Acustik-Lab SR Bolero loudspeaker & Forte woofer

The Acustik-Lab SR Bolero loudspeaker ($1580/pair) debuted at the 1988 SCES in Chicago. I must own up right from the outset that I know nothing about the Swiss SR Trade (Acustik-Lab) company. I do know, however, that Audio Advancements' Hart Huschens was getting an intensely musical sound from their little Bolero speakers, driven by the German Klimo Kent tube amplifiers, at the 1988 Summer CES. I immediately asked for a pair for review; in addition, Mr. Huschens sent along a pair of the matching Bolero Forte woofers ($920/pair).

SR's Bolero is a well-made two-way minimonitor using drive-units from the French Focal company: a version of their high-power inverted-dome tweeter, this using a 24oz magnet, a resin-impregnated glass-fiber diaphragm with a foam surround, and a 5.25" doped-paper-cone woofer. The last features dual voice-coils, driven independently. One will be operative in the midrange, while the second is gradually rolled in as the frequency decreases. Both will therefore be operating in the bass, doubling the drive current and thus the unit's sensitivity, lowering the bass cut-off point. The woofer is reflex-loaded with a 6.25" by 0.5" slot at the base of the front baffle, this some 4.75" deep, equivalent to a conventional circular port some 2" in diameter. As far as I am aware, there is no intrinsic advantage to the slot shape over a circular port (except for an aesthetic one, of course).

Both drivers are rebated into the baffle and the front vertical edges of the speaker are beveled to provide a minimum of acoustic obstacles for the emitted sound. The crossover uses polyester capacitors, is mounted on a printed circuit board on the rear panel above the gold-plated binding posts, and appears to feature a second-order slope for the tweeter and first-order slopes for the woofer, different-sized series air-cored and ferrite-cored inductors being used for each of the two woofer voice-coils. The enclosure is loosely filled with a roll of bonded acrylic fiber.

The review samples were finished in an attractive walnut veneer. The grille consists of brown material stretched over a wooden frame, but as this is quite thick and has no profiling to minimize adverse diffraction effects, I auditioned the speakers without it.

The Bolero Forte subwoofer is a slim tower, veneered in walnut and styled to match the Bolero. It stands just over 2' tall on its four screw-in spiked feet. These can be adjusted to alter the spacing between the downward-firing woofer and the floor, though the gap must never be less than 20mm (0.8"). The woofer has a 6.5" doped-paper cone, its large half-roll surround suggesting good excursion capability, and appears to have conventional sealed-box loading. Electrical input and output is via gold-plated binding posts identical to those used in the Bolero: two sets at the speaker's base offer parallel inputs to the high- and low-pass legs of the crossover to facilitate bi-wiring and bi-amplification, while a third set at the top is for connection to the Bolero.

No details on the crossover were supplied, but measuring the response in the nearfield of the woofer (see later) suggests an approximate crossover frequency of 150Hz with probably first-order slopes. This combination of frequency and slope suggests that the woofer would best be used in close proximity to the satellites: in fact, it would seem obvious to place one upon the other; Audio Advancements supplies four small "puck" feet, made from what appears to be Sorbothane, to separate the two. (I also tried small stainless-steel cones and a sheet of Sims Vibration Dynamics Navcom—the last proved to give the cleanest midband.)

The Boleros were first set up on the Arcici "Rigid Riser" stands, set to 26" to position the speakers at the same height as when they stand on the Forte subwoofers, and placed 3' from the rear wall and 5' from the sidewalls. The Boleros seem rather sensitive to listening height. The smoothest response is on the tweeter axis, though a cancellation notch can be heard to travel down in frequency as the listening height increases, giving a rather hollow midrange when the listener can see the cabinet top. In addition, a somewhat shrieky quality to the upper mids is alleviated by listening 15° or so off the horizontal axis. The Boleros were therefore set up only slightly angled in toward the listening seat, though the exact degree of tonal modification has to be balanced against a degree of soundstage blur.

First impressions were very favorable. An open quality to the Bolero's sound is matched by good dynamics and a relatively neutral presentation of tone colors. The only significant coloration present seemed to be an "eee" quality to strings, also apparent as a slightly throaty edge to female voice. Is this what Martin Colloms refers to as "cone cry," I wonder? The transition from woofer to tweeter seemed well-managed, though there was a degree of sibilance emphasis noticeable at the top of the tweeter's passband. This also could be heard to "whiten" tape hiss, while soprano voices had a slight HF "fuzz" added. Bass extension was moderate, though upper-bass definition was particularly good for a reflex design. Double-bass was a little nasal, but the leading edges of its sound had excellent definition.

