MEASUREMENTS

Iused DRA Labs’ MLSSA system, a calibrated DPA 4006 microphone, and an Earthworks microphone preamplifier to measure the Wharfedale Dovedale’s quasi-anechoic frequency- and timedomain responses in the farfield. I used an Earthworks QTC-40 mike for the nearfield and in-room responses and Dayton Audio’s DATS V2 system to measure the impedance magnitude and electrical phase angle. I examined the farfield behavior on the tweeter axis, which, with the speaker on its stands and spikes, places the tweeter 35" from the floor. As designer Peter Comeau recommends that the speaker be used with its grille, I left the grille in place for all the farfield measurements.

Wharfedale specifies the Dovedale’s voltage sensitivity as a high 89dB/2.83V/m. My estimate, calculated by comparing the Dovedale’s B-weighted SPL at 50" with that produced by a Rogers LS3/5a, was 89.1dB(B)/2.83V/m. The Dovedale’s impedance is specified as 6.5 ohms, with a minimum value of 3.6 ohms. The impedance magnitude (fig.1, solid trace) varied between 4 ohms and 8 ohms over most of the audioband, with a minimum value of 3.37 ohms at 117Hz. The electrical phase angle (dotted trace) is sometimes high, reaching –39° at 62Hz and +27° at 313Hz. Consequentially, the effective resistance, or EPDR,1 lies below 3 ohms between 65Hz and 362Hz, with minimum values of 1.76 ohms at 81Hz and 2.1 ohms at 228Hz.

The Dovedale is a demanding load for the partnering amplifier.

I investigated the enclosure’s vibrational behavior with a plastic-tape accelerometer and found resonant modes at 207Hz and 832Hz on the top and side panels (fig.2). These modes, however, were very low in level and have a relatively high Q (quality factor), which will work against any audible consequences.

The woofer’s response, measured in the nearfield (fig.3, blue trace), has the 1 EPDR is the resistive load that gives rise to the same peak dissipation in an amplifier’s output devices as the loudspeaker. See “Audio Power Amplifiers for Loudspeaker Loads,” JAES, Vol.42 No.9, September 1994, and stereophile.com/reference/707heavy/ index.html.

expected minimum-motion notch at a low 24Hz, which implies extended low frequencies. The port’s nearfield output (fig.3, red trace) peaks slightly below the tuning frequency and, other than a low-level peak just below 200Hz and others an octave higher, its upper-frequency rollout is clean. I haven’t shown the nearfield output of the midrange unit because it was affected by crosstalk from the adjacent woofer. However, the crossover frequency between these two drivers appeared to be close to the specified 560Hz. The complex sum of the woofer and port responses (fig.3, black trace below 300Hz) has the usual peak in the midbass region due to the nearfield measurement technique, which assumes that the drive units are mounted in a true infinite baffle.

The black trace above 300Hz in fig.3 shows the Dovedale’s quasi-anechoic farfield response, averaged across a 30° horizontal window centered on the tweeter axis and taken with the grille. Other than a small suckout between 1kHz and 2kHz, the response is flat, with then a sharp rolloff above 19kHz. The pair matching between the two samples was excellent, the difference in the farfield response falling within ±0.25dB limits from 1kHz to 5kHz and ±0.5dB limits from 5kHz to 20kHz. Without the grille, the energy in the presence region increased by up to 3dB.

Fig.4 shows the Wharfedale’s horizontal dispersion with the grille in place, normalized to the response on the tweeter axis, which thus appears as a straight line. The off-axis behavior to the side of the baffle closest to the tweeter and midrange unit is shown to the front of this graph. There appears to be more midrange energy off-axis on the other side of the baffle, and there is more presence-region energy on both sides. The relatively wide baffle means that the Dovedale’s output rolls off sharply offaxis above 12kHz. The speaker’s dispersion in the vertical plane, again normalized to the response on the tweeter axis (fig.5), shows that the response is maintained up to 10° above the tweeter axis. A suckout develops in the crossover region 15° below

that axis.

The red trace in fig.6 shows the spatially averaged response 2 of the Wharfedale Dovedales with their grilles in my room. With their ports open, the Wharfedales maximally excite my room’s lowestfrequency mode. Their in-room response is even above 500Hz, with a slight excess of energy between 4kHz and 7kHz. The response in the midrange was a little more uneven than that of my long-term reference KEF LS50s (blue trace), though the latter’s output in the top two audio octaves is suppressed compared with that of the Wharfedales. The gentle slope down above 3kHz in the LS50s’ response is due to the increased absorption of the room’s furnishings as the frequency increases; the Dovedales have a little too much midtreble energy.

In the time domain, the Dovedale’s step response (fig.7) indicates that the tweeter and midrange unit are connected in inverted acoustic polarity, the woofer in positive polarity. The decay of each unit’s step smoothly blends with the start of the next driver’s step, which implies optimal crossover implementation. The Dovedale’s cumulative spectral-decay plot on the tweeter axis (fig.8) features a clean initial decay, though ridges of delayed energy are present in the low treble. (As always, ignore the apparent low-level ridge of delayed energy just below 16kHz, which is due to interference from the MLSSA host PC’s video circuitry.)

The Wharfedale Dovedale offers generally excellent measured performance, especially that flat on-axis response and the extended low frequencies. However, both the demanding impedance and the slight excess of presence-energy in the in-room balance will make amplifier choice critical in getting the best from this speaker. —John Atkinson 2 Using the FuzzMeasure 3.0 program, a Metric Halo MIO2882 FireWire-connected audio interface, and a 96kHz sample rate, I average 20 1/6-octave–smoothed spectra, individually taken for the left and right speakers, in a rectangular grid 36" wide × 18" high and centered on the positions of my ears. Averaging these in-room responses reduces the effect of room standing waves, and I have found this measurement, slightly weighted toward the spectra at the listening seat, to correlate with the perceived balance of loudspeakers in my room.

Stereophile Wharfedale Dovedale Impedance (ohms) & Phase (deg) vs Frequency (Hz) Fig.1 Wharfedale Dovedale, electrical impedance (solid) and phase (dashed) with ports open (2 ohms/ vertical div.).

Fig.2 Wharfedale Dovedale, cumulative spectraldecay plot calculated from output of accelerometer fastened to center of side panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

Fig.4 Wharfedale Dovedale, lateral response family at 50" with grille, normalized to response on tweeter axis, from back to front: differences in response 90°–5° off axis on side opposite drive units, reference response, differences in response 5°–90° off axis on drive unit side.

Fig.3 Wharfedale Dovedale, anechoic response with grille on tweeter axis at 50”, averaged across 30° horizontal window and corrected for microphone response, with the nearfield responses of the woofer (blue), port (red), and their complex sum (black), respectively plotted below 300Hz, 500Hz, and 300Hz.

Fig.5 Wharfedale Dovedale, vertical response family at 50" with grille, normalized to response on tweeter axis, from back to front: differences in response 20°–5° above axis, reference response, differences in response 5°–15° below axis.

Fig.8 Wharfedale Dovedale, cumulative spectraldecay plot on tweeter axis at 50" (0.15ms risetime).

Fig.6 Wharfedale Dovedale, spatially averaged, 1/6-octave response in JA’s listening room (red) and of the KEF LS50 (blue).

Fig.7 Wharfedale Dovedale, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).