Speaker Box Calculator

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Sealed boxes are compact and tight. Ported boxes extend bass but require more volume and a tuned port.
The volume of air that has the same compliance as the driver's suspension. Found on the driver spec sheet.
litres
The driver's total quality factor combining electrical (Qes) and mechanical (Qms) losses. Typically 0.2-1.2.
The frequency at which the driver resonates in free air. Found on the driver spec sheet.
Hz
0.707 gives flat Butterworth response. Lower values (0.5-0.6) give tighter bass. Higher values (0.8-1.0) extend low end slightly but add a hump.
Box volume (Vb)Either type works
30.02

Required net internal air volume

Box volume (alternate unit)1.06
System frequency (Fc / Fb)49.5Hz
-3 dB cutoff (F3)49.5Hz
System Q (Qtc)0.707
Efficiency bandwidth product (EBP)70
70 EBP
Sealed preferred<50Either type works50-100Ported preferred100+

Sealed box needs 30.02 litres, with a -3 dB point at 49.5 Hz.

  • A Qtc near 0.707 gives the classic Butterworth flat response, widely regarded as the best all-round choice.
  • EBP of 70 means this driver can work well in either sealed or ported designs.
  • These are calculated targets. Always build slightly large (10-15% excess) and add fill material (polyester fiberfill) to fine-tune the acoustic volume.

Next stepMeasure your internal box volume carefully, accounting for wood thickness, driver displacement, and any bracing. Then check F3 against your desired bass extension.

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