Table of Contents
Find Thiele and Small parameters from an unknown speaker
| Parameter name | Significance |
|---|---|
| Fs (=2πωs) | Resonance frequency (Hz) |
| Re | Electrical resistance (ω=0) (Ω) |
| Le | Electrical inductance (ω»ωs) |
| Bl | Force factor (N/A) |
| Mms | Mobile mass (Kg) |
| Cms | Suspension swiftness |
| Rms | Mecanical losses |
| Sd | Mobile area (m²) |
| VAS | equivalent of Cms |
| Qes | Electrical quality factor |
| Qms | Mecanical quality factor |
| Qts | Total quality factor |
Re
Re is the continuous current impedance (not the average impedance).
1st solution
Use a precise multimeter, a good one, 20,000 pts or so.
2nd solution
Put a high (relative to measured value) value resistor in series with the voicecoil, power the thing from a big 12V battery (so that the voltage does not drop during measure).
Ex: Re is arround 10Ω, we choose a 100Ω 1% resistor as burden resistor (>=5W).
Sd
Sd is the pushing area, that is the area of the mobile part.
Measure mobile part diameter, including half the suspension suround.
Impedance
The impedance curve is constructed on log scale using a probed test amp and a fequency generator.
Le
Extracted from where
is the measured impedance.
Bl
Put a coin on the mobie apparatus (or a precisely known mass). For a fixed frequency increase the applied voltage, catch its value when the mass starts to “take off”.
, where g = 9.81m/s² (at this moment the mobile part speed is
The speaker MUST be even. The “take off” can be detected using a microphone, looking at the moment when the sinus signal starts to deteriorate.
Mms
This parameter is measured using a known mass placed on the mobile part, the applied signal is small enough to avoid the mass takin off.
The resonant frequency is measured without () and with (
) the mass.
, where
= 1.2 Kg/m^3 and a = ???
Cms
Rms