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Boston Acoustics A360 Design Overview

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Built on a petite 8 ¼” wide by 42” tall frame, the 4-driver 3-way A360 tower loudspeaker hits a sweet spot by providing sizeable dynamic range and surprising bass response without being beastly.  Starting at the top and working our way down, the faux leather textured hardboard top and back provides a contrast and point of reference from the rest of the glossy piano black finish. A black magnetic mesh speaker cover veils the stark contrast of white loudspeaker drivers on a black baffle.  Below the bottom woofer, the cabinet juts out a little so that the speaker cover profile is aligned with the cabinet providing a little more material in the bottom half of the baffle.  The covered front of the cabinet has a lazy parabolic shape that is a nice visual touch.  Analogies aside, a rear firing 2.5” diameter port serves to enhance the lower registers. As was the tradition many years ago in a far away land, tiny feet jutting a few inches from the base function as a form of beauty that ultimately inhibits usefulness.  If these feet are not on solid ground or augmented with spikes, the entire structure is prone to toppling.  Although it lacks some of the beauty of exotic woods and wild designs, the A360s sit pretty in most spaces.

 

Since it’s often what is on the inside that counts, the loudspeaker cover was stripped followed by the 4 Boston Acoustics proprietary drivers revealing the guts of the A360.  The cabinet construction is a minimum of ¾” medium density fiberboard on all sides with adequate internal bracing including a diagonal panel spanning from the bottom back to a few inches below the bottom woofer.  The midrange has a separate chamber isolated by a thick cardboard tube.  The midrange chamber and main cabinet have purposely placed polyfill.  A strange circular reinforcement disc is glued to the inside top of the cabinet.  This is either there to help the cabinet pass the knuckle wrap test or to damp vibrations.  The bass reflex cabinet is tuned to approximately 35Hz by way of a 6 inch long by 2 1/2 inch diameter rear port which is flared on the outside only.  The overall cabinet weight with drivers installed is a rather average 44 pounds.  The loudspeaker is a true 3-way loudspeaker with a 20-component crossover transitioning from the woofers to midrange at 800Hz and the midrange to tweeter at 2.7khz.  Boston Acoustics appeared to use a mixture of polypropylene and electrolytic capacitors as well as air and iron core inductors.  Since I didn’t reverse engineer the crossover, I have to assume the right types of crossover components were used in critical places.

 smA360_Crossover.jpg

 A360 Crossover

Boston Acoustics A360 Drivers

The 3 ½ “ midrange and 6 ½ “ woofers are made from a ceramic and glass fiber polymer material.  The woofers have, what Boston Acoustics calls, Deep Channel Design (DCD) magnet structures providing a driver geometry allowing more voice coil travel without bottoming out.  The drivers are metal stamped baskets with standard ceramic magnets.  The magnet structure and spider appear to have good build quality.  The conical shaped dust cap on the midrange and woofers is not a genuine phase plug as it is glued to the cone material.  Phase plugs in general are used to reduce cancellations at higher frequencies.  The phase plug fashioned dust caps used in the A360s provide a modern attractive touch and meet the design goals for the driver.  The tweeter is a 1-inch Kortec soft dome tweeter.

Editorial Note From Steve Feinstein on Kortec:

The tweeter in the Boston Acoustics speaker is a treated cloth, with extra damping on the underside surface. This makes it a very well-behaved tweeter, pistonic but not ‘ringy.’

The baffle configuration hosts a traditional three-way alignment with the tweeter at the top of the cabinet with the midrange and woofers below.

smA360_Drivers.jpg

Boston Acoustics A360 Drivers

Set-Up

I’ve never been too interested in reading about the unboxing process so I’ll spare you too much detail.  As you might imagine, I received the A360s in boxes with Styrofoam at the top and bottom of the box.  The A360s base sits on a ¼” piece of fiberboard for added rigidity.  Intuitively, I would suspect that this configuration is sufficient to protect the loudspeakers from damage.  As I’ve learned the hard way, package delivery services are not as careful with packages as we would like.  I’m not really sure how it happened, but one of the dainty plastic outriggers was decimated to a nub.  Considering the relatively unstable base of the A360 with two working feet, the broken plastic foot was detrimental to the A360s balance.  Luckily, a light bulb went off and I determined I could shim the broken side to prevent any accidents. 

Boston A360 Terminal Cup

Boston A360 Terminal Cup

The A360’s had those annoying plastic plugs inserted into the back of the binding posts.  But, I was able to remove them with a small flathead screwdriver so I could insert my banana terminated speaker cables. 

 

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Recent Forum Posts:

DCmoe posts on June 13, 2013 07:01
gtpsuper24, post: 972123
Like Klipsch who uses the tweeters sensitivty to falsely jack up the SPL.

Same thing for BIC speakers.
gtpsuper24 posts on June 12, 2013 13:49
Pablo Albino, post: 972120
82,7 dB? That really disappointed me a lot! Couldn't be a defective sample?
I was planning to purchase an little integrated amp (75 W) to feed that towers. However, that measurements has made me reconsider my original plan.

Or it could be accurate given how so many manufacturers falsely inflate their specs. Like Klipsch who uses the tweeters sensitivty to falsely jack up the SPL. When actually they are probably closer to 91-92 as a system.
gene posts on June 12, 2013 13:49
Pablo Albino, post: 972120
82,7 dB? That really disappointed me a lot! Couldn't be a defective sample?
I was planning to purchase an little integrated amp (75 W) to feed that towers. However, that measurements has made me reconsider my original plan.

you're gonna find that most manufacturers fudge sensitivity ratings on speakers. We measure sensitivity from 300Hz to 3kHz which is the IEC standard way of doing so. Most manufacturers simply do a fullrange test to give the illusion of higher sensitivity. We've measured Klipsch speakers to be a whopping 8dB less efficient than their published spec. Bryston's new tower speaker was measured by the NRC to be 4.5dB less sensitive than published spec.

You will probably be ok with the amp you want to use if you power these speakers in a small to medium sized room. Otherwise, you may want to get a bigger amp or go with a more sensitive speaker.
Pablo Albino posts on June 12, 2013 13:42
Sensitivity

82,7 dB? That really disappointed me a lot! Couldn't be a defective sample?
I was planning to purchase an little integrated amp (75 W) to feed that towers. However, that measurements has made me reconsider my original plan.
internetmin posts on May 15, 2013 10:22
Boston Acoustics

Ah, I had a pair of Boston Acoustics HD-series monitors back 20+ years ago. Those speakers got me into the high-fi hobby. I haven't listened to any of the recent speakers but I've always had a special sentimental affinity for BA.
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