Measurement of Thiele-Small Parameters

Loudspeaker system performance can be quantitatively related to a set of electro-mechanical parameters. These parameters are known in the industry as Thiele-Small parameters. They were first introduced by A.N.Thiele and Richard H.Small in a series of famous articles published in the 1971-72 Journal of AES (Audio Engineering Society).  Over the years these parameters have become standards in the industry, and are used by loudspeaker designers worldwide.

Three sequences have been included in SoundCheck for the purpose of measuring Thiele-Small Parameters, one sequence for each of the following methods: Added Mass, Known Volume, Known Driver Mass.

Thiele-Small Parameter Sequence Overview
Added Mass
The sequence begins with an option to recall stored example data. If the user chooses to recall data, the acquisitions in the sequence will be skipped, and the data from file will be used to calculate the parameters.  Regardless of the option chosen, the user is prompted to enter the driver diameter in centimeters.  If the user chose not to recall data a first acquisition is run using a stepped sine sweep.  This should be done without the added mass attached.
Next the user is prompted whether to enter the DCR of the loudspeaker or use the minimum impedance method.  Using minimum impedance involves searching for the lowest value of the impedance curve.  Finally the user is prompted to enter the value of the added mass in grams and to attach it to the loudspeaker.  Another acquisition is done and a second impedance curve is calculated.  A series of post processing steps uses the data entered and measured to generate the Thiele-Small Parameters in two tables.

Known Volume
The sequence begins with an option to recall stored example data. If the user chooses to recall data, the acquisitions in the sequence will be skipped, and the data from file will be used to calculate the parameters.  Regardless of the option chosen, the user is prompted to enter the driver diameter in centimeters.  If the user chose not to recall data a first acquisition is run using a stepped sine sweep.  This measurement is done with the driver mounted vertically in free air.
Next the user is prompted whether to enter the DCR of the loudspeaker or use the minimum impedance method.  Using minimum impedance involves searching for the lowest value of the impedance curve.  Finally the user is prompted to mount the driver in the known volume and enter the value in liters.  Another acquisition is done and a second impedance curve is calculated.  A series of post processing steps uses the data entered and measured to generate the Thiele-Small Parameters in two tables.

Known Driver Mass
Before starting this sequence the user needs to know three parameters: driver mass, effective cone diameter, and the coil resistance.  The sequence begins with user prompts to enter all three of these.
Next a stepped sine sweep is used to calculate the impedance of the loudspeaker.  A series of post processing steps uses this curve and the data entered by the user to generate the Thiele-Small Parameters, which are displayed on two tables.