RD consistently noted problems with optimizing the Vienna Acoustics' low frequencies in his room. Try as I might, I couldn't find any particular measured problems in the bass. The midrange units hand over to the woofers below 80Hz or so, with the ports covering the range below 40Hz. I suspect that the limited bandpass covered by the woofers, as well as having six radiating areas all contributing to the speaker's output in the upper bass and below, makes its interaction with the room complex.

Fig.6 shows the Mahler's horizontal response family 90 degrees to either side of the tweeter axis. There is a general lack of off-axis energy in the presence region, which I initially associated with the crossover suckout on this axis. However, if you look at fig.7, which shows the same information but now normalized to the tweeter-axis response, you can see that the crossover suckout tends to fill in to the speaker's sides. I conjecture that the lack of off-axis energy between 800Hz and 2.4kHz is actually due to the relatively large diameter of the upper midrange unit restricting its radiation pattern at the top of its passband.

Fig.6 Vienna Acoustics Mahler, lateral response family at 50", from back to front: responses 90 degrees-5 degrees off-axis; reference response on tweeter axis; responses 5 degrees-90 degrees off-axis.

Fig.7 Vienna Acoustics Mahler, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90 degrees-5 degrees off-axis; reference response on tweeter axis; differences in response 5 degrees-90 degrees off-axis.

In the time domain, the Mahler's step response (fig.8) indicates a non-time-coherent output, despite the slanted-back front baffle. The tweeter is wired in the opposite acoustic polarity to the midrange units in order to steer the response down below the tweeter axis, as mentioned earlier. The waterfall plot on the tweeter axis (fig.9) is disturbed by the crossover suckout, which is associated with some delayed energy, but is otherwise very clean, particularly in the treble. This is basically good measured performance.—John Atkinson

Fig.8 Vienna Acoustics Mahler, step response at 50" (5ms time window, 30kHz bandwidth).

Fig.9 Vienna Acoustics Mahler, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).