Exploring Common DIY Terminology - Vas

Vas (Thiele/Small Parameter)

Vas stands for "equivalent compliance volume" or "effective volume of compliance". Vas represents the volume of air that has the same compliance (springiness) as a driver's suspension system. In other words, it measures the air volume that would produce the same acoustic compliance as the driver's mechanical suspension. Vas is typically expressed in liters (L) or cubic feet (ft³) and is an important parameter when designing loudspeaker...

Fs (Thiele/Small Parameter)

The Thiele/Small parameter "Fs" refers to the resonant frequency of the loudspeaker driver. Fs stands for "Free-air resonance" or "System resonance." It is a crucial parameter that characterizes the natural frequency at which a driver's diaphragm vibrates with maximum efficiency when operating in free air, without any enclosure or load. This resonant frequency is determined by the combined effects of the mass of the driver's...

Bl (Thiele/Small Parameter)

Refers to the Bl product, also known as the force factor or motor strength of a loudspeaker driver. It is a key parameter used to describe the performance characteristics of a driver’s motor assembly. Bl is a measurement of the interaction between the magnetic field generated by the driver's permanent magnet and the current flowing through its voice coil. It determines the ability of the driver to convert electrical power into mechanical motion and produce...

Acoustic Phase Center

The point in which sound emanates from a speaker element such as a tweeter, midrange, or woofer. A novice may assume this point is along the surface of a woofer dust cap, and while some may incorrectly use this as an estimate, the actual location varies from driver to driver. Unless marked on the individual component (as only a handful of manufacturers do, typically for pro audio equipment) the only way to determine this point is through frequency response measurements....

Preface

I started this article with the intention of offering a guide to DIYers, mostly those new to the field, that defines and explains the terminology you often see in discussions on the topic of DIY loudspeakers. Now, I have plenty of learning to do myself, and am under no illusion that what I do know is complete and correct. Because of this, I want these articles to be living documents. By that I mean, I'd like the DIY community to offer input on each definition to expand and clarify...