Lumen White Whiteflame loudspeaker Measurements part 2

Could the plateau above 1kHz be associated with MF's dislike of the Whiteflame's "sharply drawn" balance when the speaker was driven by a solid-state amplifier? It sounds plausible, but comparing figs. 4 and 1, it looks as if the higher output impedance of a tube amplifier will actually pull down the level slightly in the octaves above this region. Therefore, I suspect that what MF heard as a welcome improvement in the Lumen White's balance was the tube amp's slight boost of the region between 300Hz and 1kHz, which will reduce the perception that the entire treble region is too high in level. However, it will still leave a slightly elevated region in the upper mids that will add to the speaker's presentation of recorded detail, but could also make the balance a little aggressive. Certainly I could hear a slight emphasis in this region in my own auditioning of the Whiteflame.

The use of a tube amp will also tend to compensate for a slight off-axis flare in the presence region (fig.5). Note the even spacing of the contour lines in this graph, which is associated with stable, accurate stereo imaging. Note also that the top audio octave is actually a little higher in level 5-10 degrees to the sides of the speaker compared with its on-axis behavior, which suggests that firing the speakers straight ahead rather than toeing them in to the listening position will give the best top-octave balance.

Fig.5 Lumen White Whiteflame, lateral response family at 50" with grille on, normalized to response on tweeter axis, from back to front: differences in response 180 degrees-5 degrees off-axis, reference response, differences in response 5 degrees-180 degrees off-axis.

Vertically (fig.6), the Whiteflame's balance doesn't change much over a ±5 degrees window centered on the tweeter axis. But stand, or sit high enough that you see the top of the cabinet, and a suckout appears at the upper crossover frequency.

Fig.6 Lumen White Whiteflame, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15 degrees-5 degrees above axis, reference response, differences in response 5 degrees-15 degrees below axis.

Lumen White claims that the Whiteflame is time-coherent. However, as revealed by the step response on the tweeter axis (fig.7), the speaker is not time-coherent. What you can see in this graph is a sharp negative-going spike from the tweeter, followed by a slower negative-going triangular step from the midrange unit, and a very slow positive-going step from the woofers that coincides with, and is obscured by, the overshoot of the midrange pulse. (The ripple at the 7.5ms mark is the first reflection of the sound from the support I used in the measurements.)

Fig.7 Lumen White Whiteflame, on-axis step response at 50" (5ms time window, 30kHz bandwidth).

I windowed out this reflection to produce the Lumen White's waterfall plot on the tweeter axis (fig.8). This is very clean throughout the treble region, with some delayed energy visible at the very top of the audioband. However, there is something going on at the top of the midrange, though the frequency resolution in this graph is insufficient to get a clear picture.

Fig.8 Lumen White Whiteflame, cumulative spectral-decay plot at 50" (0.15ms risetime).

The gorgeous-looking Lumen White Whiteflame offers enigmatic measured performance. As Mikey found, the interaction between the speaker's impedance and the relatively high source impedance of a tube amplifier will result in a reasonably even tonal balance through the midrange and treble. Its waterfall plot reveals high frequencies that are superbly free of grain, and its dispersion is well-controlled. But set against these positive attributes are the anomaly at 850Hz and the severe enclosure resonance at 120Hz. It's always possible that high-Q problems like these will be hidden much of the time with many different types of music, but that doesn't mean that they won't be audible some of the time.—John Atkinson

Lumen White
Acoustic Dreams
RR 5, Box 429
Fairfield, IL 62837
(618) 847-7813