Swans Speaker Systems Baton Measurements

Sidebar 3: Measurements

Other than impedance, all acoustic measurements were made with the DRA Labs MLSSA system and a calibrated B&K 4006 microphone. To minimize reflections from the test setup, the measuring microphone is flush-mounted inside the end of a long tube. Reflections of the speaker's sound from the mike-stand hardware will be sufficiently delayed not to affect the measurement.

Although the audiophile grapevine has it that the Baton is well-suited for use with low-powered tube amplifiers, its B-weighted sensitivity weighed in at a moderate 85dB/2.83V/m. In addition, its impedance (fig.1) drops below 4 ohms in the lower midrange, coinciding with a moderately demanding phase angle in the same region. The saddle at 46Hz in the magnitude trace coincides with the port tuning and suggests reasonably respectable low-frequency extension.

666Swanfig1.jpg

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

Fig.2 shows the Baton's acoustic crossover on the tweeter axis, this 34" from the floor, with the port and woofer low-frequency outputs measured in the nearfield and the microphone almost touching the woofer cone. As expected, the port's bandpass output is centered on 46Hz, this coincident with the null in the woofer's output. The latter's response is a little exaggerated in the upper bass, however. Higher up in frequency, the woofer/tweeter crossover lies at 2kHz. The woofer's steep rolloff is broken up by a couple of peaks, but these are well down in level. The tweeter's on-axis output is commendably flat in its passband.

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Fig.2 Swans Baton, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield woofer and port responses plotted below 300Hz and 800Hz, respectively.

Averaged across a 30° window on the tweeter axis, the Baton's overall response is shown in fig.3, married to the complex sum of the nearfield low-frequency responses weighted in the ratio of the radiating diameters. The bass rolls off at the expected 24dB/octave below the port resonant frequency—though both port and woofer have just 12dB/octave rolloffs, these are in antiphase and subtract from one another. The –6dB point is a low 38Hz. The midrange and treble are commendably flat, though a slight lack of energy in the low-presence region (1–3kHz) might tie in with the "taming" effect the Baton had on rawly recorded rock. The top octave is also a little shelved-down.

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Fig.3 Swans Baton, sample 2, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz.

For reference, and for the information of those who have older Batons, fig.4 shows a similar graph, measured under identical conditions, for an earlier version of the Swans Baton that was submitted for review (footnote 1). This speaker, serial number A4.112 (compared with A4.160 for the later one), is noticeably less flat, with exaggerated bass and high-treble regions. It did have a slightly higher sensitivity, however, and its waterfall plot was superbly clean.

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Fig.4 Swans Baton, sample 1, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz.

The Baton's horizontal dispersion is shown in fig.5. As well as having a shelved-down top octave, the Baton beams in the same region, its output falling off above 5kHz to the speaker's sides. In all but very lively, undamped rooms, this will add to the lack of air in the speaker's perceived balance.

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Fig.5 Swans Baton, horizontal 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.

Note also that the woofer has difficulty in maintaining its on-axis output at extreme angles to the speaker's sides. Vertically, MK found that he preferred the Baton's balance sitting quite low. The vertical-dispersion family of curves (fig.6) reveals that sitting on or below the tweeter axis does indeed give the optimal tonal balance. Sit so you can see the top of the cabinet, and an immediacy-robbing suckout appears. The room reverberant field, however, will lack energy in this region, subtracting from the Baton's sense of liveliness and perhaps making it sound too polite.

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Fig.6 Swans Baton, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 20°–5° above tweeter axis; reference response; differences in response 5°–10° below tweeter axis.

In the time domain, the step response on the tweeter axis (fig.7) indicates that the two drive-units are connected with the same positive acoustic polarity, but that the speaker is not time-aligned, the spike from the tweeter leading that of the woofer by 0.5ms or so. The cumulative spectral-decay, or waterfall, plot (fig.8), however, is commendably clean.—John Atkinson

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

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



Footnote 1: Dick Olsher, now with Fi magazine, originally worked on a review of this sample of the Baton, but as Swans is now marketing a loudspeaker for which Dick did the preliminary design work, that review was aborted and a new review with new samples commissioned from MK.—John Atkinson
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Swans Speaker Systems
11630 Goldring Road
Arcadia, CA 91006
(626) 930-060
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