.
Frequently asked questions
Why not count the whole basket envelope?
Most baskets are open frames. Air between the spokes remains part of the enclosure, so treating the full tapered envelope as solid would greatly overstate displacement.
Does this include the cone and air behind it?
No. The model estimates solid structure protruding behind the baffle. The moving cone and internal air paths are not represented as a simple solid volume.
What should I do with a published driver displacement?
Use the manufacturer's value instead of this estimate when it clearly applies to your exact driver and mounting arrangement.
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