Snell Acoustics LCR7 XL loudspeaker Measurements

Sidebar 4: Measurements

The Snell LCR7 XL was of average voltage sensitivity, at an estimated 88dB(B)/2.83V/m. Its electrical impedance drops below 4 ohms for most of the midrange, with a minimum value of 2.25 ohms at 244Hz and a combination of –45° phase angle and 5.5 ohms magnitude at 100Hz (fig.1), meaning that a good, 4-ohm–rated amplifier will be optimal for driving this speaker.

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Fig.1 Snell LCR7 XL, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The impedance traces are free from the discontinuities associated with cabinet vibrational resonances. The only mode I could find on the small, rigidly braced enclosure was on its side, at a relatively high frequency of 504Hz (fig.2). This is both low in level and decays very quickly, meaning that the cabinet behavior will not negatively affect sound quality. Listening to the cabinet walls with a stethoscope while I played the half-step–spaced toneburst track on Stereophile's Editor's Choice (CD, Stereophile STPH016-2), I could hear this liveliness toward the top of the octave above middle C, but the cabinet is otherwise usefully inert.

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Fig.2 Snell LCR7 XL, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet's side panel level with the tweeter (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The single impedance peak at 70Hz both confirms the sealed-box woofer alignment and suggests that the LCR7 XL has only limited bass extension. This was revealed by a nearfield measurement of the woofer's output (fig.3). The LF response is down 6dB at 50Hz, a little lower than the tuning frequency because of the exaggerating effect of the nearfield measurement technique. The rolloff, however, is a gentle 12dB/octave, which will allow the speaker to produce more midbass in-room than might be expected from its limited measured bass extension.

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Fig.3 Snell LCR7 XL, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the farfield responses of the woofers (blue) and tweeter (red), and the nearfield response of the woofers (black).

Higher in frequency in fig.3, the woofers (blue trace) cross over to the tweeter (red) at approximately 2kHz as specified, with high-order filter slopes, and their rollout is free from any narrow peaks that would imply the existence of undamped breakup modes in the magnesium cones. The overall farfield response, averaged across a 30° horizontal window centered on the tweeter axis (the LCR7 XL was set up vertically), is superbly flat. A small peak does develop in the top octave due to the metal-mesh grille, which was in place for the measurements. This will not be audible to old guys like me whose hearing cuts off above 15kHz, but can be eliminated by removing the grille.

The Snell's lateral dispersion is wide and even (fig.4), with the small suckouts at 4kHz and 8kHz in the tweeter-axis response filling in to the speaker's sides. The LCR7 does get quite directional above 10kHz, however. In the vertical plane (fig.5), the use of twin spaced woofers reduces the off-axis energy between 1 and 3kHz at extreme off-axis angles, but the Snell's neutral low-treble balance is maintained over a ±15° window, which will be useful if the LCR7 is used on its side as a center-channel speaker. In-room, the LCR7 XL's spatially averaged response—assessed by averaging 120 1/3-octave spectra taken for the left and right speakers individually in a grid centered on the position of my ears in the listening seat—was impressively flat between 100Hz and 20kHz, but with a slight excess of mid-treble energy apparent (fig.6). The Snells also have little bass response in-room, but the smooth rolloff will help with successfully integrating them with a subwoofer, if required.

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Fig.4 Snell LCR7 XL, lateral 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.

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Fig.5 Snell LCR7 XL, 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.

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Fig.6 Snell LCR7 XL, spatially averaged, 1/3-octave response in JA's listening room.

In the time domain, the LCR7's farfield step response on the tweeter axis (fig.7) indicates that all three drive-units are connected with positive acoustic polarity, with the tweeter's output slightly leading that of the woofers. The smooth handover from the tweeter step to that of the woofers is broken by a small spike, presumably due to the reflection of the tweeter's output from the grille and associated with the small peak at 15kHz in the frequency response. Some small ripples can be seen in the delay of the woofers' step; the Snell's cumulative spectral-decay plot (fig.8) indicates the presence of a small amount of delayed energy in the presence region, but the graph is otherwise very clean.

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Fig.7 Snell LCR7 XL, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

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Fig.8 Snell LCR7 XL, cumulative spectral-decay plot at 50" (0.15ms risetime).

As might be expected from a Joe D'Appolito design, the Snell LCR7 XL offers superb measured performance.—John Atkinson

COMPANY INFO
Snell Acoustics
300 Jubilee Drive, PO Box 3717
Peabody, MA 01961-3717
(978) 538-6262
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