MartinLogan CLS loudspeaker Jack English, CLS IIA, February 1992

Jack English wrote a Followup on the CLS IIA in February 1992 (Vol.15 No.2):

Acoustic Sciences Corporation Studio Traps had been selected specifically to deal with in-room problems identified with the use of MartinLogan CLS IIAs. Specifically, the CLS IIAs had the following problems that could potentially be minimized with the ASC STs: an emphasis of midbass energy, often giving the speakers one-note bass; a lack of sufficient deep bass, causing the speakers to sound lightweight overall; and a beamy/phasey character in the trebles which caused the speakers to have different tonal characters depending upon the listening position.

When the IIAs were located closer to the rear wall, the midbass resonances were worse but the deep bass extension was slightly improved. Placing the panels closer to the rear wall proved a mixed blessing. The STs worked splendidly with this setup, doing nothing to diminish the newfound deep bass extension but significantly minimizing midbass boom. With the STs, overall bass performance became more coherent. There was a reduction of the elevated midbass without losing any of the newfound deep bass extension. The net effect was a significantly more realistic bottom-end performance. Music once again had a semblance of bass foundation. The STs, coupled with the repositioning of the IIAs, led to a significantly improved tonal balance. In this application, the STs made improvements with virtually all recordings, including the Stones' mono hits.

With the IIAs well out in the listening room, the midbass was more boomy, the deep bass greatly attenuated. Listening to a recording such as the soundtrack from The Commitments (MCA MCAD 10286) was simply not satisfying. The performance lacked the foundation essential for this type of music. Moving the IIAs back toward the rear wall and adding the STs improved things significantly. The bottom became more believable, more realistic. With the firmer foundation, the music became more solid and natural. I was able to concentrate more on the vocals of Andrew Strong and Maria Doyle covering those classic soul tracks. My frustrations with the lightweight character of the IIAs, while not ameliorated, were at least somewhat pacified.

With the IIA panels placed closer to the rear wall and having the STs placed in the rear focal point of the back wave, the overall performance in the bottom was better but still far from complete. For example, the playful first movement of Shostakovich's Symphony 15, with Bernard Haitink and the London Philharmonic (London 417 581-2), was listenable and enjoyable, but sounded as if it had been written by someone else. The tympani whacks sounded like toy drums! I could hear something, but it certainly wasn't what was intended, or what was actually played.

However, tonal balance wasn't the only thing changed in this new arrangement. With the back wave damped, the overall soundstaging of the M-L speakers was altered. Without the STs, there were many more problems with front wave/back wave cancellations. This has often been described as a "venetian blind" effect. With the STs in place, much of the back wave was absorbed and diffused. The net result was less cancellation of the front wave.

Without the STs, the overall performance of the Shostakovich was more distant and spacious. In fact, the absorption of the back wave significantly diminished the overall spaciousness of everything played through the IIAs. This loss may be unacceptable for many listeners, as it robs the speakers of one of their unique attributes. With the STs in place, the performers were closer, the sound more immediate. The soundstage had less depth, but more precise placement. Spotlighted soloists were more obviously taken out of their proper soundstage locations. In fact, this was more accurate but less satisfying (to me). I preferred the more distant and spacious presentation of the soundstage without the Studio Traps.

A similar result occurred with the surreal sonic landscapes of Robert Rich and Steve Roach's Strata (Hearts of Space HS 11019-2). With the STs in place, the presentation was closer and more immediate. There was less depth and space. On the upside, the tonality was warmer and richer. Without the STs, the sound was more distant and spacious but placement was less precise. This hauntingly beautiful new age music was more "spacey" without the Studio Traps.

With music lacking either a naturally expansive soundstage (such as the Shostakovich) or a euphonically desired one (Strata), there was not as much of a difference with or without the STs in terms of soundstaging. A good illustration of this was heard on Paul McCartney's Unplugged (Capitol CDP 7 96413 2). The performers were spread across the stage with little natural depth. Since most of the instrumentation was acoustic, the performers were closely miked. They should sound like they are "in the room" as opposed to being located well behind the speakers. This is exactly what was heard, with or without the STs.

The MartinLogan CLS IIAs specifically, and other dipoles in general, present unique problems in a typical home listening room. The IIAs' problems include a midbass emphasis, limitations of deep bass extension, and various front wave/back wave cancellations. The Studio Traps worked very well to temper these problems. Use of the STs allowed the IIAs to be placed closer to the rear wall, which led to an improvement in deep bass extension. With the STs located at the rear focal point of the IIAs with the absorptive side facing the dipole, midbass bloom was meaningfully tamed. However, these improvements did come at a cost. In this case, the openness and spacious presentation of the IIAs was diminished. The soundstage had less depth and was located closer to the listening position. However, the placement of performers became more precise, the overall sound more immediate.