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ra.ra

Design Acoustics D-4

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Not long ago, two pairs of previously unknown-to-me Design Acoustics D-4 speakers came my way, and I am just trying to gather information-advice-opinions on them as I begin to explore and disassemble them for restoration efforts. D-A was a California enterprise which at some point was bought by Audio Technica, and some of the drivers used in various models will look familiar to some of you who have seen them used in other loudspeaker products from the era. All four of these speakers appear to date from 1975, according to stamped markings on the woofers.  

D-A made a few iconic odd-looking speaker models, but I personally think the original D-4 is very elegant: it measures 38"h x 17.5"w x 9.5"d, and my first impression was that it must have been partially influenced by the AR-MST - - at least the aesthetics, since it otherwise has few similarities with the AR product. The D-4 has five drivers: (2) small super tweeters located high on angled faces; phenolic ring tweeter low on front face; cone midrange higher up on front face; and 10" rear-firing woofer. The crossover seems to consist of two caps, seven resistors, and (2) two-position switches. Cabinet build quality is rather robust, but internal components are largely unimpressive. Will post more info as I dig further.

Two pics attached show the two sets of D-4's with AR-MST for comparison, and naked view of front side. First pic is mine; second pic is from the web. I am currently too sheepish to try to remove these grilles until there is absolute necessity. While some AR's (or KLH's) may be a bit difficult to crack open, these things are like breaking into Fort Knox.

P1120022.jpg

nudie.jpg

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Whoa!.......the level of interest in this thread has been so fast and furious that I've barely been able to keep up. :lol:

In any case - - - just a few more pics for posterity here. Both the woofer and the (3) tweeters have two-position switches for varied output, while the midrange runs full-tilt all the time. The 10-inch woofers were manufactured by ROLA (also used in ADC speakers), and I've never seen anything like these amendments added to the cone surface. Apparently, these three little strips of balsa wood have been added to the OEM driver in order to provide a slight increase in mass and/or stiffness.

Most of this information - - and much more - - comes to me courtesy of a very kind and generous fellow I've contacted who used to work in the company's wood shop in CA in the mid-70's when these speakers were first produced. He has been a trove of information and immense help, and his comments often refer to the ideas and practices of the founder and lead designer for Design Acoustics, George Sioles.  

 

rear terminals.jpg

woofer front 3.jpg

woofer rear 3.jpg

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11 hours ago, ra.ra said:

Whoa!.......the level of interest in this thread has been so fast and furious that I've barely been able to keep up.

I will try to slip in a question in hopes it will be noticed before the the next wave of posts pushes mine out of sight.  I remember when you posted this and waited to hear your listening impressions.  They are obviously built on the idea of actively adding reflected sound as part of the listening experience.  Have you powered them up or is this strictly a reverse assembly project? 

image.png.01664e78975616a3ffb3fa946eed7b5b.png

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Hey, thanks for adding that little blurb from the buying guide. These speakers were partially disassembled for inspection, and then the project was slowed down as I was seeking additional information. Now that I've found my lodestar, I'll probably be tackling these next month.

Before any disassembly, I did wire up the speakers (in pairs) for an initial listen and to confirm that the drivers are all functional. This was by no means any type of serious test run. The sound provided a nice blend amongst the many drivers, but first impressions suggested that top-most and bottom-most frequencies were muddy and lacking. Until any post re-build demonstrations occur, my guess is that the lack of high sparkle might be due to several broken switches and/or cheap, tiny, aged capacitors. Regarding bass output, the cone mass/stiffness needs to be addressed, and I think the placement is probably critical with rear-firing woofers. Also, considering this is a non-ported speaker, I was surprised to find no gaskets sealing the woofer frame to the cabinet.

(Edit: I forgot to mention that in the original DA series (D-2, D-4, D-6, D-8, D-12), the notion was that the model number referred to the number of planes that contained a driver - - - I've been able to confirm this for all but the rare D-8.)

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I have four of these same speakers that belonged to my late husband. I would like to find them a good home as I am moving. Any suggestions would be welcomed. 

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I would suggest listing them in our For Sale section. Be sure to say where they are located.

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I have a pair of DA D-4 speakers I bought new in 1973. Have used them very little the past few years. Have renewed interest in getting them refurbished. Looking at the speakers it looks like access may be from the backside. Am interested if anyone has tried this and if they are held on by the visible staple holes in back and also if back is glued. From the above photo is looks like taking the front grill off is not fruitful and does not permit access to the internal parts. ra ra if you have made progress on your attempts at this would love to hear. Also if you are able to share your contact that used to work at DA would love to talk and see what they know. I have an instruction sheet and promotion brochure with specs and would include but have not figured how to attach a photo. Will see if I can work it out later. 

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On 3/28/2020 at 8:52 PM, Mark T said:

I have a pair of DA D-4 speakers I bought new in 1973.

Hi Mark, and welcome to the forum. It's always interesting to hear from someone who has held on to the same pair of speakers for nearly 50 years. Even after more than a year, I have not completed work on the four DA D-4's shown in this thread, but I'll attach a few pics which may be helpful for you. 

You are correct to not attempt to remove the front grille cloth and underlying grille panel. The only exception might be to facilitate a driver replacement, and I don't even want to think about that procedure. Pertinent access can be accommodated after removing the rear switch panel and the woofer and its screen covering. See pics attached.

Even removing the woofer screen/grille is a bit of a challenge. First, you can see from the pic that the frame is constructed from four masonite (actually more like MDF) slats butt-jointed and stapled together, and this prevents the grille frame from remaining stiff and planar as you remove it. These are held in place with many small industrial headless nails, and the only way to remove grille is to be patient using correct tools to slowly and gently pry up the grille around its perimeter. Slightly painstaking, but I was able to remove all four with no damage to the black rear grilles.

Removing the switch plate is mostly straightforward, but after removing screws, you can see from pic that there was a material used (latex caulk?) to seal the metal plate to the wood cabinet, and it takes a thin slicing tool to break this seal. On the backside, you will find a jumble of components that make up the bulk of the crossover, but there will also be another capacitor and a couple resistors elsewhere inside the cabinets. 

I've got some additional pics, but please ask questions as you go along. With one-owner speakers as you have, you may not have some of the problems that I've found - - - in my case, some of the switches and wire terminals have been damaged and will be getting replaced. The very helpful DA expert I've found goes by the name "stickman" on the Audiokarma forum. 

woofer opening.jpg

rear grille.jpg

x-o plate.jpg

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One more pic here - - view looking at inside of front panel thru woofer hole. On left is phenolic ring tweeter and at right is the Danish midrange driver with its capacitor, which will be either 20uF or 33uF. Associated sand cast resistors are either attached to driver terminals or globbed onto cabinet panel.

view inside.jpg

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