S1 quasi-anechoic measurements (above about 500Hz) reveal a loudspeaker with very smooth frequency response in the mid and high frequency range, with sensitivity deviation not exceeding, in any case, the ±3dB interval. The more "lively" part of the response appears between 1kHz and 5kHz while in the region above 5kHz deviation is minimized towards ±1dB, up to 20kHz, the best performance we have encountered for some years now. Additionally, the loudspeaker seems to have some significant energy to offer well above 30kHz.
Summed frequency response, obtained by the splicing near field/far field (on axis) measurements does not significantly alter our first impression. S1 remains in the ±3dB interval throughout its useful range and exhibits a very smooth behavior towards the lower part of the spectrum. This is determined both by the expected slope of 12dB/oct below the system's resonance frequency and by a very reasonable accentuation centered at approximately 70Hz at about 2.5dB compared to its average sensitivity. The latter was estimated at 80dBSPL/2.83Vrms/1m, a rather low value that is -however- somewhat justified both by the closed-box cabinet and the mid/woofer size. Based on the average sensitivity, the cutoff frequency points are 43Hz/25kHz and 37Hz/35kHz for -3dB and -6dB attenuation respectively. Average response (estimated using a series of measurements both on and off-axis in the horizontal/vertical plane) shows a significant attenuation for signals with frequency above 2kHz, an outcome that -probably- reflects some sensitivity to the listening position.

S1 appears to be a load with reasonable behavior, without being particularly easy. Minimum impedance magnitude at low frequencies is 4.3 Ohms and drops at about 3.3 Ohms at 15kHz, a part of the spectrum where the power demand is rather small, so the amplifier is not stressed. Magnitude variation, about 23 Ohm, appears to be typical, but puts some limits on the use of amplifiers with a small damping factor (i.e., high output impedance) whose response might slightly be affected. The relevant graph shows two peaks at 56Hz and 2.4kHz for which we couldn't find a satisfactory explanation. Most probably they are not due to standing waves inside the cabinet, but just filter artifacts. Impedance phase variation appears to be quite high reaching +43° (inductive) close to 500Hz and -52° (capacitive) to about 3kHz. These findings lead to the conclusion that to drive the S1, an amplifier with ample current reserves, high enough dynamic headroom and a good heatsink is required. Obviously, all these are reasonable requirements for a loudspeaker in this price and quality level.
Step response is very smooth, with good transition between the two drivers and extremely smooth damping in woofer (with the exception of a single "second" energy arrival).

Cumulative spectral decay diagram shows a loudspeaker with low indication of coloration at the mid band, where one can discern a resonance around 1.6kHz (with a 2.2mS decay time for -25dBr). This resonance appears to be the most powerful in the range between 500Hz and 20kHz as at high frequencies S1 proved extremely fast and well behaved. One could isolate two more resonances, at 11.1kHz and 15.4kHz, but they both appear to have quite a short decay time, at 0.9mS and 0.7mS respectively, making the S1 one of the best loudspeakers we measured lately, at least in this respect.
Directivity in the horizontal plane shows a very smooth behavior. S1 response remains within the -6dB limit for a ±30° listening angle, even at 16kHz (towards the 20kHz measurement limit, a higher response drop rate and some beaming effects are evident). This, for starters, means that there is no need for toe-in if someone is willing to make small concessions in response at very high frequencies. More importantly, it is a good indication that a well balanced reverberation field is produced (given a room with decent acoustics). On the other hand, given the significant drop in high frequencies which becomes evident in the average (listening window) response, one can assume that there is some serious dependency on the listening position height. This is a detail in which due consideration must be given during the initial loudspeaker setup.

Finally, the cabinet resonance diagram is quite interesting given both the material used and its way of construction. The two graphs show a considerable uniformity in terms of cabinet-induced coloration components, which are mainly confined to the region between 500Hz and 2kHz. Mind that, for the purpose of these measurements, the accelerometer was positioned in the area between the two drivers and in the middle of the side surface, respectively. Level of acceleration in both cases appears to be very low, below -50dBm/s² and is not expected to have any effect on the loudspeaker performance.

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