Dayton Audio ND91-8 3-1 - Manual (Page 5)

Nonlinear Parameters
The displacement limits XBL, XC, XL and Xd describe the limiting effect for the force factor Bl(x),
compliance Cms(x), inductance Le(x) and Doppler effect, respectively, according to the threshold
values Blmin, Cmin, Zmax and d2 used. The thresholds Blmin= 82 %, Cmin=75 %, Zmax=10 % and
d2=10% generate for a two-tone-signal (f1=fs, f2=8.5fs) 10 % total harmonic distortion and 10 %
intermodulation distortion. The thresholds Blmin= 70 %, Cmin=50 %, Zmax=17 % create 20 % total
harmonic distortion which is becoming the standard for acceptable subwoofer distortion thresholds.
Traditionally, Xmax has been defined as the physical overhang of the voice coil, 15% times the
physical overhang, or the point where BL has dropped 70% from its X=0 value (same as X Bl). The
additional nonlinear limits allow us to quantify the other factors that limit a loudspeaker’s performance.
These parameters are defined in more detail in the papers: “ AN04 – Measurement of Peak
Displacement Xmax” , “ AN05 - Displacement Limits due to Driver Nonlinearities.” , “AN17 - Credibility of
Nonlinear Parameters” , “ Prediction of Speaker Performance at High Amplitudes” , “Assessment of
Voice Coil Peak Displacement Xmax” , and “Assessing Large Signal Performance of Loudspeakers”
Symbol Number Unit Comment
Displacement Limits thresholds can be changed in Processing property page
X Bl @ Bl min=70% 5.1 mm Displacement limit due to force factor variation
X C @ C min=50% 7.1 mm Displacement limit due to compliance variation
X L @ Z max=10% 5.7 mm Displacement limit due to inductance variation
X d @ d2=10% 18.9 mm Displacement limit due to IM distortion (Doppler)
Parameters at the Rest Position
The value of the nonlinear parameters at the rest position (x=0) may be used as input for the traditional
linear modelling and may be referred as “linear parameters”. Please note that these parameters
depend on the instantaneous state of the driver (voice coil temperature, peak value of displacement)
and are presented for three different modes of operation:
Mode Properties
LARGE+WARM the transducer is operated in the large signal domain, the peak value of the
displacement is high (|x| < xmax), the variation of the parameters is not
negligible, the voice coil temperature is increased (D TV > 0) due to heating.
LARGE+COLD the transducer is operated in the large signal domain, the peak value of the
displacement is high (|x| < xmax), the variation of the parameters is not
negligible, the effect of heating is compensated while considering the cold voice
coil resistance Re(D TV =0).
SMALL SIGNAL the transducer is operated in the small signal domain, the amplitude of the
excitation signal is sufficiently small, the displacement is small in comparison to
the allowed maximal displacement (|x| << xmax ), the variations of the nonlinear
parameters are negligible, the increase of voice coil temperature is negligible (D
TV » 0), the effects of the nonlinear, thermal and time-varying mechanisms are
negligible, the transducer behaves almost linear.