The first thing that stands out in the Reference One’s impedance characteristics is its relatively low minimum magnitude, which reaches 2.4Ω in the very low-frequency region, at 34Hz. At the same time, the overall impedance magnitude variance is among the narrowest we have measured, extending up to 12Ω. This means that the loudspeaker can be driven by amplifiers with a low damping factor, without significantly affecting the system’s overall frequency response. It is also worth mentioning that the minimum impedance magnitude occurs at an almost purely resistive phase angle (-0.58°). The electrical phase itself varies considerably, over a range of [+49.2, -36.3]°, but here too, the loudspeaker remains relatively amplifier-friendly, with impedance magnitudes of 5Ω and 7Ω at the respective positive and negative phase extrema.
The loudspeaker’s quasi-anechoic response, above 300Hz, reveals a remarkably smooth system, with very small variations in both sensitivity and bandwidth. Over most of the spectrum up to 10kHz, the response remains comfortably within ±3dB. Toward the top end, there is a gradual reduction in sensitivity, possibly intended to ensure proper integration with the rear-firing tweeter and the reflection it creates.

The summed response, obtained by splicing the near-field and quasi-anechoic measurements, shows a highly uniform character, particularly through the midrange and high-frequency regions, together with a very good low-frequency extension. The (always pessimistic) calculated average sensitivity is 87dBSPL/2.83Vrms/1m. Based on this figure, the -3dB bandwidth limits are 35Hz and 18kHz, respectively, with the rear tweeter excluded from the measurements and the calculations.
The averaged response over measurements taken within a ±10° solid-angle acoustic window has the expected shape, closely matching the corresponding on-axis response while showing a smooth reduction in sensitivity toward the high-frequency region. This points to smooth, well-controlled power response and sound radiation into the listening room. The Reference One’s step response is remarkably clean, confirming Kellenberger’s approach to a smooth driver time alignment. The transition from the tweeter to the mid/woofer is well-behaved, low-frequency decay is clean, and there are no significant signs of resonant activity in the high-frequency region.

The cumulative spectral decay plot shows a loudspeaker with fast decay times, clearly faster than what we typically measure. The strongest resonance occurs at approximately 12.5kHz and takes only 1.5ms to be damped below -25dBr, while other findings are at or below approximately 1.2ms.
The loudspeaker’s horizontal directivity is excellent. The Reference One is the only loudspeaker among those we have tested over the past (many) years that remains within -6dB all the way to the measurement limit of 20kHz over a ±30° listening angle. In theoretical terms, therefore, it does not require toe-in, although there is certainly no harm in angling the speakers toward the listener to get even better balance. Clearly, No Limit’s tweeter/waveguide combination performs extremely well in this respect.

The situation is different in the vertical plane. Here, the interaction between the two drivers appears to have a greater influence on the response than the tweeter’s radiation characteristics. Particularly at positive angles, that is, above the reference axis, the response exhibits significant variations. Below the axis, the behavior is considerably smoother. In practical terms, these results simply mean that the listening position should not place the listener above the loudspeaker’s reference axis—which is difficult to do with a floorstanding loudspeaker anyway, so there should be no problem here—and that some attention should be paid to early reflections from the floor and ceiling. These are entirely reasonable requirements for the setup of a loudspeaker in this price category.
Acceleration measurements on the loudspeaker’s head module are entirely satisfactory and indicate low levels of cabinet coloration. Clearly identifiable resonances are present, but they remain around and below -60dB m/sec², both on the baffle and on the side panels.

The woofer cabinet is similarly well controlled, with most of the measured resonances concentrated in the 30–100Hz region and at levels below -68dB m/sec².

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