TD-SPICE / Introducing a SPICE model to simulate Thermal Distortion in Speakers



also for modelling of current distortion in any conductors & modelling of any mass cooling or heating system in general
( even for a star in universe *if* you like and are able to get translation of parameters straight ;)

by Ing. Michael Gerstgrasser



rev 3.1.2 LT-SPICE Model
for download

rev 3.1.2 LT-SPICE Plot config
for download

Grafik  Grafik 

Above you'll find the LT-SPICE modell for download, I provide for free for non-comercial use.
You should be fairly familiar with SPICE simuation to get the model running and being able to explore its enormous capabilities.

Comments and corrections are welcome at "From Power Compression towards Thermal Distortion / developing on a point of view"

A brief summary about the topic of Thermal Distortion in loudspeakers can be found under TD / Introducing "Thermal Distortion"

Revision 3.1.2 Thermal Distortion model is capable to simulate the three major sonic impacts of Thermal Distortion in speakers

- Melt down of SPL at the time scale of signal frequencies directly affecting signal integrity. This is covered by wave form deformation due to TD
- Melt down of SPL at a time scale that is within the pianissimo and fortissimo course of music (roghly within 10-20sec). This is covered by Thermal Overshot
- Melt down of SPL at very large time scales meaning after minutes and hours of power injection close to the limits of a driver. Tthis is what is covered by the common "power compression" figures

Thermal model rev. 3.1.2 can mimic one or two time constant behaviour and also thermal loss through radiation.
It provides improved consistency for analysing qualitative and quantitaive behaviour of Thermal Distortion in speakers
The core of the thermal model can easily be expanded for additional branches of thermal flow providing possibility to detailled analysis of any variety of coupled thermal masses

Rev 3.1.2 model supports constant voltage amplifier and constant current amplifier operation. Referencing the thermal model is simplifyed by
- ready for use modelling of high pass filter of amplifier
- ready for use modelling of source impedance of amplifier, cables and connectors
- ready for use modelling of high pass filter of sound card input

On top of above,
- Modelled speaker impedance response can be inserted as a series network
- Temperature increase markers for Safe Operating Area are provided
- Single sinus and dual sinus signal generation ready for use
- Burst on/off generation ready for use to simulate "Thermal Overshot" effects

You can investigate qualitative and quantitative behaviour of wave form deformation due to Thermal Distortion


Also you can look at Thermal Overshot from burst behaviour:


Also you can check SOA "Safe Operating Area" to prevent from thermal overload or to calculate maximum safe power injection - be it ultra short term or continuous


Also you can inject and investigate any signal you like using FFT analyzing or any powerful tool, LTSPICE provides.


To provide some start-up help for the novice, I have set the variables in the model according to my measurements of the SEAS Excel Millennium tweeter T25CF002.
Below I present pictures of the normalized SPL melt down at various power injection levels. These measurements were take with the free software AUDACITY.


Measurement performed at 10W power injection 10kHz


Measurement performed at 5W power injection 10kHz


Measurement performed at 1W power injection 10kHz

LT-SPICE / Switch-CAD can be downloaded from the LinearTechnology webpage for free.

Special thanks to the developer of LT-SPICE for his gorgeous work !



Austria, in Dez 2008

keep swingin' !