Vas and Cms are Thiele-Small parameters that describe the compliance, or flexibility, of a speaker’s suspension system. These values help explain how easily a speaker cone moves and how the speaker may perform in different enclosure designs.
Cms, or Compliance of Mechanical Suspension, measures how flexible or stiff the speaker’s suspension is. This includes components such as the surround and spider, which control how the cone moves forward and backward during operation.
Vas refers to the equivalent volume of air that has the same compliance as the speaker’s suspension. In simple terms, it helps indicate how the speaker may interact with an enclosure and how much air volume may be required for the driver to perform correctly.
A speaker with a more compliant, or softer, suspension may be more suited to deeper low-frequency movement, depending on the overall design. A stiffer suspension may provide greater control and precision, but it must still be matched correctly to the enclosure, amplifier and intended application.
A useful way to think about Vas and Cms is like a vehicle suspension system. A softer suspension can allow more movement, while a firmer suspension can improve control. In speaker design, this balance affects bass response, accuracy, efficiency and overall sound character.
When choosing Focal speakers or subwoofers, Vas and Cms should not be judged on their own. They should be considered alongside other specifications such as Fs, Qts, Xmax, RMS power handling, sensitivity, impedance and enclosure requirements.
For the best result, Focal Australia recommends speaking with an authorised Focal Australia dealer. A professional installer can interpret the speaker data correctly and recommend the right speaker, subwoofer or enclosure design for your vehicle and listening goals.
