Sidebar 3: Measurements
I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone with an Earthworks microphone preamplifier to measure the Magico S5 2024's farfield frequency behavior and dispersion. I used an Earthworks QTC-40 mike for the nearfield and in-room responses and Dayton Audio's DATS V2 system to measure the impedance magnitude and electrical phase angle. I measured one of the S5 2024s in my listening room, but the loudspeaker was too heavy for me to lift off the floor. To avoid having to aggressively window the MLSSA time-domain data, which would reduce the measured response's midrange resolution, I took a full set of farfield measurements with the microphone 1m away. To make sure I wasn't introducing errors, I then repeated some of the measurements with the microphone at my usual 50". However, the geometry of my room meant that it wasn't possible to measure the off-axis response more than 60° to each side of the tweeter axis.
The peak at 27Hz in the impedance magnitude trace in fig.1 suggests that this is the tuning frequency of the woofers' sealed-box loading. The red trace in fig.3 shows the summed nearfield response of the two woofers, which behaved identically. The 3dB rise in the midbass region will be due to the nearfield measurement technique, which assumes that the drive units are mounted in a true infinite baffle (footnote 2). As expected, the woofers' output is down by 6dB at the tuning frequency, but with the usual "room gain" at low frequencies resulting from boundary reinforcement, the S5 2024 should give 20Hz extension in all but very large rooms. The woofers' output rolls off rapidly above 200Hz.
As I expected from my prior experience of Magico loudspeakers, the Magico S5 2024 offers superb measured performance.—John Atkinson
Footnote 1: EPDR is the resistive load that gives rise to the same peak dissipation in an amplifier's output devices as the loudspeaker. See "Audio Power Amplifiers for Loudspeaker Loads," JAES, Vol.42 No.9, September 1994, and stereophile.com/reference/707heavy/index.html. Footnote 2: This means that the loudspeaker is firing into hemispherical space rather than a full sphere. A speaker that has a truly flat response in the usual "4pi" space will therefore appear to have a boosted upper-bass output with a nearfield measurement, the center frequency of that boost depending on the physical dimensions of the speaker and the woofer alignment. See stereophile.com/content/measuring-loudspeakers-part-three-page-6 or aes2.org/publications/elibrary-page/?id=7171.
Footnote 3: Using the FuzzMeasure 3.0 program, a Metric Halo MIO2882 FireWire-connected audio interface, and a 96kHz sample rate, I average 20 1/6-octave–smoothed spectra, individually taken for the left and right speakers, in a rectangular grid 36" wide by 18" high and centered on the positions of my ears.
Fig.1 Magico S5 2024, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Magico specifies the S5 2024's sensitivity as 88dB, with no voltage or power mentioned. My B-weighted estimate was slightly lower, at 86.5dB(B)/2.83V/1m. The S5 2024's impedance is specified as 4 ohms. My measurement (fig.1, solid trace) dropped below 4 ohms between 40Hz and 650Hz and above 10kHz. The minimum values were 2.8 ohms at 59Hz and 2.69 ohms between 270Hz and 285Hz. As the electrical phase angle (dashed trace) is occasionally high, the effective resistance, or EPDR (footnote 1), drops below 3 ohms for several regions between 31Hz and 1253Hz and below 2 ohms between 32Hz and 76Hz, between 322Hz and 724Hz, and between 6.9kHz and 20kHz. The minimum EPDR values are 1.03 ohms at 42Hz, 1.81 ohms at 406Hz, and 1.05 ohms at 20.6kHz. As music has high levels at the two lower frequencies, the S5 2024 demands a lot of current from the partnering amplifier.
Magico S5 2024, cumulative spectral decay plot calculated from the output of an accelerometer fastened to the center of a sidewall level with the lower woofer (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.).
When I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer, I didn't find any resonant modes at all (fig.2). The enclosure's surfaces were all completely inert, as predicted by Magico's Alon Wolf.
Fig.3 Magico S5 2024, anechoic response on tweeter axis at 1m, averaged across 30° horizontal window and corrected for microphone response, with the nearfield responses of the woofers (red), midrange unit (blue), and their complex sum (black), respectively plotted below 390Hz, 500Hz, and 310Hz.
The blue trace in fig.3 shows the nearfield response of the midrange unit, with its level plotted in the ratio of the square root of its radiating area to that of the woofers. (The bump between 50Hz and 60Hz in the midrange unit's high-pass rolloff in this graph is due to crosstalk from the woofers. As there is only a single pair of binding posts, it wasn't possible to measure the midrange unit's and woofers' nearfield responses in isolation from each other.) The crossover between the midrange and low-frequency drive units lies close to 200Hz.
