PHD FB 4.1 Midbass

PHD FB 4.1 Midbass Testing

Note:  Though these speakers are called ‘midbass’, I think their size and parameters lends them much more to a midrange use.

A set of these PHD speakers was loaned to me last year to test and I’m finally getting around to doing so.  While PHD is a 20-year old company, their presence hasn’t been really known (at least in my past 5-6 years in the car audio hobby) until the past couple years.  Given that, there’s very little actual testing on any of the PHD products that I’ve seen, and I hope to help change that.

Product info can be found at PHD’s website here.



Small Signal Parameters:

Electrical Parameters
Re 3.32 Ohm electrical voice coil resistance at DC
Le 0.181 mH frequency independent part of voice coil inductance
L2 0.257 mH para-inductance of voice coil
R2 3.79 Ohm electrical resistance due to eddy current losses
Cmes 319 µF electrical capacitance representing moving mass
Lces 6.21 mH electrical inductance representing driver compliance
Res 28.71 Ohm resistance due to mechanical losses
fs 113 Hz driver resonance frequency
fm 72.9 Hz resonance frequency of driver with additional mass
Mechanical Parameters
(using add. mass)
Mms 5.335 g mechanical mass of driver diaphragm assembly including air load and voice coil
Mmd (Sd) 4.933 g mechanical mass of voice coil and diaphragm without air load
Rms 0.582 kg/s mechanical resistance of  total-driver losses
Cms 0.371 mm/N mechanical compliance of driver suspension
Kms 2.69 N/mm mechanical stiffness of driver suspension
Bl 4.088 N/A force factor (Bl product)
Loss factors
Qtp 0.677 total Q-factor considering all losses
Qms 6.51 mechanical Q-factor of driver in free air considering Rms only
Qes 0.753 electrical Q-factor of driver in free air considering Re only
Qts 0.675 total Q-factor considering Re and Rms only
Other Parameters
Vas 1.3283 l equivalent air volume of suspension
n0 0.245 % reference efficiency (2 pi-radiation using Re)
Lm 86.09 dB characteristic sound pressure level (SPL at 1m for 1W @ Re)
Lnom 86.9 dB nominal sensitivity (SPL at 1m for 1W @ Zn)
Sd 50.27 cm² diaphragm area

fb 4.1 kms impedance

Large Signal Parameters:


Displacement Limits thresholds can be changed in Processing property page
X Bl @ Bl min=82% 1.4 mm Displacement limit due to force factor variation
X C @ C min=75% 2.6 mm Displacement limit due to compliance variation
X L @ Z max=10 % 1.9 mm Displacement limit due to inductance variation
X d @ d2=10% 9.4 mm Displacement limit due to IM distortion (Doppler)
Asymmetry (IEC 62458)
Ak 6.41 % Stiffness asymmetry Ak(Xpeak)
Xsym 0.91 mm Symmetry point of Bl(x) at maximal excursion

fb 4.1 bl fb 4.1 bl symmetry fb 4.1 cms fb 4.1 kms symmetry fb 4.1 kms fb 4.1 l(x) fb 4.1 lx(i)



Frequency Response:

The below is FR measured at 2.83v/1m, 0, 15, 30, 45, and 60 degrees with the accompanying polar.  You can see I stitched NF and FF at approximately 400hz, as this is where they lined up best for all axes.  These are smoothed to 1/12 octave.

  • Black= 0 Degrees (on-axis)
  • Red = 30 Degrees
  • Green = 60 Degrees

FR @ 0 30 60 2.83v

Non-Linear Distortion:

Harmonic Distortion, measured at approximately 5 inches from the cone, SPL emulating 90dB @ 1m and 96dB @ 1m.

  • Blue = THD
  • Red = 2nd Order
  • Pink = 3rd Order
  • Green = 4th Order
  • Teal = 5th Order

90dB @ 1m equivalent:HD 90db

96dB @ 1m equivalent:

HD 96db


IMD at 90dB/1m.  F1=110hz, F2=880hz (-6dB from F1).

IMD 90db 110_880

IMD at 96dB/1m.  F1=110hz, F2=880hz (-6dB from F1).

IMD 96db 110_880

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