Added-Mass, Dual-Mass, And Test-Box T/S Methods
The secondary measurement is only as accurate as the added mass or effective air volume applied to the driver.
Single and dual added mass
Measure the free-air curve first. Use accurately weighed, firmly attached, symmetric mass near the voice-coil region. Dual-mass methods add another measurement and can expose poor mass placement or model fit.
Do not deform the radiator
- split mass into equal pieces
- place symmetrically
- avoid the outer cone edge
- do not load only one side
- verify the mass did not move
- repeat removal and installation
Known-volume test box
Use true internal net volume after the driver, braces, terminals, fixtures, and other displacement. Verify airtightness, panel rigidity, driver sealing, and temperature. Gross dimensions are not the effective test volume.
Effective radiation area
Sd strongly affects Vas and efficiency. Record the manufacturer value, effective-diameter convention, or measured radiation-area method. Frame diameter, cutout diameter, and piston area are not interchangeable.
Cross-check the result
Review resonance shift, measured-versus-modelled overlays, repeated placement, free-air recovery, and an independent secondary method when the design is sensitive to Vas or Mms.