Floor Loudspeaker Reviews

I used DRA Labs' MLSSA system, a calibrated DPA 4006 microphone, and an Earthworks microphone preamplifier to measure the T+A Solitaire S 530's quasi-anechoic frequency- and time-domain behavior in the farfield. The center of the line-source tweeter is just 32" from the floor, but as the loudspeaker on its feet is slightly tilted back, I examined the farfield behavior on an axis at right angles to the front baffle with the microphone aimed at the center of the tweeter. The grille was left off for these measurements.

When measuring a loudspeaker's farfield response, the microphone should be at least as far away as the drivers' vertical dimension (footnote 1). Otherwise, the low frequencies will be boosted due to the nearfield proximity effect. As the S 530's midrange array is 24" tall and the magnetostatic tweeter is 33.5" tall, I placed the microphone 55" away rather than my usual 50". To check that the microphone was sufficiently in the farfield, I repeated the response measurements on the same axis at 1m, 2m, and 3m. The 1m response had a slight nearfield rise in the lower midrange and bass; the response at 55" was identical to those at the greater microphone distances. (The 2m and 3m measurements suffered from earlier reflections than that at 55", which is why I discuss the farfield behavior at the latter-distance measurement.)

T+A specifies the S 530's voltage sensitivity as 86dB/2.83V/m, the units otherwise unspecified. My B-weighted estimate was 84.6dB(B)/2.83V/m, though the quasi–line-source behavior will slightly increase the in-room sensitivity. The S 530's impedance is specified as 4 ohms. The impedance magnitude (fig.1, solid trace), measured with Dayton Audio's DATS V2 system and with the tone controls set to their default, central "LIN" positions, varied between 4 ohms and 8 ohms over most of the audioband, with minimum values of 3.46 ohms at 105Hz and 3.2 ohms at 20kHz. The effective resistance, or EPDR (footnote 2), lies below 4 ohms between 39Hz and 197Hz, between 331Hz and 939Hz, and above 10kHz. The minimum EPDR values are 2.24 ohms at 131Hz, 3.31 ohms at 512Hz, and 1.2 ohms at 20kHz.

Fig.2 shows the impedance magnitude and phase with the controls set to their +1.5 and –1.5 positions. The +1.5 setting increases the amplitude of the low-frequency peak at 19Hz but lowers the minimum magnitude at 110Hz to 2.77 ohms. The EPDR now lies below 2 ohms between 120Hz and 152Hz and above 10kHz, with minimum EPDR values of 1.85 ohms at 135Hz and 1.2 ohms at 20kHz. Even at the other tone control settings, the S 530 is a demanding load for the partnering amplifier.

I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer. The panels were quite inert; the only resonant modes I found were at 309Hz and 1066Hz on the sidewalls level with the central midrange unit (fig.3). As these modes are very low in level, this behavior shouldn't have audible consequences.

The woofers' response, measured in the nearfield with an Earthworks QTC-40 mike (fig.4, blue trace), has the expected minimum-motion notch at a low 27Hz, which implies extended low frequencies. The downward-firing port's nearfield output (fig.4, red trace) peaks slightly below the tuning frequency, and other than low-level peaks at 295Hz and 550Hz, its upper-frequency rollout is clean. The output of the woofers crosses over to that of the midrange unit (green trace) close to the specified 180Hz. The peak between 40Hz and 150Hz in the complex sum of the midrange, woofer, and port responses (fig.4, black trace below 300Hz) is due to the nearfield measurement technique, which assumes that the drive units are mounted in a baffle that extends to infinity in both the vertical and horizontal planes.

The black trace above 300Hz in fig.4 shows the S 530's quasi-anechoic farfield response, taken without the grille and averaged across a 30° horizontal window centered on the central tweeter axis mentioned earlier. The midrange is elevated, and there is a lack of energy in the presence region. Repeating the measurement with the grille in place slightly reduced the levels between 2.5kHz and 9kHz and above 13kHz.

Fig.5 shows the effect of the three tone-control switches on the measurement axis, set to their +1.5 positions (red trace) and to their –1.5 positions (blue trace). The response with the controls set to their central, default position has been subtracted from each measured response so that just the differences are shown. The Bass controls raise or lower the level of the woofers by 1dB, the Mid control changes the midrange units' output by +1.5dB/– 1.9dB, and the Treble control adjusts the tweeter level by +2dB/–1.8dB.

The T+A's horizontal dispersion, normalized to the response on the central tweeter axis (which thus appears as a straight line), is shown in fig.6. The off-axis behavior to the side of the baffle closest to the tweeter is shown to the front of this graph. A suckout close to the upper crossover frequency appears at extreme off-axis angles, but the traces are otherwise fairly even. There appears to be more presence-region energy off-axis on the midrange side of the baffle, which T+A says should face away from the room's sidewalls. The S 530's dispersion in the vertical plane, again normalized to the response on the tweeter axis (fig.7), appears to show that the response is better maintained above the central tweeter axis. It wasn't possible to investigate the vertical behavior response at off-axis angles greater than ±20°, but the height of the tweeter and midrange array should narrow the radiation pattern in those regions.

In the time domain, the S 530's step response (fig.8) indicates that all the drive units are connected in positive acoustic polarity. The decay of each unit's step smoothly blends with the start of the next driver's step, which implies an optimal crossover topology. The S 530's cumulative spectral-decay plot on the tweeter axis (fig.9) features a clean initial decay, though a lot of "hash" is then visible in the region covered by the Magnetostatic tweeter. As I have written in the past (footnote 3), with a large drive unit like this tweeter, this behavior is not so much due to actual resonances but to the diaphragm behaving in a chaotic manner (footnote 4). The individual elements of the diaphragm "shimmer" as their average position responds in a linear manner to the driving force.

The T+A Solitaire S 530's measured performance is difficult to interpret, but it would appear that its balance will be somewhat polite. However, given the effects of the tone controls, it should be possible with careful setup and experimenting with toe-in to the listening seat to get an even, full-range tonal balance.—John Atkinson

Footnote 2: 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 3: See this discussion.

Footnote 4: Chaotic in the formal mathematical sense: "the inherent unpredictability in the behavior of a complex natural system."