Boston Acoustics M350 loudspeaker

Boston Acoustics made its name in the early 1980s with the A40, an inexpensive two-way bookshelf design that became one of that decade's best-selling speakers. Stephen Mejias was impressed by the A40's spiritual descendant, the Boston Acoustics A25 bookshelf speaker ($299.98/pair), when he reviewed it in November 2011, and I was similarly impressed when I had the speaker on the test bench for measurement. So when, in the fall of 2012, Boston's soon-to-be-departing PR representative Sara Trujillo let me know that the company was introducing a range of more expensive speakers, I asked to review the top-of-the-line, floorstanding M350.

More expensive, maybe, but still not expensive in absolute terms: the M350 costs $2498/pair. It features a 1" Extended Wide Bandwidth (EWB) soft-dome tweeter. This has a small dimple in the middle of the dome, and what's claimed to be a larger-than-usual radiating area for a 1" design. The tweeter handles all frequencies above 3kHz and is mounted below a 4.5" midrange driver on the front baffle. The latter has a polypropylene cone, mass-loaded to achieve a smoother frequency response at the top of the driver's passband.

Rather than a single, large woofer to cover the range below 400Hz, the M350 uses a vertical array of four 5.25" polypropylene-cone woofers, these fitted with aluminum shorting rings on their voice-coil formers to lower distortion. Boston's reason for using such an array, which is equivalent in radiating area to a single 9" cone, was that the multiple floor reflections from the units will both minimize the speaker's sensitivity to its position in the room while optimizing low-frequency reproduction. The woofers are reflex-loaded with a flared port, 2" in diameter, on the rear of the cabinet above the single recessed pair of binding posts.

The M350's elegantly proportioned enclosure is made from a material Boston calls Lo-Q: two layers of medium-density fiberboard separated by a thick layer of adhesive, to damp vibrations. A reinforcing brace near the top of the cabinet both increases rigidity and isolates the midrange cone from the woofers, and there are other cross-braces lower in the enclosure. The cabinet sidewalls are beveled at their tops and bottoms and finished in high-gloss black; the front baffle and the top and bottom panels are covered in a black faux leather material. A black, cloth-covered plastic grille is provided; I preferred the look and sound of the M350 without the grille. Four short aluminum pillars lift the enclosure above the pedestal; the result is a visually attractive tower.

The M350 was designed in the US but is manufactured in China.

Nothing's better left unsaid
As promised, the M350s seemed relatively insensitive to where they were placed in the room. On the other hand, no matter how I fine-tuned their positions, I couldn't eliminate an excess of energy in the upper bass. When I listened to the M350s at the speaker's press launch, Boston's Andy Clark was experimenting with foam inserts in the ports. These can be used either to fully block the port or, with the central cylinder of foam removed, to reduce the port's diameter. According to Clark, "in my experience so far with the M350 in a variety of rooms, unless they are in a relatively large room and off the rear wall, the the half-blocked port usually provides the balance I prefer. In really small rooms the full block may be beneficial, but I find myself using the half-blocked port most often."

I experimented with the foam plugs, which Boston includes free of charge with every pair of M350s. Yes, this mod went a long way toward addressing the problem. The double bass in "Killing the Blues," from Alison Krauss and Robert Plant's Raising Sand (24-bit/96kHz ALAC file transcoded from FLAC download, Rounder/HDtracks 11661), remained heavy-sounding but lost its oppressive character. On the other hand, Kurt Sanderling's 1972 traversal of the four Brahms symphonies with the Dresden Staatskapelle (CD, BMG Classics 69220-2), which has a rather lean sound, benefited from the lower-midrange warmth added by leaving the Bostons' ports fully open. I ended up doing much of my listening with the ports unblocked. For example, the synth-bass line in "The Trader," from the Beach Boys' Holland (24/192 needle drop from LP, Brother/Reprise K54008), though balanced a little high in the mix with the ports open, better balanced this recording's forward high frequencies.

And even as I write these words and "Sloop John B," from the HDtracks hi-rez release of the Beach Boys' Pet Sounds (24/192 ALAC files transcoded from FLAC), is playing, I reach for the foam plugs, that wonderful unison combination of plucked double bass and plectrum-played Fender bass sounding way too generous with the ports fully open.

Without the port plugs, the low-frequency warble tones on Editor's Choice (CD, Stereophile STPH016-2) were powerfully reproduced between 125 and 80Hz. The 32Hz tone was reinforced by the lowest mode in my room, but the 25Hz tone was weak and the 20Hz tone inaudible. Played at moderate levels, the low-frequency tones were free from audible distortion, and there was no wind noise coming from the port. With the ports half-closed, the region between 80 and 125Hz was less powerful, but the 63 and 50Hz tones now sounded weak. With the ports half-blocked, the half-step–spaced low-frequency tonebursts on Editor's Choice sounded commendably even, with good weight down to 32Hz. However, when I listened to the cabinet's side and rear walls with a stethoscope as this track played, I could hear a very strong resonance between 256 and 300Hz.