Soundstage localization was precise laterally, but using both my own recordings and some pure-Blumlein master-tape copies loaned by Water Lily Acoustics' Kavi Alexander, there was rather less depth apparent in the treble than with the more expensive Celestion SL700s or the similarly priced Acoustic Energy AE1s. With spaced-omni recordings, such as those produced by Peter McGrath, the recorded ambience extended to beyond the speaker positions. There was one anomaly: normally when a dual-mono signal is fed to the two speakers out of phase, the image widens to fill the entire stage width as well as the sound losing any sense of bass power. Playing the Boleros out of phase gave the expected cancellation of low frequencies, but the image smearing was not as severe as usual. This is perhaps an indicator that the speaker is not as time-coherent as might be thought desirable.

To audition the subwoofers, the Boleros were placed upon them in the same positions as they had been on the Arcici stands. I first tried single wiring, but bi-wiring gave a considerable improvement in lower-midrange clarity. All subsequent listening was carried out bi-wired with Monster M1 cable. Initially using the stainless-steel cones, I ended up using a ½" sheet of non-reactive Navcom material between the Bolero and the Forte. This gave the lowest levels of midrange spuriae and the cleanest piano tone.

I must admit from the outset that I share Dick Olsher's reservations about the use of subwoofers. The problems of integrating even one subwoofer into an existing high-performance system are complex, and it takes considerable skill and expertise if the added bass extension is not to be achieved at the expense of lower-midrange clarity. The safest course is to let the manufacturer of the satellite speaker do all the work for you, as is the case here.

The name "Forte" is well-deserved, as the SR woofers allow the Bolero to play considerably louder without a sense of strain. The VTL amplifiers reached clipping on orchestral climaxes before the speaker showed obvious signs of being driven too hard. And on music with limited dynamics and no low-bass information, some of Kavi Alexander's choral recordings for example, the Fortes added significantly to the sense of "space." Perversely, this was not the case with the drum track on the HFN/RR Test CD, where the tom-toms moved forward overmuch with the Fortes, giving the illusion that the drummer had to have had very long arms. Kick drum, however, did acquire a suitable degree of weight.

Overall, the added extension and dynamics of the Fortes improved the tonal balance of the Boleros, rendering the "eee" coloration less noticeable. Cellos and violas, in particular, as well as the piano, now had more accurate tonalities. Male spoken voice, however, boomed, and double basses and organ pipes became more indistinct even as they acquired a more natural weight to their sound. On orchestral and choral recordings, this was noticeable but didn't offset the musicality of the sound. Rock recordings, however, and closely miked double bass on jazz recordings, just became too rich in the upper bass, giving the music too "slow" a feel. No amount of experimenting with position and the height of the screw-in feet could alleviate this problem. The Forte would probably need a good solid-state power amplifier to give of its best, therefore.

Beautifully made and finished, the Acustik-Lab SR Bolero is a true high-quality minimonitor, capable of giving very musical results when carefully set up with the right ancillaries. Being an import, it is a little expensive for the sound quality on offer, but this will be inevitable given the weak state of the post-Reagan dollar against most European currencies. Nevertheless, the Bolero is a good Class C performer and can be recommended.

The Forte offers a mixture of improvements and degradations to the sound of the Bolero. On the plus side, it renders the speaker's tonal balance more neutral in the midrange, improves the system's dynamics, and adds to the sense of space on recordings which don't have high levels of low-frequency energy. It also is relatively affordable for a stereo pair of woofers, is a good-looking piece of furniture in its own right, and the combination of Forte and Bolero offers an aesthetically acceptable solution to the problem of how to get almost full-range sound in a small room without giving up too much space to a pair of monstrous armoire-like cabinets. On the downside, I feel that its working range of dynamics is quite limited if it is not to interfere with the Bolero's presentation of musical information in the upper bass and lower midrange, and that a lack of real extension means that it should really be considered a woofer rather than a subwoofer. The Boleros deserve more than the Fortes are able to give, in my opinion.

Distributor: Audio Advancements
Verona, NJ 07044
no longer available (2018)