Design Acoustics D-12, Omnidirectional Dodecahedron

In continuation of the recent series of speaker review threads, I felt like taking some time this evening to pull my blue dice out of storage and give them a bit of a listen.

The D-12 was a very unusual speaker for 1973 and remains to this day as a particularly odd unit for its dodecahedral design, something still being copied to various degrees of success to this day. It was George Sioles brain-child, the first design put forward by his start-up company, and a momentary sensation at a time when the industry was being flooded by new start-ups. The D-12 ranked at the top of reviewed speakers and made an impression on those who heard examples back in the day.

An early promotional advertisement showing George and his speakers:


The D-12, the D for 'Design' and the number for the sides, is a dodecahedron that spans ~24" at its widest, a set of opposing tips, at a weight approximately 40lbs a piece. Most units sold were the D-12W variant, W meaning that the finish was oiled walnut veneer with black grill cloth on each of the pentagonal grills. Other configurations were available as an option where the veneer was painted black and the grill cloths came in Burnt Orange (the most common option), Avocado Green, and Electric Blue (the least common) colors. The default stands were either a walnut stand for the D-12W or chrome-plated for the colored options. A special bracket designed to allow the D-12s to be hung from the ceiling were available. (For maximum '70s effect, the best configuration was thick shag carpet the same color as the grills and the optional mount to hang these via chains.)

At the bottom is a down-firing woofer, a specially chosen 10" CTS unit (Fs = ~10Hz), that crosses out by 750Hz. The cabinet arrangement is ported out the rear panel directly above the connectors -- an odd choice for a driver designed for sealed alignments, but not unexpected as Sioles designed more by ear than by technical theory. At the very top is a 5" sealed back Peerless cone midrange that crosses out at 1600Hz. About the periphery are nine 2" Peerless cone tweeters that cover the remainder of the frequency response until their natural roll-off at ~15kHz. The large size of the baffles and the choice of the cone tweeters rather than domes is intentional to shape the dispersion such that all the tweeters together create a uniform sound field with minimal comb-filtering due to overlap. The crossover is simple 1st order (6dB/oct) with a set of jumpers and screw terminals by the connectors that may be adjusted to input varying resistors to adjust the output of the midrange and/or woofer compared to the tweeters. (Schematic available here.) The spec'd frequency response was 70 Hz - 15000 Hz +/- 2 dB (reviews put the in room bass response down to <35Hz @~-4dB) at an efficiency of 90dB/w/M at 8Ω.

Further details and the official reviews may be found at the Design Acoustics Yahoo! Group.

Regarding the sound, it is difficult to provide an accurate description as the sonic character of these speakers is quite different from conventional designs. The frequency response is audibly quite flat with no regions calling particular attention to themselves. As per usual with DA speakers, the lower midrange and midbass is lacking due to the down-firing woofer resulting in a leaner, more telephonic sound. This dip is less than the peaks found in most other speakers, but it is distracting in that it makes most familiar instruments in this range, especially male voices sound a bit lacking, as though being heard through a clock radio at times (an exaggerated comparison). At first, the bass was sounding quite one-noted, but I had just recently refoamed the woofers and no break-in had been allowed for before this listening session. As time progressed, the bass quality did improve as did definition and more midbass was evident later on. Still, this is a ported design and it sounds like it with the bass a bit slow, a bit tubby, and not as fine in resolution as sealed or dipole designs. The top-firing midrange did make for some significant difference in the sound between a seating position where the ears are at or below the level of the top and standing. Indeed, these speakers should sound best in these regards on their original 11" tall stands, which I do not have, rather than the 15" tall flower pot holders used in this review. Despite the cone tweeters, the treble is never beaming and is really quite smooth and sweet. The highs are a bit stronger than preferred, but much of this is due to known faults with the source and the room -- with these as with all omnidirectional speakers, you listen far more to the room than the speaker. The lack of extension on the top end is noticeably, but not terribly so and the overall smoothness of response in the treble makes it less evident.

The soundstage is where the D-12 sets itself apart from most early '70s speakers. No matter where one walks while listening, the image holds fairly stable such that instruments and voices hold their relative positions quite well. Even when one is standing beside one unit, the music seems to be coming from between them and not from the one, rather the trick is that the closest seems not to be radiating at all. The overall presentation is similar to dipole speakers with the holographic effect of three-dimensionality, but better in some ways as the perception of instruments extends to the outside a distance nearly equal to the separation of the dodecas. The resolution of the image is a bit smeared horizontally, but not abnormally so. The only major failing here is that the musicians sound about knee-high due to the need to place these units on fairly short stands below ear height.

Ultimately, the D-12 was an excellent speaker for its time, but sonically is only so-so compared to good speakers today. The presentation offered by the omnidirectional is intriguing and sets these apart from conventional speakers still. The strength of their appeal lies both in their relative rarity and retro-groovy looks. There is no doubting the uniqueness of this design particularly with those examples with the optional grill colors.

The review equipment used was a NAD 7060 receiver and a Kyocera DA-410CX. While the D-12s aren't the greatest sounding speakers, the NAD receiver's weaknesses overlapped those of the speakers exacerbating the failings in the midbass and midrange. The Kyocera was a good sounding CD player for 1987, but its DAC is below even the early '90s average and so makes the treble sound a bit harsher. Of particular note is its weakness in properly decoding the higher frequencies making cymbals sound more like static crashes. I'm certain that with the Pioneer SX-838, the sound would've been much better.

