Music in the Round #56 Page 2

Between the Channel 3 group and the right handle are the fuse post, AC switch, and IEC power connection. Between the Channel 1 group and the left handle are 12V loop-through jacks, a switch for selecting the turn-on option, and a control for Turn On Threshold. I chose to use the audio-controlled, automatic on-off option, and it worked flawlessly.

I switched the power cord, XLR interconnects, and speaker cables to the Halo A 31 from the McIntosh MC303 three-channel amp, which fairly loomed over the new arrival. I switched on the A 31 and just lived with it for a week or so, listening mostly in stereo, before getting analytical. In the interim, I experienced no problems or quirks with the Parasound, and quickly grew to appreciate the automatic on-off, which saved me an oh, so long walk to the other end of the room every day. Then I tweaked the gain of the Meridian 861 pre/pro to balance the rear channels with the new front amp.

Immediately, I was struck by the Halo A 31's treble. Whether in two channels or more, it seemed to reveal more detail across the soundstage, and not only in terms of minor matters not noticed before. It also revealed subtleties of texture, such as the changes in harmonic structure that accompany changes in bow-on-string pressure, whether in solo passages or with massed strings. The entire treble range wasn't brighter but lighter, as in more transparent. The overall balance was as I've grown to expect from the 800 Diamonds in my room, but with somewhat less glint in the extreme treble than I'm used to. This was advantageous not only for fiddles, but also for voices: sibilants were explicit, but not excessively so, let alone spitty.

The remarkable definition continued down into the midrange and bass. The result was that the Halo A 31 could resolve individual voices and musical lines in dense and even turbid scores. With the resulting clarity, spatial imaging also improved, and although the soundstage wasn't significantly wider or deeper, it was extremely rich in specific information. The bass was firm and extended, and even running the L/C/R channels full range and full bore, I never lacked for power and weight.

Then again, my listening diet may not be yours. I don't listen much to loud music of narrow dynamic range, which might make greater demands of long-term power. Nor did I use the Halo A 31 for the train-wreck scene in Super 8 on Blu-ray at reference levels. On the other hand, I did play the San Francisco Symphony at 100 BD (see above) at unconscionably glorious levels, and a gleaming recording of Shostakovich's Symphony 8 by Andris Nelsons and the Royal Concertgebouw Orchestra (BD, C Major 710004), in which the basses and cellos snarled and the bass drum was fairly walloped.

The clean, luminous sound of the Halo A 31 was distinguishable from the slightly opaque treble of the Bel Canto Ref1000 Mk.2 monoblocks, though the latters' greater power output might be an advantage in some applications. On paper, the Parasound is slightly less powerful than the McIntosh MC303 into 8 ohms, and somewhat more powerful into 4 ohms, at which impedance the B&W 800 Diamond swings from 60 to 800Hz. The Mac's greater richness in the upper bass gave it a more authoritative, more forward sound, but its treble was a bit recessed compared with the A 31's. The 800 Diamonds didn't lack for midbass clout or for treble extension with the Parasound. In addition, at $3000, the Halo A 31 costs significantly less than either the McIntosh ($10,000) or the Bel Cantos ($5990/pair).

MSR Acoustics Dimension4 SpringTraps
Talking to a manufacturer about acoustical treatments can be like talking to your physician. As he tells you all the things you should be doing—and you know he's right—you give him only grudging responses while thinking up all sorts of excuses for not doing what he advises. I know because I count both doctors and acousticians among my friends. Yeah, I'll call you in the morning and order a bunch of your humongous and ugly bass traps, I think, inwardly smirking.

But while I don't always do what I know is good for me, I'm not one to deny the truth. Granted, non-dedicated listening rooms (ie, most of them) have acoustical problems that will impose themselves on the sound no matter how good your equipment or how much effort you expend in optimizing setup. It is a fact of physics that some frequencies will be emphasized or canceled at various points in the room. At higher frequencies, this can be effectively mitigated with absorbent or diffuser panels, and often with furnishings and designs that accomplish the same end. Problems at lower frequencies, however, require larger, more heroic devices because of the longer wavelengths involved.

Although it's generally accepted that the best places to trap bass modes are a room's corners, because that's where the energies of multiple modes converge, that energy is at its highest pressure near boundaries, hence air velocity is at its minimum. Resistive, or frictional, bass absorbers are most effective where there is high air velocity, which means spacing them away from the corners. My room's corners are not up to that. In each corner is an adjacent window and a pillar, which make the horizontal profile of the corner more like a W or M than an L. Those corners can't be neatly spanned by a flat bass panel.

That's why I've relied on and written so often in this column about DSP-based room equalization. But while room EQ works well, and takes up no space in the room, it's not perfect. There's a choice between automatic EQs, which give the user limited control, and sophisticated manual EQs, which demand more hardware and training than most are willing to invest in. Moreover, given the widely varied and irregular patterns of acoustical interactions, no electronic EQ can compensate for what's occurring at each and every point in a room.

