Sidebar 4: Measurements
I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone with an Earthworks microphone preamplifier to measure the Wharfedale Super Linton's farfield frequency behavior and dispersion. I used an Earthworks QTC-40 mike for the nearfield responses. I usually leave a loudspeaker's grille off for the measurements. However, as the Super Linton's front baffle is set into the enclosure and the grille frame provides some acoustic profiling around the drive units, as I had done with the Wharfedale Heritage Series Dovedale that I reviewed in April 2024, I left the grille in place for most of the farfield measurements.
Footnote 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. Footnote 2: This means that the loudspeaker is firing into hemispherical space rather than a full sphere. A speaker that has a truly flat response in the usual "4pi" space will therefore appear to have a boosted upper-bass output with a nearfield measurement, the center frequency of that boost depending on the physical dimensions of the speaker and the woofer alignment. See stereophile.com/content/measuring-loudspeakers-part-three-page-6 or aes2.org/publications/elibrary-page/?id=7171. The nearfield measurement and a truly anechoic measurement are what is called "limiting cases." The speaker's in-room low-frequency behavior will be somewhere between these extremes, depending on the size of the room.
Fig.1 Wharfedale Super Linton, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Wharfedale specifies the Super Linton's sensitivity as 90dB/2.83V/1m; my B-weighted estimate was within experimental error of the specification, at 89.5dB(B)/2.83V/m. The Super Linton's impedance is specified as 6 ohms, with a minimum value of 3.9 ohms. I used Dayton Audio's DATS V2 system to measure the impedance magnitude and electrical phase angle. My measurement (fig.1, solid trace) indicated that the amplitude remained between 4 ohms and 8 ohms for most of the audioband, with a minimum value of 2.87 ohms at 137Hz. The electrical phase angle (dashed trace) is often high; the effective resistance, or EPDR (footnote 1), therefore drops below 3 ohms for much of the audioband, with minimum EPDR values of 1.26 ohms at 101Hz and 2.34 ohms at 6kHz. The Super Linton is a demanding load for the partnering amplifier.
Fig.2 Wharfedale Super Linton, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of sidewall. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).
The impedance traces are free from the small discontinuities that would imply the presence of panel resonances. When I investigated the Wharfedale enclosure's vibrational behavior with a plastic-tape accelerometer, I found several resonant modes on all the loudspeaker's panels (fig.2). However, as these modes are low in level and have a high Q (Quality Factor), it is unlikely they will have audible consequences.
Fig.3 Wharfedale Super Linton, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with grille (black) and without grille (red), with the nearfield responses of the midrange unit (green), woofer (blue), and ports (red), respectively plotted below 500Hz, 600Hz, and 300Hz.
The saddle centered at 36Hz in the impedance magnitude trace in fig.1 suggests that this is the tuning frequency of the woofer's reflex loading. The blue trace in fig.3 shows the nearfield response of the woofer; there is the expected notch at the reflex tuning frequency, which is when the back pressure from the port resonance holds the driver's cone still. The nearfield response of the two ports on the rear panel (red trace) peaks at the tuning frequency, and while the upper-frequency rolloff is rapid, there is a small peak centered on 190Hz in their output. The rise in the woofer's upper-bass output will be due to the nearfield measurement technique, which assumes that the drive units are mounted in a true infinite baffle (footnote 2).
The green trace in fig.3 shows the nearfield response of the midrange unit. The crossover from the woofer appears to be set to 300Hz with a broad overlap between the two drive units, but I suspect that this measurement is affected by crosstalk from the adjacent woofer. (As the Super Linton has a single pair of binding posts, it wasn't possible to measure each drive unit's nearfield output individually.)
The black trace in fig.3 shows the Super Linton's quasi-anechoic farfield response, averaged across a 30° horizontal window centered on the tweeter axis, and taken with the grille; the red trace repeats this response measurement without the grille. This is identical to the response with the grille below 1.5kHz, but the slight boost in the mid-treble region is greater without the grille in place.
Fig.4 Wharfedale Super Linton with grille, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis on the tweeter side of baffle, reference response, differences in response 5–90° off axis on the opposite side of baffle.
Fig.5 Wharfedale Super Linton with grille, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45–5° above axis, reference response, differences in response 5–45° below axis.
Fig.4 shows the Super Linton's horizontal dispersion taken with the grille, normalized to the response on the tweeter axis, which thus appears as a straight line. There is a slight lack of energy at the top of the midrange unit's passband at extreme off-axis angles, and the tweeter's output in the top octave rolls off rapidly to the speaker's sides. The latter will be due to the relatively wide baffle. The Wharfedale speaker's radiation pattern in the vertical plane, again normalized to the response on the tweeter axis, is shown in fig.5. A sharply defined suckout at 2.66kHz develops more than 10° above and 15° below the tweeter axis, which suggests that this is the crossover frequency between the midrange unit and the tweeter.
Fig.6 Wharfedale Super Linton, step response without grille on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.7 Wharfedale Super Linton, cumulative spectral-decay plot with grille on tweeter axis at 50" (0.15ms risetime).
In the time domain, the Super Linton's step response on the tweeter axis (fig.6) reveals that the tweeter and midrange unit are connected in negative acoustic polarity, the woofer in positive polarity. The tweeter's output arrives first at the microphone, followed by that of the midrange unit, then by that of the woofer. The decay of each unit's step smoothly blends with the start of the next lower in frequency's step, which suggests an optimal crossover topology. The Wharfedale's cumulative spectral-decay, or waterfall, plot on the tweeter axis is shown in fig.7. It is generally clean, though there is a small ridge of delayed energy at the top of the midrange unit's passband. (As always with my cumulative spectral-decay plots, ignore the ridge of delayed energy close to 16kHz, which is due to interference from the MLSSA host PC's video circuitry.)
The Wharfedale Super Linton's measured performance is similar to that of the Linton Heritage, which Herb Reichert reviewed in September 2019. The farfield response and dispersion measurements suggest that the Wharfedale's tonal balance could be optimized by experimenting with toe-in.—John Atkinson
Footnote 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. Footnote 2: This means that the loudspeaker is firing into hemispherical space rather than a full sphere. A speaker that has a truly flat response in the usual "4pi" space will therefore appear to have a boosted upper-bass output with a nearfield measurement, the center frequency of that boost depending on the physical dimensions of the speaker and the woofer alignment. See stereophile.com/content/measuring-loudspeakers-part-three-page-6 or aes2.org/publications/elibrary-page/?id=7171. The nearfield measurement and a truly anechoic measurement are what is called "limiting cases." The speaker's in-room low-frequency behavior will be somewhere between these extremes, depending on the size of the room.
