AudioFrog GB40 4″ Midrange

Up for test is AudioFrog’s GB40 4″ Midrange.

The GB15 1.5″ tweeter was tested here.

It’s worth noting this review is based on mostly objective data.  These drivers – as well as the others from the AudioFrog GB series speakers – include a LOT of installation hardware to make installs quicker and easier.  I simply don’t have the time right now to really delve in to the facets of this here.

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Small Signal Parameters

Results as measured via Dayton’s DATs measurement tool.  Which is a very little handy tool to have.  😉

  • f(s)= 105.60 Hz
  • R(e)= 3.30 Ohms
  • Z(max)= 12.93 Ohms
  • Q(ms)= 2.654
  • Q(es)= 0.908
  • Q(ts)= 0.676
  • V(as)= 2.332 liters (0.082 cubic feet)
  • L(e)= 0.34 mH
  • n(0)= 0.29 %
  • SPL= 86.70 1W/1m
  • M(ms)= 4.81 grams
  • C(ms)= 0.47 mm/N
  • BL= 3.40

gb40 impedance

Frequency Response

Frequency Response and the following Harmonic Distortion measurements were taken using Dayton’s OmniMic measurement system.

The frequency response measurements below are on-axis (0 degrees) and off-axis (15, 30, 60 degrees), measured at 2.83v/1m.

gb40 fr 0 15 30 60



Harmonic Distortion

The following HD graphs are done in the nearfield, emulating 90dB at 1 meter as well as 96dB at 1 meter, respectively.

gb40 HD 90

gb40 HD 96


I’m going to have to make this quick…

FR indicates average sensitivity in the 85dB @ 2.83v/1m ballpark.  There’s an upward climb on-axis above 2khz, which is similar to what I measured with the JL Audio C5-400cm here and the ScanSpeak 10f I measured here.  Seems to indicate this may be better placed off-axis.  There’s a fairly small breakup at 6.7kHz that doesn’t bother me much, but does show up in all axes.  That said, this peaking is about 2 octaves above the nominal low-pass crossover and so benign it will be mitigated by the crossover anyway.

The THD at 96dB overall is quite low, though there’s an anomaly that shows up around 400hz.  I’m not sure what this could be, though it’s worth noting I saw the same issue with the Scanspeak 10f I measured a couple years back.  This doesn’t show up in any other of my measurements, which indicates that it’s not the measurement setup itself.  Not sure what this could be, exactly, but it’s interesting that this occurs with both these 4″ drivers. Outside of that issue, the THD measured at 96dB breaks down as follows: 3% THD is met at approximately 100hz.  At 200hz the THD measured is approximately 1.25%.  At 300hz the THD is approximately 0.60% and above 500hz the THD is below 0.50% and as low as 0.30% in some places.  Very good.

Overall: Given the upper frequency crossover is determined by the beaming point, with a 4″ driver you can expect to cross this driver on the high end at about 3khz (give or take depending on the slope).  The low end crossover is typically driven by the amount of distortion you get.  I’d say, if you pay attention to the trend (and ignore the 400hz concern) the appropriate crossover for this driver would be in the 200-250hz ballpark which would provide you plenty of output at low distortion.  Also this provides the ability to cross this lower than I typically recommend for the ScanSpeak 10f (one of my go-to suggestions). The mid 80’s sensitivity is likely due to the tradeoff of low frequency extension.  In other words, if the sensitivity were higher, distortion would be higher, lower in frequency meaning you may have to cross at 300hz rather than 200hz to achieve the same level of THD.

Speaking of the 10f comparison, the below pictures show the difference in size between the newer, smaller neo magnet version of the 10f (this one):

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PS:  If you would like to help me keep up funds for testing, there’s a little ‘contribute’ button that goes through Paypal all the way at the bottom of every page.  Any little bit helps.

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