PBN Montana SP loudspeaker Barry Willis June 1997
PBN engineer and chief executive Peter Noerbaek has made some improvements to the design of his model SP loudspeaker, reviewed by me in the January 1997 issue (p.225). The new production model, designated the Series 2, retains the same drivers, crossover network, and front-baffle dimensions, but differs from the original in that its cabinet is 2" deeper, increasing its internal volume by 844 cubic inches, or 17%. A foam pad added inside the cabinet just below the lower woofer is said to act as an acoustic low-pass filter. Frequencies above 200Hz are contained in the upper chamber, but the entire cabinet acts as a resonant chamber for the propagation of bass.
The round 2" by 3" port in the rear has been replaced by a rectangular flared port whose cross-sectional area is exactly matched to the moving mass of the unit's two woofers. The vertical position of the port has been raised from near the floor to a height of 18", thereby reducing the low-bass loading effect when the speaker is positioned too near the rear wall. The original SP required about 2' of space between it and the rear wall for a reasonably smooth bass response; the Series 2 can be moved to within about 16" without adverse effects.
All of these modifications have tremendously helped the Montana's bass performance, which was the only aspect of this otherwise excellent product that I negatively criticized. The original SP was marred by a 70Hz hump in its bass curve that made it difficult to integrate into my smallish listening room, and by a fairly steep rolloff below 35Hz. The improved SP sounds as though it has a much smoother and deeper bass response. Peter Noerbaek now claims a flat response to 30Hz. In other words, the bottom half of the bottom octave is all that's missing now. That's not much to complain about.
The Series 2 has all that I found enjoyable in its predecessor: excellent soundstaging and imaging abilities, a smooth, quick midrange, and a delicate, grain-free top end. It's as amplifier-friendly a speaker as you're likely to encounter this side of horn-loaded loony-land: I drove it to neighbor-alienating levels with a 20Wpc NAD 7225PE receiver without audible distortion (which means it's also fairly abuse-resistant), and spent many enjoyable evenings with it yoked to an old Dyna Stereo 70. The tube amp's warmth and intimacy were a perfect complement to the SP's slightly cool tonal characteristic. Vocal and acoustic recordings were especially enjoyable with this combination, although the Dyna's woolly bass was badly exposed by the PBN. It also mated well with a Parasound HCA-1000A that was here for review, the two forming a neutral, extremely efficient, and musically satisfying team.
The particular pair of SP Series 2s I've been using intermittently during the past few months came finished in rosewood veneer. The rosewood, while not as durable as the hard piano-black lacquer of the original SP, has a warm, inviting quality about it that may be more appropriate in settings with traditional furniture.
Owners of the original Montana SPs will be disappointed to learn that their loudspeakers are not upgradeable to the Series 2. While the two speakers have much in common, the construction of the 2's cabinet is different enough to render an upgrade impossible.
It's always gratifying when a manufacturer takes a reviewer's well-intended comments to heart and improves an already good design. The PBN Montana SP Series 2 will provide the serious music lover years of enjoyment.—Barry Willis