Epos M5i loudspeaker Measurements
Robert J. Reina comments on the sound of the two-way, port-loaded Epos M5i ($899/pair), and compares it with its predecessor, the M5, which he favorably reviewed in April 2005. Although the M5i looks very similar to the M5, its drive-units are new and derived from those used in the floorstanding M16i. Given Bob's enthusiastic response to the new version's sound, I thought it worthwhile to examine the measured performance of the review samples (serial nos. M5i-0109-1144a and 'b). I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Eposes' frequency response in the farfield, and an Earthworks QTC-40 for the nearfield responses.
Epos specifies the M5i as having a sensitivity of 87dB/2.83/m. My estimate was within experimental error of this figure, at 87.1dB(B)/2.83V/m, which is very slightly lower than the 88dB I estimated for the earlier version. The M5i's plot of impedance and phase (fig.1) is very similar in broad outline to that of the earlier speaker, though the twin peaks in the bass are higher in magnitude. Although Epos specifies the M5i as having a 4 ohm nominal impedance, the value remains above 5 ohms at all frequencies, making the speaker relatively easy to drive.
Fig.1 Epos M5i, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)
The individual responses of the tweeter (green trace), woofer (blue), and port (red) are shown in fig.2. The notch at 57Hz in the woofer's output confirms that this is the tuning frequency of the rear-facing porta little higher than that of the M5and the upper-frequency crossover is set at 3750Hz, almost an octave higher than the 2kHz of so many two-way designs. The woofer has a slight excess of energy in its output at the top of the midrange, but rolls off smoothly above the crossover point.
Fig.2 Epos M5i, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield responses of woofer (blue) and port (red) plotted below 300Hz and 1kHz, respectively.
Bob found that the M5i sounded more transparent with its grille off. I measured the speaker's farfield responses with the grille on and off, averaged across a 30° horizontal window centered on the tweeter axis. You can see from fig.3 that the primary effect of the grille (red trace) is to suppress the top octave very slightly, but it also reduces the energy between 3.5 and 5kHz by up to 3dB compared to the response without the grille (blue). The shape of the new speaker's response sans grille in fig.3 is almost identical to that of the original M5 (green trace, offset by 3dB for clarity). Both models have a slightly excessive output at the top of the midrange and a depression in the presence region. As I mentioned in the earlier review's measurements section, this on-axis depression tends to counteract the effect of an off-axis response flare in the same region; the M5i's high frequencies will tend to sound relatively neutral in all but very large or overdamped rooms. At the other end of the spectrum, the new version's low-frequency tuning is a little less damped than that of the M5, trading off absolute extension for a slightly richer balance.
Fig.3 Epos M5i, anechoic response on tweeter axis at 50" with (red trace) and without (blue) grille, averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz. Green trace shows the response of the M5 without grille, offset by 3dB.
The Epos's step response (fig.4) indicates that its two drive-units are connected in the same, positive acoustic polarity. As with the M5, a slight ripple in the tail of the M5i woofer's step is associated with some delayed energy between 1 and 2kHz in the cumulative spectral-decay plot (fig.5), though the decay of the high frequencies in this graph is commendably clean.
Fig.4 Epos M5i, step response on HF axis at 50" (5ms time window).
Fig.5 Epos M5i, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).
Overall, nothing in its measured performance indicates why the M5i sounds appreciably better than the original M5. But it does appear to be a well-balanced design at its price.John Atkinson