LABORATORY TEST REPORT
In order to acquire the frequency responses shown in Graph 1, Newport
Test Labs used a near-field microphone measurement technique that effectively returns the same response one would expect when measuring the QB12 in an anechoic chamber. The top (black) trace shows the Q Acoustics QB12 subwoofer’s response with the crossover control in the AV position and you don’t need me to tell you that it’s flat. Indeed it’s so flat that I’m sure that it’s the flattest response that Newport Test Labs has ever measured from any subwoofer. So flat, indeed, that I would not be at all surprised to find that Q Acoustics was using DSP to help the bass driver deliver it.
As you can see from the scale at the left of the graph, the QB12’s frequency response is within ±1.25dB all the way from 31Hz up to 210Hz. That’s flat. Measured using more conventional dB criteria, this graph shows that Newport Test Labs’ measured response was 26Hz to 230Hz ±3dB. The red trace on Graph 1 shows the QB12’s frequency response when the crossover control is at its minimum setting (40Hz) and you can see that the QB12’s maximum output is at exactly 35Hz, and it returns a frequency response of 23Hz to 58Hz ±3dB for this setting of the crossover control. Since the frequency response of most floorstanding speakers rolls off below 50Hz, this would be an ideal setting when paired with such speakers.
Graph 2 also shows the near-field frequency response of the Q Acoustics QB12, this time for multiple settings of the crossover control. I was a tad surprised at the lack of difference between the response in the AV setting versus the response with the crossover set to 130Hz.
In the AV setting the response is 6dB down at 230Hz, whereas with the crossover set to 130Hz, it’s 6dB down at 220Hz. Looking at the huge difference in roll-offs between the 130Hz setting and the 100Hz setting, I suspect that the calibration of the crossover control isn’t overly accurate in this area, and it may be that Q Acoustics has optimised the control to be more accurate at the lower-frequency segment of the control’s rotation.