The Thiele Small Parameters (often referred to as T/S Parameters) are provided in specification sheets by most manufacturers – but what are they for? If you read through the section on parameters you’ll get a more detailed explanation on the significance of each parameter, but put simply they are a set of parameters which define the electromechanical properties of the loudspeaker driver, which are a measure of how it behaves electrically, and mechanically.
Once you understand some of the basics of the Thiele Small parameters, you will know what to look for when it comes to choosing a loudspeaker driver. If you’re not interested in the nitty gritty, then it’s probably sufficient to be aware that the parameters are normally used when it comes to doing simulations of loudspeaker behaviour for purposes of optimising cabinet design.
For those of you who are keen to understand a little more about these parameter, you should find almost everything you need to know in this section.
The following are small signal mechanical parameters, and are measured at small signal levels
- BL – Motor strength, product of magnetic field strength (B) and length of wire in field (L)
- Mms – The Moving Mass of the cone, including air load.
- Cms – Compliance of the driver suspension (compliance is the opposite of stiffness)
- Rms – Mechanical resistance of the suspension
- Le – Voice coil inductance
- Re – DC Resistance of the voice coil
- Sd – area of the cone (diaphragm) in square metres
Since the above characteristics are not always easy to measure, it is often easier to measure other parameters, and derive any missing parameters from those that are available. Other parameters, known as small signal parameters, are as follows:
- Fs – Free Air Resonance (also described as Resonant Frequency)
- Qes – Electrical Q at Fs
- Qms – Mechanical Q at Fs
- Qts – Total Q (derived from Qes and Qms)
- Vas – Compliance Equivalent Volume
Large signal parameters, listed below, are used when predicting driver behaviour at high power levels:
- Xmax – Maximum Linear Excursion of the cone and voice coil.
- Xlim – Maximum physical excursion before damage (sometimes known as Xmech or Xdamage)
- Pe – Power Handling Capacity
- Vd – Peak Displacement Volume