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<p><img class="story_image" src="http://www.stereophile.com/images/713boston.promo_.jpg" /></p>
Boston Acoustics made its name in the early 1980s with <a href="http://www.stereophile.com/content/boston-acoustics-a40-loudspeaker">the A40</a>, 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 <a href="http://www.stereophile.com/content/boston-acoustics-25-loudspeaker">November 2011</a>, 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.
<p>
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.
</p><p>
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.
</p><p>
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.
</p><p>
The M350 was designed in the US but is manufactured in China.
</p><p>
<b>Nothing's better left unsaid</b><br />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."
</p><p>
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 <i>Raising Sand</i> (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' <i>Holland</i> (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.
</p><p>
And even as I write these words and "Sloop John B," from the HDtracks hi-rez release of the Beach Boys' <i>Pet Sounds</i> (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.
</p><p>
Without the port plugs, the low-frequency warble tones on <i>Editor's Choice</i> (CD, <a href="http://www.stereophile.com/musicrecordings/853/index.html">Stereophile STPH016-2</a>) 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
[Source: http://www.stereophile.com/content/boston-acoustics-m350-loudspeaker]
Boston Acoustics made its name in the early 1980s with <a href="http://www.stereophile.com/content/boston-acoustics-a40-loudspeaker">the A40</a>, 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 <a href="http://www.stereophile.com/content/boston-acoustics-25-loudspeaker">November 2011</a>, 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.
<p>
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.
</p><p>
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.
</p><p>
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.
</p><p>
The M350 was designed in the US but is manufactured in China.
</p><p>
<b>Nothing's better left unsaid</b><br />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."
</p><p>
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 <i>Raising Sand</i> (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' <i>Holland</i> (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.
</p><p>
And even as I write these words and "Sloop John B," from the HDtracks hi-rez release of the Beach Boys' <i>Pet Sounds</i> (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.
</p><p>
Without the port plugs, the low-frequency warble tones on <i>Editor's Choice</i> (CD, <a href="http://www.stereophile.com/musicrecordings/853/index.html">Stereophile STPH016-2</a>) 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
[Source: http://www.stereophile.com/content/boston-acoustics-m350-loudspeaker]