Measurement of Thiele-Small Parameters
Test sequences for Added Mass, Known Volume, and Known Driver Mass methods.

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.
Hardware
- SCM-3 calibrated measurement microphone Part # 4004
- AmpConnect all-in-one hardware interface Part #4042 OR
- SoundConnect Microphone power supply Part # 4020 AND Power amplifier (SCAmp Part # 4060)
Software
- SoundCheck 10.0 or later
- Transducer QC Plus or equivalent modules PN 1102
- Equation Editor PN 2012
Setup & Calibration
- Calibrate the amplifier as instructed in the SoundCheck manual.
- Calibrate the reference microphone as instructed in the SoundCheck manual.
- Connect the channel 1 (or Left) output of your soundcard to the input of the amplifier.
- Connect the output of the amplifier to the female banana terminals of the impedance box.
- Connect the male banana terminals of the impedance box to your loudspeaker.
- Position your reference microphone at the desired test distance from the loudspeaker, and connect it to the microphone power supply.
- Connect the output of the mic supply to the channel 1 (or Left) input of your soundcard.
- Connect the output of the impedance box to the channel 2 (or Right) input of your soundcard.
You are ready to start the sequence. If you just want to look at stored measurement data, select Recall Data at the beginning of the sequence.
Download Sequence (zip file)
Download Sequence documentation (PDF)
To run the sequence in SoundCheck, please save the zip file to your hard drive, then follow the instructions in ‘Sequence Editor: Exporting/Importing a Sequence’ section of the manual.