With pink noise, I got the smoothest balance when I sat with my ears level with the tweeters, 34" above the floor, though the overall balance was somewhat dark. When I sat up a little to put my ears on the midrange axes, which are 37.5" from the floor, I now heard an isolated band of presence-region energy. Playing "Whaling Stories," from Procol Harum's Live in Concert with the Edmonton Symphony Orchestra (ALAC ripped from CD, Mobile Fidelity Sound Lab), Gary Brooker's distinctively phlegmy voice (footnote 1) sounded uncolored, though that ascending bass line was not as clearly defined as I'm used to, and the choir sounded a little "hooded." However, it's fair to point out that the M350s suffered the misfortune of following the superbly transparent, astonishingly uncolored YG Acoustics Sonja 1.3 speakers in my room. Of course, the big YGAs, which I reviewed in July, cost more than 40 times the Bostons' price—sonic perfection is to be expected with a speaker having a six-figure price tag. In absolute terms, the M350's shortfall in lower-midrange transparency was not a serious fault.

The M350s' stereo imaging was well defined, if not up to the standard set by minimonitors like the BBC LS3/5a and KEF LS50. The central image with dual-mono pink noise was wider in the midrange than at high frequencies.

I recently downloaded pianist Angela Hewitt's 2008 recording of Bach's The Well-Tempered Clavier (24/44.1 ALAC files; CD, Hyperion CDA67741/4). There is more than four hours of music to come to grips with here, but already I particularly like her performance of the Prelude in e, from Book I. The melodic line in the first half, over that insistent arpeggio figure in the left hand, is almost song-like in its lyricism, while she keeps the lines in the double-speed coda clear, but without forcing the notes into a metronomic straitjacket. The piano's upper registers were clean and uncolored through the M350s, and while I could still hear that cabinet resonance excited if I listened with a stethoscope, I heard nothing untoward at the listening position, no emphasis of some notes but not others, no blurring. It must be noted, however, that this recording is on the dry side, and lacks the sense of space audible from Concert, my two-decades-old live recording of Robert Silverman performing the E-flat major and minor preludes and fugues from Book I (CD, Stereophile STPH005-2). The Bostons successfully presented the piano within the warmly supportive church acoustic, and Silverman is even more lyrical than Hewitt while matching her clarity of line.

The M350's high frequencies sounded smooth, though with a slight excess of energy in the top two octaves. Earlier this year, Stereophile reviewer Erick Lichte asked me to prepare the master from the original 24/88.2 files for a new CD, A Drop in the Ocean, by the Portland State Chamber Choir, conducted by Ethan Sperry. (Erick, one of the singers, had co-produced and edited the recording.) The first work on this CD, O Salutaris Hostia, by the young Latvian composer Eriks Esenvalds, features a duet for two sopranos and is one of the most beautiful pieces of choral music I have heard. The two women float an interwoven tapestry of twin vocal lines over a slow-moving chorale in the lower voices. Through the Bostons, the sopranos sounded pure and uncolored; perhaps a touch forward in the mid-treble, but without excessive sibilance, and with all the singers set within the luscious acoustic of St. Stephen's Catholic Church, in Portland, Oregon.

I finished my auditioning of the Bostons with Sibelius's Symphony 2, with Sir John Barbirolli conducting the Royal Philharmonic (ALAC files ripped from CD, Chesky Gold Series CG903). This 1962 recording, recorded by the dream team of Chuck Gerhardt and Ken Wilkinson for The Reader's Digest, played to the strengths of the Boston M350: the darkish balance reduced the audibility of the tape hiss; the warm lower mids added to the sense of authority of the lower strings, even with the ports half-closed; and the well-defined stereo imaging allowed the space of London's Walthamstow Town Hall to be readily apparent around the pizzicato strings.

Life is like a beanstalk . . . isn't it?
Whether or not Boston Acoustics' M350 will be a worthwhile purchase will depend very much on the speaker's excessive upper-bass energy not being a problem in the prospective owner's room and system. Other than that, the M350 offers a neutral tonal balance and is commendably free from overt coloration. Its only real failing is the congestion in the lower midrange, but this only occasionally got in the way of my enjoyment of the music, and must be put in the context of the M350's price.

I had a good time with these speakers; I predict that you would, too. Recommended.

Footnote 1: Procol fans should check out this live 2006 performance of "A Whiter Shade of Pale" with the Danish National Concert Orchestra and Choir at Ledreborg Castle, Denmark. My thanks to reader Pierre Aubin for sending Art Dudley and me the link.
Boston Acoustics
7 Constitution Way
Woburn, MA 01801
(201) 762-6429

James.Seeds's picture

You make it a point by saying "The M350 was designed in the US but is manufactured in China" it doesn't lesson the fact that it's still made in China to American specifications. 

It's a shame that something costing $2500.00 is being built in China and exported to the States, it's bad enough some of food like American Apple Pie comes from that poluted country but now speakers like Boston Acoustics as well, oh the humanity.

Coi Laman's picture

Mr. Atkinson, of course you are having a lot of problems with mid-bass and the congested lower midrange. These speakers are too big for your room. I struggle with the mid-bass of my PSB Image 4T and they are a lot smaller and only have two 5.25 inch drivers, where one of these drivers also takes care of the mid-range frequency duties (2.5-way design).

I can only imagine the problems with this speaker, having 4 dedicated bass drivers. The sound was probably a lot worse than what you made it seem. Big speakers always take all the life out of music in the average size rooms and there is nothing we can do about it.

Bobbersound's picture

Hello !!! This review almost made me not purchase these speakers !! Wow what a shame and mistake that would have been these gems sound beautiful !!!Clean clear and sound stage to die for !!! Its all their !!! Ive been an avid reader of Sterophile for many years and must say this i one of the first recommended components i could afford do to discontinued pricing and i love my music !!!!