Question about "old" technology: the wiiide baffle of the Boston Acoustics "A" series - Page 3 - diyAudio
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Old 6th November 2011, 01:40 AM   #21
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Originally Posted by 454Casull View Post
That's... mine.
Condolences on the loss of your monkey, I'm sure he's in a better place now.
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Old 6th November 2011, 05:18 AM   #22
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Originally Posted by planet10 View Post
An example of a CGR.
+1

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Condolences on the loss of your monkey, I'm sure he's in a better place now.


That type of enclosure had a better chance of looking good back in the 50s and 60s when mid-century modern was in style i.e. usually in the form of sharp clean lines with interesting geometric shapes (found in the detailing of the box - box itself stuck with the golden ratio or close to it), rich wood veneers and grill cloths of various textures & colors. Nowadays, as far as commercial designs, the emphasis is on almost always on selling black, unadorned "hi-tech" boxes which can end up looking really unattractive, to me anyway, and makes one think of an actual casket much more quickly.
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Old 6th November 2011, 05:28 AM   #23
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An example of a wide baffle speaker, with a supraBaffle to reduce the edge diffraction downside.

Click the image to open in full size.

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Old 6th November 2011, 05:34 AM   #24
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Originally Posted by vinylkid58 View Post
Actually, they were much closer to the Bostons in tonal balance than one would expect.
Interesting. Those stiff looking surrounds and the horn tweeter seemed to add up to "lively". I shouldn't make assumptions on just the visuals then!

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Unfortunately, there was no low bass at all, which I thought was a bit strange, given the 12" woofers.
Don't feel bad - those Pioneer CS-99As I had were also quite anemic bass-wise despite their fifteen inch woofer. But that woofer was crammed into a really small enclosure.... a sealed enclosure.....and the woofer's cone did not seem particularly heavy like the cones used in Advents or other acoustic-suspension models of the time.

The manual that came with them included a frequency chart and it clearly indicated that immediately under 100Hz is when their response began to drop off. IIRC they barely made it to 50Hz and then faded out completely. While my own Boston Acoustics CR9s - ported single 8" woofer - cannot not nearly match the 99s as far as overall output level, at least they can make it to the low forties before hitting their 3dB down point.

I finally sold them mostly because of the bass issue - btw they were fully functional and had never been repaired during their 35 year life span - but will admit they were beautiful speakers with excellent craftsmanship (e.g. the grill's lattice work is not plastic but actual wood strips bent into that shape!). Even people not into audio commented on how attractive they were. I kind of miss them actually.
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Old 6th November 2011, 05:39 AM   #25
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An example of a wide baffle speaker, with a supraBaffle to reduce the edge diffraction downside.
Those look great! I assume the supraBaffle is the round plate the driver is mounted on?
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Old 6th November 2011, 06:02 AM   #26
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yes

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Old 6th November 2011, 09:26 AM   #27
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Philips did a lot of research on enclosure geometry. They came up with several design rules for their "HiFi DIN 45500" models:

- The cabinet depth was less than 1/4 wavelength at the crossover frequency of the woofer to prevent resonances developing between the woofer and the back panel.

- The drivers were placed assymetrically on the baffle to spread the "baffle step" and other diffraction frequencies.

- The cabinet was stuffed with fibreglass batts, thus putting the bulk of material in the centre of the cabinet airspace - more efficient than covering the walls with it.

- The drivers were mounted on the front of the baffle. The grille cloth was mounted on a form-fitting panel which filled the spaces between the drivers, making them effectively flush mounted. The speakers were designed to be used with the grilles on.

(Philips were well aware of diffraction effects, especially around tweeters - their top-end AD0160 tweeter came with instructions for flush mounting in a rebated hole.)
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Old 9th November 2011, 01:06 AM   #28
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- The drivers were placed assymetrically on the baffle to spread the "baffle step" and other diffraction frequencies.
I see this done much more with speakers sold in the 70s and 80s, but by the 90s most speakers, even hi-end gear like those from Wilson Audio and dynaudio's Evidence series, had all their drivers in a tidy vertical line. Maybe at least as far as commercial manufacturers were concerned, when the cost of mirror-imaged baffles were factored in, off-axis issues were deemed more important than baffle and diffraction issues?

This thread has been very informative - thanks to everyone who participated (you can keep contributing if you want! ). I think for my first 100% from scratch speaker I'll stick with the semi-narrow but deep enclosure I started out with, something along the lines of the Klipsch RF-7, if I build one of those double-chamber bass reflex enclosures. My design will be using a 10" woofer and due to my fascination with inexpensive but good sounding speakers (I'm a big fan of Henry Kloss' design philosophy) plus the fact I just plain don't have a lot of $$ to throw around, it will probably be a 2-way - yep a little beamy in certain mid frequencies but this is equal parts a learning project and also something fun to do i.e. no hand-wringing over barely audible sonic artifacts.

The other option is something borrowed from yesteryear: a sealed design. Finding a modern woofer with T/S parameters like those from AR and EPI is pretty much impossible but would try to find something close - as long as it can make it relatively flat to 40Hz is all I ask. Plus it would be more efficient anyway (todays' mid-priced A/V receivers don't do so well with low-efficiency speakers) and it has a better chance of sounding acceptable than the double chamber enclosure with its various port interactions.

Styling: either something clean w/sharp lines like certain stand-mounted B&Ws of the 80s*, along with black-stained wood veneer with a thin black grill that stands away from the baffle using @1" posts OR a tribute to the designs of the 50s and 60s, using a rich/reddish walnut color with tan grill tha mounts inside the front trim surrounding the baffle, but the grill would differ in that it would have cutouts (as Philips recommended) with rounded edges so diffraction would be much less than what those vintage designs caused.

Lastly, I have considered a 10" two-way where the woofer is allowed to operate "full range" to eliminate the cost of the low-pass crossover, but it looks like finding a woofer with the correct roll-off characteristics would be difficult. I thought about just going through with it anyway and taking a chance, but have read about the nastiness of IM distortion written by many different experienced hobbyists so I'll stick with at least a 6dB/octave xover for the woofer.



* B&W DM18 (scroll down) - warning! don't go to this page if you're pressed for time! That's because it contains many nicely staged and photographed pics of many classic pieces of gear in their natural habitat i.e. no dull pics of gear on sheets or in a messy garage. Man that JBL "Decade" is such a clean design, electrically and its styling......

Last edited by River757; 9th November 2011 at 01:09 AM.
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