DALI Zensor 1 loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the DALI Zensor 1's frequency response in the farfield; and an Earthworks QTC-40, with its small, ¼" capsule, for the nearfield responses. (The small capsule doesn't interfere with the airflow.)

My estimate of the Zensor 1's voltage sensitivity was 88dB(B)/2.83V/m, which is both surprisingly high for such a small speaker and 1.5dB higher than specified. The plot of the DALI's impedance magnitude and electrical phase (fig.1) suggests that the speaker is relatively easy to drive. The minimum impedance is 5 ohms, and though the phase angle is quite large around 100Hz, the impedance magnitude is also high, mitigating the adverse effect of the phase angle.

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

There are small wrinkles in the impedance traces at just under 400Hz and between 500 and 600Hz, suggesting the presence of enclosure resonances. However, when I examined the cabinet's vibrational behavior with a plastic-tape accelerometer, I found resonances of relatively high Quality Factor (Q) at 266, 441, and 1400Hz (fig.2). This graph was taken with the accelerometer on the DALI's top panel; the 441Hz mode was also present on the side panels (not shown). These resonances are sufficiently high in frequency and low enough in level that, given their high Q, they should have no subjective consequences.

Fig.2 DALI Zensor 1, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of top panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The saddles centered on 55Hz in the impedance-magnitude trace suggest that this is the tuning frequency of the small reflex port on the Zensor 1's rear panel. Confirming this, the woofer's nearfield response (fig.3, blue trace) had a deep notch at the same frequency, this due to the back pressure from the port resonance holding the cone stationary. The output of the port itself (fig.3, red trace) peaks between 40 and 100Hz, and its upper-frequency rolloff is smooth, unmarred by resonant peaks. The complex sum of the nearfield responses (fig.3, black trace below 300Hz) peaks by 4dB, but this will be almost entirely an artifact of the nearfield measurement technique. The Zensor 1 appears to be flat down to the upper bass, with then the usual 24dB/octave reflex rolloff giving a response down by 6dB at the port tuning frequency of 55Hz. This is approximately the frequency of the note A, the third string of the four-string double bass and electric bass guitar.

Fig.3 DALI Zensor 1, anechoic response on HF axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield responses of woofer (blue trace), port (red), and their complex sum (black), plotted below 350, 700, and 300Hz, respectively.

Higher in frequency in fig.3, the DALI speaker's balance, measured with its grille removed, tilts up toward the treble, which is probably why my estimate of the speaker's sensitivity was higher than specified. With the well-damped bass alignment, the Zensor 1's response reminds me of the classic ProAc Tablette minimonitor from the mid-1980s. However, the perceived balance will also depend on the speaker's radiation pattern.

Fig.4 shows the DALI's lateral dispersion. The speaker's output to its side is wide and even below 8kHz, but the Zensor 1 quickly becomes quite directional above that frequency, which, in small rooms, will compensate for the exaggerated top-octave response on the tweeter axis. In the vertical plane (fig.5), deep suckouts centered on the crossover frequency of 3.5kHz develop more than 5° above or below the tweeter axis. Stands of the optimal height, at least 24", should be used with these speakers.

Fig.4 DALI Zensor 1, lateral response family at 50", normalized to response on HF axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

Fig.5 DALI Zensor 1, vertical response family at 50", normalized to response on HF axis, from back to front: differences in response 45–5° above axis, reference response, differences in response 5–45° below axis.

In the time domain, the Zensor's step response on the tweeter axis (fig.6) indicates that both drive-units are connected with positive acoustic polarity. The decay of the tweeter's step smoothly bends with the rise of the woofer's step, which suggests optimal crossover design. The cumulative spectral-decay plot (fig.7) is remarkably clean for such an inexpensive speaker. The single resonant mode present, at 1465Hz, is well suppressed.

Fig.6 DALI Zensor 1, step response on HF axis at 50" (5ms time window, 30kHz bandwidth).

Fig.7 DALI Zensor 1, cumulative spectral-decay plot on HF axis at 50" (0.15ms risetime).

This is impressive measured performance for a budget loudspeaker.—John Atkinson

Company Info
DALI A/S
US distributor: The Sound Organisation
159 Leslie Street
Dallas, TX 75207
(972) 234-0182
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mkrzych's picture
Off Axis response

Hello,

Does it mean based on the measurements that Zensor 1's should be slightly toed in to get the best frequency response? If so, how much?

John Atkinson's picture
Re: Off Axis response

mkrzych wrote:
Does it mean based on the measurements that Zensor 1's should be slightly toed in to get the best frequency response?

Yes.

mkrzych wrote:
If so, how much?

That will depend on the size of your room, that room's acoustics, and what music you prefer to play. Experiment with toe-in and use the amount of toe-in that gives the best balance of frequency response and stability of stereo imaging. There are no wrong answers. John Atkinson
Editor, Stereophile

mkrzych's picture
Thank you very much. Do you

Thank you very much. Do you have similar measurements for Zensor 7 as well? Do you think that will be much step up from 1's?

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