Recently, I met with Anthony Grimani, of MSR Acoustics. His prescription for my room was to add to it a pair of large physical devices, in this case ones that actually fit: MSR's new Dimension4 SpringTraps ($1818/pair). Each one is triangular, much like a corner horn-speaker enclosure, stands 46" tall (including 4" feet) and extends 18" along each sidewall. Construction is of an undefined wood product, but is very sturdy and well finished. The entire front of the cabinet is a diaphragm of 9-layer apple plywood suspended by six precision metal springs and sealed around its perimeter. The half-round rubber surround looks like a KEF woofer design. The springs connect the front panel to an intermediate panel behind it. Deeper in the enclosure, a third, smaller panel defines the small volume connected to the port on the bottom. In summary, a SpringTrap contains three port-connected spaces, resulting in what Grimani calls "a spring-loaded, triple cavity, ported, pistonic-Helmholtz bass absorber."

Placed in a corner, the SpringTrap's tuned and coupled subenclosures convert the mechanical energy of low-frequency soundwaves into heat at three calculated (but undisclosed) frequencies. The graphs on MSR's website suggest that SpringTraps are effective from just below 100Hz to as far down as 40Hz, with most absorption taking place in the 60—90Hz range. This is pretty broadband, and should be very effective with a typical ceiling height. My ceiling is 8' high, which means that its primary mode is at 70Hz. In addition, there a major axial mode at 65Hz, with some closely spaced tangential and oblique modes in the 90Hz region.

For the sake of convenience and my lower back, I decided to measure the effects of the SpringTraps before I did any listening, though I did my best not to read or interpret the measurements until later. First I used XTZ Pro to measure the room's behavior with the Ready Acoustics Chameleon traps that I wrote about in September 2009; then removed them for another set of measurements; finally, I installed the MSR SpringTraps. The XTZ microphone was in the same position for all three sets of measurements.

But first I'll tell you what I heard. When I removed the Ready traps, there wasn't much of a change in the bass except what I could detect with stepped sinewaves or organ-pedal notes. The room seemed a bit boomier with musical examples, but the difference was still small. However, when I installed the SpringTraps, the bass seemed to just disappear—the balance of the sound took a tilt in favor of the midrange and treble.

I knew this was the sort of overreaction about which I've cautioned others: Even with the transience of aural memory, what one has been listening to becomes one's internal reference. I always tell those who think that room EQ has removed all their bass to just listen to the corrected sound for a week before doing another A/B comparison. The establishment of a new internal reference will always bias you in favor of it, but it does make you more analytical in assessing the what and why of the difference.

With the SpringTraps, I needed only a night's sleep to clear my aural bias. The next morning, I was bowled over by the sound. The best tests for what had occurred were recordings of lower strings and piano. On a new release, double bassist Rick Stotijn plays delightful pieces by Bottesini, assisted by various soloists and Candida Thompson conducting the Amsterdam Sinfonietta (SACD/CD, Channel Classics CCS SA 32612). Through it all, his instrument was solid and defined, from the bottom to the top of its range, with a clear distinction between string and body tones, and the orchestra fit into the same soundstage. The piano music of Brahms might have been my next choice even had I not just received a marvelous disc from SIBA (Yay! Another SACD label!) with Terhi Dostal playing four sets of the composer's variations (SACD/CD, SIBA SACD-1006). So much of Brahms's melodic declamation is in the lower half of the keyboard, often with accents of even lower pitch. Dostal paces it all well; the sound was rich, warm, and powerful, in no way sapped by what, only the day before, I'd perceived as a loss of bass.

What was happening? The plots of frequency response showed little diminution of bass levels, and only a slight flattening of the traces. But the bass I now heard was clean and tight in ways I'd never before perceived in this room. Moreover, the entire lower end of the audioband, up to about 1kHz, was amazingly clear and open.

I suspected that the impact of the SpringTraps was not so much on frequency response but on the decay of bass tones; my measurements demonstrate that. Figs.1 and 2 show the spectral decays of bass tones with no corner/bass treatment, and with the two SpringTraps, respectively. Note the overall faster decay across most of the frequencies with the SpringTraps. In particular, the longer decays between 70 and 100Hz and around 30Hz seen in the graph of the untreated room are drastically curtailed by the SpringTraps.

Fig.1 Room acoustic decay, 8–300Hz, 0–250ms, without any acoustic treatment.

Fig.2 Room acoustic decay, 8–300Hz, 0–250ms, with two MSR Dimension4 SpringTraps.

Having heard what they can do and confirmed those effects with measurements, I am now a fan of MSR Acoustics' Dimension4 SpringTraps. At $909 each, they're a bit more than inexpensive, but their impact on the sound of my system in my room has been substantial. See if they'll fit your space.

Article Contents
Share | |
Site Map / Direct Links