Jean-Marie Reynaud Twin Mk.III loudspeaker Measurements

Sidebar 3: Measurements

The Twin Mk.III was of slightly above-average sensitivity, at an estimated 88dB(B)/2.83V/m. The impedance (fig.1) stayed above 6 ohms almost all the time, with a minimum value of 4.5 ohms at 190Hz. The speaker will therefore work well with modestly specified amplifiers. There is a significant glitch in both the magnitude and phase traces around 250Hz and a smaller one at 700Hz, which implies the existence of cabinet resonances of some kind. Investigating the enclosure's vibrational behavior with an accelerometer didn't reveal anything untoward at those frequencies, but a fairly strong mode at 309Hz was present on the side panels (fig.2).

Fig.1 JM Reynaud Twin Mk.III, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

Fig.2 JM Reynaud Twin Mk.III, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet's side panel. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Though the JM Reynaud Twin is specified as using a transmission-line bass alignment, the bass saddle in the fig.1 magnitude trace is no different from a conventional ported design with a highish tuning frequency of 60Hz. To the left of fig.3 are shown the nearfield responses of the woofer (driven by both voice-coils) and the vent at the end of the transmission line. The woofer response shows the usual reflex notch at the port-tuning frequency, where the back pressure from the internal resonance holds the cone stationary. The woofer's output below the notch is in opposite phase to that from the vent, again just as in a reflex design. And again like a reflex design, the output from the Twin's vent peaks approximately in the same region as that of the woofer's notch. However, the port suffers from resonances at the frequencies of the glitches in the impedance traces. These are strong enough to lead to peaks or notches in the farfield response.

Fig.3 JM Reynaud Twin Mk.III, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield responses of woofer and port plotted below 300Hz and 1kHz, respectively.

When a speaker has biwire terminals, I usually plot the individual farfield responses of the tweeter and woofer. However, while the Twin Mk.III's lower pair of terminals drives just the woofer, the upper pair appears to drive the full-range winding of the woofer's two voice-coils as well as the tweeter. What is shown in this graph, therefore, is the response of the woofer low-pass filtered above 1kHz, and the upper-frequency response on the woofer axis, which peaks up significantly in the mid- and high treble. (I chose the woofer axis for the acoustic measurements, because the tweeter is mounted on the bottom of the front baffle and will therefore be below ear height with BJR's 24" stands.)

When the farfield response is averaged across a 30 degrees horizontal angle on the woofer axis (fig.4), the HF plateau becomes a little more subdued due to the tweeter's limited dispersion in its top octave. But the plateau still exists, and perhaps is to be preferred to a more flat treble response, given the Twin's low-frequency behavior: significantly kicked up at 100Hz, even when the effect of the nearfield measurement technique is taken into account. Nevertheless, Bob Reina did find the high treble to be slightly tipped up, even "spitty" at times. By contrast with both the upper bass and the low treble, the midrange is a little depressed in the farfield, even with the speaker driven by both sets of terminals. The smoothness of the midrange is also broken by a peak due to the line resonance noted earlier.

Fig.4 JM Reynaud Twin Mk.III, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the complex sum of woofer and port responses, taking into account acoustic phase and distance from the nominal farfield point plotted below 300Hz.

The Twin's lateral dispersion is commendably uniform, at least up to the region where the tweeter becomes directional (fig.5). The same cannot be said for the vertical dispersion (fig.6), the speaker's balance changing to quite a large extent with listening axis. Surprisingly, given the speaker's inverted driver configuration, the flattest response is to be found on the tweeter axis, though a large notch develops below that axis. The top octave also rolls off severely above the woofer axis, which suggests that either very high stands be used with this speaker, or even that it be used upside-down on regular-height stands.

Fig.5 JM Reynaud Twin Mk.III, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90 degrees-5 degrees off-axis, reference response, differences in response 5 degrees-90 degrees off-axis.

Fig.6 JM Reynaud Twin Mk.III, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45 degrees-5 degrees above axis, reference response, differences in response 5 degrees-45 degrees below axis.

In the time domain, the JM Reynaud Twin's step response indicates that, even on the woofer axis, the tweeter's output leads that of the woofer (fig.7). Both drive-units are connected in the same positive acoustic polarity, but the tail of the step is disturbed by ringing associated with the 700Hz port resonance. The farfield cumulative spectral-decay plot (fig.8) is very clean throughout the upper midrange and treble, though a low-level mode can be seen at 2kHz. The 700Hz resonant peak is also evident.

Fig.7 JM Reynaud Twin Mk.III, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.8 JM Reynaud Twin Mk.III, cumulative spectral-decay plot at 50" (0.15ms risetime).

Some of the JM Reynaud's measured performance is excellent—the even lateral dispersion, the clean waterfall plot, the smoothly balanced midrange and low treble. It will also be an easy amplifier load. However, looking at the lower-frequency behavior, the woofer's twin-coil arrangement doesn't seem to extend the bass to any useful extent. I can only assume that, yet again, a designer has been betrayed by the empty promises of a so-called "transmission line" woofer alignment into producing a version of a reflex design that doesn't go particularly low in frequency yet suffers from resonances in the upper bass and midband.—John Atkinson

Jean-Marie Reynaud
US distributor: Fanfare International
500 E. 77th St., Suite 2923
New York, NY 10162
(212) 734-1041