Picture shows the test setup.

- JP

Attached Image (Click thumbnail to expand)

Incredibly well-written!

Very enjoyable review JP! I agree with TDH about the writing quality - it's excellent.

I knew this day would come.

Now, don´t forget to post a review of your "Galaxy Commander Receiver" over at Solit State.

Jorge

Very good review from an incredible futuristic speakers from the 70's.
I wonder if they sell a lot of this speakers, in the 70's ?

How about a review of the Galaxy Commander with the D-12s?

Overall, the sound is much better with the Kenwood than the NAD despite the KR-1000's leaner sound. The midrange is still a bit lacking, but it is a bit richer.

- JP

Attached Image (Click thumbnail to expand)

Now, there´s a thought.

Jorge

JP,

I keep thinking about this post.

It's one of the better I've read- on any site, any magazine.

When I first started reading your posts over at AK, I was incredibly impressed with your wording/phraseology of your posts, your depth of knowledge, your odd and thoroughly enjoyable sense of humor(one that's an aquired taste, it seems), your fair and even-keeled writing style, and your overall general writing style.

You are opinionated, 'tis clear, but you have the teeth and the smarts to back your opinions up. In conjunction with that, you've always been fair, and respectable of other's opinions- with the occasional friendly jibes lobbed at some fanatical fans, of course.

Your "open-door" policy to be influenced by a good point or arguement that may be against your grain of thought or formed opinion is essential for any good writer.

Your assessment of gear, and your ability to write about it as eloquent and entertaining as you do, is a gift.

Have you thought about submitting this to Marc Marcantonio's Affordable $$ Audio? I think you should- it's an excellent piece worthy of his magazine.

Please consider it!

I´ll second that. Besides, Marc will certainly appreciate your input.

Jorge

I'm afraid I haven't the high opinion of my words you seem to express, Paul. It was just something I sat down and wrote up real quick in the informal, recursive style I use with friends, family, and forums. It would rather bug me to have it be an official representation of my abilities, plus I can't duplicate the endless fawning and hyperbole required of more official reviews. (You know the type "feather on the erogenous zones" type of commentary.)

As to opinions, it's impossible to be in this hobby without them else any gear is as good as the rest and a boombox would suffice. So why restrain from voicing them? I figure that if they're presented reasonably with an acknowledgement to the opposing position, then they can serve as a good seed for discussion. Sadly, though, it seems more than a few folks are unable to differentiate between discussion of opinion and personal insult (or just as an opening to dismiss with a slicing one-liner but without any backup of evidence or explication), as some emails from a particularly abusive person this weekend attest to (from a different group, so no matter here). It can take the fun out of the hobby real quick or make one suddenly dislike a former favorite pair of speakers just for the association to those cutting comments, as happened with the D-12s.

Sigh.
- JP

I'm with you wholeheartedly on the need for opinions, and strong ones, at that.

As stated previously, I find your opinions to be fair (always), even-keeled, and backed by a strong, well-formed, well-educated foundation.

What makes your opinions even more valid (besides the afformentioned), is your willingness to hear others viewpoints, and allowance for growth and modification, if appropriate.

Now, for another opinion, of mine- your writing style is excellent, and belies your training, your skills, your goal and desire of becoming a teacher.

You don't even come close to being "quick on the pen" or lacking as you may feel you are.

I understand your concern for your writing style to mark an official representation of your abilities, so I will not prod you further.

But be aware your writing of this review haunted me in a pleasant way all through the night. I was impressed!


As for the fawning/hyperbole "feather on the erogenous zones" commentary, as long as you can pruduce that during conversation on a date, I won't pressure you any further.

Add me in as another who likes the style and content of your reviews. There's actual meat there. The hours of DIY show.

Now sounds like a good time to plug that port and see what the bass sounds like if you haven't already tried it. I assume all the other gaskets/cabinet joints are airtight.

Big thanks to hakka26 for taking the time to photocopy and mail me copies of his D-6 owner's manual and, better yet, the Design Series brochure!

Reading through this, I immediately noticed some glaring inconsistencies regarding the specifications provided here and those listed in the reviews of early models. No surprise there as I've already found those reviews to be way off on the list price, saying the MSRP was nearly $500 lower than actual prices on the D-12. Same goes for what the former dealers I've chatted with have said, but that's excusable -- the grills came in yet another color; black, avocado, blue, gold, and mandarin (burnt orange as I've called it).

So, the correct frequency response is 30 Hz-15000Hz +/-2dB. The Fs of the CTS woofer is actually 23Hz, not the 10Hz as claimed by a former DA employee and self-proclaimed designer (though one who didn't even know what a Zobel network is when questioned). I'm more than a little curious, though, as to why two system resonance frequencies are given.

I've attached the excerpt.

- JP

Attached Image (Click thumbnail to expand)

Any ported enclosure has two resonances that show up on the impedance graph as... Twin Peaks. I think that's what the DA guys are talking about. I don't know why they put it on their spec sheet, but there it is.