Floor Loudspeaker Reviews

I measured the Unity Signature 1 with serial number 4405051. The Signature 1's impedance magnitude and phase are shown in fig.1. The cursor position—2.7 ohms at 138Hz—reveals the speaker to be a very demanding load; although RD didn't have sonic problems with his low-powered Luxman tube amps other than limited loudness, I suspect that this speaker will generally work much better with good, current-capable, solid-state designs. The large difference in impedance below and above 1kHz means that the speaker will tend to sound uptilted in response with an amplifier having any appreciable output impedance. Its sensitivity is also on the low side, at about 85dB/2.83V/m (B-weighted), which is rather lower than specification and again means the Signature 1 will probably be at its best driven by good solid-state power.

Turning to the frequency domain, the rather complicated-looking graph in fig.2 shows, from left to right: the response of the port, taken in the nearfield; the nearfield response of the downward-facing woofer; and the nearfield response of the midrange unit, coupled to the response of the midrange unit on the tweeter axis at a distance of 45". The port can be seen to handle the speaker's low-bass output, while there appears to be significant overlap between the woofer and the midrange unit. The woofer also has a peak in its output at 610Hz, which was quite audible when this driver was auditioned on its own. There also appeared to be some coupling between the drive-units, there being some output from the midrange unit when just the woofer was driven.

To get an estimate of how these nearfield responses sum at the listening position, I used the MLSSA software to calculate the complex sum (magnitude and phase) of the port, woofer, and midrange outputs. This is shown to the left of fig.3 and consists of a broad 4dB–high peak in the midbass, covering the octave from 50Hz to 100Hz. Here, undoubtedly, is the reason for RD's noting a "lower-midbass rise" in the speaker's character. Below this peak, the bass rolls out at the sealed-box rate of 12dB/octave, indicating that the port actually does not do a great deal of reinforcement.

To the right of fig.3 is shown the quasi-anechoic response on the Signature's tweeter axis, averaged across a 30° lateral window to eliminate interference effects dependent on microphone position. Noticeably unflat, the response features a broad trough in the crossover region between the tweeter and midrange unit, and a generally elevated level in the region handled by the tweeter. Nothing in Bob's auditioning suggested an unflat response in this manner (although a speaker's lack of ability to develop image height on the LEDR test often does correlate with tonal-balance problems). I therefore looked at the way in which this response changed with listening height; Bob was not sitting on the tweeter axis for his listening, but actually below it, with his ear at a 38" height.

Fig.4 shows that the crossover suckout fills in for listeners standing or sitting so that they can see the top of the speaker's enclosure; the actual response obtained on this axis is shown in fig.5. While balanced to be commendably flat through the midrange and lower treble, there is still an excess of top-octave energy, as there is on the midrange axis. This correlates with RD's noting of a "slight treble emphasis," though he did add that it came across as "air" and "quickness" rather than "hardness" or "brightness."

Laterally (fig.6), the Unity Audio maintains its response to 15° off-axis, the mid- and high trebles then shelving down. Fig.6 suggests, in fact, that the excess of HF energy on-axis could be tamed by pointing the speakers straight ahead rather than toeing them in to the listening seat. (I note that RD did toe them in only a small amount.)

Turning to the time domain, all three drive-units appear to be connected with the same acoustic polarity. The overall impulse response on the tweeter axis can be seen in fig.7; the step response calculated from this impulse is shown in fig.8, which reveals the tweeter's output to arrive significantly before that of the midrange unit, on this axis. (Ignore the wrinkle between 6ms and 8ms in this and the next three graphs, which is due to a room reflection.) Moving the microphone higher, where the flattest measured response (fig.5) was obtained, gives the step response shown in fig.9—the tweeter's output arrives even earlier. Moving the microphone down to the midrange axis moves the tweeter's output back a little in time (fig.10); moving it down even further, to 7.5° below the midrange unit, gives a much more time-coherent step response (fig.11), though fig.4 reveals that the frequency response on this low axis is far from flat.

These measurements reveal, in my opinion, that the Signature 1's crossover is not particularly well-engineered, regarding the speaker's performances in both the frequency and time domains. Regarding the manufacturer's claims of "phase coherence," fig.12 shows the speaker's excess phase on the tweeter axis at a distance of 45". (Excess phase is that left over after the elimination of the phase deviation correlating with a minimum-phase speaker's departure from a flat response.) Correlating with the speaker's non–time-coherent step response on this axis (fig.8), there is a relatively large amount of phase error throughout the treble.

Actually, this is not serious, as it has yet to be shown that the absence of high-frequency phase error is a major contributor to good perceived quality. But why did RD like this speaker so much? I suspect that much of the answer lies in fig.13, the cumulative spectral-decay, or "waterfall," plot. Although a couple of minor resonant modes can be seen at 5 and 10kHz, the Signature 1's decay is very clean.

All in all, an enigmatic set of measurements. My advice? I agree with RD: Listen to this speaker for yourself.—John Atkinson