Ruark Equinox loudspeaker Measurements
I estimated the Ruark's B-weighted sensitivity to specification as 87dB/2.83V/m. Its plot of impedance magnitude and phase (fig.1) reveals it to be a moderately easy load to drive. It only drops below 6 ohms, and then only by a little, in the lower midrange and mid-treble. The "saddle" between the low-frequency impedance peaks reveals the speaker's reflex tuning frequency, a moderate 40Hz.
Fig.1 Ruark Equinox, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Fig.2 shows the individual responses of the tweeter, woofer, and port. The latter is the bandpass centered on the tuning frequency of 40Hz and coincident with the woofer's minimum-motion point. There is a refreshing freedom from higher-frequency spikes and peaks in the port output. The woofer rises through its passband, peaking at 1100Hz, before beginning its crossover rolloff. The tweeter's response is flat within its passband, but has a slight lack of on-axis energy between 2.5kHz and 4kHz.
Fig.2 Ruark Equinox, individual responses of tweeter and woofer on tweeter axis at 50", corrected for microphone response, with nearfield woofer and port responses plotted below 300Hz and 900Hz, respectively.
The manner in which these outputs sum on the tweeter axis is shown in fig.3. Flat through the lower middle-midrange and treble, the Equinox's balance is spoiled by the peakiness in the upper midrange expected from fig.2. This type of curve always results in some added nasality to a speaker's balance; though I note that KR was bothered by a "caw" coloration, he did find that it could be ameliorated by suitable room placement, this bringing up the lower midrange level. In the bass, the speaker is 6dB down at a quite low 38Hz. As KR found, this speaker can produce quite good midbass levels.
Fig.3 Ruark Equinox, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of nearfield woofer and port responses plotted below 300Hz.
Vertically (not shown), there is little change in the Ruark's balance as long as the listener sits within ±10° or so of the tweeter axis. Laterally (fig.4), the dispersion is wide and even, with a well-controlled HF rolloff with increasing angle. Such behavior always correlates with stable, accurately defined stereo imaging.
Fig.4 Ruark Equinox, horizontal response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90°–5° off-axis; reference response; differences in response 5°–90° off-axis.
There are no surprises in the Equinox's step response (fig.5), the two drive-units both being wired with positive acoustic polarity and the tweeter's output arriving slightly before that of the woofer. The associated cumulative spectral-decay plot (fig.6) reveals a ridge at the upper-midrange peak frequency of 1200Hz, but is otherwise pretty clean, especially in the mid and high treble.
Fig.5 Ruark Equinox, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.6 Ruark Equinox, cumulative spectral-decay plot at 50" (0.15ms risetime).
Finally, while the impedance plot (fig.1) was free from resonance-induced ripples and wrinkles, investigating the panel behavior with a simple plastic-tape accelerometer did reveal some problems. Fig.7, for example, a waterfall plot calculated from the output of the accelerometer when it was fastened to the center of the side panel, shows two quite strong resonant modes between 300Hz and 410Hz. The latter could actually be detected on all surfaces, even the side of the stand/crossover. However, KR did not note any midrange congestion, so I must assume it looks worse than it sounds.—John Atkinson
Fig.7 Ruark Equinox, cumulative spectral-decay plot of accelerometer output fastened to center of side panel. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)