Audes Jazz loudspeaker Measurements

Sidebar 3: Measurements

The Audes Jazz is significantly more sensitive than average, at an estimated 90.6dB(B)/0.83V/m, this made even more beneficial by an impedance curve that remains above 6 ohms for much of the audioband (fig.1) and drops to a minimum value of 4.2 ohms at 190Hz. The saddle at 42Hz in this graph's magnitude trace indicates the tuning frequency of the speaker's twin ports, which in turn implies moderate low-frequency extension (42Hz is the frequency of the E string on a four-string electric bass guitar or double bass).

Fig.1 Audes Jazz, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

There are two significant discontinuities in the impedance traces, one at 150Hz and one at 550Hz, which imply the existence of serious cabinet resonances. Investigating the behavior of the enclosure walls with a plastic-tape accelerometer did reveal some strong resonances, but the strongest was at 320Hz (fig.2). This mode was present on all panels and, all things being equal, might be expected to obscure midrange clarity.

Fig.2 Audes Jazz, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the center of the cabinet's wooden side-panel cheek. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Fig.3 shows the individual farfield responses of the tweeter and twin woofers, the latter spliced to the summed nearfield woofer response below 350Hz and overlaid with the summed nearfield response of the ports, these scaled in the ratio of the square root of the radiating areas. (The individual woofer and port outputs did not significantly differ from one another.) As implied by the impedance plot, the output of the ports peaks at 42Hz, the minimum-motion point of the woofers, but rolls off steeply above 150Hz. There is a step in the nearfield response of the woofers at the same frequency, which is also the frequency of a major discontinuity in the fig.1 impedance traces. I didn't find a panel resonance at 150Hz, but the cabinet obviously has an acoustic resonant mode.

Fig.3 Audes Jazz, acoustic crossover on tweeter axis at 50", corrected for microphone response, with the summed woofer nearfield response and summed nearfield port response plotted below 350Hz and 1kHz, respectively.

Higher in frequency, the woofers start to roll off smoothly above 1kHz, the slope steepening above the nominal 2kHz crossover point. The tweeter is flat on-axis within its passband. Fig.4 shows the overall response of the Jazz, averaged across a 30 degrees horizontal angle on the tweeter axis and spliced to the complex sum of the nearfield responses. It is extremely flat, suggesting that the problems Kal Rubinson occasionally noted in his auditioning did not stem from the speaker's frequency balance.

Fig.4 Audes Jazz, anechoic response on tweeter axis at 50", averaged across a 30 degrees horizontal window and corrected for the microphone response, with the complex sum of the nearfield woofer and port responses plotted below 300Hz.

KR did note the Jazz's moderate low-frequency extension, and the speaker does roll off rapidly below the 42Hz tuning frequency of the twin ports. To my surprise, the actual rolloff is closer to 36dB/octave than the 24dB/octave typical of a reflex alignment. (When calculating the complex sum of the nearfield responses, I did take into account the time delay introduced by the ports being positioned on the speaker's back panel.) There is also less of the usual "nearfield hump" apparent in the upper bass in fig.4, which suggests a reflex alignment that has been optimized for dynamic range rather than bass extension.

KR had some difficulty in getting the Jazzes to provide soundstage center-fill, particularly when the tweeters were on the inside edges of the speakers. This suggests some serious asymmetry in the Jazz's lateral dispersion. Yet, as can be seen from fig.5, any such asymmetry is mild. (The off-axis behavior on the tweeter side of the front baffle is toward the front of this graph.) However, the usual flare at the bottom of the tweeter passband is apparent in fig.5, and it is slightly more pronounced on the woofer side of the baffle. As KR found that the speakers imaged best with the woofers on their inside edges, perhaps this flare otherwise results in treble-excessive wall reflections that disturb the imaging stability and precision. However, I suspect the lively cabinet is mainly behind this behavior, as musical information that lies at the same frequency will tend to "splash" to the speaker positions.

Fig.5 Audes Jazz, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90 degrees-5 degrees off-axis on woofer side of baffle, reference response, differences in response 5 degrees-90 degrees off-axis on tweeter side of baffle.

In the vertical plane (fig.6), the Jazz tends to maintain its even frequency balance for 5 degrees above and below the 33"-high tweeter axis. However, a large suckout at the crossover frequency becomes evident for listener ear heights level with or above the top of the enclosure.

Fig.6 Audes Jazz, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15 degrees-5 degrees above axis, reference response, differences in response 5 degrees-15 degrees below axis.

Looking at the Audes speaker's time-domain behavior, the tweeter's step response (fig.7, red trace) hands over smoothly to the woofers' (blue). However, some strong reflections of the tweeter's output can be seen in the first millisecond after its arrival at the microphone, these probably coming from the edges of the baffle. (Ignore the reflection at the 7ms mark, which is from the stand supporting the Outline speaker turntable I use to take these measurements; it was windowed out when the DRA Lab MLSSA program was used to calculate the frequency-domain behavior.)

Fig.7 Audes Jazz, step response on tweeter axis at 50" with individual tweeter (red) and woofer (blue) step responses (5ms time window, 30kHz bandwidth).

KR noted that some treble piano notes were thrown forward in the soundstage, yet the Jazz's cumulative spectral-decay plot (fig.8) is superbly clean throughout the treble. I suspect, therefore, that this coloration stems from the cabinet's resonant problems. The top panel, for example, has a serious resonant mode apparent at 1kHz, which is in just the right region to affect the sound of the piano.

Fig.8 Audes Jazz, cumulative spectral-decay plot at 50" (0.15ms risetime).

All in all, the Audes Jazz offers good performance in the traditional areas of speaker performance, and is both sensitive and an easy amplifier load. However, its lively cabinet works against that achievement.—John Atkinson

US distributor: Audes USA
58 Winding Brook Drive
Matawan, NJ 07747
(732) 921-1241
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