Question about "old" technology: the wiiide baffle of the Boston Acoustics "A" series

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Question about "old" technology: the wiiide baffle of the Boston Acoustics "A" series

Besides being a fan of BA speakers (before their takeover by D&M) this series of large floorstanding speakers, equipped with a 10" acoustic-suspension woofer, sold during much of the 1980s has always intrigued me because of their very wide baffles. IIRC those baffles were employed to better "launch" the sound waves from the tweeter, and midrange if so equipped.

I fully realize such a design is not "commercially viable" nowadays and its WAF is very low, but I don't care about either of those issues (though I do think they look pretty cool ;)). I just want to know if there are any sonic advantages to using a wide baffle for the floorstanders I am considering building.

Thanks!

Since there is now a new "A" series that just debuted (typical narrow tower, dual small woofers etc etc), finding pics of the originals became more difficult, so here are some I found myself:

A100 - 2-way version* (I don't know this guy - I'm just using his page for reference sake)

A150 - 3-way version

A200 - "up scale" 3-way version. The woofer, which is different than the other A series' woofers, is mounted much lower in this model (the speaker pictured on the left is equipped with the original version); there is a later model equipped with dual 8" woofers

* I think this version is the most elegant: because of its simple 2-way design and its clean styling with pleasing ratios. And a version with black woodgrain - NOT black gloss paint - I think would look even better.
 
Last edited:
Yes.

With a large baffle, BSC is required only for a smaller portion of the bass spectrum, if at all, and therefore the power response attained from true half-space radiation is uniform for a wider range of the audible frequency spectrum. Power requirements will go down.

The drawbacks are:

1) ugly (usually)
2) the transducing elements (cones/domes) are small compared to the baffle and therefore will effect larger dips and peaks in the response due to baffle diffraction until such frequencies where beaming occurs. This can be modeled in various software such as Edge. Putting the drivers off-center, or better yet, using sizeable amounts of foam/felt/fiberglass to attenuate the waves traveling along the baffle, will reduce this effect.

Wide-baffle speakers (some people call them monkey coffins) are just a hop and skip away from in-wall systems, which tend to have much better power response than typical 2/3-way narrow floorstanders.
 
Last edited:
diyAudio Moderator
Joined 2008
Paid Member
The change in directivity index is brought closer the the Schroeder frequency (at least that's the way I've been looking at it). I've had a penchant for wider baffles for decades and feel it is one way to achieve a more balanced bass/mid region.
 
Here's something I posted in another thread that seems to be of relevance here too.

chris661 said:
When a wave from the driver goes across the baffle, the edges diffract the sound, acting as a secondary sound source, with a small delay between the output from the edge and the driver itself.

If your system has a balance control, sit much closer to one speaker than the other, then adjust the balance so you can hear both speakers. Note there's still not much of a stereo image.
The reason for this, so far as I can tell, is that stereo imaging also needs low-level delayed signals, such as room ambiance.

When you have these wide baffles, you get a delay that's constant for each instrument (assuming a single driver, centred on a baffle), as well as the varying delays in the recording to indicate room position. This has to screw up the imaging at least a little.

Angling the edges reduces the actual output from the baffle edge, as well as making the baffle narrower, so these delays won't have so much effect. The narrow baffle has a delay so small that you'd simply think it was from the driver.

Chris

Hope this helps.
 
I owned the Boston A100s in the mid eighties and have fond memories of them. They were my first "hi-fi" speaker and were my inspiration for my latest project.

The main advantages I have found with the wide baffle is a better presentation of bass, especially male voices, and better efficiency (less baffle step compensation required).
Also if you are in a situaiton where you HAVE to put your speakers close to the wall (probably most of us), a wide-baffle speaker tends to reduce the negative impacts of such a placement.

Negatives -:
- more susceptible to diffraction effects so attention needs to be made to asymmetric driver placement or curving/beveling the baffle edges.
- Imaging is not as precise as a narrow baffle, but some would say that pinpoint imaging is not very realistic anyway.
- Size and weight (the main reason they lost favor with most manufacturers).

The best overall summation I've heard is that narrow baffles bring the performers into your room, wide baffles take you to the recording venue.

In an era of wide-screen TVs, I dont see a wide baffle speaker presenting much of a WAF issue.


An externally hosted image should be here but it was not working when we last tested it.


Gattiweb
 
Last edited:
diyAudio Moderator
Joined 2008
Paid Member
The best overall summation I've heard is that narrow baffles bring the performers into your room, wide baffles take you to the recording venue.

Yes, or put another way, there are more reflections due to the wider directivity thus adding the room into the equation.