The black trace above 310Hz in fig.3 shows the S5 2024's quasi-anechoic farfield response, averaged across a 30° horizontal window centered on the tweeter axis. The response is impressively smooth and even, with a small excess of energy between 9kHz and 11kHz. There is a very slight lack of energy above 13kHz before the response starts to rise, peaking at 35kHz (not shown in this graph), which will be due to the tweeter's fundamental dome resonance. The pair matching between the two samples was superb, meeting ±0.5dB limits between 500Hz and 20kHz.
Fig.4 Magico S5 2024, lateral response family at 1m, normalized to response on tweeter axis, from back to front: differences in response 60–5° off axis, reference response, differences in response 5–60° off axis.
Fig.5 Magico S5 2024, vertical response family at 1m, normalized to response on tweeter axis, from back to front: differences in response 20–5° above axis, reference response, differences in response 5–15° below axis.
Fig.4 shows the S5 2024's horizontal dispersion, normalized to the response on the tweeter axis, which thus appears as a straight line. The radiation pattern is impressively even, which correlates with accurate and stable stereo imaging. The dispersion narrows in the top two octaves, which will be due to the tweeter being mounted in a fairly wide baffle. The Magico speaker's radiation pattern in the vertical plane, again normalized to the response on the tweeter axis, which is 40" from the floor with the speaker supported on its feet, is shown in fig.5. A sharply defined suckout develops more than 5° above the tweeter axis, indicating that this is the crossover frequency between the midrange unit and tweeter. Don't listen seriously to the S5 2024 while standing. However, the loudspeaker's response doesn't change appreciably 5° below the tweeter axis, which will be appropriate for seated listeners.
Fig.6 Magico S5 2024, spatially averaged, 1/6-octave response in JA's listening room (red) and of the Magico S5 Mk.II (blue).
The red trace in fig.6 shows the Magico S5 2024s' spatially averaged response in my listening room (footnote 3). The spatial averaging hasn't completely eliminated the small peaks and dips between 50Hz and 500Hz, but the in-room response is generally even above that region. The slight downward slope in the treble is due both to the increased absorption of the room's furnishings and the speaker's restricted dispersion as the frequency increases. The blue trace in fig.6 is the spatially averaged response of the Magico S5 Mk.II, which I reviewed in 2017. Other than the earlier speaker's slight presence-region boost, the upper-frequency in-room responses of the two speakers are similar.
Fig.7 Magico S5 2024, step response on tweeter axis at 1m (5ms time window, 30kHz bandwidth).
Fig.8 Magico S5 2024, cumulative spectral-decay plot on tweeter axis at 1m (0.15ms risetime).
Turning to the time domain, the S5 2024's step response (fig.7) indicates that all four drive units are connected in positive acoustic polarity. The tweeter's output arrives first at the microphone, followed first by that of the midrange unit, then by that of the woofers. The decay of each drive unit's step smoothly blends with the start of the step of the next one lower in frequency, implying optimal crossover implementation. Ignore the discontinuity at 6.4ms in the step response, which is due to the first reflection of the woofers' output from the floor. However, the presence of this reflection meant that I had to aggressively window the time-domain data when I calculated the cumulative spectral decay (waterfall) plot (fig.8). The S5 2024's waterfall is very clean overall, though some low-level delayed energy is evident at the top of the midrange unit's passband. (As always with my cumulative spectral decay plots, ignore the ridge of delayed energy close to 16kHz, which is due to interference from the MLSSA host PC's video circuitry.)
Footnote 1: EPDR is the resistive load that gives rise to the same peak dissipation in an amplifier's output devices as the loudspeaker. See "Audio Power Amplifiers for Loudspeaker Loads," JAES, Vol.42 No.9, September 1994, and stereophile.com/reference/707heavy/index.html. Footnote 2: This means that the loudspeaker is firing into hemispherical space rather than a full sphere. A speaker that has a truly flat response in the usual "4pi" space will therefore appear to have a boosted upper-bass output with a nearfield measurement, the center frequency of that boost depending on the physical dimensions of the speaker and the woofer alignment. See stereophile.com/content/measuring-loudspeakers-part-three-page-6 or aes2.org/publications/elibrary-page/?id=7171.
