|Auditioning the KEF LS50 Black Edition, powered by SMSL SA300 Class D amp on computer workstation.|
I. Let's get practical...
|As per CTA-2034. There's also discussion of height variability and front baffle to POR maximum distance of up to 5cm/2".|
II. The subject of investigations today - the KEF LS50
III. Let's Test!
|"LEFT" KEF LS50. For a bit more stability, I put a small weight in front of the speaker stand.|
|3dB contour lines turned on. +/-180° range.|
|It's important to standardize the aspect ratio for curves due to the potential to change perception if the image is spread out too wide or the Y-axis too compressed. I'll use 25dB/dec for my graphs.|
A couple of notes about this. First, the miniDSP UMIK-1 USB microphone I'm using is limited to 48kHz sampling rate and appears to implement a sharp linear phase filter for the ADC resulting in visible pre-ringing. Also, the microphone polarity is inverted so I had to flip the graph to what you see above. Other than the pre-ringing, this is basically what Atkinson found in Stereophile. As we can see, the tweeter (initial negative deviation) is hooked up with opposite polarity to the woofer (larger positive low-frequency step and roll-off). This is a common arrangement with passive 2-way speakers. While the crossover between the drivers are not "time/phase coherent", the step response is nonetheless temporally nice and "tight" as a coaxially arranged driver.
The assumption here is that the whole system from DAC to preamp to amp to measurement microphone is more linear than the speaker itself when reproducing tones of various amplitudes (probably a safe bet!). While I cannot know the accuracy to an absolute degree, I can still make relative comparisons between devices. I've measured other speakers with this technique and what I can say is that the result here with the LS50 is very impressive. Within the 30dB amplitude range of 70-100dB SPL; there <0.7dB deviation from ideal. We'll talk about the results from other speakers in the days ahead for comparison.
|So as not to clutter the graph, plot down to 6th harmonic.|
Looks great! The two speakers are almost identical. Impedance is precise suggesting well-matched crossovers and drivers. Frequency response is basically within 1dB of each other. Time domain CSD waterfall over 3ms looks clean for both with similar pattern. This speaks well for KEF's manufacturing standards (made in China) and suggests that stereo performance should be excellent with precise soundstage and imaging.