The concern is that after you consider the directivity of the tweeter, beaming of the woofer, and the baffle step, do they all line up across the spectrum to form a smooth 'homogenous' transition?
 
frugal-phile™
Joined 2001
Paid Member
Wide-baffle speakers (some people call them monkey coffins)

Not so. Monkey coffin refers to any rectangular prism shaped box that resembles the kind of shape you would use as a coffin. The monkey part indicative of the size.

A good exmple

246325d1319523600-pentaview-results-my-latest-inspiration-the_formiva_iso.gif


dave
 
When i worked retail hifi we sold a ton of these BA. I remember a very memorable Sunday afternoon where we did a number of basic mods to a set of A200s and transformed them.

I bet the pair I had were originally sold by you. They had the light oak trim with beige grills, quite attractive actually. They had the usual mods, duct-seal on the woofer baskets and modge podge treated cones. I was going to have at the crossover, but the way it's designed doesn't lend to mods that easily.

One day a neighbor was having a garage sale. I spotted a pair of Sansui SP-2700A's in the garage, and ended up bringing them home. Hooked them up and heard music that never came out of the A200's, so that sealed there fate. I sold the A200's shortly there after.

jeff
 
Yes.

With a large baffle, BSC is required only for a smaller portion of the bass spectrum, if at all, and therefore the power response attained from true half-space radiation is uniform for a wider range of the audible frequency spectrum. Power requirements will go down.
Thanks!

The drawbacks are:

1) ugly (usually)
Ah they're not that bad. I've seen quite a few thin towers that had lousy W/H/D ratios, some almost like square tubes that looked, well, never mind :p and stuck out in a room like a sore thumb (though if you have a dedicated room for audio, then no harm done). If no one minds me going off on a tangent for a sec......

I'm not a pro industrial designer or feng shui expert, but IIRC there's something called the golden rectangle(?) that many speakers in the past used and so were at least pleasant to look at. As far as thin speakers, as long as they have enough depth, like Definitive Technology's BP series, then I like them.

Wide-baffle speakers (some people call them monkey coffins).
I think you're speaking of models like the Large Advent, because these Bostons are very shallow vs. their width, resulting in a sort of living room/wood-veneered version of Mr. Clark's monolith and how could that classic shape be unattractive? ;)
 
Here's something I posted in another thread that seems to be of relevance here too.



Hope this helps.
Yes it did, thanks.

Yes, but see Troel's take on a Sonus Faber:
I'd forgotten about that Sonus model, but since it is just a wee bit out of my price range, I probably had a mental block on it! I did use it as an example a few years ago to show someone elsewhere that large woofers were still in use by some brands (another one of those threads discussing the "speed" of various woofer diameters).
 
Last edited:
- Imaging is not as precise as a narrow baffle, but some would say that pinpoint imaging is not very realistic anyway.

The best overall summation I've heard is that narrow baffles bring the performers into your room, wide baffles take you to the recording venue.
Not to start an off-topic discussion but I know what you mean about precise stereo imaging: I generally prefer it, but depending on the type of music, for me it can sometimes be a little distracting. It's similar to when you make a pot of chili but haven't allowed it to simmer long enough i.e. all those various ingredients need to blend a bit for best flavor before you call everyone to the table. And at a live peformance most people sit far enough back that they cannot make out individual instruments all that well anyway.
 
One day a neighbor was having a garage sale. I spotted a pair of Sansui SP-2700A's in the garage, and ended up bringing them home. Hooked them up and heard music that never came out of the A200's, so that sealed there fate. I sold the A200's shortly there after.

jeff
Going by reputation and my own experience with a pair of vintage Pioneer CS-99A five-way speakers with multicell horn tweeters, those Sansuis were probably the polar opposite of the Bostons: the output of the A200s being much more "warm" vs. the (probably) very lively character of the Sansuis. I actually like many Klipsch models for example...but not for more than an album's worth of music.
 
Going by reputation and my own experience with a pair of vintage Pioneer CS-99A five-way speakers with multicell horn tweeters, those Sansuis were probably the polar opposite of the Bostons: the output of the A200s being much more "warm" vs. the (probably) very lively character of the Sansuis.

Actually, they were much closer to the Bostons in tonal balance than one would expect. When I hooked them up, I heard multitracked male vocals that I'd never heard with the A200's. Unfortunately, there was no low bass at all, which I thought was a bit strange, given the 12" woofers.

I'd be tempted to try the A400's bi-amped. Tubes for the mid/tweets, and SS for the woofers.

jeff
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.