Design Acoustic D-12 speakers

I'm going to update this thread again with my latest discovery. One of my first comments about these speakers was a bit of a "telephony" sound they had to them. I had done things that helped alleviate this issue - moving them to the middle of the room, putting in PIO caps - but it never totally went away. So recently I got to thinking about the value of the tweeters. I thought they could benefit from being tamed a little, so I put in a lower value. They come with 6uf, so I tried a 5uf/600V GE motor run cap. BINGO! I think it's just what they needed. The sound is much more blended with the mid and woofer, and reducing their output just slightly with 5uf even helps the tweeters focus the sound by clearing the "telephony" frequencies out. No longer do high frequency spikes sting my ears when I've got them up loud either. Sound is much more transparent and holographic, and I think this is a good upgrade to take these speakers up a notch.
 
I want to try PIO caps at some point. Always read good things about their sonic qualities.

Film oil motor run caps are a very cheap way to experiment. There are a couple surplus stores nearby that have them, and I've been pretty happy with how they sound. They're all over eBay too. Try and find some made in USA ones, those seem to be the highest quality.
 
Film oil motor run caps are a very cheap way to experiment. There are a couple surplus stores nearby that have them, and I've been pretty happy with how they sound. They're all over eBay too. Try and find some made in USA ones, those seem to be the highest quality.
Thanks for this. Seems the Russian military spec PIO's are suppose to be pretty good too. Have you compared the U.S. Vs Russian caps? Curious if anyone has and their findings.
 
Seems like replacing a 6 uf cap with 5 uf would lower the crossover point, allowing just a smidge more midrange into the tweeter. I'm not sure how this 'tames the tweeters'. It should not affect their output at higher frequencies (out of the neighborhood of the crossover point). If anything, lowering the crossover frequency would boost the lower end of the tweeter's signal. But if it sounds better, maybe it's because the midrange was more sensitive in that range, and shifting some of the signal to the less sensitive tweeter resulted in lower volume around the crossover frequency. Just spitballing.
 
Seems like replacing a 6 uf cap with 5 uf would lower the crossover point, allowing just a smidge more midrange into the tweeter. I'm not sure how this 'tames the tweeters'. It should not affect their output at higher frequencies (out of the neighborhood of the crossover point). If anything, lowering the crossover frequency would boost the lower end of the tweeter's signal. But if it sounds better, maybe it's because the midrange was more sensitive in that range, and shifting some of the signal to the less sensitive tweeter resulted in lower volume around the crossover frequency. Just spitballing.

Agreed. Scratching head here a bit.

I didn't notice a telephone sound to mine. Relative/subjective of course. They have their limits of course. To my ears they a rolled off and the top (ring tweets). Considering their funkadelic design they were serious speakers for their day and reviewed very well. Very/very balanced sound.

Good luck with your project.
 
Hmmm...am I wrong in thinking that decreasing capacitance actually increases the crossover point, and thus reducing the mid frequencies? That's how I had been thinking about it and I may absolutely be wrong. Or maybe I'm just explaining it poorly. I too am spitballing here...

Whatever the case may be, I much prefer their sound now to what they were in the space I've got them in, which is on the dry/dead side. Donkey Karma, what is the room like that you have your D-12's?
 
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No, you're right, I said it wrong. Changing the cap from 6 uf to 5 uf raised the crossover point and allowed less midrange into the tweeter.

Take a look at the big table on this page:

http://www.colomar.com/Shavano/crossover6db.html

As an example, the table shows that a two-way first-order crossover at 8 ohms has crossover points of 3200 Hz at 6 uf and 4000 Hz at 5 uf.

I am still not convinced that this 'lowered the output' of the tweeter, which is usually accomplished with a resistor or L-pad, but this may have been just a shorthand way to describe it. It did cut off a little of the low end of what had been going to the tweeter - i.e. upper midrange - and kept that at the midrange driver. If the midrange driver is a little less sensitive, the overall volume output in that range would decrease. Still explainable even after my screwup. :biggrin:
 
Great site - thanks for the share. I've bookmarked that one.

I think you explained it just right! They really do sound like they are slightly quieter, but it's probably that they're just blending in better and the output is about the same. It's incredible how much that small shift really opened the sound and cleared the highs up (to my ears).
 
My Brother's friend worked at the original factory in Torrance, CA. (It was just a small shop in a small industrial park near the railroad tracks) When he described the speakers, I was intrigued. He said you could go to the factory and purchase Blems for $380 per pair (check early 1975 suggested list.) It seems at those prices a small flat in one or more of the many corners was not acceptable. I went to the factory and looked around and felt the blems were quite acceptable for the price. I was told by the shop manager, when I purchased the speakers, that they were better for more "open" music: orchestra, jazz, acoustic etc.; but they would do well with any music that was mixed and produced well. Since they were intended for more "balanced" music, that was part of the reason for the the option to attenuate the woofer output through the strapping options.

I went ahead and purchased a pair of the blems. I took them home and attached them to my Marantz 2270. I placed " A Long Train Running" on my turntable with a Shure V15 III cartridge and fell in love by the time the intro was done. My wife (girlfriend at the time) also fell in love with the speakers. So much so, she asked me to go back to the factory and purchase a pair for her. When I returned to the factory, I was able to purchase a pair made from oak. Since they were significantly lighter, I decided I had to try suspending the speakers and they sounded even better. The music seems to be more even open and omnidirectional with suspension and so the speakers have remained suspended whenever possible.

