Hales Revelation Three loudspeaker Measurements part 3

In the time domain, the Revelation Three's step response (fig.5) indicates that all three drive-units are connected with the same positive acoustic polarity, but as expected from the use of high-order filters and a flat baffle, the speaker is not time-coherent. As RD noted, this does not appear to have had any negative effect on the speaker's soundstaging. The associated cumulative spectral-decay plot (fig.6) reveals a superbly clean decay, marred only by a residual mode at the cursor position in this plot at 3250Hz. This is low enough in level that it probably doesn't have any serious subjective consequences.

Fig.5 Hales Revelation Three, step response on HF axis at 50" (5ms time window).

Fig.6 Hales Revelation Three, cumulative spectral-decay plot at 50" (0.15ms risetime).

When I removed the grille cloth for the measurements, I was somewhat surprised to see that the framework for the sculpted grille outline consisted of a wire armature. Without the grille cloth, the armature rang audibly when tapped. But with the speaker's cloth in position, the wire appeared to be well damped. Overall, however, the cabinet was quite lively. Fig.7, for example, shows a waterfall plot calculated from the output of a simple plastic-tape accelerometer taped to the front baffle between the drive-units. (The grille cloth was in position for this measurement.) Resonant modes can be seen at 180Hz, 324Hz, and 460Hz, and these were also detectable on the other surfaces of the enclosure. Their subjective effect is hard to predict, however.—John Atkinson

Fig.7 Hales Revelation Three, cumulative spectral-decay plot of accelerometer output fastened to cabinet baffle above woofer. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Footnote: 1 For details on how I measure loudspeakers and what measurements I consider subjectively most important, see "Loudspeakers: What Measurements Can Tell Us—And What They Can't Tell Us!," AES Preprint 4608, presented at the 103rd Audio Engineering Society Convention, New York, September 1997, and available from the AES, 60 E. 42nd Street, New York, NY 10165-2520. Tel: (212) 661-8528. Internet: www.aes.org.—JA
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