Hales Revelation Three loudspeaker Measurements
The Hales Revelation Three was measured with a DRA Labs MLSSA system in the Stereophile listening room, mounted on an Italian Outline speaker turntable.1 Its B-weighted sensitivity was calculated to be a hair under 87dB/2.83V/m, while its impedance (fig.1) dropped below 4 ohms between 50Hz and 600Hz. Couple this with a high phase angle in the bass and a good amplifier is called for. Tube amplifiers should definitely be used from their 4 ohm taps. The single peak in the bass, at 28Hz, indicates the sealed-box tuning, and in turn implies respectable low-frequency extension.
Fig.1 Hales Revelation Three, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
This is confirmed by fig.2, which shows the Hales' quasi-anechoic response on its tweeter axis, averaged across a 30-degree horizontal window, spliced to the complex sum of the nearfield woofer and midrange responses. As is typical of a sealed-box system, the output is 6dB down at the box tuning frequency, rolling out at 12dB/octave below that frequency. As RD noted, the relatively small Revelation gives excellent bass. Higher in frequency, the woofer/midrange crossover appears to be set at a sensible 250Hz, and I didn't note any anomalies in the 100Hz region, as RD suspected. The Revelation Three's midrange and treble can be seen to be superbly flat.
Fig.2 Hales Revelation Three anechoic response on tweeter axis at 50", averaged across 30-degree horizontal window and corrected for microphone response, with the nearfield woofer response plotted below 300Hz.