I took the walnut pair to her apartment and sold her the Marantz 2270 for a very good price. I purchased a Marantz 2325 and the speakers have been driven by that receiver ever since. Although we eventually divorced, I was able to gain custody of all the speakers in the settlement. Which brings me to their current status. For the last 10 years, they have been in storage patiently waiting for their return. My current wife is not to keen on the idea of hanging a couple big spheres from the ceiling.
 
By this point you need to check the woofer surrounds. Woofers with both foam and butyl rubber surrounds were utilized and if they have foam surrounds they are likely damaged or disintegrated by now. In contrast the butyl rubber surrounds can be rejuvenated with a good quality silicone based rubber treatment liquid. The cross-over capacitors could also use replacement due to their age since they are now over 40 years old.

I worked part time off and on at D-A from about 1975 to 1980 starting at the Oregon Court address location referred to in the previous post and well remember the stack of D-12 blems in the production building (I worked next door in the cabinetry woodshop). The only speakers I ever purchase from D-A while working there were a used pair of EPI-100's the owner had purchased to use for comparison purposes in designing the D-2 model. I did use the money I earned there to purchase a used pair of Rectilinear 5's which suited my musical taste in loud rock music at the time much better than anything D-A was making during my early years there. When the D-8 was introduced it was a speaker I could have happily lived with but the Rectilinear 5's were still going strong and I felt no need to upgrade although the woofer surrounds did fail about the time the original D-A was sold to Audio-Technica (about 1980).
 
After a week or so of listening, I've discovered that (surprise, surprise) placement of these speakers is huge! I've found they sound much better away from the wall. The sound flattens out significantly and the "scooped" sound I had mentioned before is reduced. I think because there are 9 tweeters to the single mid, the wall can greatly increase the high frequencies and disrupt the balance with the midrange driver, which could account for the "scooped" sound. I'd love to see how'd these sound in the middle of a room, or maybe even some sort of 'baffling' behind them against the wall. Thoughts?

I'm going to ask the original owner and see if he was told anything by the salesman in terms of their recommended placement.
They were originally designed to be hung from the ceilings and very thick shag carpeting or thick rugs were suggested as acoustical treatments because the sub was designed the be suspended facing downward. In fact the stands were only designed as an option because the idea hanging them from the ceiling thus transforming them into chandeliers of sound was too radical for the customers but would prove equally challenging to demo properly in the HiFi dealer showroom. They were doing alot of acid back then and listening to all the appropriate psychedelic rock of the times! I'm sure Floyd's Dark Side of the moon has been played synched to The Wizard of Oz on thousands of occasions per of D-12s lol. Anyway enjoy! I've had the pleasure to demo these on multiple occasions and I also know where another pair are currently being housed and he is the 2nd owner of that pair. Also, they came in a variety of colors, well at least 3 that I've seen. I have seen them in Red, Blue, and black. I can only assume they came in green as well; however, I can not confirm this.
 
They were designed using Crown solid state gear with the amp being a DC-300A, and George preferred classical and jazz recordings.An excerpt from an ad in 1973 :

"Julian Hirsch has already stated "Without a
doubt, the Design Acoustics D-12 is one of the
finest -sounding home -speaker systems we have
ever encountered."
What makes the D-12 sound so good? Well, as Mr. Hirsch said elsewhere "In our judgement, wide dispersion at all frequencies is the major
factor separating an excellent speaker from a
merely good one . . . unlike many other controversial
(and often arcane) speaker properties . . . the unique sound can be heard by anyone, under
almost any circumstance."

From an ad in 1975:

"Design Acoustics: our name might tell you something. From the beginning, our objectives have been to design truly different speaker
systems-systems which achieve accurate reproduction
as a result of uniquely flat power
response and wide dispersion.
Take the unconventional D-12, for example.
It houses nine high -frequency drivers producing
uniform dispersion over the entire listening area. The smooth midrange is there, as is the clean,
solid bass. Hirsch -Houck Laboratories writes:
"Without a doubt, the Design Acoustics D-12 is one of the finest -sounding home speaker systems we have ever encountered." "

Whenever I listened to them I always felt the midrange frequencies were a bit depressed compared to the rest of the frequency spectrum, which might account for you calling the sound "scooped". Mounting the midrange drivers on the surface of their panels with a routed recess area for them to sit flush would likely improve midrange dispersion over the stock configuration.

The Peerless mids used had a stiff cone surround which may have indeed become even stiffer over the last few decades. In the D-12A model George used a soft dome midrange driver on a forward facing panel (they were designed to have directional orientation unlike the original D-12). You might want to consider substituting the later Peerless mids which had a foam surround and backing cannister as used on the D-8 model. These mids were used by Infinity and Phase Linear in their Andromeda III among many other brands and models. They are not common on FleaBay but do turn up now and then.

Have fun!
 
yes, i bemoan the fact that i didn't strive to get a pair. oh, i went on in different directions and got infinity monitor jrs and rogers LS3/5As, Fried Model RIIs, Spendor S3/5s, and MMGs.
 
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