6 Loudspeaker cabinets
6.13 Thiele-Small parameters
In the past, two gentlemen, Albert Thiele and Robert Small, have developed a measurement standard for loudspeaker characteristics. The Thiele/Small parameters, T/S parameters in short, are what defines a loudspeaker. These parameters are a list of figures of mechanical and electrical constants:
| Para- meter |
US unit |
EU unit |
Description | Interpretation |
| Fs | Hz | Hz | Free air resonance frequency | Specifies the frequency at which the driver resonates in free air, floating in an infinite space. |
| Qms | - | - | Mechanical Q factor | These three figures describe how the driver resonates. The bandwidth of the resonance is split into motional resonance (Qms) and electrical resonance (Qes). Their value is combined in Qts. This value is of great importance to cabinet design. |
| Qes | - | - | Electrical Q factor | |
| Qts | - | - | Total Q factor | |
| Vas | ft3 | dm3 | Equivalent air volume | Specifies the volume of air to have an equivalent suspension to the cone's suspension |
| Cms | in/N | mm/N | Suspension compliance | See 6.1  . Specifies the force needed to move the cone assembly a given distance |
| B | T | T | Magnetic field strength | Strength of the magnetic field inside the air gap in Tesla |
| BL | N/A * | N/A * | Force factor | Specifies how much force the voice coil will apply to the cone at a given current |
| Xmax | in | mm | Maximum linear cone displacement | See 6.1 |
| Xdmg | in | mm | Maximum cone displacement before damage occurs | See 6.7 |
| η0 | dB | dB | Reference efficiency | See 6.10 |
| Sens | dB | dB | Sensitivity is the measured, real world efficiency | See 6.10 |
| Pth, Pcont | W | W | Thermal power or continuous power | See 6.7 |
| Ppeak | W | W | Peak power | See 6.7 |
* Note: this is Newton per Ampère, it doesn't mean "Not Available"
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© Joris van den Heuvel 2001-2009