LABORATORY TEST REPORT
Newport Test Labs measured the frequency response of the Q Acoustics Concept 500 it had for testing in its acoustic laboratory as being 42Hz to 30kHz ±3.5dB and it is this response that is shown in Graph 1. It’s the result of measuring the speaker using two different techniques. The trace below 550Hz is the averaged result of nine individual frequency sweeps measured at three metres, with the central grid point on-axis with the tweeter using pink noise test stimulus with capture unsmoothed. This has been manually spliced (at 550Hz) to the gated high-frequency response measured at one metre on axis, an expanded view of which is shown in Graph 2. You can see that the response is extraordinarily flat, with the variations in it being primarily the result of the inevitable roll-offs at either end of the frequency spectrum. For example, if we look only at frequencies between 110Hz and 21kHz, the Concept 500’s response was around ±1.25dB. Between 150Hz and 5.5kHz, it was even better at ±0.7dB. This level of linearity is a stunning achievement in a passive loudspeaker system.
Note too, that the overall spectral response is not skewed to favour the bass or the treble… or indeed the midrange.
The high-frequency response of the Q Acoustics Concept 500 is shown in greater detail in Graph 2, by virtue of changing the horizontal axis to ‘zoom in’ on the region between 400Hz and 40kHz. This graph also adds a trace (green) showing the response with the loudspeaker grille in place (the black trace being the response without the grille.) You can see that the grille is remarkably acoustically transparent with the only significant difference being that drop in level between 9kHz and about 13kHz. It is interesting that the very minor dip in the response without the grille (at 7.5kHz) shifts down at little to 7kHz when the grille is in place. Also interesting is the slight increase in output centred at 2.4kHz. While I can’t explain the first, this latter effect is no doubt crossover-related since Q Acoustics specifies the crossover frequency as being at 2.5kHz.
Low-frequency performance is shown in Graph 3. You can see that the performance of
At ±0.7dB, the level of linearity is a stunning achievement in a passive loudspeaker system
the bass/midrange driver Q Acoustics is using is excellent, extending upwards from 100Hz very smoothly within about ±1dB. Its response starts rolling off at 85Hz and then does so at the expected rate to its minima at exactly 40Hz. As you’d expect of such a large port, it delivers its output over a wide bandwidth. There’s no real ‘peak’ as such in its output, with the port delivering almost the same output from 35Hz to 55Hz. Rather than rolling off smoothly above 55Hz, there’s a curious ‘shelf’ in the output between 100Hz and 140Hz. As you can see, there’s also some unwanted leakage of higher frequencies centred around 425Hz, 590Hz and 725Hz, but it’s very low in level, and the port is at the rear, which will ameliorate any audible effects. The impedance of the Q Acoustics Concept 500 is well-controlled in its bass reflex incarnation, with the two bass resonant peaks at 36Hz and 78Hz, with the minima between them at 40Hz. Except for the higher-frequency bass peak, the impedance remains above 4 and below 20 right across the audio band, except for at 200Hz, where it drops to 3.7 , which was not unexpected, since Q Acoustics flags this in its specifications. However whereas Q Acoustics specifies the Concept 500’s ‘nominal’ impedance at 6 I would personally rate the Concept 500 as a 4 design. You can see that Q Acoustics must be saying that it’s the acoustic crossover that’s at 2.5kHz, because Newport Test Labs’ graph clearly shows that the electrical crossover point is somewhat lower, at around 1.7kHz. I was also pleased to note that there’s a rising impedance at high frequencies, which will make the Concept 500 very amplifier-friendly, particularly with older Class-D amplifier designs.
Whereas Q Acoustics specifies the Concept 500 with an efficiency of 90dBSPL at one metre for a one watt input, Newport Test Labs reported its estimate of efficiency at 89dBSPL at one metre, for a 2.83Veq input. The small difference could obviously be due to the different measurement techniques used (watts vs. volts!) as well as other factors, but is in any case well within the realms of both measurement uncertainty and sample-to-sample variations in production. But whether it’s 89dBSPL or 90dBSPL, the Concept 500 is still more efficient than the average floor-stander and thus able to deliver high sound pressure levels even with quite low-powered amplifiers.
Graph 5 shows an in-room response using pink noise, with the higher graphing limit deliberately restricted to 10kHz and you can see that the response extends from 300Hz to 10kHz ±0.7dB.
Graph 6 shows the effect of the rear-panel jumper on the high-frequency response of the Q Acoustics Concept 500. Newport Test Labs has limited the low-end display to 2kHz, because below this frequency there is no effect on response at all. Above 2kHz, the effect on response gradually increases until it reaches its maximum at around 4kHz, at which point you can vary response by ±2.5dB… or, if you prefer, over a total range of 5dB, which is a significant adjustment that will be easily audible. Other than adjusting level, the jumper has no other shaping effect on the frequency response, which is as it should be.
When you pay one of the top speaker design consultancies in the world to build you a high-end speaker, you expect highend performance, and I’d have to say that Fink Consulting has done a superb job for Q Acoustics. I’d even have to suggest that a bonus might be in order. The Concept 500 is a superb loudspeaker design. Steve Holding
In the Concept 500 design, as in other of its ‘gel-core’ designs, Q Acoustics has also mechanically decoupled the 28mm soft dome tweeter from the gel-core cabinet