Thiele Parameters
Thiele parameters provide a precise description of driver behavior. They are now routinely provided by speaker manufacturers, and can be measured by a number of systems such as CLIO. There are three cautions:
Acoustic vs. mechanical parameters
Acoustic parameters contain an "A" in the subscript, and are normalized by the effective piston area of the driver. The corresponding mechanical parameters, which contain an "M" in the subscript, are obtained by multiplying by the square of this area in the case of mass and resistive loss, or dividing by the square of the area in the case of compliance.
Parameter definitions and units
All equations in the ThieleSmall analysis section use MKS units. Two examples of units as provided by the CLIO system, and by the Solen catalog, are given in the table below. (Solen units are those actually provided for my Vifa driver, which differ from the definitions given in the front of the catalog).
Parameter 
Description 
MKS units 
CLIO units 
Solen units 
Bl 
Force factor 
Namps^{1} 
Namps^{1} 
Namps^{1} 
C_{MS} 
Suspension compliance 
mN^{1} 
mmN^{1} 

C_{AS} 
Acoustic compliance 
m^{5}N^{1} 
m^{5}N^{1} 

R_{MS} 
Suspension loss 
kgs^{1} 


R_{AS} 
Acoustic suspension resistance 
kgs^{1}m^{4} 
see note 

M_{MS} 
Moving mass 
kg 
grams 
grams 
M_{AS} 
Acoustic mass 
kgm^{4} 
kgm^{4} 

S_{D} 
Effective piston area 
m^{2} 
mm^{2} 
cm^{2} 
V_{AS} 
Equivalent air volume 
m^{3} 
liters 
liters 
R_{E} 
DC voice coil resistance 
Ohms 
Ohms 
Ohms 
L_{E} 
Voice coil inductance 
Henries 
mH 
mH 
f_{S} 
Resonance frequency in air 
Hz 
Hz 
Hz 
Q_{MS} 
Mechanical Q factor 
 
 
 
Q_{ES} 
Electrical Q factor 
 
 
 
Q_{TS} 
Total Q factor 
 
 
 
Note: CLIO denotes this as kOhms, but that is incorrect.
Supplementary equations
If the following parameter values are not available, they may be calculated using the following equations. Some of the results are approximate, and measured values are always preferred.
A comparison of measured vs. calculated values shows fairly good agreement.
Parameter 
CLIO 
Calculated 
M_{MS} 
0.00642 
0.00657 
R_{MS} 
2.13 
2.18 
C_{MS} 
0.000700 
0.000686 
Comparison of catalog and measured values
The catalog values are from Solen, for my P13WH0008 5" Vifa driver. The measured values are again from my CLIO system. As noted above, there are some significant differences.
Parameter 
Catalog 
Measured 
f_{S} 
60 
74.99 
Qts 
0.33 
0.4 
Q_{ES} 
0.43 
0.56 
Q_{MS} 
1.38 
1.42 
Bl 
6 
5.57 
M_{MS} 
0.0075 
0.0064 
Vas 
0.01 
0.00725 
R_{E} 
5.7 
6.4 
Le 
0.7 
1.09 