Onix x-ls Measurements and Analysis
The impedance minimum 0f 6.56 ohms at 42 Hz indicates the vented box tuning frequency. There are two other local minima, found at 164 Hz (6.386 ohms) and 3.4 kHz (4.97 ohms). That the first two minima are proximal in magnitude indicates an efficient reflex action. The large impedance peak, found at ~ 850 Hz arises as a result the interaction of the crossover network's high- and lowpass sections, setting up a parallel resonance.
The impedance phase swings between +39° and -54° across the audible spectrum. With a lowest magnitude minima value of 4.97 ohms, the system nominal impedance (per IEC standards) value would be 6 ohms. Overall, the x-ls will present whatever amp that sits upstream of it a relatively benign load.
Impedance curves are useful in diagnosing pathologies such as pronounced mechanical resonances, defective drive units, etc. In this impedance curve we see no tell-tale symptoms indicating underlying pathologies.
Figure 3: xl-s system amplitude response, scaled to 1m, 2.828 Vac drive level.
Figure 3 shows the x-ls full-range frequency response, obtained by combining a 1m, on-axis gated response with a nearfield woofer & port response, appropriately summed and scaled. System sensitivity averages 87.5 dB in the 300 - 3000 Hz segment of the system's passband, an average value for a system of this type. The data is 1/12 octave smoothed.
Relative to the 87.5 dB sensitivity value the low frequency, -3dB point is 60 Hz. The high frequency -3dB point is about 23 kHz. (Note: the slight up tick in response seen at 35 kHz and above is the result of the measurement microphone detecting the acoustic output of a motion detection security system that happened to be operating in the vicinity at the time of measurement. It's not a system-sourced pathology). Across the 60 Hz - 23 kHz passband, system response varies by ± 1.8 dB. Excellent!
Figure 4: xl-s acoustic crossover frequency measurement, fxover @ 1.7 kHz
The acoustic crossover frequency was determined to be approximately 1.7 kHz (Figure 4) by measuring the on-axis response of the woofer & tweeter, separately.
Figure 5: x-ls, system A & B amplitude response match comparison.
The x-ls pair were well matched acoustically and electrically for speakers in this price range, as indicated in figure (Figure 5) and (Figure 6), never straying more than ~ ± 2 dB across the audible spectrum. A good match, such as this, is indicative of a system capable of stable imaging.
Figure 6: Voltage transfer function of each filter when it is loaded by its driver, both systems.
In Figure 7, we see the acoustic step response of the system. The woofer peak occurs some 3.10 ms behind that of the tweeter, as measured at the microphone position. We also see the typically fast tweeter rise time and the much slower rise time of the woofer. The system is not time coherent.
Only modest weight is given to this measurement as the presence of so many other acoustical artifacts tend to swamp the subtle effects of the time difference as shown in figure 7.
Figure 7: x-ls system step response
