Calculating Thiele-Small Parameters of a Loudspeaker (100 Things #71)

SoundCheck can be used for loudspeaker design, performing measurements of loudspeaker performance in an enclosure, known as Thiele-Small parameters. SoundCheck includes three different methods for calculating Thiele-Small parameters: known mass, added mass, and known volume. Depending on what driver measurements are known and unknown, these three sequences provide options for all testing scenarios. Operator messages steps are included in all sequences, making testing a wide variety of devices easy with one sequence.

Calculating Thiele-Small Parameters of a Loudspeaker

Try it Yourself

You can try these sequences for yourself! Check out all three Thiele-Small Parameter test sequences in our sequence library, where you can download them free of charge and try them on your own SoundCheck system.

Learn more about Thiele-Small Parameters

Listen founder and president Steve Temme, and support manager Steve Tatarunis, co-wrote a technical article on practical impedance measurement. The paper dives into both single channel and dual channel measurement methods, considerations, techniques, measuring thiele-small parameters, and more.

Video Script:

Thiele-Small (T/S) Parameters define the mechanical, electrical and electromechanical properties of a loudspeaker and predict how a driver will work in an enclosure. It’s a common measurement for loudspeaker designers, and it’s easy to do in SoundCheck. 

SoundCheck offers 3 built-in methods for calculating the Thiele-Small parameters – known mass, added mass, and known volume. You can also use a laser, but that’s a subject for another video. Let’s take a look.

The ‘known mass’ method is when the mass of the driver is known along with the effective cone diameter and 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.

Thiele-Small parameters can also be measured when the mass of the driver is not known. In this case, we use the ‘added mass’ method. First the user is prompted to enter the driver diameter and a stepped sweep is run to calculate the impedance curve without the added mass attached.

Next the user can either enter the DC Resistance of the loudspeaker or use the minimum impedance method.  Using minimum impedance involves searching for the lowest value of the impedance curve.  Now, we enter the value of the added mass in grams and attach it to the loudspeaker. This added mass can be modeling clay or mounting putty stuck to the cone close to the voice coil to change the resonant frequency of the loudspeaker. Another stepped sweep is run 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.

The third method, known volume, assumes we know the total volume of the enclosure. In this case, we enter the driver diameter and we make an impedance measurement using a stepped stweep with the driver mounted vertically in free air. Like before, we can enter the DC Resistance of the loudspeaker or use the minimum impedance method.The second impedance measurement is made with the driver mounted in the known volume and a series of post processing steps uses the measured and user-input data to generate the Thiele-Small Parameters.

If you already have SoundCheck, you can download test sequences for all 3 methods from our website – check it out!